Assessment and Management of Pipeline Dents

API RECOMMENDED PRACTICE 1183 FIRST EDITION, NOVEMBER 2020

ERRATA 1, JANUARY 2021

Special Notes

API publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed. The use of API publications is voluntary. In some cases, third parties or authorities having jurisdiction may choose to incorporate API standards by reference and may mandate compliance.

Neither API nor any of API's employees, subcontractors, consultants, committees, or other assignees make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. Neither API nor any of API’s employees, subcontractors, consultants, or other assignees represent that use of this publication would not infringe upon privately owned rights.

API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any authorities having jurisdiction with which this publication may conflict.

API publications are published to facilitate the broad availability of proven, sound engineering and operating practices. These publications are not intended to obviate the need for applying sound engineering judgment regarding when and where these publications should be utilized. The formulation and publication of API publications is not intended in any way to inhibit anyone from using any other practices.

Any manufacturer marking equipment or materials in conformance with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. API does not represent, warrant, or guarantee that such products do in fact conform to the applicable API standard.

All rights reserved. No part of this work may be reproduced, translated, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher. Contact the Publisher, API Publishing Services, 200 Massachusetts Avenue, NW, Suite 1100, Washington, DC 20001.

Copyright © 2020 American Petroleum Institute

Foreword

Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.

The verbal forms used to express the provisions in this document are as follows.

Shall: As used in a standard, “shall” denotes a minimum requirement in order to conform to the standard.

Should: As used in a standard, “should” denotes a recommendation or that which is advised but not required in order to conform to the standard.

May: As used in a standard, “may” denotes a course of action permissible within the limits of a standard. Can: As used in a standard, “can” denotes a statement of possibility or capability.

This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 200 Massachusetts Avenue, Suite 1100, Washington, DC 20001. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director.

Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually by API, 200 Massachusetts Avenue, Suite 1100, Washington, DC 20001.

Suggested revisions are invited and should be submitted to the Standards Department, API, 200 Massachusetts Avenue, Suite 1100, Washington, DC 20001, standards@api.org.

iii

Contents

Page

1. Scope 1

2. Normative References 2

3. Terms, Definitions, Acronyms, and Abbreviations 3

   1. Terms and Definitions 3

   2. Acronyms and Abbreviations 8

4. Guiding Principles 10

   1. General 10

   2. Dent Background 12

5. Dent Integrity Management Process 14

   1. Overview 14

   2. Dent Integrity Management Process Overview 15

   3. Significant Parameters 21

   4. Pipeline Service 22

   5. Coincident Features 24

6. Pipeline Dent and Operational Condition Characterization 24

   1. Pipe and Dent Geometry 24

   2. Dent Geometry Profile Characterization 25

   3. Identification of Dents with In-Line Inspection Data 30

   4. Restraint Condition 32

   5. Coincident Features and Interacting Defects 34

   6. Operating Condition Severity 39

   7. Material Properties 45

7. Dent Screening 46

   1. Qualitative Risk Screening 47

   2. Indentation Formation Strain 47

   3. Failure Pressure 49

   4. Fatigue Life Dent Screening 49

   5. Finite Element Modeling Screening. 55

8. Detailed Fitness-For-Service Assessment Approaches 55

   1. Dent Failure Assessment 56

   2. Dent Formation Induced Cracking Potential (Dent Strain Assessment) 58

   3. Dent Fatigue Life Assessment 64

   4. Safety Factors/Conservatism 72

   5. Probabilistic Assessment 73

9. Field Guidance 73

   1. Excavation 73

   2. In-Service Monitoring and Inspection 75

   3. Documentation and Feedback 77

   4. Cutting and Removal 78

10. Mitigative and Repair Action Guidance. 79

    1. Mitigative Actions 79

    2. Pressure Reduction 80

    3. Re-Evaluation of Operational Pressure History 80

    4. Managing Pressure Cycles 80

       v

       Contents

       Page

    5. Coincident Feature and Interacting Defect Mitigation 80

    6. Repair 82

Annex A (informative) Sample Calculations 87

Annex B (informative) Dent Crack Initiation Surface, Location, Orientation, and Form, 102

Annex C (informative) Field Guidance Listing 103

Annex D 108

Annex E (informative) Capabilities of In-line Inspection Systems for Plain Dents and

Specific Types of Coincident Features 109

Annex F (informative) PRCI Dent Fatigue Shape Parameters 113

Annex G (informative) Scaling Factors for Unrestrained Dent Shape Factors in Equation (23) 116

Annex H (informative) Gas Pipeline—Sample Semi-Quantitative Screening Tool for Dents 118

Bibliography 122

Figures

1. PDCA Cycle Applied to Dent Management Program 11

2. Illustrative Dent Formation Process Stages 13

3. Elements of a Dent Management Program 16

4. Example of an Acceptable Smoothed Dent Profile, (a) Axial Profile, (b) Transverse Profile 26

5. Schematic Showing 10 % Axial Length and Area and 75 % Axial and Transverse Length and Area . 29

6. Spline Interpolation for Cases where No Data Point is Available at the Specified Deformed

   Pipe Wall Position in the Dent 30

7. Dent Definition Parameters 31

8. Interaction Zone Definition for Spiral Weld Seams 36

9. Dent Fatigue Interaction Zone Definition for Corrosion Features 37

10. Criteria for Multiple Dent Interaction 39

11. Operational Sample Pressure Time History and Pressure Range Histogram

    from SCADA System 41

12. Range-Mean Operational Pressure Histogram 44

13. Spectrum Severity Indicator Description 45

14. Local Dent Gouge Geometry Definition 58

15. Specimen Initial Radius ro, and Radius of Neck, r. 61

16. Specimen Initial Radius ro, and Radius of Neck, r 62

17. Dent Angle Estimation 66

18. Dent Manual Field Measurement Setup 77

1. Hypothetical Dent Axial Profile 88

2. Hypothetical Dent Transverse Profile 88

3. Spectrum Severity Indicator Description 97

4. Sample 1-Year Discharge Pressure Time History 98

5. Pressure Range Histogram—1-Year Time History 99

B.1 Photographs Showing Fatigue Crack Location and Orientation Relative to the Total Dent

Deformation Depth and Restraint Condition of a Dent 102

1. Main Process 119

2. Process to Estimate the Type of Metal Loss 119

3. Process to Determine the Severity of a Dent 120

   vi

   Contents

   Page

4. Process to Determine the Response to Dent with Gouge in a Gas Pipeline 121

Tables

1. Relationship Between Program Elements and Parameters 23

2. Single-peak Dent Geometric Parameters Required to Capture Dent Shape at Dent Peak

   and the Restraint Parameter and the Shape Parameter Calculation 27

3. Coefficients for Dent Girth Weld Interaction 35

4. Parameters for Dent Longitudinal Seam Weld Interaction 35

5. Liquid Pipeline Cyclic Operational Pressure Range Interpolation Model Constants 43

6. Dent Fatigue Life Spectrum Severity Criteria 50

7. Quadratic Function Constants for Equation (15) for the Pipe Geometries 54

8. Constants aij for Regression Equation (16) 55

9. Excavation Pressure Reduction Assessment 75

10. Acceptable Dent Repair Methods 86

1. Characteristic Length and Area of the Example Dent 87

2. Pipe Characteristics for Example 2 89

3. Pressure Cycles for Example 3 90

4. Quadratic Function Constants for Equation (A.6) for Various the Pipe Geometries 91

5. Calculated Level 0.5 Maximum Stress Magnification Factor for Example 3 92

6. Pipe Characteristics for the Level 2 Example Case 93

7. Dent Geometric Lengths and Areas for Example Dent 93

8. Hypothetical Pressure Cycle 93

9. Shape Factor and Shape Parameter Coefficients 94

10. Damage Calculation 95

11. Sample Pressure Range Histogram 95

12. 1-Year Damage Accumulation Calculation 100

1. Shape Parameter Coefficients for Deep Restrained Dents 113

2. Shape Parameter Coefficients for Shallow Restrained Dents 114

3. Shape Parameter Coefficients for Unrestrained Dents 115

1. Scale Factors for the Truncated Mean Pressure (TMP) = 10 117

2. Scale Factors for the Truncated Mean Pressure (TMP) = 20 117

3. Scale Factors for the Truncated Mean Pressure (TMP) = 30 117

4. Scale Factors for the Truncated Mean Pressure (TMP) = 40 117

5. Scale Factors for the Truncated Mean Pressure (TMP) = 50 117

6. Scale Factors for the Truncated Mean Pressure (TMP) = 60 117

7. Scale Factors for the Truncated Mean Pressure (TMP) = 70 117

   
   

   Introduction

   
   

   This Recommended Practice (RP) provides guidance to the pipeline industry for assessing and managing dents present in pipeline systems as a result of mechanical contact by rocks, machinery, or other forces. Emphasis is placed on conditions where dents are either closely aligned or coincident with other threats, and the applicable data screening and assessment methods available to guide decision making on mitigation, remediation, or repair. Additional emphasis is placed on the pipeline operational parameters and the influence of those parameters on dent fatigue.

   
   

   The RP presents comprehensive guidance for developing a dent assessment and management program including:

   
   

   1. Selecting suitable methods for inspecting and characterizing the condition of the pipeline with respect to dents;

      
      

   2. Establishing data screening processes to evaluate dents relative to extent and degree of deformation and operational severity;

      
      

   3. Provide response criteria for dents based upon the dent shape and profile as determined by in-line inspection;

      
      

   4. Applying engineering assessment methods to evaluate fitness-for-service of dents including reassessment interval;

      
      

   5. Presenting remediation and repair options to address dents;

      
      

   6. Developing preventive and mitigative measures for dents in lieu of, or in addition to, periodic dent integrity assessment, including pressure reductions and pressure cycle management.

This document provides guidance on elements of an engineering critical assessment for dents to determine fitness- for-service.

This RP may be used to supplement requirements included in 49 CFR 195, 49 CFR 192, CSA Z662, SOR/99-294, and other integrity management codes and standards. The RP provides the process and tools to conduct screening and engineering assessment (e.g., fitness for purpose, engineering critical assessment) for dents. These processes and tools represent criteria for the assessment of dents accounting for the factors that lead to pipeline failures caused by dents.

While this RP is generally applicable to all pipeline systems, it does not:

• include detailed requirements for new construction to prevent dents. For information on this, reference API 1169 and API 1177,

  
  

• provide guidance on prevention of dents in-service,

  
  

• outline design precautions for preventing and limiting susceptibility to denting,

  
  

• provide guidance on the assessment of wrinkles, ripples, long seam misalignment, ovalized bends, or buckles, and

  
  

• explicitly identify the differences between onshore and offshore pipeline systems.

This RP is intended for use by pipeline operators to support planning, developing, implementing, and improving a pipeline dent management program. This RP is closely aligned with and augments the API 1160 RP for liquid hazardous pipeline integrity management. It is also equally applicable to natural gas pipeline systems, and is written as a framework for both hazard liquid and gas pipelines.

This RP provides guidance based upon an understanding of the current state of industry knowledge and expertise. Research to improve upon the current state of knowledge continues and it is expected that this RP will be updated to incorporate future enhancements in industry knowledge and expertise.

A prior API publication, API Publication 1156, described the effects of dents on liquid petroleum pipelines but was issued prior to the hazardous liquids pipeline integrity management rule. The RP provides the current industry understanding of dent formation and post-formation behavior and response to environmental and operational factors. This understanding is based on the practical experience of pipeline operators that have been managing dents under the pipeline integrity management regulations included in 49 CFR §192 and §195 and integration of over 20 years of research on dents through work completed by the pipeline industry.

Assessment and Management of Pipeline Dents

1 Scope

This recommended practice (RP) is applicable to any pipeline system used to transport hazardous liquid or natural gas. This RP includes detailed technical discussion on dent formation, strain and fatigue, and failure modes and mechanisms. These details are provided to give pipeline operators the information and knowledge necessary to make informed integrity management decisions regarding the management of dents on their systems. This RP describes preventive and mitigative measures that pipeline operators can apply to manage dents after detection. The in-service response of dents to a range of loading conditions is discussed in detail.

Mechanisms that promote denting are discussed, methods to inspect dents are described, and approaches and tools to estimate dent fitness-for-service (i.e., dent formation induced cracking, failure pressure, and pressure cycling fatigue life) are presented. Selection of the appropriate dent integrity assessment methods and integration of pipeline operating data is also discussed.

This RP is specifically designed to provide the operator with guidelines on industry-proven practices in the integrity management of dents. The guidance is largely targeted to the line pipe along the right-of-way, but some of the processes and approaches can be applied to pipeline facilities, including pipeline stations, terminals, and delivery facilities associated with pipeline systems.

This RP includes a review of currently available in-line inspection (ILI) technologies for detecting and characterizing dents, and provides guidelines for collecting data in the ditch when excavation is performed based on ILI data review and the pipeline and dent is exposed. Data integration practices are also addressed. Mitigation and repair techniques and approaches are discussed.

This RP provides general information on the dent formation process and describes approaches to evaluate fitness-for-service of dents regarding their potential to reach a structural limit state. A limit state represents an operator-defined condition where the pipe is no longer fit for purpose. This document provides tools to address three primary limit states: formation strain, failure pressure, and fatigue damage. The document provides screening tools and detailed assessment methods to address each of these limit states. This methodology is consistent with other design and fitness-for-service codes that address both static and fatigue limit states1.

In the context of plain dents, the assessment of formation strain is considered to be an indication of the potential for cracking due to dent formation, and has been included as part of ASME B31.8 since 2006.

The assessment of failure pressure is typically not performed for most dents. Plain dents regardless of shape with depths up to 10 % of the pipe diameter, without coincident features such as metal loss, welds, or cracks have been shown in testing to have the same failure pressure as plain line pipe2. Consequently, failure pressure is typically addressed for dents with coincident features or in detailed fitness-for-service assessments.

1. ASME Boiler and Pressure Vessel Code

2. Bood, R., Gali, M., Marewski, U., Steiner, M., Zarea, M., “EPRG Methods for Assessing the Tolerance of and Resistance of Pipelines to External Damage (Parts 1 + 2),” European Pipeline Research Group (EPRG)