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Cathodic Protection Calculation Review In

Accordance With the Utilized Equipment

The right of intellectual property of this document is CHAGALESH

reserved to Chagalesh Consulting Engineers Company. CONSULTING
Neither the whole nor any part of this document shall be ENGINEERS
reproduced, copied, lent or disclosed, directly or indirectly, CHCE Document
in any retrieval system or transmitted in any form or any Number:
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1 ISSUED FOR REVIEW/ 18.05.1399

REV. PURPOSE OF ISSUE PREPARED BY REVIEWED BY APPROVED BY DATE

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REVISION INDEX
PAG

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OWNER / MC CONTRACTOR OWNER / MC CONTRACTOR
E

0 1 2 0 1 2 3 4 5 6 0 1 2 7 8 9 10 11 12 13
1 *
2 *
3 *
4 *
5 *
6 *
7 *
8 *
9 *
10 *
11 *
12 *
13 *
14 *
15 *
16 *
17 *
18 *
19 *
20 *
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CONTENTS

1. PURPOSE

2. REFERENCE DOCUMENTS

3. STRUCTURE TO BE PROTECTED

4. DESIGN BASIS

5. DESIGN CALCULATION
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1. PURPOSE

This document is prepared for Cathodic Protection calculation and analysis review in
accordance with actually utilized equipment in the process area of the END Hydro
treatment unit project in BouAli, Iran.

2. REFERENCE DOCUMENTS

The cathodic protection design is based on the following standards:

 GN-ESS-EL-520,
Specification for Cathodic Protection.

 British Standards Institution (BSI)

BS 7361(1991): “Cathodic Protection Part 1 .Code of Practice for Land & Marine
Applications”

 National Association of Corrosion Engineering

NACE Standard Recommended Practice RP0169-2002:
“Control of External Corrosion on Underground or Submerged Metallic Piping
System”
NACE RP 0285 Corrosion Control of Underground Storage Tank Systems by Cathodic
Protection

 American Petroleum Institute

API 651: “Cathodic Protection of Aboveground Petroleum Storage Tanks”

 Iranian Petroleum Standards

IPS -E-TP-820: Engineering Standard for Electrochemical Protection
IPS -M-TP-750: Material and Equipment for Cathodic Protection
IPS -C-TP-820:Construction Standard for Cathodic Protection

3. STRUCTURE TO BE PROTECTED

Cathodic protection current shall be applied to the whole underground metallic pipelines
listed in table 1. Total surface area of the structures to be protected is also calculated and
mentioned in the below tables as following procedure:

Area (m2) = Diameter (m) * Length * π

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1-1 Table: list of buried pipelines specifications for Process area

Total Surface
Item Diameter(inch) Diameter(m) Length(m)
Area(sqm)
1 1 0.0254 28.63 2.28
2 2 0.0508 1234.38 196.90
3 3 0.0762 293.8 70.30
4 4 0.1016 829.68 264.69
5 8 0.2032 192.53 122.84
6 10 0.254 72.6 57.90
7 12 0.3048 162.09 155.13
8 20 0.508 83.4 133.03
Total
Average Total area(sq
Average diameter (inch) diameter (m) length(m) m)
4.34 0.1103 2897.11 1003

TOTAL SURFACE AREA(sqm) = 1003

TOTAL SURFACE AREA WITH COEFFICIENT (20%) (sqm) = 1204

NOTE 1: Coefficient factor of 20% has been applied to U/G piping surface area for other
structures in close vicinity.

NOTE 2: overall coating damage for pipelines will be considered as 30% for 25 years design
life. 5% initial damage and 1% annual damage will be considered for pipelines coating.
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4. DESIGN BASIS

4.1 Ambient Air Temperature and Humidity

 Maximum recorded temperature: 52˚C

 Minimum recorded temperature: -3.5˚C
 Design Relative Humidity: 90%
 Climate Continental dusty

4.2 Choice of Cathodic Protection

Impressed current system is selected for protection of external surfaces of buried metallic pipes in
response to variable conditions, such as: min. current demand , anode condition and coating
quality.( HSCCI) High Silicon Chrome Cast Iron anodes are considered as impressed current
anodes for underground pipelines. This kind of HSCCI anodes are canister, C-Type tantiron
anodes , to be used , coke breeze around the anode filled in canister around the anode. The
chemical composition of Type C tantiron anodes are shown in below table.
:
Chemical composition element (wt%)
Type C(HSCCI) Type N(HSCI)
0.9-1 0.9-1 C
14.25-14.75 14.25-14.75 Si
Max 1.5 Max 1.5 Mn
Max 0.2 Max 0.2 Mo
Max 0.5 Max 0.5 Cu
4.3-5 0 Cr
Remained Remained Fe

The generally accepted design guideline for anodes buried in coke breeze is 0.1 Kg/per amp-
year. The maximum output current density and consumption rate of C TYPE , HSCCI(high silica
chrome cast iron ) anodes in different environmental conditions are as follows:

Consumption rate Maximum of output current Environmental

(Kg/A ×Year) density(A/m2) Condition
0.1 15 (with canister) Carbon
backfill
The canister type, coke breeze filled anodes advantages are as follows:
i. Reduce the resistivity of the environment surrounding the anode to increase the amount of current the anode can
discharge.
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ii. Extend the anode surface area, thus increasing the amount of current the anode can discharge.
iii. Reduce consumption of the anode since the carbon becomes the part of the anode consumed
before the anode itself.

These anodes are produced in of 2 × 60 inches. It should be noted that output current of anode with
2 × 60 inches dimension in carbon backfill environment (coke breeze) is about 2 ampers for 25
years life time.

Dimensional specifications and weight of the bare and canister anodes are as follows:

weight length Head Dia. of anode Dia. of anode

)kg( )mm( )mm( )mm(

22.5 1525 76 51

Dimensional specifications and weight of the canister anodes are as follows:

Net anode Anode Anode Canister Canister

Anode Prepackaged
Packing weight length L diameter Ø length LP diameter
Type weight (kg)
(kg) (mm) (mm) (mm) ØP (mm)
IS-23 Bare 22.5 - 1525 51 - -
ISP-23 Prepackaged 22.5 76 1525 50 2000 203

The anodes shall be installed in shallow vertical beds in order to maintain a uniform protective
current distribution.
4.3 Coating System
The conjoint use of coating and cathodic protection takes advantages to the most attractive
features of each method of corrosion control. Although coating and cathodic protection are
mutually supportive, it is important to recognize in their joint use.
4.4 Protection level
The system is so designed that the potential at any point of the protected pipelines shall be
in the range of -0.85 volts to -1.2 volts, when current ON with respect to a Cu/CuSo4
reference electrode. in the case of sulfate reducing bacteria (SRB) existence the minimum
negative potential shall be considered as -0.95 volts with reference electrode Cu/CuSo4.
4.5 Soil Condition
The soil resistivity measurements have been conducted along the main right ways of the
structures. According to attached report the average soil resistivity is equal to 70.7 Ώ.cm for
underground pipelines which is in the range of very corrosive.
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Table 2: Soil Resistivity vs. Degree of Corrosiveness

Soil resistivity
(ohm-cm) Degree of Corrosiveness

0–500 Very corrosive

500–1,000 Corrosive
1,000–2,000 Moderately corrosive

2,000–10,000 Mildly corrosive

Above 10,000 Negligible

Reference: NACE Corrosion Basics.

In accordance with standard code API 651, guidelines for the chemical analysis of the soil
for corrosive contaminates are discussed in table 4. According to the attached report of
Research Institute of Petroleum Industry the soil analysis are as table 4.

Table 4: Guidance for Resistivity Soil Analysis Data

Constituent Corrosive Very Corrosive

pH 5.0–6.5 < 5.0

300–1,000
Chloride PPM > 1000 PPM
1,000–5,000
Sulfates PPM > 5000 PPM

4.6 Current density demand

In order to calculate the amount of cathodic protection current required to achieve sufficient
protection of the total structures, a cathodic protection current density is applied to the
structure. According to the standard code IPS-E-TP-820 (Appendix B-clause b.1.2) the
minimum current density value required for protecting 3 layer PE coated pipe surface area
is equal to 0.25 mA /m2 and for bare metal 20mA/m2.
NOTE: Because very high corrosiveness of soil the coated and the bare pipe current
density assumed 0.35 mA /m2 and 30 mA /m2 respectively in this calculation and
analysis.
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4.7 Design life

Cathodic protection system shall be sized to last at least 25 years. The design life shall be
specified by the client; however we suggest that the client should also consider the
likelihood of the design life to be extended.

5. DESIGN CALCULATION

5.1 Process area

5.1.1 Protective Current Demand

According to the total surface area of the pipelines, with considering the protective current
density for bare pipe (= 30 mA/ m2 refer to clause 4.6) and coated surface area (=0.35
mA /m2 refer to clause 4.6) as mentioned in clause 3, the protection current shall be
calculated as table 5.
Table 5 : Cathodic Protection Calculation Notes
(Pipe for Process area)

Total Initial Total final

Total Surface Initial Current Initial Current Final Current Final Current Average Current
Diameter Diameter Length Total Surface Current for Current for To tal Final
A rea (sqm) for Bare Arae for Coated for Bare Arae for Coated for Coated and
Item (inch) (m) (m) Area (sqm) Coated and Coated and Current
with coeff. (A ) Arae (A ) (A ) Arae (A ) bare Arae (A )
bare Arae (A ) bare Arae (A )

A=D*L*Ω At=A*1.2 Icb=At*5%*CDb Icc=At*95%*CDc Icb+Icc Fcb=At*30%*CDb FCc=At*70%*CDc Fcb+Fcc (Icb+Icc+Fcb+Fcc)/2 Icb+Icc+Fcb+Fcc

1 1 0/0254 28/63 2/28341428 2/740097136 0/004110146 0/000780928 0/004891073 0/024660874 0/000739826 0/0254007 0/015145887 0/030291774
2 2 0/0508 1234/38 196/8984226 236/2781071 0/354417161 0/067339261 0/421756421 2/126502964 0/063795089 2/190298053 1/306027237 2/612054474
3 3 0/0762 293/8 70/2969384 84/35632608 0/126534489 0/024041553 0/150576042 0/759206935 0/022776208 0/781983143 0/466279592 0/932559185
4 4 0/1016 829/68 264/6878323 317/6253988 0/476438098 0/090523239 0/566961337 2/858628589 0/085758858 2/944387447 1/755674392 3/511348784
5 8 0/2032 192/53 122/8433814 147/4120577 0/221118087 0/042012436 0/263130523 1/32670852 0/039801256 1/366509775 0/814820149 1/629640298
6 10 0/254 72/6 57/902856 69/4834272 0/104225141 0/019802777 0/124027918 0/625350845 0/018760525 0/64411137 0/384069644 0/768139288
7 12 0/3048 162/09 155/1318005 186/1581606 0/279237241 0/053055076 0/332292317 1/675423445 0/050262703 1/725686149 1/028989233 2/057978465
8 20 0/508 83/4 133/033008 159/6396096 0/239459414 0/045497289 0/284956703 1/436756486 0/043102695 1/479859181 0/882407942 1/764815884
CDb(current density for bare pipe )= 30 mA/m2
CDc(current density for caoted pipe )= 0.3 mA/ m2
Desigen life= 25 Years Total current demand 13/31 A
Anode mass consumption rate = 0/1kg/A× Year , but Total current demand with 150% coefficient 19/96024223 A
assumed 0.25 kg/A× Year in base of soil
corrosiveness
(current demand*design life*consumption rate)
Total Required Mass of Anode(kg) in base of (utilization factor*efficiency) 19/96*25*0.25
499/0060557
consumption(Kg) 0.5*0.5
19.96 (A) x 25 (Years) x .52(kg/A Year )/ (0.5 x 0.5)

Mass of Single Anode(kg) 22.5 Kg

Total Required Mass of Anode(kg)

Mass of single Anode(kg) #24 NO.S
Total Anode Required (No.) 22/17804692
499/0060557 ( kg)/22.5 ( kg)
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5.1.2 Comparison of anode requisition

5.1.2.1 Anode requisition to cover the consumption

As above calculation 24 anode required to cover the 25 years anode consumption with 20 amperes
current demand.

5.1.2.2 Anode requisition to cover the ground bed resistance

Rg = Rb + Ra , Rb = backfill to earth resistance and Ra = anode to backfill resistance, and

Rg is ground resistance

Where:
ρ: resistivity of soil (ohm.cm); ρ=70.7 ohm.cm
L: Length of active column canister (m); L=2m
d: Diameter of canister (m); d=0.0.2m
Rb= 0.00159*70.7/2 (Ln (8×2/0.2)-1)=0.074(Ln80-1)=0.074×3.38= 0.324ohm

Where:
ρ: resistivity of backfill material; ρ= 50 ohm.cm
L: Length of anode (m); L=1.525m
d: Diameter of anode (m); d=0.051m
Ra= 0.00159*50/1.525 (Ln (8×1.525/0.051)-1)=0.052(Ln239.2 -1)=0.052×4.48=
0.234 ohm

Rg = 0.234+0.324=0.5648

Maximum acceptable ground bed resistance is 0.6 ohm so one anode covers the ground bed
resistance requisition.

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5.1.2.3 Anode requisition to cover the current demand

According to IPS 850-E-TP-820, clause 13.6.1.6, anode life is influenced by the current density of
operation and the total current emitted. In free flowing sea water, a maximum output of 10 A/m²
is allowed and the total anode weight requirement shall be based on a consumption rate of 0.4 kg
per ampere per year.
Anode Output Current (A):Πdl*current
density=3.14*0.0508*1.524*10=2.43 Amperes
Total Requirement Anode (No.): Total Required Current (A) / Anode Output Current (A)
20/2.43=8.23#9
Regarding to the above calculation 6Nos of anodes cover the current demand requisitions.
With Comparison of the required Nos of anodes to cover the ground bed resistance and system
current demand and anode consumption, the maximum amount of anodes is required to
compliance with the anode mass consumption, that is 24 numbers .

5.1.2.4 System Calculations for underground Pipelines

Considering coating quality is suppressed by the time, higher current demand is required in order
to grant sufficient structure protection during the expected life of (25 years) which has been
considered in the design.

NOTE 3: Details Calculation for Underground Pipelines is given in the clause 5.1.1.
According to the calculation 24 numbers of anodes is required to apply cathodic protection
to the external surface of the underground pipelines, but because of obtaining the
satisfactory ground bed resistance and also current distribution to pipes, the number of
anodes has been increased to 30

Anode Distribution
Attenuation

Pipelines attenuation calculation and protective length

- Attenuation: Attenuation usually depends on the type of external coating and the lineal
resistance of the pipeline. A high quality coating will result in better protection spread. If
Cathodic Protection current is impressed to a Pipeline, the length of a pipeline that may be
protected may be protected from a single cathodic protection station (in each direction
from the drain point) can be calculated using the following equation:
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Pipeline lineal resistance:

The calculation formula for longitudinal resistance of pipeline:

RI = (Rs * 1000)/ (π * (D - s) *s) [Ohm/ Km] (4.2)
Where:
Rs : steel specific resistivity (Ohm. m) =18 e-7 Ohm m =18×10−7 Ω m
D : Outside diameter of pipeline (m)=0.1203
S : Wall thickness of pipe (m) = 0.01
Rl=(18×10−7 ×1000) / (3.14×11.03×0.01)= 18×10−4 / 0.3463 =0.0052 Ohm/ Km
 Coating leakage resistivity (Rt):
The calculation formula:
Rt = Ri / (π * D * 1000) [Ohm. Km] (4.3)
Where:
Ri : insulation resistance for Polyethylene/Polypropylene coating 25 years old
2
(Ohm.m²)=2000 ohm.m .
Rt=2000 /3.14×0.1203×1000=5.3 Ohm/ Km
The coating conductance is a measure of the conductivity of the coating per unit length
and is usually calculated from an estimate of the coating resistance. This is because there is
virtually no published data on the resistance of commercially available coatings and very
few specifications that actually quote real values. A value of 30000 Ohm.m2 has been
considered for PE/PP coating for 25 years design life.

Attenuation coefficient:

The calculation formula for attenuation coefficient of pipeline:

Where:
RI : Pipeline lineal resistance
Rt : Coating leakage resistivity
α =√(0.0052/5.3)= √0.00038 =0.019
following table includes Attenuation Coefficient Calculation Results:
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Phpeline Diameter( Wall Lineal Coating Attenuatio

m) thickness(m) resistance resistance n
(Ohm/Km) (Ohm/Km) coefficient
(Km ̄ ¹)
Average equal of 0.1103 0.01 0.0052 5.3 0.019
project underground
pipe

- Protective Length:

The calculation formula for protected length of pipeline:

Where:
α : Attenuation coefficient of pipeline
ΔUs : Change in pipeline potential at drain point due to application of impressed current
ΔU0 : Change in pipeline potential at a point at distance Lmax due to application of
impressed current.
U0 : Pipeline native potential (-0.5V for steel).
ΔUs = −1.2 − (−0.5) = −0.7V (refer to clause 4.4)
ΔU0 = −0.85 − (−0.5) = − 0.35V (refer to clause 4.4)
Lmax=1/0.0309 Ln( -0.7/-0.35- √( -0.7/-0.35)²-1)=32.36Ln2-√4-1=32.36Ln2-√3
=32.36×o.27= 8.74 km

Table 4.5: Maximum Length of Protection Calculation Results

Pipeline Diameter( Attenuation Protective
m) coefficient length from
(Km ̄ ¹) each side of
source (Km)
Average equal of project 0.1103 0.019 8.74 km
underground pipe

8.74 km˃˃2.90/2 km, and 8.74 km˃˃1.45km

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Above calculation has been done for average equal pipeline with 4.34 inch diameter
and 2897.11 m length, the calculation indicated that the CP system is adequate for
8.74 km pipeline cathodic protection .So for protective pipes with average length of
2897.11 m, is workable.

5.1.3 Ground Bed Design

Ground Bed Design for Pipelines

Impressed current ground beds are designed to have a resistance that will permit current
output with an impressed voltage within rating of D.C power supply to be used. Anodes are
installed in distributed a shallow vertical ground beds to avoid risk of damage to the coating
and poor distributed of protective current. Alternatively anodes may be installed in shallow
vertical ground bed with different spacing. Where feasible, anode placement shall be
designed to shallow discharge of nearly equal currents from all anodes in the ground bed.
For (4) ground beds have been designed for protecting the pipelines, with same numbers of
anodes : Five ground bed with 6 Nos anode with 1.5˷3 m spacing. ( In view of more safety
and longevity of serviceable life of anodes , totally 30 Nos of Canister type High
Silicon , Chrome Cast Iron anodes will be installed in the site).

 Ground Bed Resistance

The most important parameter for ground bed design is the calculation of the total ground
beds resistance.
The resistance for each ground bed is:

Rbg = 0.00159ρ/NL[Ln8L/d-1+Ln0.656N]
Rbg: anode canister to electrolyte resistance for a group of vertical anodes (ohms)
L: Length (m) of backfill column length=2m
N: Number of Anodes = 6
ρ: Average backfill Resistivity=70.7 ohm.cm
S: Anode Spacing= AVERAGE 1.5-3m
d: Backfill Column Diameter (canister type)=0.2m

Rbg = 0.00159ρ/NL[Ln8L/d-1+Ln0.656N]
Rbg = 0.00159ρ/NL[Ln8L/d-1+Ln0.656N]=0.00159×70.7/6×2[Ln8× 2/ 0.2-1+Ln0.656 ×6]= 0.0322
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Rab = 0.00159ρ/NL[Ln8L/d-1+Ln0.656N]
Rab: anode to backfill resistance for a group of vertical anodes (ohms)
L:Anode Length (m) =1.525m
N:Number of Anodes = 6
ρ: Average backfill Resistivity=50 ohm.cm
S:Anode Spacing= AVERAGE 1.5-3
d:Anode Diameter (canister type)=0.051m
Anode Weigth~22.5 Kg
Rbg = 0.00159ρ/NL[Ln8L/d-1+Ln0.656N]
Rab = 0.00159ρ/NL[Ln8L/d-1+Ln0.656N]=0.00159×50/6×1.525[Ln8× 1.525/ .051-1+Ln0.656 ×6] = 0.0508
Rmv = Rtg = Rbg + Rab = 0.0508+0.0322=0.083 Ω
THEREFORE:

Rmv2 = (according to the layout drawing with 6 Nos. Anodes) = 0.083 ohms
Rmv3 = (according to the layout drawing with 6 Nos. Anodes) = 0.083 ohms
Rmv5 = (according to the layout drawing with 6 Nos. Anodes) = 0.083 ohms
Rmv6 = (according to the layout drawing with 6 Nos. Anodes) = 0.083 ohms
Rmv9 = (according to the layout drawing with 6 Nos. Anodes) = 0.083 ohms

1/R=1/RGB2 + 1/RGB3 +1/RGB5 + 1/RGB6 + 1/RGB9

RGBT = 0.0166 Ω

Ground Bed Distance from Structures

The minimum anode ground bed distance from the buried pipes of adjacent structure to
be protected shall such be designed to provide a considerable cathodic swing potential
shift to pipes caused by the positive swing of the earth near the ground beds.

CP Circuit Resistance
The total electrical resistance of the cathodic protection circuit is included of three main
resistances as follows:

1. Anode to soil resistance that is known as “ground bed resistance”.( RGBT)

2. Structure to soil resistance
3. Connecting cable resistance is determined by the size and length of cable used
4. Pipe coating resistance
Cables for circuits are 1x95mm2 and 1x35mm 2 XLPE/PVC coated. According to
manufactures’ specification and the total lengths for each circuit, the resistance of each circuit
is determined separately. In order to calculate the circuit cable resistance, total cable for each cathodic
station is calculated.
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2 2
The resistance of 1x95mm and 1x35mm XLPE/PVC cable, which are used as circuit
cable at 50˚C, are determined by the following formulas: Cable Length x 0.216 x
0.001= Cable Resistance (1*95)
Cable Length x 0.586 x 0.001= Cable Resistance (1*35)

Cable
Item Cable Size Positive Cable
Length (m)
2 31 1*35 AJB2-CCB1
3 30 1*35 AJB3-CCB1
4 15 1*35 CCB1-PBB
6 33 1*35 AJB5-CCB2
7 44 1*35 AJB6-CCB2
8 40 1*35 CCB2-PBB
11 58 1*35 AJB9-CCB
12 72 1*35 CCB3-PBB
13 110 1*95 PBB-TR

Cable
Item Cable Size Negative Cable
Length (m)

1 20 1*35 NBB-NCB1
2 9 1*35 NCB1-NCB2
3 8 1*35 NCB2-NCB3
4 7 1*35 NCB3-NCB4
5 17 1*35 NCB4-NCB5
6 23 1*35 NCB5-NCB6
7 9 1*35 NCB6-NCB7
8 20 1*35 NCB7-NCB8
9 13 1*35 NCB8-NCB9
10 7 1*35 NCB9-NCB10
11 24 1*35 NCB10-NCB11
12 7 1*35 NCB11-NCB12
13 11 1*35 NCB12-NCB13
14 11 1*35 NCB13-NCB14
15 62 1*35 NCB14-NCB15
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Cable
Item Cable Size Negative Cable
Length (m)

16 5 1*35 NCB15-NCB16
17 5 1*35 NCB16-NCB17
18 10 1*35 NCB17-NCB18
19 17 1*35 NCB18-NCB19
20 25 1*35 NCB19-NBB
21 110 1*95 NBB-TR
AJB: Anode Junction Box
CCB: Current Control Box
PBB: Positive Bond Box
NCB: Negative Connection Box
NBB: Negative Bond Box
1/R=1/R1+1/R2=1/R3=1/R4+…………………+1/R19+1/R20=1/R21
1/R*= 1/R2*+1/R3*+1/R4*+1/R6*+1/R7*+1/R8*+1/R11*+1/12*+1/R13*
R1 ~ R21=Negative Cable Resistance
* *
R1 ~ R13 =Positive Cable Resistance
RN=Total Negative Cable Resistance
RP=Total Positive Cable Resistance
2
1*35 mm Cable resistance per unit length= 0.586Ω/km
Cable resistance =cable length (m) x cable resistance per unit length (Ω/km) x 0.001

R1= 20 x 0.586 x 0.001= 0.01172 Ω

R2= 9 x 0.586 x 0.001= 0.00527 Ω R*2= 31 x 0.586 x 0.001= 0.01816 Ω
R3= 8 x 0.586 x 0.001= 0.00468 Ω R*3= 30 x 0.586 x 0.001= 0.01758 Ω
R4= 7 x 0.586 x 0.001= 0.00410 Ω
R5= 17 x 0.586 x 0.001= 0.00996 Ω R*4= 39 x 0.586 x 0.001= 0.02285 Ω
R6= 23 x 0.586 x 0.001= 0.01347 Ω R*6= 33 x 0.586 x 0.001= 0.01933 Ω
R7= 9 x 0.586 x 0.001= 0.00527 Ω
R8= 20 x 0.586 x 0.001= 0.01172 Ω
R9= 13 x 0.586 x 0.001= 0.00761 Ω R*7= 42 x 0.586 x 0.001= 0.02461 Ω
R10= 7 x 0.586 x 0.001= 0.00410 Ω R*8= 45 x 0.586 x 0.001= 0.02637 Ω
R11= 24 x 0.586 x 0.001= 0.01406 Ω R*11= 58 x 0.586 x 0.001= 0.03398 Ω
R12= 7 x 0.586 x 0.001= 0.00410 Ω R*12= 72 x 0.586 x 0.001= 0.04219 Ω
R13= 11 x 0.586 x 0.001= 0.00644 Ω R*13= 110 x 0.216 x 0.001= 0.02376 Ω
R14= 11 x 0.586 x 0.001= 0.00644 Ω
R15= 62 x 0.586 x 0.001= 0.03633 Ω
R16= 5 x 0.586 x 0.001= 0.00293 Ω
R17= 5 x 0.586 x 0.001= 0.00293 Ω
R18= 10 x 0.586 x 0.001= 0.00586 Ω
R19= 17 x 0.586 x 0.001= 0.00996 Ω
R20= 25 x 0.586 x 0.001= 0.01465 Ω
R21= 110 x 0.216 x 0.001= 0.02376 Ω
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Cathodic Protection Calculation REVIEW OF THE CALCULATION

REV. 00 Page 18 of 20

RN=1/R= 0.0029Ω

RP=1/R*=0.0016Ω
Ω

Total CP circuit resistance shall be calculated as the following formula:

RTotal = RGB + R Positive Cable + R Negative Cable + R Structure (negligible) + R Coating(negligible)

R R R R
Total = GBT + N+ P

RTotal = 0.0166 Ω + 0.0029+ 0.0016 = 0.0211 Ω

5.1.4 Power Supply Requirement

Power supply requirements, namely current and voltage, are determined from the required
current for protection of the structures and the calculated total circuit resistance. It must be
considered that the actual power supply requirement should allow for future lodes, rectifier
aging film formation and seasonal changes in the soil resistivity. Factor of 1.5 is considered
for the capacitance of the selected Transformer / Rectifier.

T/R :
I=Current requirement=I =19.96Amps
R=Actual total circuit resistance =0.0211 Ω

Efficiency of T/R considered as 90 %

Back voltage of system considered = Vb=2 v

T/R output voltage = (I* R /Efficiency) + 2=(19.96*0.0211/0.9)+2=6.595 V

According to the client request we consider T/R with 100 volt, 125 Amperes capacity
for considering load factor and worst weather conditions.
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Cathodic Protection Calculation REVIEW OF THE CALCULATION

REV. 00 Page 19 of 20

5.1.5 Pipelines Specifications

5.1.5.1 Anode Requirement

5.1.5.1.1 Anode aging and deterioration

According to the table of pipeline calculations:

Total final current (A):13.31

Total Final Current (with 1.5 coefficients) (A): 19.96

Total Required Mass of Anode (kg):

(Current demand*design life*consumption rate) / (utilisation
factor*efficiency)

11.1 (A) x 25 (Years) x 0.25(kg/A Year)/ (0.5 x 0.5) =499 kg

Mass of Single Anode (kg) without insert rod: 22.5kg

Total Anode Requirement (No.): Total Required Mass of Anode (kg) /

Mass of single Anode (kg) =24, enhanced to 30 Nos.

5.1.5.1.2 Anode current capacity

According to IPS 850-E-TP-820, clause 13.6.1.6, anode life is influenced by the
current density of operation and the total current emitted. In free flowing sea
water, a maximum output of 10 A/m² is allowed and the total anode weight
requirement shall be based on a consumption rate of 0.4 kg per ampere per year.
Anode Output Current (A):Πdl*current
density=3.14*0.0508*1.524*10=2.43 Ampers
Total Requirement Anode (No.): Total Required Current (A) / Anode
Output Current (A) =8.23 #9 Nos.

5.1.5.1.3 System Resistance

With comparing of two above calculations the maximum No. Of anode 24
(enhanced t0 30 nos.) shall be selected.
Ra=0.00159ρ/L (Ln8L/d-1) =0.33Ω

Ra=Anode Resistance (Ώ)

ρ=Environmental Resistivity (Ώ.cm) =70.7
d=Diameter of Anode (m)=0.0508
L=Length of Anode (m) =1.524
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REV. 00 Page 20 of 20

Ia=It/Nmax.

Ia=Anode Output Current (A)=19.96/30=0.66

It=Total Current Requirement (A) = 19.96
Na=Max.Total No. of Anode = 30

Rc= (Ep-Ea) / Ia

Ea=Driving Potential (V) = -Ra x Ia = - (0.33 x 0.24) =-0.0792

Ep=Protected Potential (V) = -0. 85
Rc =Circuit Resistance (Ώ)= (-0.85-(-0.0792))/0.66=0.77
With comparing Ra & Rc:
Ra=0.33Ω and Rc=0.77Ω so, Ra<RC
Therefore:
30 No.s of anode is required and perfectly copmly with site requisitions.