Eni S.p.A.

Exploration & Production Division

COMPANY SPECIFICATION

UNDERWATER INSPECTIONS OF CATHODIC

PROTECTION SYSTEMS

20311.VAR.COR.SDS
Rev. 1 – April 2011

1 General Revision TEMM TEMM TEMM 06/04/2011

0 Issue 01/2009
REV. DESCRIPTION COMPILED VERIFIED APPROVED DATE

ENGINEERING COMPANY STANDARD

This document is property of Eni S.p.A. Exploration & Production Division.

It shall neither be shown to Third Parties not used for purposes other than those for which it has been sent.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 2 of 53

PREMISE

Rev. 1 April 2011

General Revision

The Document deals with underwater activities for the inspection of cathodic protection systems of
fixed steel offshore platforms, submerged pipelines and other offshore steel facilities used for the
hydrocarbon production. The Document provides the requirements to be adopted in the planning
phase of the inspection as well as in the operating phase. For platform and submerged pipelines, the
Specification integrates other COMPANY documents on underwater inspection.

Underwater inspections are periodically performed to assess the integrity of submerged oil
production facilities, including:
 steel jackets of offshore platforms;
 risers;
 submerged pipelines;
 subsea wellheads;
 other structures as FPSO, PLEM, etc.

These structures are normally protected against corrosion in seawater by cathodic protection (CP),
commonly performed by the galvanic anodes technique. Depending on the type of structure, CP can
be applied in combination with a coating system (for instance in case of submerged pipelines), or on
bare steel (for instance in case of steel jackets).

The inspection of the CP system is normally carried out as a part of the entire underwater
inspections, with the aim to verify the protection conditions, the presence of any corrosive attacks,
the integrity of the components of the CP system and the consumption of the galvanic anodes.

Compared to Revision 0, Revision 1 includes the following main modifications:

 definition of minimum requirements for the general visual inspection (GVI) and the Close visual
inspection (CVI);
 definition of minimum requirements for the inspection of the CP of risers;
 review of the inspection techniques for nodes;
 measurement of the electrical field gradient of anodes for the estimation of the instantaneous
consumption and the residual life;
 revision of the Appendix dedicated to sampling criteria, which have to be adopted for the selection
of the elements to be inspected;
 forms for the collection of inspection data of the platform.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 3 of 53

INDEX

1. INTRODUCTION.................................................................................................................... 5
1.1 Scope..................................................................................................................................... 5
1.2 Document organisation ....................................................................................................... 5
1.3 Codes & Standards .............................................................................................................. 5
1.3.1 Codes & Standards ENI E&P................................................................................................. 5
1.3.2 International Codes & Standards ........................................................................................... 6
1.4 Definitions............................................................................................................................. 6
1.5 Symbols and Abbreviations................................................................................................ 6

2. PERSONNEL, MEASUREMENTS & INSPECTION TECHNIQUES..................................... 8

2.1 Introduction .......................................................................................................................... 8
2.2 Personnel.............................................................................................................................. 8
2.3 Measurements and inspection techniques ....................................................................... 8
2.3.1 Visual inspection .................................................................................................................... 9
2.3.2 Potential measurements of the structure ............................................................................... 9
2.3.3 Measurements and inspections of anodes .......................................................................... 11
2.3.4 Potential and potential gradient profiles of submarine pipelines.......................................... 13

3. REQUIREMENTS FOR THE PLANNING ........................................................................... 14

3.1 Inspection targets .............................................................................................................. 14
3.2 Requirements for the inspection of platforms................................................................ 14
3.2.1 Planning of inspections ........................................................................................................ 14
3.2.2 Annual visit P0 ..................................................................................................................... 15
3.2.3 Subdivision of the structure into homogenous portions. Codification system...................... 15
3.2.4 General visual inspection ..................................................................................................... 16
3.2.5 Close visual inspection......................................................................................................... 16
3.2.6 Potential measurements of the structure ............................................................................. 16
3.2.7 Measurements and inspections of sample anodes.............................................................. 18
3.2.8 Sample anodes .................................................................................................................... 19
3.2.9 Measurements and inspections of additional anodes.......................................................... 21
3.2.10 Permanent monitoring system ............................................................................................. 21
3.2.11 Buried elements ................................................................................................................... 22
3.2.12 Riser ..................................................................................................................................... 22
3.2.13 Impressed current system.................................................................................................... 23
3.2.14 Documentation ..................................................................................................................... 24
3.2.15 Summary.............................................................................................................................. 25
3.3 Requirements for the inspection of submarine pipelines ............................................. 26
3.3.1 Cathodic protection .............................................................................................................. 27
3.3.2 Planning of inspections ........................................................................................................ 27
3.3.3 Homogeneous portions ........................................................................................................ 27
3.3.4 Visual inspection .................................................................................................................. 27
3.3.5 Pipelines protected by galvanic anodes: potential profiles and potential gradient .............. 28
3.3.6 Pipelines protected by impressed current system ............................................................... 28
3.3.7 Shore approach.................................................................................................................... 29
3.3.8 Measurements and inspections of anodes .......................................................................... 29
3.3.9 Potential measurements at the pipeline extremities ............................................................ 30
3.3.10 Documentation ..................................................................................................................... 30
3.4 Requirements for the inspection of subsea wellheads and other offshore
structures............................................................................................................................ 30
3.4.1 Planning of inspections ........................................................................................................ 30
3.4.2 Subsea wellheads ................................................................................................................ 31
3.4.3 FSO FPSO SPM .................................................................................................................. 32

4. INSPECTION EXECUTION. PLATFORMS......................................................................... 33

4.1 Job Specification ............................................................................................................... 33
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 4 of 53

4.2 Documentation to be issued in the bid phase ................................................................ 33

4.3 Inspection execution plan ................................................................................................. 33
4.4 Requirements for the execution of inspections ............................................................. 34
4.4.1 Potential measurements of the structure ............................................................................. 34
4.4.2 Measurements and inspections of galvanic anodes ............................................................ 34
4.4.3 Permanent monitoring system ............................................................................................. 34
4.5 Impressed current system ................................................................................................ 35
4.6 Reports and documentation ............................................................................................. 35
4.6.1 Daily Reports........................................................................................................................ 35
4.6.2 Preliminary Report ............................................................................................................... 35
4.6.3 Final Report.......................................................................................................................... 35

5. INSPECTION EXECUTION. SUBMARINE PIPELINES ..................................................... 37

5.1 Job Specification ............................................................................................................... 37
5.2 Documentation to be issued in the bid phase ................................................................ 37
5.3 Detailed inspection execution plan.................................................................................. 37
5.4 Requirements for the execution of inspections ............................................................. 37
5.4.1 Potential and potential gradient profiles............................................................................... 37
5.4.2 Measurements and inspections of anodes .......................................................................... 38
5.5 Impressed current system ................................................................................................ 38
5.6 Reports and documentation ............................................................................................. 38
5.6.1 Daily Reports........................................................................................................................ 38
5.6.2 Preliminary Report ............................................................................................................... 38
5.6.3 Final Report.......................................................................................................................... 38

6. INSPECTION EXECUTION. OTHER STRUCTURES......................................................... 40

6.1 Job Specification ............................................................................................................... 40
6.2 Documentation to be issued in the bid phase ................................................................ 40
6.3 Detailed inspection execution plan.................................................................................. 40
6.4 Requirements for the execution of the inspections ....................................................... 40
6.4.1 Security ................................................................................................................................ 40
6.4.2 Potential measurements of the structure ............................................................................. 41
6.4.3 Measurements and inspections of galvanic anodes ............................................................ 41
6.4.4 Permanent monitoring system ............................................................................................. 41
6.5 Impressed current system ................................................................................................ 41
6.6 Reports and documentation ............................................................................................. 41

APPENDIX A. SUBMARINE PIPELINES: POTENTIAL PROFILE AND POTENTIAL GRADIENT

PROFILE.............................................................................................................................. 42

APPENDIX B. MEASUREMENT OF THE ANODIC ELECTRIC FIELD GRADIENT ........................ 45

APPENDIX C. SAMPLING METHODS .............................................................................................. 47

APPENDIX D. FORMS FOR DATA COLLECTION ........................................................................... 53

Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 5 of 53

1. INTRODUCTION

1.1 Scope
The aim of the present Document is to define the requirements for the correct execution of
underwater inspections of cathodic protection (CP) systems of offshore platform steel jackets,
submerged pipelines, subsea wellheads and offshore floating structures.

The Document defines:

 the applicable measurements and inspection techniques;
 the requirements for the design and planning of the inspections;
 the requirements for the execution of the inspections and all related activities.

The present Document integrates some ENI E&P norms dealing with underwater inspections, and in
some cases it replaces some of the content as indicated in the text.

The following issues are not within the scope of the present Document:
 analysis, elaboration and management of the inspection results;
 requirements for equipment and instrumentation to be used for the execution of the inspection
(e.g. supply vessels, underwater equipment, ROV, etc.), with the exception of the instrumentation
used for the CP measurements and inspections;
 the safety requirements for the execution of the inspection.

1.2 Document organisation

Section 2 reviews the applicable measurements and inspection techniques.

Section 3 provides the criteria for the planning of the underwater inspections of the CP system of
platforms, submarine pipelines and other structures. It covers:
 the criteria for the planning of inspections;
 the applicable measurements and inspection techniques to carry out;
 the sampling criteria for the selection of the positions where the potential measurements shall be
performed and the anodes shall be inspected.

Section 4 provides the minimum requirements for the execution of platform inspections.

Section 5 provides the minimum requirements for the execution of submarine pipelines inspections.

Section 6 provides the minimum requirements for the execution of the inspections of other
structures, including subsea wellheads and floating structures (FPSO).

The following informative appendixes deal with specific issues:

 Appendix A: Potential and potential gradient profiles of submerged pipelines
 Appendix B: Measurement of the electrical field gradient of the galvanic anodes
 Appendix C: Sampling criteria
 Appendix D: Forms for data collection

1.3 Codes & Standards

1.3.1 Codes & Standards ENI E&P
07669.GPF.OFF.SPC Criteri di programmazione delle ispezioni periodiche su piattaforma
offshore.
20181.STR.OFF.FUN Piattaforme offshore - Esecuzione delle Ispezioni.
27589.VAR.COR.PRG Linee guida per la progettazione e l’attuazione di sistemi di
protezione catodica.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 6 of 53

27604.VAR.COR.SPC Galvanic anodes for cathodic protection in sea water and saline mud.
23033.SLI.OFF.SDS Ispezione del tratto fuori acqua del riser.
23032.SLI.OFF.SDS Procedura di ispezione straordinaria dei riser
23034.SLI.OFF.FUN Functional specification for in-line inspection.
23035.SLI.OFF.FUN Functional specification for the external survey of pipelines in the
offshore areas.
23036.SLI.OFF.FUN Functional specification for the external survey of pipelines in the
nearshore areas.

1.3.2 International Codes & Standards

API RP 2A-WSD Recommended practice for planning, designing and constructing
fixed offshore platforms – working stress design.
EN 12473 General principles of cathodic protection in sea water
EN 12474 Cathodic protection for submarine pipelines
EN 12495 Cathodic protection for fixed steel offshore structures
EN 13509 Cathodic protection measurement techniques
EN 15257 Cathodic protection competence levels and certification of cathodic
protection personnel
ISO 15589-2 Cathodic protection of pipeline transportation systems. Part 2:
Offshore pipelines
DNV RP-F103 Cathodic protection of submarine pipelines by galvanic anodes
DNV RP-B401 Cathodic protection design, October 2010
NACE SP0169 Control of external corrosion on underground or submerged metallic
piping system
ASTM E122 Standard practice for calculating sample size to estimate, with
specified precision, the average for a characteristic of a lot or
process.
IMCA S 008, IMCA R012 Digital video offshore. A review of current and future technologies.
IMCA S014, IMCA R014 Discovering digital video. An introducing to digital video and its
benefits.

1.4 Definitions
COMPANY ENI E&P or a COMPANY appointed by ENI E&P (operator of the
structure)
ENGINEER ENI E&P or a company appointed by ENI E&P to perform the design
of the inspection
CONTRACTOR A company appointed by ENI E&P to perform the underwater
inspection and its authorized sub-Contractors and representatives

1.5 Symbols and Abbreviations

Ag/AgCl Silver/silver-chloride/seawater reference electrode
CVI Close Visual Inspection
CP Cathodic Protection
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 7 of 53

FPSO Floating Production Storage and Offloading

FSO Floating Storage and Offloading
GVI General Visual Inspection
H Residual height of galvanic anode
KP Kilometer Point
LCIRC Residual circumference of a cylindrical galvanic anode
LMAX Residual maximum length of a galvanic anode
LMIN Residual minimum length of a galvanic anode
MSC Mean Sea Level
NAC Number of sample anodes
NNC Number of sample nodes
NPC Number of sample positions for the execution of potential measurements of the structure
NS Number of homogenous portions of a platform
P Depth
PLEM Pipe Line End Manifold
RC Reference Cell
ROV Remotely Operated Vehicle
SCM Subsea Control Module
SPM Single Point Mooring
W Residual width of a galvanic anode
WHPS Wellhead Protection Structure
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 8 of 53

2. PERSONNEL, MEASUREMENTS & INSPECTION TECHNIQUES

2.1 Introduction
Cathodic protection of offshore structures is usually carried out by galvanic anodes; only in a few
cases impressed current cathodic protection (ICCP) systems are used.

A CP system of galvanic anodes for application in seawater includes the following components:
 structure (cathode);
 galvanic anodes in aluminium or zinc alloy;
 coating systems (normally always present in submerged pipelines) or painting systems (for
example within the splash zone of platforms); nonetheless coating and painting systems are
absent in the substructure of platforms;
 permanent monitoring system (optional), which consist of:
- reference cells (RC);
- monitored anodes;
- cables;
- conduits;
- acquisition and control unit.

The impressed current system includes, in addition to the above mentioned components, the
following components:
 inert type anodes;
 electrical components like: feeding cables; the feeding unit(s), junction box;
 anode support systems (clamps, ropes, sleds, etc.).

In seawater applications, the impressed current systems are specifically used for the retrofitting of
CP systems of steel platforms.

The design life of the CP system is usually equal to one of the structure to be protected. Thus, cases
with an extension of the design life of the CP system are frequent.

For the design and material requirements for the CP of offshore structures, reference can be made to
the ENI norm 27589.VAR.COR.PRG and to the Normative mentioned in the present Document.

2.2 Personnel
The inspections of cathodic protection systems shall be performed by divers or by ROV (Remotely
Operated Vehicle) under the supervision of qualified personnel possessing the basic knowledge in
cathodic protection (CP) and corrosion control.

2.3 Measurements and inspection techniques

For underwater inspections of cathodic protection systems, the following measurements and
inspection techniques are covered in this Document:
 visual inspections documented by photographs and/or video;
 measurements of the potential of the structure;
 measurements of the potential of the galvanic anodes;
 dimensional readings of galvanic anodes;
 sampling of anodes for chemical and metallographic analysis;
 verification of efficiency of the monitoring system;
 profiles of the potential and of the potential gradient of submerged pipelines.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 9 of 53

2.3.1 Visual inspection

The visual inspection has the scope to determine the existence and extent of any deterioration,
defect or damage on the immersed part of the structure as a result of corrosion.
Based on the level of investigation, the following types of visual inspection are considered:
 General visual inspection (GVI).
 Close visual inspection (CVI).

Visual inspection has to be documented by video and photographs. The use of high-definition video
camera and the recording of data on digital media (DVD), according to the practices recommended in
the IMCA guidelines, are recommended.

The minimum requirements for visual inspection are defined in section 3 of this Specification.

2.3.2 Potential measurements of the structure

The measurement of the potential is used to assess the correct CP level of the structure (see also
Standard EN 13509).

The potential measurements can be performed on bare submerged structures, with the exclusion of
parts or components buried in sea mud. They are not applicable to normally coated submarine
pipelines, except for bare components, like for instance flanges or valves, or at location where the
coating is missing or it has been intentionally removed.

Potential measurements can also be performed on painted surfaces, like subsea wellheads or splash
zone of jackets, provided that the coating has a sufficient degree of defectiveness.

2.3.2.1 Execution and instrumentation

The potential difference is measured between the structure and a portable reference electrode
connected to the negative terminal of a voltmeter.

The silver/silver-chloride/seawater (Ag/AgCl/seawater) is the portable reference electrode commonly

used in seawater. In particular cases, other portable electrodes such as zinc/seawater electrodes can
also be used.

The most common measurement device is the so called gun type probe, which incorporates a
metallic tip (made of stainless steel) for the contact to the structure, a reference electrode and a
voltmeter. The tool is handled by a diver which takes and records the potential readings. The same
device or an equivalent one can be assembled on a ROV (contact probe or proximity probe); the
potential measurements can be recorded on board of the ROV or can be transferred directly via
umbilical to the acquisition unit located on board of the survey vessel.

The tip of the probe shall be sufficiently acuminated in order to establish the electrical contact with
the structure. In case hard layers of calcareous deposit or of marine growth are present, they shall be
removed before the execution of the measurement. The stability of the potential reading is a
qualitative index of adequate electrical contact; fluctuations greater than a few millivolts (5 mV), shall
be interpreted as evidence of a bad electrical contact between the tip and the structure.

2.3.2.2 Interpretation criteria

The measurements of the potential of the structure are interpreted as illustrated in Figure 2.1
(EN 12473). The figure indicates the potential ranges referred to the high purity zinc/seawater
reference electrode and the silver/silver-chloride/seawater reference electrode.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 10 of 53

Ag/AgCl/seawater zinc/seawater
Severe corrosione
-0,40 +0,65

-0,50 +0,55
Free corrosion conditions
-0,60 +0,45
Partial protection
-0,70 +0,35

-0,80 +0,25
Limit for full protection (aerobic conditions)

-0,90 +0,15
Partial over-polarization, reccommended in
anaerobic conditions
-1,00 +0,05
Increasing over-polarization

-1,10 -0,05
Risks of hydrogen embrittlement of susceptible
materials and reduction of the fatigue life

Figure 2.1 Potential ranges for corrosion, cathodic protection and over-protection of steel structures
in seawater.

In a real structure, the potential distribution is the result of the following main factors:
 the position of the anodes;
 the operating potential of the anodes;
 the current delivered by the anodes;
 the local protection current demand, expressed by the protection current density; (current
demand, expressed by the protection current)
 the local geometry of the structure.

The measured value of the potential expresses the level of protection, or polarization, of the structure
in the exact position of the reading. For this reason, each potential measurement shall be associated
to the position where it has been taken.

2.3.2.3 Variations of potential of the structure

The measured potential values reflect the local polarization conditions and its variation over time, in
particular in the initial phase of polarization of the structure.

In CP systems using galvanic anodes, once correct protection conditions have been achieved, the
potential and current distributions within a homogeneous portion of the structure (see par. 3.2.3) are
uniform, including variations of a few tens of millivolts. Figure 2.2 shows the potential distributions
elaborated from sets of potential measurements taken on a steel jacket in two different moment of its
life: the first a few months after launch and the second after five years of exposure.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 11 of 53

0.060
1 year after launch

5 years after launch

0.050

0.040
Probability Density

0.030

0.020

0.010

0.000
-1050 -1040 -1030 -1020 -1010 -1000 -990 -980 -970 -960 -950 -940 -930 -920

Structure Potential (mV vs Ag/AgCl/Seawater)

Figure 2.2 Normal distribution calculated from sample of potential measurements (more than 500
readings for each curve) taken on a real structure located in about 150 m water depth, in two
different moments of its operating life.

For large size structures (e.g. steel jackets), uncoated and protected by galvanic anodes, it can be
assumed that the potential measured in a given position is representative approximately for a surface
area of about 1 m2. The case is different for partially shielded area, such as the apex of nodes, where
the local variation of potential can be more sensitive in relation to geometric factors (higher because
of local ohmic drops).

The potential measurements can be affected by a systematic error (bias) due for instance to an error
incorporated in the reference electrode.

2.3.3 Measurements and inspections of anodes

Underwater measurements and inspections of anodes include, namely:
 anode potential measurements;
 potential measurements of the structure in close proximity to the anode;
 visual inspections (GVI, CVI);
 dimensional reading of anode;
 cutting of an anode sample.

The aims of anode measurements and inspections are:

 to assess the correct performance and quality of anodes;
 to estimate the actual anode consumption.

The measurements and inspections are applicable to all submerged structures protected by galvanic
anodes, provided that the anodes are accessible to divers or ROV.

2.3.3.1 Anode potential measurements

The procedures and instrumentation for the measurement of the operating anode potential are the
same as above illustrated in par. 2.3.2.1.

The measurements of the operating anode potential shall be taken on the anode as found, without
any cleaning operation. As seen above for potential measurements of the structure, the tip of the
probe usually allows realizing the electrical contact with the anode.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 12 of 53

Only in case anodes are covered by massive and hard layers of corrosion products or of marine
growth and thus no electrical contact is allowed, the anodes shall be cleaned before the execution of
potential measurements.

The operating potential of the anodes shall be measured in more than one position. Where possible,
in particular for anodes installed on steel jackets of offshore platforms (see par. 3.2.8.2), also
potential measurements of the structure around the anodes shall be taken.

2.3.3.2 Measurements of the electric field gradient of the anode

The measurements of the electric field gradient of the anode and of the seawater resistivity allow
calculating the anodic current density, a parameter which can be adopted for the estimation of:
 current consumption of the anode;
 local protection current demand;
 the residual life of the anode and thus of the cathodic protection system.

The entire measurement methods and the instrumentation are presented in APPENDIX B.

2.3.3.3 Dimensional readings

The dimensional readings of the anodes are aimed to calculate the residual net mass of the anodes
(keeping into account the volume of the insert) and their actual consumption. The anodes
consumption is estimated also with visual inspection in the ambit of the General visual inspection,
nevertheless the dimensional readings allow a much more precise estimation of the residual mass.

In order to perform the calculations of the residual mass of the anodes, the As-Built dimensions of
the anodes shall be available before the beginning of the underwater inspection survey.

The consumption of the anode often occurs irregularly (unevenly). Therefore the dimensional
readings (required for the calculation of volume and mass of the anode) shall be acquired in different
positions in order to allow the calculation of the mean value and other significant parameters (e.g.
standard deviation).

As the taken readings have to be those relating to the residual metallic component of the alloy, any
layer of corrosion products or of marine growth shall be removed before taking measurements. The
cleaning techniques shall be decided on a case by case basis depending on the extent and hardness
of the layers. In less severe cases, cleaning can be performed by manual brushing at the positions
where measurements have to be taken. In presence of adherent layers, hydro-cleaning has to be
carried out.

The size measurements shall be taken with suitable instrumentation: meter; compass; etc.

For the case of inspections of anodes installed on jacket platforms, the requirements for the reading
of the potential measurements are given in par. 3.2.8.3.

2.3.3.4 Cutting of an anode sample

In the case of evidence of anomalous consumption of the anode than expected, a cutting of an
anode sample is taken in order to verify the chemical composition and metallographic microstructure
of the anode.

The mass of the anode sample shall be at least 100 g of the alloy. The sample has to be extracted
from the anode bulk material below the surface layer exposed to seawater, which is the material not
yet consumed by anodic activity.
The chemical analysis of the anode sample shall cover all elements of the alloy and all impurities. In
particular, reference shall be made to the available documents and to the certificates of chemical
composition of the anodes installed on the structure. Table 2.1 shows the main elements and
impurities for typical aluminium and zinc alloy anodes (see ENI E&P norm ENI
27604.VAR.COR.SPC).
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 13 of 53

Table 2.1 – Chemical composition of aluminium and zinc alloy anodes.

Zinc alloys
Element Aluminium alloys Element
Alloy Z-1 Alloy Z-2
Zn 2–6% Al 0.1 – 0.5 % 0.005 max
In 0.010 - 0.030 % Cd 0.025 – 0.07 % 0.003 max
Sn - Fe 0.005 % max 0.0014 max
Fe 0.10 % max Cu 0.005 % max -
Si (NOTE 1) 0.10 % max Pb 0.006 % max -
Cu 0.005 % max Other 0.10 % max -
Other 0.10 %max Zn remaining 99.99
Al remaining - - -
NOTE 1. For some alloys, silicon is intentionally added up to 0.21 %.

2.3.4 Potential and potential gradient profiles of submarine pipelines

The submerged pipelines, usually protected by galvanic anodes, show some specific difficulties for
the potential measurements in relation to:
 the impossibility to perform a direct electrical contact to the structure because of the presence of
coating, in some cases of concrete cover, thermal insulation and the absence of test posts;
 eventual burial of pipelines in the seabed;
 in some cases submarine pipelines are laid in high water depth.

The potential profile method (compared to a remote reference electrode) has been specifically
developed to overcome the limitations mentioned above. It provides the use of several reference
electrodes and is performed using a submarine vehicle (ROV) and a survey vessel. The acquired
potential profiles are integrated with a number of other parameters measured simultaneously, such
as: pipeline route, burial depth, the presence of free spans, visual inspections, where applicable.

The principle of the method is illustrated in APPENDIX A.

Regarding submarine pipelines protected by an impressed current system, the potential can be
monitored by a diver who moves along the pipeline and acquires potential measurements at fixed
intervals by proximity probe.

For the inspection techniques of submarine pipelines protected by an impressed current system see
par. 3.3.6.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 14 of 53

3. REQUIREMENTS FOR THE PLANNING

In this section the guidelines for the planning of CP underwater inspections are given.

The requirements for the inspection shall be defined by a Job Specification (or Project Specification)
issued by the COMPANY or by the ENGINEER on behalf of COMPANY in accordance with this
Document.

3.1 Inspection targets

The underwater CP inspections shall have the following targets:
 check for the presence of any corrosion attack;
 check the status of proper protection of the structure;
 check the integrity of the components of the cathodic protection system;
 assess the consumption of the anodes (for the systems with galvanic anodes).

In accordance with ENI norm 07669.GPF.OFF.SPC (relevant only to inspections of offshore

platforms), the following types of underwater inspections are defined, applicable to all structures
covered in this Document:
 initial inspection;
 periodical inspections (in the case of platforms: annual visit P0, periodical visit P1, periodical
visit P2);
 unplanned inspections;
 special inspections.

The CP inspections are normally planned and performed periodically in conjunction with other
inspections for the verification of the integrity of the structure. Thus costs of mob/demob and costs
associated with the execution of underwater work (especially in cases of intervention in deep water)
are optimized.

3.2 Requirements for the inspection of platforms

In this section, guidelines for the planning of CP underwater inspections of the accessible submerged
parts of offshore steel platforms, including the mono-tubular and cluster types are defined. The
platform’s substructure includes the following parts or components:
 jacket (splash zone and immersed part);
 caissons;
 risers;
 conductors and conductor sleeves;
 skirt piles;
 mud muts (upper side);
 J-tubes.

Other components, in particular driven piles and well casing, are not accessible for inspection.

3.2.1 Planning of inspections

For the new platforms, the execution of the first inspection is recommended after 1 year and no more
than 2 years after launching in order to visualize whether or not the structure is correctly polarized. In
any case, the initial inspection shall not be performed before 6 months since the launch in order to
allow the formation of calcareous deposit and the achievement of at least partial polarization
conditions.

For planning of periodical inspections (periodical visit P1, periodical visit P2), the requirements
defined in the ENI norm 07669.GPF.OFF.SPC, based on the Risk Class / Exposition of the structure,
are applicable, which are:
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 15 of 53

 Class C-1 / L-1: N. 1 inspection every 4 years;

 Class C-2 / L-2: N. 1 inspection every 5 years;
 Class C-3 / L-3: N. 1 inspection every 7 years.

Above indicated frequencies shall be intended as applicable also if a permanent monitoring system
was installed. The permanent monitoring system, where present, shall be considered itself as a part
of the CP system to be inspected (see par. 3.2.10).

Special inspections shall be promptly planned when evidences of corrosion attacks exist, in particular
corrosion fatigue cracks, and when under-protection conditions or accelerated anode consumptions
are verified.

For the execution of unplanned inspections and special inspections, reference can be made to the
ENI norm 07669.GPF.OFF.SPC.

3.2.2 Annual visit P0

The annual visit P0 regards the emerged part of the structure, including the splash zone, and
includes the following controls:
 General visual inspection;
 check the status of the components of the CP monitoring system (cables, conduit, monitoring
boxes, data acquisition unit and transmission of data);
 acquisition of potential measurements of the substructure using the permanent monitoring
system;
 potential measurements from the lower deck with portable electrodes;
 acquisition of potential measurements of the riser using portable electrode dropped by gravity
from the lower deck;
 control of insulating joints on risers.

The potential measurements, carried out using portable electrode and high impedance voltmeter, will
be acquired at each leg and each riser at the following depths (measured from the mean sea-level -
MSL):
 -2 m;
 -5 m;
 -10 m.

3.2.3 Subdivision of the structure into homogenous portions. Codification system

For the execution of potential measurements and underwater inspections, the structure has to be
divided into an appropriate number of portions (NS), assumed as homogeneous from the viewpoint of
corrosion protection conditions.1 The definition of homogeneous portions shall be carried out based
on water depth. Guidelines for the subdivision of steel jacket sub-structures into homogeneous
portions are given in APPENDIX C.

A codification system shall be available for each homogeneous portion in order to identify:
 nodes;
 structural elements (bracings, segment of legs, etc.);
 galvanic anodes.

Each of the above listed components shall be identified by a univocal code and the relevant
(average) depth.

The codification system shall be used for the random extraction of sample-elements, sample-nodes
and sample-anodes, where potential measurements shall be taken.

1
A similar approach is adopted in the design phase of the CP system; see for instance norm DNV RP-B401, where different
protection current density values are given based on water depth (see also Appendix C).
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 16 of 53

In case a codification system is not available, it will be necessary (for inspection purposes) to create
one.

3.2.4 General visual inspection

The General visual inspection (GVI) does not include the cleaning of the structure, it has to be
carried out with a camera mounted on a ROV and has to be extended to all immersed elements of
the structure to be inspected (bracings, nodes, conductors, skirt piles, caissons, etc.), with the aim of:
 evaluating the presence of corrosive attack;
 evaluating the presence of foreign bodies;
 estimating the growth of marine vegetation;
 checking the general condition of the anodes (100 % of the anodes).

If any defects or damages are found, they have to be detected, identified and subject to Close visual
inspection.

The General visual inspection shall be documented in accordance with the requirements described in
paragraph 2.3.1.

3.2.5 Close visual inspection

The Close visual inspection (CVI), carried out by divers, consists of a detailed inspection of the areas
pre-selected during the General visual inspection (GVI). These areas have to be enough cleaned
from marine deposits in order to perform more extensive inspection.

Any corroded or damaged areas have to be subject to dimensional and photographic survey (in order
to define, report and monitor dimension and position) and to the acquisition of potential
measurements in accordance with the techniques described in section 2.3.2 of this Document.

The most typical corrosion forms regarding offshore structures are:

 general corrosion;
 pitting corrosion, more frequent in the weld area;
 corrosion fatigue cracks.

The Close visual inspection has also to be extended to:

 anode samples (Ref. par. 3.2.8);
 components of the monitoring system (Ref. par. 3.2.10).

The Close visual inspection has to be documented in accordance with the requirements of par. 2.3.1.

3.2.6 Potential measurements of the structure

The potential measurements of the structure have to be carried out for each homogeneous portion as
previously identified. The measurements have to be taken in correspondence to:
 a sample of nodes;
 a sample of random positions (or elements) of the structure;
 specific components: caissons, conductors, skirt piles, etc.

The samples (nodes, random positions, specific positions) shall be selected for each inspection,
independently from previous inspection samples. The sampling criteria are defined in APPENDIX C
of this Specification.

3.2.6.1 Sample of nodes

The apex of the nodes is one of the positions of the jacket, where polarization is more difficult to be
achieved: compared to individual braces the effect of the ohmic drops at the cathode is greater. If
protection conditions are verified at the apex of the nodes, it can be reasonably assumed that the
connected braces are also protected.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 17 of 53

In the absence of previous indications of damages at the nodes, the minimum number of nodes to be
inspected has to be defined according to the criteria specified in APPENDIX C. If though, evidences
of localized corrosion or of cracks at the nodes exist, the inspection shall be extended to all the
nodes affected by corrosion damages.

In correspondence to each sample node a set of potential measurements shall be recorded as

indicated in Figure 3.1.

The maximum spacing between adjacent measurement positions of the same structural element is
1 m.

The potential measurements shall be taken on each brace of the sample node, indicating the
presence of a possible anode installed nearby and the anode-to-node distance.

Figure 3.1 Side view of a jacket node with indication of the positions where the potential
measurements shall be taken.

3.2.6.2 Sample of randomly selected positions

The sample of positions for potential measurements shall be randomly selected. This excludes any
conditioning effect in the selection procedure, as for instance: greater or lower criticality regarding the
distribution of the electrical field, ease of access, exposure. The number of random positions (NPC)
shall also be defined in relation to the inspection costs. The sampling criteria and the definition of the
sample size can be found in APPENDIX C.

For each position corresponding to a brace of the structure should be taken N. 1 potential
measurement. If the measured value was close to the threshold of protection (-800 mV vs
Ag/AgCl/Seawater), another measurement in the diametrically opposite position shall be performed
for this item.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 18 of 53

The potential measurements shall preferably be acquired at the midpoint of each brace. If, near the
midpoint an anode was installed, the potentials, if possible, shall be measured at a distance of not
less than 2 m from the galvanic anode.

3.2.6.3 Sample of measurements at selected positions

Additional measurements compared with those defined in the two preceding paragraphs may be
acquired at selected positions, which are considered of particular importance due to the criticality of
the component because of different potential distribution on the structure. These positions have to be
selected in advance in relation to the specific characteristics of the platform under consideration.

Some general guidelines are given here below:

 skirt pile: where present, skirt piles can show different protection conditions
than the jacket, depending on the distribution of the galvanic anodes
and on the current demand of the buried piles;
 splash zone: it is normally coated and protected by galvanic anodes installed
immediately below; the polarization condition can be different from
the bare parts of the jacket;
 conductors, caissons, can represent an important part of the surfaces of the jacket to be
conductor sleeve, J tube, protected; if not already included in the sample of random positions
casing: (see 3.2.6.2), potential measurements of conductor, conductors
sleeve, caissons, j-tube and casing shall be provided as
measurements in additional positions. As a general rule for
conductors, caissons, j-tube and casing, to be validated case by
case, the measurements shall be acquired at the end and the
midpoint between two adjacent planes.

3.2.6.4 Reporting
The results of the potential measurements shall be reported together with all the information useful
for their further evaluation. In particular, the following data shall be associated to each potential
reading:
 reference sample;
 for measurements at the nodes, a sketch of the node with univocal indication of the position of
each potential reading taken;
 identification code of the component to which the measurement is referred;
 water depth.

3.2.7 Measurements and inspections of sample anodes

100% of the anodes of the platform will be submitted to General visual inspection, while a sample of
anodes (defined as anode-sample) shall be subject, in addition to General visual inspection, to the
following readings:
 Close visual inspection;
 potential and gradient measurements;
 dimensional readings.

Table 3.1 summarizes the inspections, which have to be carried out on the anodes.
Table 3.1 – Inspections of anodes
Anode Category Type of exam Quantity
Anode-general  GVI 100 %
 CVI
At least N. 5 for each
 Potential and gradient
Anode-sample homogeneous portion (Ref.
measurements
APPENDIX C)
 Dimensional readings
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 19 of 53

3.2.7.1 General visual inspection

The General visual inspection has the aim to document the integrity status and the surface of the
operating anode.

The General visual inspection includes the following:

 verification of anode consumption;
 verification of anode position compared to installation drawings;
 check of the integrity of the support;
 the presence of bio-fouling and corrosion products on the surface of the anode.

Regarding the consumption, the following categories are identified:

 null;
 expected;
 excessive.

These categories shall be determined case by case on the basis of the installation year and the
residual life of the platform at the time of the inspection.

Defective anodes and/or excessively worn shall be reported and documented with videos and photos
in accordance with par. 2.3.1.

3.2.8 Sample anodes

The measurements and inspection of anodes shall be conducted on a sample of anodes (sample
anodes), which have been selected for each homogeneous portion as previously identified.

The sample size of anodes shall be defined in accordance with the guidelines defined in
APPENDIX C of the present Document.

Sample anodes shall be identified at each inspection according to the sampling methods defined in
APPENDIX C. In special cases, for example of different anode consumptions as expected, an
inspection of a single anode analyzed in previous inspections can be performed. In these cases, the
anodes to be inspected shall be considered as an additional sample (to be treated independently
from the selected sample anodes).

3.2.8.1 Close visual inspection

The Close visual inspection in addition to the General visual inspection provides the following
controls:
 verification of the connection of the anode support to the jacket;
 estimate of marine growth;
 presence of cracks and possible mechanical damages.

The Close visual inspection shall be documented in accordance with the requirements described in
par. 2.3.1.

3.2.8.2 Potential and gradient measurements

In correspondence to each sample anode the following potential measurements shall be taken (see
also Figure 3.1):
 directly in contact with the anode;
 on the structure in close proximity to the anode.

The first measurements have the aim to verify the operating potential of the anode, at least N. 3
readings have to be acquired.

The potential measurements in close proximity to the anode integrate the potential measurements of
the structure and they can be used to estimate the actual driving voltage between structure and
anode under consideration.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 20 of 53

The gradient measurements, aimed at estimating the actual anode current density and the residual
life (Ref. APPENDIX B), shall be taken in positions where contact measurements have been
acquired.

The potential measurements shall be taken as indicated in Figure 3.1.

1.0 m 1.0 m 1.0 m 1.0 m

Figure 3.1 - Side view of a ‘slender’ anode installed on a tubular element with indication of the
positions where potential measurements have to be taken.

3.2.8.3 Dimensional readings

The galvanic anodes for installation on offshore platforms are normally of slender type, trapezoidal or
cylindrical. The net mass of the anode is calculated with the external dimensions of the trapezoid or
the cylinder minus the mass of the insert.

To assess the residual net mass of the installed anodes, the following readings shall be taken: for
trapezoidal anodes:
 the minimum length, LMIN, and the maximum length, LMAX, of the anode;
 the width, W, and the height, H (see Figure 3.2 - a) in at least N. 3 positions,

and for cylindrical anodes:

 the minimum length, LMIN, of the anode;
 the circumference, LCIRC, (see Figure 3.2 - b) in at least N. 3 positions.

In case the anode consumption is quite irregular, the number of measurements of width and height or
of circumference shall be taken in correspondence of a greater number of sections.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 21 of 53

LMIN

LMAX W

a – Trapezoidal anode

LAVG

LCIRC
LCIRC,1 LCIRC,2 LCIRC,3 D

b – Cylindrical anodo

Figure 3.2 - Side and section views of a ‘slender’ anode installed on a tubular element of a jacket
with indications of the size measurements to be taken. Trapezoidal anode (a); cylindrical anode (b).

3.2.9 Measurements and inspections of additional anodes

Based on specific requirements of the structure under examination, the execution of measurements
and inspections of anodes in addition to the sample anodes can be requested.

The additional anodes will be selected based on specific criteria and needs, as for instance:
 information from previous inspections (for instance anodes showing anomalous consumption);
 need to inspect anodes located in specific positions;
 need to extend the set of the sample anodes, in case limiting the extent of the measurements.

The measurements and inspections to be performed on the additional anodes can be:
 the same specified for the sample anodes (see par. 3.2.7);
 or they can be limited to only a few measurements and inspections; for instance: only visual
inspection; visual inspection and anode potential measurement; only dimensional readings.
3.2.10 Permanent monitoring system
On platforms with a permanent cathodic protection monitoring system, the following measurements
and inspections shall be planned:
 permanent reference cells:
- visual inspection and photographic documentation;
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 22 of 53

- verification of the installation positions with respect to the drawings;

- estimation of marine growth; potential measurement (where applicable);
- potential measurement of the reference cell (where applicable);
- potential measurement of the structure around the reference cell.
 monitored anodes:
- verification of the position of the monitored anode with respect to the drawings;
- visual inspection (according to par. 3.2.8.1) and photographic documentation;
- visual check of the integrity of isolating joints installed on the insert;
- potential and dimensional measurements according par. 3.2.8.2 e 3.2.8.3;
- measurement of the ohmic drop on the shunt in order to determine the current supplied by
the anode; alternatively, the current provided by the monitored anodes can be performed by
an ammeter with very low internal resistance.
 cables, conduit and accessories:
- visual inspection;
- verification of electrical continuity of cables (where applicable).

The potential measurements of the permanent reference cells can be performed on zinc cells only;
the silver/silver-chloride probe, in fact, is usually not accessible because of the presence of plastic
material protection. In this case, measurements shall be taken on an element of the platform
positioned at the reference cell; these measurements shall then be compared with those of the same
reference cell acquired at the junction box, what represents an indirect verification of the proper
functioning of the cell.

In case the reference cells appear to be heavily covered by marine growth, the manual cleaning of
the cell shall be carefully performed not damaging any components of the cell.

The conditions of the reference cells and of the monitored anodes shall be adequately documented
by photographs or video.

The inspections of the permanent monitoring system shall be foreseen:

 on all installed cells;
 on all monitored anodes.

The inspection of the monitoring system is completed by potential readings, carried out above
waterline, at the junction box to which the cables of the reference cell are derived.

3.2.11 Buried elements

In case that the items to be inspected are buried, the feasibility of the inspection shall be evaluated
case by case based on the degree and type of covering.

3.2.12 Riser

3.2.12.1 General
The following inspections shall be carried out on all the risers of the platform:
 visual inspection;
 verification of cathodic protection.

3.2.12.2 Visual inspection

Each riser shall be subject to visual inspection, as well in the part above waterline and as in the
immersed part, to the point of connection with the relative pipeline.

The aims of the visual inspections are:

 determination of the external condition of riser, including joints, coating, flanges, clamps, elbows,
spools, etc.;
 verification of the installation position of the riser and the various components (elbows, clamps,
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 23 of 53

etc..) compared to the project drawings;

 location and measurement of any corroded areas
 assessment of marine vegetation;
 localization of any obstacles and foreign bodies found in the vicinity of the riser.

For the inspection of the above water part of the riser, it is referred entirely to the Company
Standards ENI div. E & P 23033.SLI.OFF.SDS Ispezione del tratto fuori acqua del riser and
23032.SLI.OFF.SDS Procedura di ispezione straordinaria dei riser.

Regarding the immersed part of the riser, the riser shall be inspected with a video-camera mounted
on a ROV moving along the tube. The ROV shall perform at least two passings on the riser, along
two opposite directions of 180°.

The extension of any corroded or in any way damaged area shall be measured and photographed in
such a way that dimension and position of the damage are understood. The length is measured
along the longitudinal axis of the riser. The percentage of bare metal compared the total area shall be
also quantified.

In case several areas on the same riser are corroded, the relative position of each zone compared to
adjacent ones shall be highlighted.

For each riser the operating temperature of the transported fluid shall be given.

3.2.12.3 Cathodic protection measurements

It is assumed that the risers are electrically isolated from the jacket through the rubber insulation at
the clamps and through isolating joints installed in the part above water.

Risers are therefore protected cathodically through the cathodic protection system installed on the
submarine pipeline. If, on the contrary, the risers are in electrical contact with the substructure of the
platform, the risers are protected by galvanic anodes installed on the jacket.

The purpose of the inspection of the cathodic protection is to assess the protection level of the riser.

In order to measure the potential of the riser, it is first necessary to establish electrical contact with
the riser itself. The contact shall be obtained without damaging the coating of the riser. Hence, the
most convenient position is at the insulating joint, or, if present, at the junction box where the cables
connected to the risers are routed.

The following potential measurements shall be acquired:

 N. 2 readings at 180° at the end of the riser (point of connection with the submarine pipeline);
 N. 2 readings at 180° every 10 m along the entire length of the riser.

The potential measurements shall be taken also at the support clamp and if present, at all the
locations with corrosive attacks.

In case that the inspection campaign is extended also to offshore pipelines, the acquisition of the
potential profile and the potential gradient profile along the riser, establishing electrical contact with
the riser in an accessible point (e.g. at the insulating joint or at the junction box, if present), is
recommended.

3.2.13 Impressed current system

The requirements for the underwater inspection of platforms protected by impressed current CP
systems shall be also defined based on the configuration of the anode system (remote anodes,
anodes supported on tensioned strings, anodes anchored to the structure, etc.).

For potential measurements of the structure, the requirements indicated in par. 3.2.6 of this
Document are applicable. However, additional measurements shall be performed at parts of the
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 24 of 53

structure where over-protection conditions are expected, i.e. closest to the anodes. The potential
measurements can be acquired in conditions ON, since the contribution of ohmic drop due to the
circulation of the protection current in seawater is negligible.

For impressed current systems instead, specific attention shall be given to the visual inspection of
the underwater components of the impressed current system in order to verify their integrity. The list
of the components to be inspected and the criteria for any sampling shall be defined based on the
design of the adopted system. Actual position and condition of the anodes, cables, conduits and the
control system shall be verified and recorded during each inspection.

For the initial inspection, the support of the Supplier of the cathodic protection system can be
convenient, in particular for the check and possible tests to carry out on the anodes.

The inspection shall be completed by verifying the functioning of the components of the system
installed on the deck of the platform (Power Supply Unit, boxes, cables, etc.). In particular, the Power
Supply Unit shall be checked at least 6 times a year at intervals not exceeding 2.5 months. The
control shall at least include the reading of the voltage output, current output, and potential. Other
components of the system, such as boxes, wiring, insulation systems have to be inspected at least
once a year at intervals not exceeding 15 months. For other inspections to be carried out annually
(periodic visit P0) it is referred to par. 3.2.2.

For security measurements to be followed during the inspection, it is referred to appendix E of the
norm EN 12495 - Cathodic protection for fixed steel offshore structures.
3.2.14 Documentation
Special requirements for the inspections of underwater substructures of platforms shall be defined in
a Job Specification in accordance with this Document. For the structure under examination, the Job
Specification shall provide the following information:
 general data of the structure to be inspected;
 environmental conditions;
 type of inspection (initial; periodical; unplanned; special);
 type of cathodic protection system;
 available information regarding the conditions of the cathodic protection systems, including
historical data and data from the permanent monitoring system, if existing;
 available information regarding the corrosion status of the structure;
 galvanic anode type, indicating the anode alloy and composition requirements;
 installation drawings (As-Built) of the anodes and of any other components of the cathodic
protection system;
 installation drawings (As-Built) of the permanent monitoring system;
 drawings (As-Built) of the structure;
 drawings of the installed anodes with dimensional data (anodes and inserts) and the data;
 calculation note of the cathodic protection system (optional);
 codification system of the structural elements and of other components of the structure;
 codification system of the galvanic anodes;
 codification system of reference cells and monitored anodes;
 sample(s) of the positions of the potential measurements;
 sample(s) of the nodes to be inspected;
 sample(s) of the anodes to be inspected;
 possible request of the cutting of a sample anode.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 25 of 53

3.2.15 Summary
Table 3.2 summarizes the general criteria for the subdivision of the substructure in homogeneous
portions and for the definition of the inspection samples of the platforms. For the sampling criteria it is
referred to APPENDIX C. Table 3.3 summarizes the minimum requirements for the execution of the
inspections.

Table 3.2 – Inspections of platforms. Sampling criteria.

Class
Parameter Symbol Unit
Shallow Medium Deep
Depth P m 0 - 40 m max. 30/40 - 80/90 m > 80/90 m
Number of homogeneous
nS no. NS = 1 NS = 2 NS > 2
portions
Number of sample nodes nNC no. Ref. APPENDIX C
Number of sample
positions for potential nh no. Ref. APPENDIX C.
measurements
Number of measurements
- - to be defined case by case
in special positions
Number of sample anodes nAC no. Ref. APPENDIX C
Number of additional
- - to be defined case by case
anodes
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 26 of 53

Table 3.3 – Minimum requirements for the execution of cathodic protection inspections of platforms.
Element Type of measurements and readings N. of measurements
General visual inspection 100% of the structure
Close visual inspection Defects / corrosive attacks
On at least N. 5 sample nodes
Jacket (braces, nodes) Potential measurements at sample nodes
for each homogeneous portion
Potential measurements at sample positions Depending on the type of the
(braces) structure (see Table 3.2)
Potential measurements at selected positions To be defined case by case
Anode - general General visual inspection 100% of the anodes
Close visual inspection For each sample anode
Anode potential measurement ≥ 3 for each sample anode
Gradient measurement ≥ 3 for each sample anode
Sample anodes Potential measurements of the structure in
See par. 2.3.3.1
close proximity
LMAX, LMIN, 3 x (H,W o LCIRC)
Dimensional readings
for each sample anode
Close visual inspection
Additional anodes Potential measurements, gradient See par. 3.2.9
Dimensional readings
Visual inspection 100% of the immersed part
Riser
Potential measurements See par. 3.2.12.3
Visual inspection:
– reference cells;
– monitored anodes; 100 % of the reference cells
– cables, conduit and accessories. 100 % of the monitored
Permanent monitoring system anodes
Potential measurements:
– reference cells (Zn cells only);
– monitored anodes.
Potential measurements above water 100 % of the boxes
Components accessoires General visual inspection 100 % of the components
(conductors, caissons, etc.) Potential measurements See par. 3.2.6.3

3.3 Requirements for the inspection of submarine pipelines

This section provides the guidelines for the planning of cathodic protection underwater inspections of
submarine pipelines, including:
 flowlines connecting subsea wellheads to platforms;
 pipelines connecting platform to facilities on land;
 pipelines connecting platforms to each other (inter-platform pipelines);
 pipelines connecting platform to floating storage system (FPSO and FSO).

Above listed categories of pipelines are usually installed with an external coating and possibly with
concrete layer. They are made of welded pipe materials, (‘solid’ or ‘clad’); possible construction
materials are:
 carbon and low alloy steel;
 internally clad carbon and low alloy steel;
 stainless steel and nickel alloys.

This Document does not cover the flexible submarine pipelines; the oil and gas submarine pipelines
are covered by the Company Specifications 23035.SLI.OFF.FUN Functional Specification for the
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 27 of 53

Survey of External Pipelines in the Offshore Areas and 23036.SLI.OFF.FUN Functional Specification
for the Survey of External Pipelines in the Near shore Areas.

The submarine pipelines can be found:

 laid on sea floor;
 buried in a trench excavated into seabed;
 naturally buried;
 fully exposed to seawater, as it occurs at free spans.

3.3.1 Cathodic protection

Cathodic protection is applied in combination with high thickness coatings and usually galvanic
anodes systems are used. In a few cases only, limitedly to short length pipelines or in case of
retrofitting of the cathodic protection system, the impressed current technique is adopted.

The galvanic anodes are normally assembled as bracelets, made of two or more segments.

For the design of the galvanic anodes of CP systems the following shall be defined:
 size and mass requirements of the anodes;
 anode spacing.

Permanent monitoring systems are generally not present, because the structure is not accessible.

3.3.2 Planning of inspections

For new pipelines, it is recommended to perform an initial inspection within 1 year after the launch, in
order to confirm, that the polarization of the structure has been occurred.

For the planning of periodical inspections, if project requirements are not available, reference can be
made to the same criteria prescribed for platforms (see par. 3.2.1).

If signs of corrosion attack, of under-protection conditions or of accelerated anodes consumption are

present, special inspections shall be planned immediately.

3.3.3 Homogeneous portions

It is convenient to divide the pipeline under investigation into portions based on:
 Proximity to platform or to subsea wellhead or to storage floating vessel: the cathodic protection
conditions can be affected by:
- higher temperature of the fluid;
- current exchange between the connected structure and the relevant CPs;
- minimum anodes spacing.
 Proximity to shore (shore approach): the protection conditions can be influenced by:
- the low sea depth (this also affects the accessibility to support vessel and ROV);
- current exchange with the onshore-pipeline section and with connected underground
structures;
- electrical interference with onshore CP systems.
 Different features of the pipeline and of the cathodic protection system: different sizes or
characteristics of the anodes or different spacing.

3.3.4 Visual inspection

In case of submarine pipelines, the visual inspection is performed with a camera mounted on ROV in
order to highlight:
 special components of the pipelines, such as anodes, flanges, valves, etc.;
 damages to coating;
 damages to concrete layer;
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 28 of 53

 accumulation of deposits;
 presence of free-spans;
 burial status;
 presence of objects or obstacles close to the pipeline;
 presence of crossings with electrical cables or other pipelines.

These events shall be documented by video and photo, indicating for each event the coordinates and
the kilometer points (KP initial and final). The visual inspection shall be extended to all accessible
sections of the pipeline (in the case the pipeline is inspected for its total length), or alternatively to the
sample sections being inspected.

3.3.5 Pipelines protected by galvanic anodes: potential profiles and potential gradient
The control of the protection conditions is performed through the potential profile technique (see
APPENDIX A), this technique allows also the simultaneous reading of the profile of the potential
gradient in order to detect and localize coating defects and the local current density.

The technique is applied:

 for the whole length of the pipeline, with the exclusion of the Surf Zone (water depth between
3.5 m and 1.5 m) and Coastal Zone (water depth lower than 1.5 m), which are not accessible by
ROV, or
 on sample sections.

Any sample sections shall be defined case by case, based on parameters like:
 total pipeline length;
 environmental variations along the pipeline route: depth; presence of free spans; etc.;
 differences of the cathodic protection system along the pipeline route: spacing of bracelet anodes;
type of coating; presence of concrete layer; presence of foreign pipelines; etc.;
 aspects regarding the inspection costs.

For the execution of the potential profile, the contact potential measurement of an anode located at
the starting point shall be taken. If the pipeline and the anode are buried, it will be necessary to dig
until the anode, or alternatively, if feasible, the contact measurement may be performed directly on
the connected structures.

The contact measurement at the anode is used to measure the potential with respect to an electrode
located in a remote position. It is recommended to take at least a contact measurement on an anode
around every km. In case the pipeline is totally buried, it is recommended to acquire the potential of
the anode every 5 km, evaluating the feasibility case by case on the base of the burial and of the
configuration of the pipeline.

The potential measurements obtained on the anodes shall be documented, indicating for each anode
its KP on the gained value.

3.3.6 Pipelines protected by impressed current system

The potential of the pipeline can be measured in conditions ON, i.e. with the active current protection.
This value includes the contribution of the ohmic drop between the electrode and the pipeline due to
the circulation of the protection current in the seawater. In general, except for areas around the
anodes, this contribution is negligible (so the measurement can be acquired in conditions ON and is
not necessarily in INSTANT-OFF). Furthermore, as the measurement of the potential in ON
conditions also contains the ohmic drop due to the circulation of the protection current along the
pipeline, it is recommended the execution of a potential measurement in INSTANT-OFF conditions at
the point of the pipeline, most distant from the anodes position.

The potential measurement shall be acquired through a portable electrode and a voltmeter. The
negative pole of the voltmeter is connected to the electrode, while the positive pole is connected to
the structure. The connection to the structure can be completed using the monitoring connection (if
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 29 of 53

present) or the negative connection of the Power Supply Unit of the cathodic protection system. The
connection shall be made when the Power Supply Unit is switched off (OFF).

The acquisition of the potential measurement provides the use of a portable electrode (proximity
probe) handled by a diver who moves along the pipeline. The measurement shall be acquired at
fixed intervals. The spacing between two successive measurements can vary between 5 and 10 m.
In the case that the extension of the pipeline would prevent the acquisition of the potential by a
portable electrode, the potential shall be controlled through the acquisition of the profile according to
the technique reported in APPENDIX A.

If the pipeline is provided with a permanent monitoring system, potential measurements in the test
post shall be acquired annually at intervals not exceeding 15 months.

The inspection shall be completed by the verification of the Power Supply Unit and components of
the cathodic protection system.

In particular, the Power Supply Unit shall be checked at least 6 times a year at intervals not
exceeding 2.5 months. The check shall include as a minimum the readings of voltage output, current
output and potential (if possible). Other components of the system, such as boxes, wiring, insulation
systems shall be inspected at least once a year at intervals not exceeding 15 months.

The underwater inspection shall be completed by a visual inspection of the structure (Ref. par. 3.3.4)
and of the components of the monitoring system.
For security measurements to be followed during the inspection, it is referred to appendix E of the
norm EN 12474 - Cathodic protection for submarine pipelines.
3.3.7 Shore approach
For submarine pipeline connected to shore, it is convenient to handle separately the section close to
shore, in which most vessels and ROV may not be able to operate because of the low water depth.
The extent of the shore approach shall be defined case by case in relation to the bathymetric profile.

In the shore section it is possible to obtain the acquisition of the potential profile with the electrical
contact with the pipeline made onshore (e.g. at the isolating joint) and the local reference electrode
moved by a diver along the route of the pipeline.

3.3.8 Measurements and inspections of anodes

Differently from platforms, the galvanic anodes on pipelines are often not accessible. Therefore there
are no general criteria for the execution of measurements and inspections of anodes and for its
sampling applicable.

If the anodes are accessible, even only partially to the divers, it is recommended the execution of:
 visual inspection;
 measurement of potential;
 dimensional readings,

in accordance with generalized requirements described for platforms (see par. 3.2.7).

For dimensional readings of bracelet anodes, suitable tools and devices shall be used in order to
measure length and consumed thickness of anode segments.

Also the integrity of the electrical connection with the structure shall be verified and documented.

The burial degree of the galvanic anodes shall be detected and reported based on the following
ranges:
 fully exposed;
 75% exposed;
 50% exposed;
 25% exposed;
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 30 of 53

 fully buried.

In the case of buried not accessible anodes, case by case the feasibility shall be evaluated for the
planning of excavations, which can give access to a sample of anodes in order to carry out the above
mentioned inspections. The extent of the anodes sample shall be evaluated for the project under
study.

3.3.9 Potential measurements at the pipeline extremities

The arrival and departure positions of the pipeline are sometimes accessible; for instance it is the
case for the riser on deck-platforms or for the isolating joints at sea-shore. In the case of pipelines
connected to subsea wellhead, there are often metal structures present electrically continuous with
the same pipeline, for example: connected to the pipeline to be inspected, like flanges, manifold,
PLEM.

At these positions, where electrical contact to the structure is feasible, it is recommended to perform
stab potential measurements. In fact, the end sections compared to the rest of the pipeline can have
different protection conditions. The stab potential measurements of the structure integrate the profiles
of the potential and of the gradient.

3.3.10 Documentation
The project requirements for the underwater cathodic protection inspections of submarine pipelines
shall be covered in a Job Specification to be issued in accordance with this Document. The Job
Specification shall provide as a minimum the following information:
 environmental conditions;
 type of cathodic protection system;
 type of inspection (initial; periodical; unplanned; special);
 pipeline data: dimensional data; materials; conveyed fluids;
 detail of the pipeline sections at its extremities; possible presence of isolating joints;
 available information on the status of the cathodic protection system and of coating;
 available information on the corrosion status of the pipeline;
 galvanic anode type, indicating the anode alloy and composition requirements;
 typical drawings of the installed anodes with indication of: anode sizes and mass; details of the
connection to pipeline;
 data about anode spacing;
 calculation note of the cathodic protection system (optional);
 codification system of the anodes;
 definition of the pipeline sections for the execution of the potential profiles;
 possible sample(s) of the anodes to be inspected;
 possible request of the cutting of a sample anode.

3.4 Requirements for the inspection of subsea wellheads and other offshore structures
In this section the guidelines for the planning of cathodic protection underwater inspections of
offshore structures for hydrocarbon production, which are:
 subsea wellheads;
 PLEM;
 FSO, FPSO, SPM;
 other similar structures.

3.4.1 Planning of inspections

Planning shall be completed on the basis of the following parameters:
 design life;
 type of inspection: initial, periodical, etc.;
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 31 of 53

 Risk Class, assessed based on human risk factors (safety), environmental factors and importance
of the asset;
 protection conditions, with particular reference to evidences of under-protection conditions or of
accelerated anode consumption;
 water depth;
 presence of permanent monitoring system.

In the absence of specific indications, reference can be made to analogous requirements for related
structures, in particular platforms.

3.4.2 Subsea wellheads

The subsea wellhead includes the following main structures:
 Xmas-trees and wellhead;
 wellhead protection structure, WHPS;
 subsea control modules, SCM;
 connection to flowline.

The protection structure is usually made of steel; the wellhead may include different materials than
steel, in particular stainless steels and nickel alloys.

Normally cathodic protection with galvanic anodes in combination with coatings or painting is
provided. Different types of anodes are often installed, which are different in sizes, anode alloy and
supplier. Slender (trapezoidal or cylindrical) and flush mounted are the most common anode types.

3.4.2.1 Visual inspection

For visual inspection the same requirements as defined for the platforms are applied. (Ref. par. 3.2.4
and 3.2.5).

3.4.2.2 Potential measurements of the structure

In any case, measurements shall be acquired on all different parts of the system.

The potential measurements of the structure shall be taken in correspondence to previously identified
positions. Since these structures are relatively small, the sampling can be easily extended to the
entire structure. In any case, measurements shall be acquired on all different parts of the system.

3.4.2.3 Measurements and inspection of anodes

The measurements and inspection of anodes shall be conducted on a sample of anodes (sample
anodes).

The sample shall consist of at least N. 5 anodes and shall include all different types of installed
anodes.

Anodes sample shall be identified at each inspection, based on the sampling criteria presented in
APPENDIX C.

For the execution of visual inspection, potential measurements and dimensional readings shall apply
the requirements as defined in the case of anodes platforms (Ref. par.3.2.7, 3.2.8).

At the wellhead shall be measured the seawater temperature. In case of hot parts, temperature
measurements of the walls of the structure and of the surface area of the anodes shall be acquired.

3.4.2.4 Documentation
Special requirements for underwater inspections of subsea wellheads shall be covered in a Job
Specification to be issued in accordance with this Document (see also par. 3.2.14).
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 32 of 53

3.4.3 FSO FPSO SPM

It is the case of steel hull floating vessels readjusted for storage (FSO e FPSO) or of steel mooring
structures (SPM) anchored on seabed.

For floating structures cathodic protection is usually performed with galvanic anodes in combination
with painting. The anodes can be either slender or flush mounted type. Alternatively, also impressed
current systems are used.

SPM structures are similar to platform jackets, with coating applied in the splash zone and cathodic
protection with galvanic anodes installed in the immersed part.

3.4.3.1 Visual inspection

For visual inspection the same requirements as defined for the platforms are applied. (Ref. par. 3.2.4
and 3.2.5).

3.4.3.2 Potential measurements of the structure

The potential measurements of the structure shall be taken in correspondence to previously identified
positions.

The set of measurement positions (number of measurements to be acquired and positions) shall be
defined on the basis of geometry and dimensions of the structure, characteristics of the coating, if
present, and the cathodic protection system.

3.4.3.3 Measurements and inspections of anodes

The measurements and inspections of anodes shall be conducted on a sample of anodes (sample
anodes).

The number of sample anodes shall be defined in the Job Specification.

Anodes sample shall be identified at each inspection, based on the sampling criteria presented in
APPENDIX C. For the execution of visual inspection, potential measurements and dimensional
readings shall apply the requirements as defined in the case of anodes for platforms (Ref. par.3.2.7
and 3.2.8).

3.4.3.4 Documentation
The special requirements for the underwater cathodic protection inspections of FSO, FPSO and SPM
shall be covered in a Job Specification to be issued in accordance with this Document (see also par.
3.2.14).
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 33 of 53

4. INSPECTION EXECUTION. PLATFORMS

In this section, the requirements for the execution of CP underwater inspections of the accessible
parts of the understructure of steel jacket offshore platforms are given. Reference is particularly
made to CP systems with galvanic anodes, which are the most common type by far. In case of
structures protected by impressed current systems, the not applicable parts shall be ignored.

The requirements provided in this section integrate the ENI norm 20181.STR.OFF.FUN, replacing all
requirements dealing with cathodic protection of the same document.

The inspections are intended to be carried out by a COMPANY specialized in underwater work
(CONTRACTOR) on behalf of the COMPANY and on the basis of a Job Specification (or Project
Specification) to be issued by (or on behalf of the) COMPANY.

4.1 Job Specification

Before the execution of the inspection, the CONTRACTOR shall receive the Job Specification and all
the documents mentioned in the Job Specification.

The Job Specification shall be approved by the CONTRACTOR. In case of deviations, these shall be
submitted for approval to the COMPANY already in the bid stage or in any case before the start of
the inspection works.

The Job Specification, including any deviations approved by the COMPANY, constitutes the
reference document for the activities of executing inspections by the CONTRACTOR.

4.2 Documentation to be issued in the bid phase

In the bid phase, the CONTRACTOR shall issue the following documents:
 list of the instrument used for the execution of the cathodic protection measurements, with
relevant technical characteristics;
 list and characteristics of equipment (if not described elsewhere);
 procedures for the calibration of instruments and relevant certificates where applicable;
 list of any deviations to the Job Specification;
 plan of inspection execution; prevention and safety plan;
 modes for reporting of results;
 qualification of the employees: employment of cathodic protection personnel qualified APCE
according to EN 15257 or equivalent qualification with NACE represents a preferred certification;
 list of references for similar activities.

In case the CONTRACTOR intends to subcontract parts of the inspection activities, the list of the
subcontractors and of the subcontracted activities shall be submitted for approval to the COMPANY.

4.3 Inspection execution plan

Before the start of the inspection works, the CONTRACTOR shall submit for approval to the
COMPANY a detailed execution plan of the cathodic protection inspections.

The detailed plan of the execution of the inspections shall be in accordance with the contract
documents and in particular with the Job Specification, with any proposed deviations and the
documentation issued in the bid phase.

The following data and information shall also be reported in the detailed execution plan:
 applicable systems for the codification of the structural elements of the jacket, of the galvanic
anodes, of the components of the permanent monitoring system (if present);
 list of the elements (i.e. braces, nodes, anodes, etc.) to be inspected completed with relevant
codification and elevation.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 34 of 53

4.4 Requirements for the execution of inspections

4.4.1 Potential measurements of the structure
The potential measurements shall be performed in accordance with the project documents (see here
above) and this Document (see par. 2.3.1 and par. 3.2.6).

The potential measurements shall be performed:

 by diver with portable equipment;
 by ROV with measuring equipment.

The potential measurements shall be taken and stored using appropriate instrumentation.

The reference electrodes for the execution of the potential measurements shall be calibrated before
each immersion (diver or ROV) in accordance with the approved calibration procedures.

4.4.2 Measurements and inspections of galvanic anodes

The measurements shall be carried out on sample anodes, selected according to this document (see
par. 2.3.3 , par. 3.2.7) and the Job Specification. If required, additional inspections will be conducted
on a sample of additional anodes (see par. 3.2.9).

Measurements and readings of the sample anodes shall be preferentially carried out by divers.
Alternatively a ROV adequately equipped could be used.

Prior to other readings and measurements, the visual inspection of the anode shall be carried out
(without removing any layers of a present coating).

The potential measurements can generally be obtained without the need to clean the anode. The tip
of the measuring device allows easily the electrical contact with the anode and the execution of
stable measurements. Otherwise the anode shall be cleaned.

The dimensional readings shall be carried out after cleaning the surface, taking care to exclude in
measurements spurious contributions associated with deposits of non-metallic corrosion products
and bio-fouling.

Cleaning can be performed either by manual brushing or by hydro-cleaning. The technique and the
degree of cleanliness shall be evaluated according to the size and hardness of the deposits.

Before and after cleaning, the surface of the sample anodes shall be properly documented by taking
appropriate photos. In all photographs, the code of the anode shall be reported.

4.4.3 Permanent monitoring system

The measurements and inspections of the permanent monitoring system, if present, shall be
performed in accordance with the requirements reported in this Document (see par. 3.2.10) and in
the Job Specification.

4.4.3.1 Permanent reference cells

Prior to any measurements, visual inspection, without removal of fouling or corrosion products, shall
be performed.

The potential measurement (in case of zinc/seawater reference cells only) can be usually taken
without the need of cleaning; the tip of the gun type probe easily guarantees the electrical contact. In
the case no electrical contact with the reference cell is allowed, the reference cell shall be cleaned.

If the reference cell is covered by marine growth, cleaning shall be carefully performed, taking care
not to damage the sensitive components of the reference cell, which are cables, electrical
connections, moulded parts, protections.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 35 of 53

The conditions of all reference cells, before and after any cleaning operations, shall be documented
by photos. In all photos, the identification code of the reference cell shall be indicated.

4.4.3.2 Monitored anodes and other components

According to what is stated in par. 3.2.10 of this Document, on monitored anodes (or on a sample of
them) visual inspections and potential measurements shall be executed.

4.4.3.3 Acquired data from the permanent monitoring system

When the permanent monitoring system is connected to the reading, acquisition and control panel
installed on deck, simultaneously to the execution of underwater inspections, potential
measurements of the reference cells and of the current supplied by the monitored anodes, as they
are acquired on the panel, shall be taken. These values shall be acquired each year during the
periodic visit P0 (Ref. par. 3.2.2).

4.5 Impressed current system

The requirements for the execution of inspections of platforms protected with impressed current
systems shall be defined in the Job Specification.

4.6 Reports and documentation

4.6.1 Daily Reports
Daily reports are issued by the CONTRACTOR and approved with comments, if any, by the
Representative of the COMPANY.

In the daily reports the following is reported:

 day activities (operation log);
 weather and marine conditions;
 each event concerning the security;
 work progress;
 each identified situation which could imply deviations from the planned activities;
 any anomalies / defects (documented by video / photo);
 all the results of measurements and inspections of cathodic protection carried out during the day.

4.6.2 Preliminary Report

Within a week from the end of the field activities, the CONTRACTOR shall issue a Preliminary Report
containing:
 all the results of performed measurements and inspections of cathodic protection;
 list of all the found anomalies / defects (documented by video / photo);
 the list of all the occurred events, with particular reference to deviations from the schedule.

4.6.3 Final Report

The CONTRACTOR shall issue the Final Report for comments within the agreed terms.

The COMPANY shall provide any comments within the agreed terms.

The version of the Final Report, which incorporates all the comments of the COMPANY, shall be
issued within the agreed terms in at least N. 3 paper copies and on CD-ROM.

The Final Report will include (minimum requirements):

 adopted normative;
 used reference document;
 all the recorded potential measurements (for structure and anodes), for each reading with
indication of:
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 36 of 53

- acquisition date;
- operator (if diver);
- identification of the position where the measurement has been taken;
- type of used reference electrode and model;
- date of last calibration;
- any comments;
 calibration certificates of the reference electrodes and of all instruments;
 the results of all measurements and inspections taken on the sample anodes, for each anode
indicating the following:
- acquisition date;
- operator (if diver);
- identification of the anode and its position;
- surface condition (photographs or video);
- method of cleaning, if performed;
- dimensional readings;
- potential of the anode;
- measurement of the gradient
- any comments;
 DVDs related to General visual inspection / Close visual inspection
 daily reports.

In the case of risers, the report of performed inspections on the riser shall include, in addition to the
above mentioned items, the following information:
 project data (temperature and transported fluid);
 results of visual inspection and photographic documentation, highlighting any encountered
anomalies;
 information on the condition of the coating.

The measurements gathered during the inspection campaign and the results of the investigations
shall be reported in dedicated forms in format MS excel, which are attached to the present
Specification (Ref. APPENDIX D).
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 37 of 53

5. INSPECTION EXECUTION. SUBMARINE PIPELINES

In this section, the requirements for the execution of CP underwater inspections of submarine
pipelines are given. Reference is particularly made to CP systems with galvanic anodes, which are
the most common type by far. In case of structures protected by impressed current systems, the not
applicable parts shall be ignored.

The inspections are intended to be carried out by a COMPANY specialized in underwater work
(CONTRACTOR) on behalf of the COMPANY and on the basis of a Job Specification (or Project
Specification) to be issued by (or on behalf of the) COMPANY.

5.1 Job Specification

Before the execution of the inspection, the CONTRACTOR shall receive the Job Specification and all
the documents mentioned in the Job Specification.

The Job Specification shall be approved by the CONTRACTOR. In case of deviations, these shall be
submitted for approval to the COMPANY already in the bid stage or in any case before the start of
the inspection works.

The Job Specification, including any deviations approved by the COMPANY, constitutes the
reference document for the activities of executing inspections by the CONTRACTOR.

5.2 Documentation to be issued in the bid phase

In the bid phase, the CONTRACTOR shall issue the following documents:
 list of the instrument used for the execution of the cathodic protection measurements, with
relevant technical characteristics;
 list and characteristics of equipment (if not described elsewhere);
 procedures for the calibration of instruments and relevant certificates where applicable;
 list of any deviations to the Job Specification;
 plan of inspection execution; prevention and safety plan;
 modes for reporting of results;
 qualification of the employees: employment of cathodic protection personnel qualified APCE
according to EN 15257 or equivalent qualification with NACE represents a preferred certification;
 list of references for similar activities.

In case of subcontracting, the activities subject to subcontracting shall be indicated.

5.3 Detailed inspection execution plan

Before the start of the inspection works, the CONTRACTOR shall submit for approval to the
COMPANY a detailed execution plan of the cathodic protection inspections.

The detailed plan of the execution of the inspections shall be in accordance with the contract
documents and in particular with the Job Specification, with any proposed deviations and the
documentation issued in the bid phase.

5.4 Requirements for the execution of inspections

5.4.1 Potential and potential gradient profiles
Potential and potential gradient profiles shall be carried out according to what is indicated in the
contract documents (see above) and in accordance with this Document (see par. 2.3.4 and par.
3.3.4).
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 38 of 53

The reference electrodes for the execution of potential and gradient measurements shall be
calibrated before each immersion (of diver or ROV) in accordance with the adopted calibration
procedures.

Regarding the monitoring of the cathodic protection, for the tracts subject to inspection, in addition to
visual inspection, the following shall be reported (minimum requirements):
 contact potential measurements;
 potential profile;
 continuous profile of the potential gradient;
 burial degree of anodes.

5.4.2 Measurements and inspections of anodes

Shall be carried out according to what is indicated in the contract documents (see above) and in
accordance with this Document (see par. 2.3.3 and par. 3.3.8).

5.5 Impressed current system

The requirements for the execution of inspections of submarine pipelines protected with impressed
current systems shall be defined in the Job Specification.

5.6 Reports and documentation

5.6.1 Daily Reports
These reports are issued daily by the CONTRACTOR and approved with comments, if any, by the
Representative of the COMPANY.

In the daily reports the following is reported:

 day activities (operation log);
 weather and marine conditions;
 each event concerning the security;
 work progress;
 each identified situation which could imply deviations from the planned activities;
 any anomalies / defects (documented by video / photo);
 all the results of measurements and inspections of cathodic protection carried out during the day;
 original files (not developed) of potential and gradient potential profiles.

5.6.2 Preliminary Report

Within a week from the end of the field activities, the CONTRACTOR shall issue a Preliminary Report
containing:
 all the results of performed measurements and inspections of cathodic protection;
 list of all the found anomalies / defects (documented by video / photo);
 preliminary graphic profiles of potential and gradient;
 the list of all the occurred events, with particular reference to deviations from the schedule.

5.6.3 Final Report

The CONTRACTOR shall issue the Final Report for comments within the agreed terms.

The COMPANY shall provide any comments within the agreed terms.

The version of the Final Report, which incorporates all the comments of the COMPANY, shall be
issued within the agreed terms in at least N. 3 paper copies and on CD-ROM.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 39 of 53

The Final Report will include (minimum requirements):

 adopted normative;
 used reference document;
 calibration certificates of the reference electrodes and of all instruments;
 graphic profiles of potential and gradient;
 any anomalies / defects found during visual inspection;
 all the potential measurements acquired on the anodes completed with relevant KP;
 daily reports.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 40 of 53

6. INSPECTION EXECUTION. OTHER STRUCTURES

In this section, the requirements for the execution of CP underwater inspections of structures of
different from platforms and submarine pipelines are given, which are for example: subsea wellhead,
floating structures, berthing facilities. Reference is particularly made to CP systems with galvanic
anodes, which are the most common type by far. In case of structures protected by impressed
current systems, the not applicable parts shall be ignored.

The inspections are intended to be carried out by a COMPANY specialized in underwater work
(CONTRACTOR) on behalf of the COMPANY and on the basis of a Job Specification (or Project
Specification) to be issued by (or on behalf of the) COMPANY.

6.1 Job Specification

Before the execution of the inspection, the CONTRACTOR shall receive the Job Specification and all
the documents mentioned in the Job Specification.

The Job Specification shall be approved by the CONTRACTOR. In case of deviations, these shall be
submitted for approval to the COMPANY already in the bid stage or in any case before the start of
the inspection works.

The Job Specification, including any deviations approved by the COMPANY, constitutes the
reference document for the activities of executing inspections by the CONTRACTOR.

6.2 Documentation to be issued in the bid phase

In the bid phase, the CONTRACTOR shall issue the following documents:
 list of the instrument used for the execution of the cathodic protection measurements, with
relevant technical characteristics;
 list and characteristics of equipment (if not described elsewhere);
 procedures for the calibration of instruments and relevant certificates where applicable;
 list of any deviations to the Job Specification;
 plan of inspection execution; prevention and safety plan;
 modes for reporting of results;
 qualification of the employees: employment of cathodic protection personnel qualified APCE
according to EN 15257 or equivalent qualification with NACE represents a preferred certification;
 list of references for similar activities.

In case of subcontracting, the activities subject to subcontracting shall be indicated.

6.3 Detailed inspection execution plan

Before the start of the inspection works, the CONTRACTOR shall submit for approval to the
COMPANY a detailed execution plan of the cathodic protection inspections.

The detailed plan of the execution of the inspections shall be in accordance with the contract
documents and in particular with the Job Specification, with any proposed deviations and the
documentation issued in the bid phase.

6.4 Requirements for the execution of the inspections

6.4.1 Security
During inspections of cathodic protection systems with impressed current, carried out by divers,
power systems shall be turned off before each immersion.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 41 of 53

6.4.2 Potential measurements of the structure

The potential measurements shall be performed in accordance with the project documents (see here
above) and this Document (see par. 2.3.1 and par. 3.2.6).

The potential measurements shall be performed:

 by diver with portable equipment;
 by ROV with measuring equipment.

The potential measurements shall be taken and stored using appropriate instrumentation.

The reference electrodes for the execution of the potential measurements shall be calibrated before
each immersion (diver or ROV) in accordance with the approved calibration procedures.

6.4.3 Measurements and inspections of galvanic anodes

The requirements in par. 4.4.3 of this Document, subject to adjustments as appropriate, are applied.

6.4.4 Permanent monitoring system

The requirements in par. 4.4.3 of this Document, subject to adjustments as appropriate, are applied.

6.5 Impressed current system

The requirements for the execution of inspections of platforms protected by impressed current
system shall be defined in the Specification of Work.

6.6 Reports and documentation

The requirements, subject to adjustments as appropriate, of par. 4.6 of this Document are applied.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 42 of 53

APPENDIX A. SUBMARINE PIPELINES: POTENTIAL PROFILE AND POTENTIAL GRADIENT

PROFILE

Potential Profile
The submarine pipelines, usually protected from seawater corrosion by galvanic anodes, show some
specific difficulties for the potential measurement:
 impossibility to perform a direct electrical contact to the structure because of the presence of the
coating and, in some cases, of the concrete or thermal insulation layers, and the absence of test
posts;
 burial status;
 high seawater depth where, in some cases the pipelines are laid.

The technique of the potential profile with respect to a remote reference electrode was developed to
overcome the above mentioned limitations. It is performed using a submarine vehicle (ROV) and it is
integrated with the other inspections normally carried out for the submarine pipelines.

The potential profile is obtained from the profile of the ohmic drops (also reported as gradient
potential); this is due to the fact that the presence of the coating, often in combination with a concrete
layer and the burial status of the pipeline do not allow the execution of contact potential readings. On
the contrary, the ohmic drops can be easily measured through two reference electrodes, one located
in close proximity of the pipeline and the other one in a remote position (namely at a distance of at
least 30 m from the pipeline).

Provided that the remote reference electrode is connected to the positive terminal of the voltmeter,
the pipeline potential is:

Ex = (Ea - ΔVa) + ΔVx

where Ea is the anode potential measured by direct contact with the anode, Va is the ohmic drop on
the anode measured between two electrodes, the remote one and local the one, VX is the lateral
ohmic drop, measured between the remote reference electrode and the reference electrode at the
progressive distance x along the pipeline.

The term (Ea - ΔVa) represents the remote potential and thus it is assumed to be constant, or it is the
average of the potential of the anodes relevant to the considered pipeline segment.

Figure 0.1 shows an example of the “construction” of the potential profile of a submarine pipeline.
The contact potential measurement is performed on an accessible galvanic anode of the pipeline
(Pos. 1) through the reference electrode C; in the meantime, the potential of the anode with respect
to the reference electrode, A, in a remote position with respect to the pipeline is measured (the
electrode A is located at sea surface fixed to the survey vessel or fixed to the umbilical of the ROV, at
a distance of at least 30 m from the pipeline).

From position 1, the ROV moves the reference electrode C (mounted on the probe) along the
pipeline route (Poss. 2 and 3 in the figure) recording at a pre-defined frequency the potential data,
the progressive distance (KP) and the potential difference between the electrodes A and C. The
potential of the remote electrode A can be assumed constant as it is outside the electrical field
associated to the pipeline (i.e. the cathode) and the galvanic anodes; accordingly, the potential
profile along the pipeline is calculated as algebraic sum of the remote potential measured in Pos. 1
(in correspondence to the anode) and the potential difference between the electrodes A and C.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 43 of 53

Pos. 1 Pos. 2 Pos. 3 Pos. 4

A, remote electrode

electrode A vs. tip: electrode A vs. tip: electrode A vs. tip: electrode A vs. tip:
-0,980 V (measured) -0.980 V const. from Pos. 1 -0.980 V const. from Pos. 1 -0,978 V (measured)

electrode A vs. electrode C: electrode A vs. electrode C: electrode Avs. electrode C: electrode A vs. electr. C:
-0,100 V (measured) +0.015 V (measured) +0,095 V (measured) -0,092 V (measured)

electrode C vs.tip: pipeline potential, pipeline potential, electrode C vs.tip:

-1,080 V (measured) calculated: -0,965 calculated: -0,885 -1,070 V (measured)

C, local electrode
coating
anode defect

Figure 0.1 – Recording of the potential profile along a submerged pipeline and reconstruction of the
potential profile.

With reference to the above figure and to the values indicated, the following relationships can be
established for the potential (E):

Pos. 1:
 E anode vs C = -1,080 V (measured)
 E anode vs A = -0.980 V (measured)
 E A vs C = -0,100 V (measured)

Pos. 2:
 E anode vs A = -0.980 V (constant from Pos. 1)
 E A vs C = +0,015 V (measured)
 E PIPELINE = -0,980 V + 0,015 V = -0,965 V (calculated)

Pos. 3:
 E anode vs A = -0.980 V (constant from Pos. 1)
 E A vs C = +0,095 V (measured)
 E PIPELINE = -0,980 V + 0,095 V = -0,885 V (calculated)

Pos. 4:
 E anode vs C = -1,070 V (measured)
 E anode vs A = -0.978 V (measured)
 E A vs C = -0,092 V (measured)
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 44 of 53

Local gradient profile

Simultaneously to the acquisition of the potential profile according to the procedure above illustrated,
the local gradient potential in close proximity to the pipeline is recorded as potential difference
between two reference electrodes. The two reference electrodes are assembled as a unique probe
together with the tip for the contact measurements at the anodes. The measurement of the gradient
is based on the presence in the seawater, close to the pipeline, of an electrical field associated to the
circulation of the protection current from the galvanic anodes toward the steel pipeline, that is the
cathode. As the pipeline is coated, the protection current delivered by the galvanic anodes does not
distribute evenly all over the pipeline surface, but it is localized on the coating defects, if present (see
Pos. 3 in Figure 0.1), where the steel is directly exposed to seawater.

The local gradient profile allows to estimate the current density profile, which can be used both to
detect the coating defects and for the calculation of the residual life of the galvanic anodes.

Current density estimation

The ohmic drop measured between two reference electrodes at a sufficiently small distance,
tentatively less than 0.5 m, is:

IR = ΔE = i  ρ  d

where d is the distance between the electrodes,  the seawater resistivity and i the average current
density. Because of the small distance between the electrodes, the current density can be assumed
constant and then easily calculated.

If a parabolic relationship is assumed between current density and distance, a correction factor equal
to about 3/2 is obtained; then:

3  ΔE
i0 
2 ρ  d

where i0 is the current density at the anode or at the coating defect.

In the case of pipelines buried at a depth H in sea mud, with H>d, the following approximate
relationship can be derived:

3  H  ΔE
i0 
2  ρ  d2

Above formula provide an approximate estimation of the current density which shall be confirmed by
finite elements calculation models. More precise formulas can be figured out case by case through a
finite element modelling which takes into account the environmental conditions as well as the survey
conditions.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 45 of 53

APPENDIX B. MEASUREMENT OF THE ANODIC ELECTRIC FIELD GRADIENT

The evaluation of the anodes consumption is fundamental for the estimation of the residual life of the
installed CP System.

Anodes consumption can be determined either directly, through the dimensional readings taken by
divers, or indirectly through the measurement of the anodic current density.

Nevertheless, the dimensional readings present some specific criticalities which lead to a difficult
assessment of the inspection data and, as a consequence, of the estimation of the residual life. The
main criticalities are:
 marine growth and organic deposits on the anodes surface;
 presence of corrosion products on the anodes surface;
 non-uniform consumption.

The above criticalities may be overcome estimating the anodes consumption through the
determination of the actual anodic current density.

The anodic current density is calculated through the measurement of the gradient of the electrical
field generated by the anode. The anodic electric field gradient can be measured by a dedicated
multi-electrode probe mounted on the ROV. The probe consists of N. 2 reference electrodes spaced
of a fixed length d. For the measurement of the gradient, the probe shall be positioned in
correspondence to the anode and maintained perpendicular to the anode surface, in contact with it.
Once the probe has been positioned, the ohmic drop between the upper and lower reference
electrodes shall be measured. The ohmic drop, IR, is then used for the calculation of the anodic
electric field gradient, grad, according to the following formula:

IR
grad 
d

The electrical field gradient is related to the anodic current density, ia, through the following relation:

grad
ia 
ρ

where  is the seawater resistivity.

The anodic current density allows the estimation of the actual anode consumption, which can be
used for the calculation of its residual life.

In particular, the anodic current density, ia, is proportional to the rate of consumption of the anode,
vanode, through the Faraday Law.

PM i A
v anode    3.1536  10 4
zF 

where:
 vanode is the anode consumption rate, mm/year;
 PM is the molar mass of the anode (in the case of Al-alloy anodes it is equal to 27
g/mol);
 z is the valence (in the case of Al-alloy anodes it is equal to 3);
 iA is the anodic current density, mA/m2;
 F is the Faraday constant, 96485 C;
  is the anode density (in the case of Al-alloy anodes it is equal to 2880 kg/m3);
 3,1536104 is the coefficient to be adopted in order to express the consumption rate in
mm/year;
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 46 of 53

Thus, from the anode consumption rate, the actual diameter and the actual mass may be estimated
(in the case of trapezoidal anodes, the calculations shall be referred to the equivalent diameter –
Refer to DNV RP-B401), and thus the residual life of the anodes can be determined too.

The above inspection technique integrates the anodes dimensional readings taken by the divers; in
addition, it allows to reduce the employment of the divers and the time required for the inspections
since the above illustrated readings are taken with the dedicated probe mounted on the ROV used to
perform the survey.

Equipment
The equipment for the measurement of the electrical field gradient consists in a multi-electrode
probe, of the same type of the one adopted for the CP surveys of the submarine pipelines. The multi-
electrode probe includes the following devices:
 N. 2 Ag/AgCl/seawater reference electrodes mounted at a fixed spacing in the range of 300-
500 mm;
 metal tip in order to obtain the electrical contact with the anode;
 probe for the measurement of the seawater resistivity (to be installed either inside or outside the
multi-electrode probe).

The metal tip allows to achieve the electrical contact with the anode in order to measure not only the
electrical field gradient but also the anode potential. Figure 0.1 provides a schematic sketch of the
electrical field gradient reading.

IR

Anode
Anodo

Platform
Asta Brace
piattaforma

Figure 0.1 – Electrical field gradient measurement on a platform anode.

Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 47 of 53

APPENDIX C. SAMPLING METHODS

The potential measurements of the structure elements as well as the dimensional and potential
readings of the anodes are usually performed on an appropriate selected sample (i.e. the
measurements are not taken on the totality of the units which form the population, but only on a
group of them).

The sample investigation, alternatively to a census investigation (i.e. reference to the whole
population), is preferred due to the lower costs and time to be sustained in order to complete it. In the
case of the CP underwater inspections, the complexity of the investigations varies as a function of
the population size and of the difficulties (water depth, positioning, etc.) in order to detect all the units
belonging to the selected sample.

With respect to the investigation of the entire population, the sample investigation is characterized by
the following main features:
 definition of a sampling method for the selection of the population units to be inspected;
 units composing the samples, which are used for the inductive generalization of the
characteristics of the population.

For sample data to be used to draw conclusions about the population, the process of sampling (i.e.
the selection of the elements – anodes, braces, etc – to be inspected) is of a great importance, since
the selected data set represents the only available information in order to carry out the inductive
generalization. The inductive generalization is mainly achieved through the inferential analysis of the
data set (e.g. confidence intervals for the average value of corrosion potential,) and it implies the
choice of an optimum sample of data which can be constructed only with a dedicated sampling
theory, aimed at optimizing the efficiency and the costs. The main target consists in selecting a
sample with either the maximum efficiency for certain costs or with the minimum costs for a certain
efficiency.

This appendix is not intended to deal with the sampling theory, but it is aimed at providing a few
elements needed for its application in the ambit of the inspections, both in the planning and in the
elaboration phases.

Samples of positions for potential measurements and anodes

The selection of a sample of units (anodes, nodes, braces, etc,) to be inspected shall be determined
by the need of optimizing the ratio between inspection costs, which are directly correlated to the
sample size, and the quality, which is based on the usefulness of the inspection results.

The easiest sampling technique which can be adopted is the random sample one. In the case of an
offshore platform, this sampling technique implies the random selection of n units to be inspected
from the population. Such sampling method can become critical when the structure and the anodes
are exposed to diversified conditions, as it is the case of deep water platforms. In order to obtain a
representative sample of the population it would be necessary to extract a large number of sample
positions, which would imply higher inspection costs.

Thus, the simple random sampling is not the most convenient and adequate one. A more convenient
approach to be adopted for the selection of the elements to be inspected is based on the design
procedure of the cathodic protection system, which is normally performed by dividing the structure to
be protected (and therefore the elements to be inspected) into homogeneous portions.

Then the most adequate sampling method is the so called stratified sampling which considers
homogeneous families of elements, where each family shall include units (braces or anodes) which
are exposed to similar operating conditions.

With respect to the simple random sampling method, the stratified sampling method allows either to
reduce the sample size with the same efficiency, or to increase the efficiency with the same sample
size. According to this method, a random sample is extracted from each stratum; thus the number of
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 48 of 53

the samples will be equal to the number of the strata. The so selected samples will be mutually
independent and can have different sizes, so that the variability of each stratum will be lower than the
total variability leading to a more accurate estimation

Each stratum shall be selected in order to represent units working at the same operating conditions,
which can be defined on the basis of the following physical parameters of the seawater:
 oxygen concentration;
 temperature;
 local turbulence.

The above mentioned parameters determine the protection current density and consequently the rate
of consumption of the anodes.

For synthesis purpose the physical parameter which sums up all the above mentioned ones is the
water-depth.

With reference to offshore platforms, the following homogeneous strata can be identified:
 jacket plans;
 conductors pipes;
 mud mats and skirt piles.

Platforms jackets: subdivision of the structure into homogenous portions.

From cathodic protection viewpoint, the homogeneous strata of the jacket, in this document reported
as homogeneous portions, are identified as part of the jacket between two plans. The deepest
homogeneous portion shall include also the buried parts of the jacket, as for instance the fixed piles
and the lower side of the mud mats. The exact definition of each homogeneous portion of a steel
jacket shall be based on the specific characteristics of the structure under study. Based on water
depth, the following classes of steel jacket can be defined:
 shallow water platforms: up to 30 ÷ 40 m;
 medium water platforms: from 30 ÷ 40 m to 80 ÷ 90 m;
 deep water platforms: above 80 ÷ 90 m.

Table 0.1 reports some examples of structures installed at various water depth, with indications of
the total surface area cathodically protected (both for seawater and sea mud) and the number of
homogeneous portions to be individuated. In the same table, the total number of installed galvanic
anodes is reported, which actually depends on the design life of the structure as well as on the
anodes dimensions.

Table 0.1 – Homogeneous portions

Surface area N. of N. of
Water
Case Class Jacket installed homogeneous
depth Seawater Sea mud anodes portions (NS)
2
(-) (-) (-) m m m2 (-) (-)
A Shallow 4 legs 36 2,500 2,000 190 1
B Shallow/Medium 4 legs 42 2,500 1,420 94 1
C Medium 4 legs 73 4,500 2,700 164 2
D Deep 4 legs 100 10,400 1,000 370 3
E Deep 10 legs 170 80,000 20,000 2,340 3-4

For shallow water platforms, installed in water-depth up to 30 ÷ 40 m, a unique homogeneous portion

can be defined (NS = 1); on the contrary, for deeper platforms, more than one homogeneous portion
shall be considered; tentatively, a single homogeneous portion shall extend vertically up to 50 m.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 49 of 53

The partition of the structure into homogeneous portions shall be carried out on the basis of the
following parameters: geometry of the jacket (for instance number of immersed plans); symmetry of
the structure; water depth. Variations of the protection conditions can occur within a homogeneous
portion, caused by local parameter variations (for instance the different exposure of the jacket
elevations to prevailing marine currents). These effects, however, can be eventually assessed by a
careful elaboration of the inspection results and can determine a greater variability of the collected
data.

In the case of wrong positioning of the anodes in the design phase, within a homogeneous portion
some specific zones, where the target polarization level can be more difficult to be achieved, may
exist; therefore, it is useful, before execution of the inspection, to review the design document of the
cathodic protection system in order to detect any possible error in the design of the CP system.

For each homogeneous portion, a codification system shall be available in order to identify:
 nodes;
 braces;
 ancillary or non-structural components;
 galvanic anodes.

Each element to be inspected shall be univocally associated to the relevant identification code and
elevation.

The codification system shall be used, for the extracting of random samples of the units to be
inspected (braces, nodes, anodes, etc.).

In absence of a codification system, it shall be defined one in the planning phase of the inspection.

Sample size
The sample size is the number of observations composing a sample. At the same conditions, a larger
sample allows a more precise estimation of the average values of the properties under study but also
increases the costs to be sustained for the inspections. Accordingly, the sample size shall be defined
on the basis of the inspection costs and on the precision required for the estimation of a given
parameter. (Refer to ASTM E 122)

The sample size shall be determined on the basis of the costs/budget for the inspections, or as a
function of efficiency of estimators. In this case it is necessary to specify the maximum sampling error
(difference between a sample statistic used to estimate a population parameter and the actual but
unknown value of the parameter) willing to accept for the estimation of the corrosion potential
average. In practice this means to choose a confidence level.

Considering the case at par. 0, a sampling method aimed at optimizing costs is proposed, provided
that the minimum number of items to be inspected (i.e. the sample size) shall always be greater or
equal to n, according the maximum acceptable level of error.

Accordingly, the minimum sample size can be defined in accordance with Standard ASTM E 122;
based on a normal distribution of the characteristic2; the equation for the size, n, of the sample is as
follows:

2
 3s 
n  (1)
 E 

Where:
 3 is the value of the normal standard distribution related to a confidence level (1-α) equal to 99%;
 n is the sample size;

2
In case the data distribution is not normal, please refer to Standard ASTM E 122.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 50 of 53

 s is the estimate of the standard deviation;

 E is the maximum acceptable difference between the unknown population average (true value)
and the sample average (estimate value). For instance, in the cases of braces or nodes, E can be
fixed equal to 10 mV, while for anodes E can be related to the anodes dimensions).

Formula (1) can be adopted in the case past inspection data are available.

Otherwise, the following criterion can be followed for the definition of the sample size:
 anodes: at least 5% of the population units, with a minimum quantity of sample size equal to 5 for
each homogeneous portion;
 nodes: at least n. 2 for each immersed plan, (at least N. 5 nodes for each homogeneous portion);
 braces: at least 5% of the population units, with a minimum quantity of sample size equal to 30 for
each homogeneous portion;

Table 0.2 summarizes all the above mentioned cases. For the construction of the sample, reference
shall be made to the next paragraph.

Table 0.2 – Sample size

Type of element Past inspection data Sample size Minimum Size
Yes Ref. formula (1) 30 per homogeneous
Brace
No 5% portion
Yes Ref. formula (1) 5 per homogeneous
Anode
No 5% portion
Yes Ref. formula (1)
5 per homogeneous
Node No at least N. 2 for portion
immersed plan

Sampling methods
Braces
As sampling method, a multi stage sampling can be used in order to consider the platform elevation
and the length of the braces. Thus, the units are firstly grouped on the basis of the elevation, while in
the second stage the units are grouped on the basis of their length.

Primarily homogeneous portions of the platform are identified on the basis of the platform elevation.
These selected homogeneous portions represent clusters of braces. Then, within each cluster a
random sampling of some braces is performed. The total number of braces where potential
measurements shall be taken is selected considering the costs of the inspection and the variability
within clusters (known through the past inspection data).

Moreover in order to take into account the structural importance of each brace, a selection criterion
based on the length of each brace is considered.

To identify the number, n, of braces to sample, the formula here below can be used:

C  H  CH  n  c (2)

where:
 C represents the total budget cost which can be supported;
 CH is the cost for each load displacement (i.e. the cost due to the movement of personnel and
instrumentation from different elevation);
 H is the total number of clusters;
 c is the cost for each measure on a brace ;
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 51 of 53

 n is the total number of brace inspected.

The total calculated number of braces to be inspected shall be greater or equal than a minimum
quantity defined case by case on the basis of the characteristics of the platform and on the inspection
data collected from previous surveys, if present.

Subsequently the number, n, of braces can be allocated in the different clusters (portions) previously
identified.

If past data are not available, the selected quantity of braces are allocated proportionally to the total
number of braces of each cluster, NH.

∑h1nh
H
The sample size (i.e. number of braces to sample) of each cluster, n h , with h  1, ...H and n 
is:

Nh
nh  n (3)
N

H
Where N is the total number of braces of the platform N   Nh .
h1

Within each cluster, the nh braces of the platform are then chosen by a random sampling stratified by
elements length. The braces are divided in strata according to their length. Then to each stratum i is
associated a weight whi (stratum i in the group h) proportional to the importance of the stratum (i.e. to
L n
the length of the elements and to the size of the stratum ni). The weight is w hi  i i , where Li is
L
I
the brace length in the stratum and L, L   L i  n i , is the sum of all the strata lengths present in the
i1
cluster.

For instance, if in the case of a shallow water platform (H = 1, Nh = 130) N. 3 strata of braces are
defined:
 braces, conductor zone, L 1  1.5 m, n1  40;

 plan-braces L 2  7 m, n 2  65;
 inter-plans braces; L 3  15 m, n 3  25;
 The weight associated to each stratum will be:
1.5  40
 braces, conductor zone, w 1,1   0.07;
1.5  40  7  65  15  25
7  65
 plan-braces, w 1,2   0.51;
1.5  40  7  65  15  25
15  25
 inter-plans braces, w 1,3   0.42.
1.5  40  7  65  15  25

The number of elements to be inspected per stratum nhi is selected proportionally to the weight
associated to each stratum according to this formula:

n hi  n h  w hi (4)

Within each group the elements to be inspected are randomly selected.

In case past data are available, the number of braces to be inspected for each cluster can be
allocated proportionally to the variability of each cluster.
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 52 of 53

Nh  Sh
nh  n H
(8)
N
h 1
h  Sh

Where, Nh, is the total number of braces of each cluster and Sh the variance (that it is known from
past studies) of each cluster.

This method allows to get more cluster samples size, nh, in correspondence of clusters whose
variability (heterogeneity) is great and to get less cluster sample size, nh, in correspondence of
clusters whose past data are homogeneous. It allows intensifying the inspections in the platform
zones which can be more heterogeneous because of the effects of marine currents or wrong design
of the CP system).

Sample Anodes
For each homogenous portion the sample anodes shall be randomly selected. The sample size can
be defined according either to par. 0 or to formula (2). In case of past inspection data, the number of
anodes within each cluster shall be selected with the same procedure illustrated for the sample
braces, otherwise the number of anodes for each homogeneous portion shall be allocated
proportionally to the total number of anodes of each cluster.

Sample nodes
The sample nodes shall be selected by the ENGINEER on the basis of the complexity, positioning
and structural importance of the node.

References
W.G. Cochran, Sampling Techniques, 3rd ed. (New York, NY: John Wiley and Sons, 1977).

P.S. Levy, S. Lemeshow, Sampling of Populations: Methods and Applications, 1st ed. (New York, NY:
John Wiley and Sons, 1999).

B. V. Frosini, M. Montinaro, G. Nicolini, Il Campionamento da Popolazioni Finite. Metodi e

Applicazioni. 1° ed. (Milano, Giappichelli, 2011).
Eni S.p.A. 20311.VAR.COR.SDS
Rev. 1 - April 2011
Division Exploration & Production
Page 53 of 53

APPENDIX D. FORMS FOR DATA COLLECTION

MOD.COR.CPS.005: General visual inspection (GVI) / Close visual inspection (CVI);

MOD.COR.CPS.006: Potential measurements on platform braces;
MOD.COR.CPS.007: Sample anodes;
MOD.COR.CPS.008: Monitoring system.