Engineering Procedure
SAEP-306 29 June 2005
Assessment of the Remaining
Strength of Corroded Pipes
Piping Standards Committee Members
Nasri, Nadhir Ibrahim, Chairman
Dib, Tony Georges, Vice Chairman
Balhareth, Nasser Mohammad
Bannai, Nabeel Saad
Fadley, Gary Lowell
Holland, Brad John
Khashab, Jaafar M.
Lewis, Trevor
Mahmoud, Khalid Ahmed
Phan, Howard Cong
Rao, Sanyasi
Rasheed, Mahmood A.
Sharif, Talal Mahmoud
Shiha, Saad Mohammed
Swar, Ahmad H. (ABQ PLANTS)
Saudi Aramco DeskTop Standards
Table of Contents
1 Scope............................................................. 2
2 Conflicts and Deviations................................ 2
3 Applicable Documents................................... 2
4 Definitions...................................................... 3
5 General........................................................... 4
6 Data Required................................................ 5
7 Defect Assessment Levels............................. 5
8 Pipeline Repair Decision................................ 8
Appendix-A: Chart-1: Corroded Pipelines
Defects Assessment Flowchart................... 10
Appendix-B: Schematic Illustrations
for Defects Measurements and Grouping.... 11
Previous Issue: 29 March 2000 Next Planned Update: 1 July 2010
Revised paragraphs are indicated in the right margin Page 1 of 13
Primary contact: Nasri, Nadhir Ibrahim on 873-4525
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
1 Scope
1.1 This Saudi Aramco Engineering Procedure (SAEP) provides guidelines for
assessing carbon steel pipelines containing corrosion metal-loss defects.
Application of the guidance will establish the remaining strength of corroded
pipelines and provide the technical basis for determining the acceptability of
defects.
1.2 The assessment methods described in this procedure are intended to be used on
corrosion metal-loss defect in pipelines that have been designed to a recognized
pipeline design code, including but not limited to ASME B31.4, ASME B31.8.
1.3 The procedure can be used for in-plant piping designed and constructed in
accordance with ASME B31.8 or ASME B31.4 such as bulk plants and pump
stations.
1.4 This procedure should be used by experienced engineers or trained inspectors or
who have demonstrated capabilities in understanding and applying this
procedure. Also, they should be familiar with SAEP-020 SAEP-310 and SAES-
L-410.
Commentary:
Attending and successfully completing fitness for service courses is highly
recommended.
2 Conflicts and Deviations
2.1 Any conflicts between this standard and other applicable Saudi Aramco
Engineering Standards (SAESs), Materials System Specifications (SAMSSs),
Standard Drawings (SASDs), or industry standards, codes, and forms shall be
resolved in writing by the Company or Buyer Representative through the
Manager, Consulting Services Department of Saudi Aramco, Dhahran.
2.2 Direct all requests to deviate from this standard in writing to the Company or
Buyer Representative, who shall follow internal company procedure SAEP-302
and forward such requests to the Manager, Consulting Services Department of
Saudi Aramco, Dhahran.
3 Applicable Documents
3.1 Saudi Aramco References
Saudi Aramco Engineering Procedures
SAEP-20 Equipment Inspection Schedule
Page 2 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
SAEP-302 Instructions for Obtaining a Waiver of a
Mandatory Saudi Aramco Engineering
Requirement
SAEP-310 Pipeline Repair and Maintenance
Saudi Aramco Engineering Standards
SAES-L-150 Pressure Testing of Plant Piping and Pipelines
SAES-L-310 Design Plant Piping
SAES-L-410 Design of Pipelines
3.2 Industry Codes and Standards
American Society of Mechanical Engineers
ASME B31G Manual for Determining the Remaining Strength
of Corroded Pipelines
ASME B31.4 Pipeline Transportation Systems for Liquid
Hydrocarbons and Other Liquids
ASME B31.8 Gas Transmission and Distribution Piping
Systems
American Petroleum Institute
API RP 570 Piping Inspection Code
3.3 Guidance Document
PRCI-273-9803 Guidance for Assessing the remaining strength of
Corroded Pipeline
4 Definitions
ERF: Estimated Repair Factor can be established by dividing the maximum allowable
operation pressure (MAOP) or design pressure by the predicted failure pressure Pf.
ILI: In-Line Inspection of Pipeline
LPC: Line Pipe Corrosion equation
PRCI: Pipeline Research Council International, Inc.
Page 3 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
5 General
5.1 This procedure mandates the use of two assessment levels which are Level-1
and Level-2 as detailed in paragraph 8. Chart-1 of Appendix-A provides
schematic diagram of the two levels.
5.1.1 A level-1 assessment only considers the maximum defect dimensions,
i.e., the maximum depth(s), maximum length(s) and separating
distance(s) of an isolated defect, and uses one of the simple failure
equations. The level-1 assessment method is used for assessing multiple
or large number of corrosion metal-loss defect so that severe or critical
defects can be identified.
5.1.2 A level-2 assessment considers not only the maximum defect dimensions
but also the shape of the metal-loss area(s) of the defect. The level-2
assessment method is more complex and less conservative than a level-1
assessment method, and requires more information about the defect
shape, support of computer software and knowledge of specialists. It
gives results with higher accuracy when compared with a level-1
assessment.
5.2 For defects, which fail to pass the level-1 assessment, a level-2 assessment shall
then be considered if the defect shape is considerably variable and detailed
measurements are available.
5.3 Numerical stress analysis techniques, such as the non-linear finite element (FE)
can be used for assessing corrosion defects which fail to pass level-2. The use
of such assessment shall be approved by the Chairman of the Piping Standards
Committee.
5.4 Limitations
5.4.1 This SAEP is applicable for internal corrosion defects or external
corrosion defects in the base material of a straight pipe section and pipe
bends.
5.4.2 The assessment methods can be empirically applied to corrosion metal-
loss defects across or immediately close to pipe welds (longitudinal seam
welds, spiral seam welds and girth welds). This is subject to the
following conditions:
a. There are no significant weld defects present that may interact with
the corrosion defects.
b. The weld material is not under-matched.
c. Fracture is not likely to occur.
Page 4 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
6 Data Required
6.1 Data Required
The assessment of the corrosion metal-loss defects in line pipe requires the
following information:
a. The outside diameter of the pipe.
b. The specified minimum yield strength (SMYS).
c. The specified minimum tensile strength (SMTS).
d. The nominal wall thickness of the pipe.
e. Longitudinal and circumferential spacing between defects.
6.2 Defect shape
6.2.1 For level-1 assessment, the data of corrosion metal-loss defect shall be
presented by rectangular boxes that envelop the maximum surface
dimensions and maximum through-wall-thickness dimension of the
metal-loss area, as shown in Figure-1 and Figure-2 in Appendix-B.
6.2.2 For level-2 assessment, a corrosion metal-loss area shall be presented by
a projected profile as shown in Figure-4 in Appendix-B. The profile
represents a longitudinal cross section through the corroded area. The
profile spacing can be taken as a regular or irregular spacing according to
the software used.
6.3 Defect Grouping
6.3.1 A single metal-loss defect is a metal-loss area that is longitudinally or
circumferentially separated from other metal-loss areas by at least 3
times the nominal wall thickness.
6.3.2 A number of metal-loss areas, which are longitudinally or
circumferentially separated by less than 3 times the nominal wall
thickness shall be considered as a single defect as illustrated in Figure-3
in Appendix-B.
6.3.3 A single defect does not interact with any other metal-loss defects.
7 Defect Assessment Levels
7.1 Level-1 Defect Assessment
Page 5 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
7.1.1 For level-1, the Line Pipe Corrosion failure equation method (LPC) shall
be used.
7.1.2 ASME B31G failure equation can only be used for level-1 if the
corrosion defects data obtained by the instrument scraper.
Commentary:
The B31G method is the most conservative method. Therefore, it is
recommended only to be used for IS data to be able to develop the
pipeline maintenance repair plan.
7.1.3 LPC failure equation is defined by:
Pf = Po R s (1)
2σ
Po = (2)
⎛D ⎞
⎜ − 1⎟
⎝t ⎠
σ = SMTS (3)
⎛d⎞
1− ⎜ ⎟
Rs = ⎝t⎠ (4)
⎛d⎞ 1
1− ⎜ ⎟
⎝t⎠ ⎛ L ⎞
2
1 + 0.31⎜ ⎟
⎝ Dt ⎠
⎛d⎞
for ⎜ ⎟ ≤ 0.85 ; all lengths
⎝t⎠
Where:
Pf Predicted failure pressure for corroded pipe, lb/in²
SMTS Specified minimum tensile strength, lb/in²
D Nominal outside diameter, in
t Nominal wall thickness, in
d Maximum depth of a corrosion metal-loss area, in
L Maximum axial length of corrosion metal-loss area, in
7.2 Level-2 Defect Assessment
Page 6 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
7.2.1 The RSTRENG effective-area method shall be used for level-2
assessment.
7.2.2 The RSTRENG effective-area method is defined by a procedure of
progressive failure predictions based on the RSTRENG equation but
assuming that the equivalent depths of the incremental "defects" are
determined by the areas of the sub-sections.
7.2.3 The procedure, as schematically illustrated by Figure-4, can be described
by the following steps:
1) for a projected defect profile with the area of the profile, A, its axial
length, L, and the maximum depth, d, divide the overall defect
length, L, by n incremental sub-sections, Li (i=1,2,3,…n and Li
contains Li-1), then obtain areas of the sub-sections, Ai (i=1,2,3,…n
and Ai contains Ai-1);
2) calculate a predicted failure pressure using the following formulae:
Pf = min {Pf 1 , Pf 2 ,..., Pfj ,..., Pfn } ( i = 1, 2, 3, …, n ) (5)
⎡ ⎛ di ⎞ ⎤
⎢ 1− ⎜ ⎟ ⎥
2σ ⎢ ⎝ t ⎠ ⎥ for ⎛⎜ ⎞⎟ ≤ 0.80
d
Pi f = (6)
⎛ D ⎞ ⎢ ⎛ d i ⎞⎛ 1 ⎞⎥ ⎝t⎠
⎜ ⎟ ⎢1 − ⎜ ⎟⎜⎜ ⎟⎟ ⎥
⎝ t ⎠ ⎣⎢ ⎝ t ⎠⎝ M i ⎠ ⎦⎥
σ = SMYS + 10000 (lb/in2) (7)
A
d = i
i
(8)
L i
2 4
⎛ L ⎞ ⎛ L ⎞ Li
M i = 1 + 0.6275⎜⎜ i ⎟⎟ − 0.003375⎜⎜ i ⎟⎟ for ≤ 7.071 (9)
⎝ Dt ⎠ ⎝ Dt ⎠ Dt
2
⎛ L ⎞ Li
M i = 3.3 + 0.032⎜⎜ i ⎟⎟ for > 7.071 (10)
⎝ Dt ⎠ Dt
Where:
Pf Predicted failure pressure for corroded pipe, lb/in²
SMYS Specified minimum yield strength, lb/in²
D Nominal outside diameter, in
Page 7 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
t Nominal wall thickness, in
d Maximum depth of a corrosion metal-loss area, in
L Maximum axial length of corrosion metal-loss area, in
8 Pipeline Repair Decision
8.1 Estimated Repair Factor (ERF)
The estimated repair factor for a corrosion defect can be established by dividing
the maximum allowable operating pressure (MAOP) or design pressure by the
predicted failure pressure, Pf, for the corrosion defect, as below:
MAOP
ERF = (11)
Pf
8.2 The remedial actions of the assessed pipeline are based on the ERF values for
the defects and shall be according to Table-1 below.
Table-1: Corrosion defects remedial action
Assessment Corrosion ERF Values ≥ 1 ERF Valves < 1
Level Type
Level-1 External Required repair or consider Required coating
level-2 assessment only to stop
corrosion.
Level-2 External Required immediate repair Required coating
only to stop
corrosion.
Level-1 Internal Required immediate repair Required periodical
corrosion
monitoring
Level-2 Internal Required immediate repair Required close
corrosion
monitoring
Page 8 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
8.3 Internal corrosion defects, which pass the assessment, shall be monitored on a
periodical basis. The inspection period shall be determined by the Engineering
of the Operating Organization.
Revision Summary
29 June 2005 Major revision.
Page 9 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
Appendix-A: Chart-1: Corroded Pipelines Defects Assessment Flowchart
Assessments start
• Report all single defects.
• Group defects that are less than 3t
Level-1
Calculate predicted failure pressures for all
reported single defects using the LPC-1 Level-2
equation (Paragraph 7.1) Are projected profiles of the critical NO
single defect(s) available?
Yes
Identify critical defect(s) Re-analyze the critical single defect(s)
and defect groups. as complex-shaped defect(s) using the
RSTRENG effective-area method
Calculate the ERF
ERF ≥1
(Paragraph 8.1) Calculate the ERF (paragraph 8.1)
Check defect(s) acceptance Check defect(s) acceptance
using ERF using ERF
ERF <1 ERF <1 ERF ≥1
Maintain the current operating
Recommend remedial
Condition and recommend defect
action
monitoring actions
Assessments completed
Page 10 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
Appendix-B: Schematic Illustrations for Defects Measurements and Grouping
Longitudinal dimension of the pipe wall
L2
Circumferential dimension of
L1
L3
the pipe wall
d1 d2 d3
Figure 1. Example of reported corrosion defects
d
t
the projected through-wall-thickness profile of a corrosion metal-loss area
Figure 2: Project profile for metal loss
Page 11 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
L L
Figure 3: Defect grouping, defects that are less than 3t should be considered
as a single defect.
Page 12 of 13
Document Responsibility: Piping SAEP-306
Issue Date: 29 June 2005 Assessment of the Remaining
Next Planned Update: 1 July 2010 Strength of Corroded Pipes
a plan view of four corrosi on pits
φ (maximum width)
projected defect profile
L (overall axial length)
A (projected area)
d
t
subsection, i
subsection, j
Figure 4: A schematic illustration of level-2 assessment.
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