PR218-05404

Pipeline Defect Assessment -- A Review & Comparison of Commonly Used Methods by John F. Kiefner and Keith Leewis

INTRODUCTION

Basic Methods This document catalogs analysis methods and computational tools for addressing defects and damage discovered on in-service pipelines. It includes example calculations where closed-form algorithms are available in the public domain. It lists and describes solution techniques not available in the public domain, and it provides information so that users can either acquire the relevant software or pursue assistance regarding a particular defect assessment technique. The methods reviewed herein are summarized below.

Methods for External or Internal Corrosion-Caused Metal Loss Method Availability Principal Application Validation

B31G Public Domain Evaluation of ILI data These methods have been validated by means of full-scale pressure tests of corroded pipes or pipes containing corrosion-simulating defects. The tests were conducted on pipes ranging from 8-inch to 36-inch in diameter, and materials ranging from Grade A through X80. The full-scale data are presented in References 18, 19, 20, and 24. Confidence levels and comparisons of the methods may be found in Reference 24.

Modified B31G Public Domain Evaluation of ILI data MODB31G.XLS Public Domain Remaining life prediction PCORRC Public Domain Evaluation of ILI data API RP 579 Level 1

Public Domain Evaluation of ILI data

DNV RP-F101 Public Domain Evaluation of ILI data KAPA Public Domain Improved predictions

based on effective area of metal missing

RSTRENG PRCI (license agreement for user)

Improved predictions based on effective area of metal missing

PCORR PRCI (license agreement for user)

Improved predictions based on effective area of metal missing, variable axial load is considered

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Methods for Longitudinally-Oriented Cracks (non-indented pipe) Method Availability Principal

Application Validation

Modified Ln-Sec Equation

Public domain Failure pressure based on crack length and depth and CVN-based toughness

These methods have been validated by means of full-scale pressure test of pipes containing simulated axial defects. The diameters of the test specimens ranged from 6 inch es to 42 inches, and the materials ranged from Grade B through X80. The test data is available in References 10, 13 and 14. Confidence limits are presented herein (see Figure 6).

MRECTANG.XLS Public domain Remaining life prediction

MELIPCEQ.XLS Public domain Remaining life prediction

MREALELIP.XLS Public domain Remaining life prediction

KAPA (Modified Ln-Sec Equation solved iteratively)

Public domain Failure pressure based on effective crack profile and CVN-based toughness

COR-LAStm DNV Columbus (purchase software)

Failure pressure based on effective crack profile and CVN- or J-based toughness and remaining life predictions

Full description of capabilities and validation are discussed in References 30 and 31.

PAFFC PRCI (purchase software)

Failure pressure based on crack length and depth and CVN- or J-based toughness and remaining life predictions

Full description of capabilities and validation are discussed in References 28 and 29.

API RP 579 Level II (FAD)

API standard Failure pressure based on, crack length and depth and CVN- or J-based toughness

The methods presented in these standards are based on many of the same references presented in the list of references in this report.

PD 6493 British Standard

BS PD 6493:1991 Guidance on Methods for Assessing the Acceptability of Flaws in Fusion Welded Structures.

BS 7910 British Standard

BS 7910:1999: Guide on methods for assessing the acceptability of flaws in metallic structures

PDAM Propietary (Penspen Integrity)

Pipeline Defect Assessment Manual

Validationa and confidence levels are provided in the document.

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Methods for Dents and Mechanical Damage Method Availability Principal Application Validation

EPRG Model

Public Domain Dents containing gouges (depth of re-rounding cracks should be taken into account)

The simplified model appears to adequately conservative if re-rounding crack depth is added to gouge depth

Battelle Q-factor model

Public Domain Dents containing gouges (depth of re-rounding cracks should be taken into account)

Supporting data is presented in Reference 41, however, the method does not seem to have been rigorously validated.

Method for Calculating Strain in a Dent Method Availability Principal Application Validation

ASME B31.8 Appendix R

ASME standard

Calculate strain in dent based on curvature

The method is based on well-accepted mechanics of materials principles.

Methods for Estimating the Fatigue Life of a Dent Method Availability Principal Application Validation

Specific approach based on recent papers

Presented herein

Acceptance criteria for smooth dent in liquid line

These methods should be considered experimental at this time because of scarcity of validating full-scale test data.

Methods for Circumferentially-Oriented Defects Name Availability Principal Application Validation

Wangs FAD-based approach

Proposed to replace API Standard 1104, Appendix A

Cracks in girth welds These methods have been validated by means of full-scale tests described in References 79, 80, and 81.

CSA Z662, App K

CSA standard Planar defects in girth welds

EPRG Guidelines

Public Domain Defects in Girth Welds Explained in PDAM (Reference 25) and not discussed in this document.

This document is intended to provide the user with basic tools for defect assessment when the information available includes knowledge of the applied static stress levels in the pipe, the material properties (strength and toughness), and the dimensions of the defect. The methods described herein can be useful for assessing the severity of a particular anomaly in a pipe as to

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whether or not repair or removal is warranted, for prioritizing in-line-inspection (ILI) data, and for making remaining life assessments. It is recognized that situations will arise from time to time where these methods may prove inadequate because of the complexity of the stress state, the uncertainty as to the effective dimensions of the defect, the exitence of conditions not accounted for in the basic models, or the existence of time-varying strain or loading conditions. In such situations the user may be compelled to employ more advanced analysis methods or to seek expert technical advice. Some recommendations for guidance in these situations are as follows.

Complex Loading For situations where both internal pressure and axial load may influence calculated failure pressures, one may consult References 25, 94, 95, and 96.

Multiple Defect Interaction Simple rules for the interaction of closely-spaced corrosion anomalies are presented both in ASME B31.4 2006 and CSA Z662 2003. The interaction rules in ASME B31.4 are based on experiments with multiple defects decribed in Fracture Initiation. J.F. Kiefner,

4th Symposium on Line Pipe Research, Dallas Texas, November, 18-19, 1969, Pipeline Research Committee of American Gas Association, Catalog No 30075. Because the experiments involved machined surface flaws, the authors believe that the B31.4 interaction rules are applicable to cracks as well as to metal loss anomalies.

Pressure-Cycle-Induced Fatigue Where pressure-cycle-induced fatigue may be a factor in the remaining life of a pipeline, one may consult the following public-domain document for guidance:

TTO Number 5, Integrity Management Program Delivery Order DTRS56-02-2-70036, Low Frequency ERW and Lap Welded Longitudinal Seam Evaluation, by Michael J. Baker, Kiefner and Associates, Inc. and CorrMet Engineering Services, PC, for the Department of Transportation, Research and Special Programs Administration, Office of Pipeline Safety, October, 2003 (Revised April 2004). Time-Dependent Strain The software program PAFFC described in References 28 and 29 has capabilities to examine the time-dependent strains at defects associated with steady-state or time varying loads.

Technical Expertise A number of consulting firms have advanced capabilities for the analysis of defect behavior. Names of specific firms are not provided herein because it would be too easy to inadvertently

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leave out some. Instead, it is noted that the list of references provides names of many current experts in the field of defect assessment. These individuals and the companies with which they are associated have techniques for advance analysis and can often provide answers for situations that cannot be adequately assessed by means of the basic methods presented in this document.

Organization of This Document This document is divided into two sections: BACKGROUND and EXAMPLES. The background section presents descriptions of the various models and how they evolved. The examples can be used as guidance for a particular defect evaluation need.

Acknowledgements The authors would like to thank Bob Francini and Harvey Haines for their careful review and helpful suggestions regarding this report. The authors would also like to thank Dave Warman and Kolin Kolovich for assistance in setting up and assessing the software associated with some of the models. Particular thanks go to Kolin Kolovich for also updating the spreadsheets and KAPA program to accommodate the Modified Ln-Sec equations. Also, the authors are extremely appreciative of the thorough review and valuable added material related to the evaluation of dents provided by Mike Rosenfeld. Finally the authors are grateful for the thorough review and comments provided by David Batte, Richard Espiner, and Tom Zimmerman.

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