Recommended Practice for Assessment and Management of Cracking in Pipelines

API RECOMMENDED PRACTICE 1176 FIRST EDITION, JULY 2016

ERRATA 1, FEBRUARY 2021

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Copyright © 2016 American Petroleum Institute

Foreword

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Contents

Page

1. Scope 1

2. Normative References 1

3. Terms, Definitions, Acronyms, and Abbreviations 2

   1. Terms and Definitions 2

   2. Acronyms and Abbreviations 10

4. Guiding Principles 12

5. Crack Management 13

   1. General Considerations 13

   2. Elements of Crack Management to Incorporate into Integrity Management Plans 14

6. Threat Mechanisms Associated with Cracking 16

   1. General 16

   2. Environmentally Assisted Cracking 16

   3. Manufacturing Defects Associated with Longitudinal Seams 19

   4. Mechanical Damage 22

7. Fitness-For-Service of Crack-like Flaws 25

   1. Assessment Methods 25

   2. Input Parameters 25

8. Crack Growth 27

   1. Pressure Cycling Analysis 27

   2. Fatigue Growth 30

   3. Stress Corrosion Cracking and Corrosion Fatigue Growth 33

   4. Remaining Life 36

   5. Reassessment Interval Determination 36

9. Gathering, Reviewing, and Integrating Data 36

   1. General Considerations 36

   2. Threat Interaction 37

10. Methods of Integrity Assessment 38

    1. General 38

    2. In-line Inspection (ILI) 38

    3. Hydrostatic Testing 39

    4. In-line Inspection and Hydrostatic Testing 39

11. In-line Inspection for Integrity Assessment 41

    1. General 41

    2. In-line Inspection Tool Types 42

    3. ILI Tool Utilization Considerations 46

    4. Capabilities of In-line Inspection Tools for Axial Cracks 49

    5. Verification of ILI Results 49

    6. Crack Tool Response Methodology 51

    7. Crack ILI Response Criteria 60

12. Hydrostatic Testing 62

    1. General 62

    2. Minimum Test Pressure-to-Operating Pressure Ratio 63

    3. Minimum Hold Time 64

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    4. Spike Testing 64

    5. Pressure Reversals 65

13. Stress Corrosion Cracking Direct Assessment 66

14. In-the-Ditch Assessment 67

    1. General 67

    2. Assessment of SCC and Other Pipe Body Cracks 68

    3. Assessment of Longitudinal Seam Cracks 69

    4. Assessment of Surface Breaking Laminations 70

15. Repair Methods 71

    1. General 71

    2. Replace as Cylinder 72

    3. Grinding 72

    4. Deposition of Weld Metal 72

    5. Full Encirclement Sleeves 72

    6. Composite Sleeves 72

    7. Compression Sleeves 73

    8. Mechanical Bolt-on Clamps 73

    9. Hot Tapping 73

    10. Fittings 73

16. Preventive and Mitigative 73

    1. Mitigating Transit Fatigue 73

    2. Reevaluation of Pressure Data 74

    3. Managing of Pressure Cycles 74

    4. Stress Corrosion Cracking 74

17. Crack Management Performance Measures 76

    1. General 76

    2. Performance Measures by Crack Threat 76

    3. Performance Measures by Crack Assessment Method 76

Annex A (normative) SCC Additional Information 79

Annex B (normative) Prioritization for Threats Associated with ERW and EFW Pipe 86

Annex C (normative) Assessment Methods for Crack-like Flaws 88

Annex D (informative) Yield Strength and Tensile Strength 93

Annex E (informative) Toughness 96

Annex F (informative) Hydrogen Effects 103

Annex G (informative) Fatigue C and n Values 104

Annex H (normative) Prediction of Crack Growth with Consideration of Variable Loading Conditions on Oil and Gas Pipelines in Near-neutral pH Environments 106

Annex I (informative) UT and Magnetic ILI Technology 111

Annex J (informative) Capabilities of In-line Inspection Tools for Specific Types of Axial Cracks and Anomalies 119

Annex K (informative) In-the-Ditch Technology 123

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Annex L (informative) Example of an ILI Response Protocol 129

Bibliography 130

Figures

1. External Surface of Pipe Sample with Sulfide Stress Cracking 16

2. Hook Crack and Fatigue Crack Extension in Low-frequency Electric Resistance Welding Pipe 19

3. Hook Crack in Flash-welded Pipe 20

4. Lack-of-Fusion Defect 21

5. Direct Current Welded Seam with Offset Skelp Edges 21

6. Weld Metal Crack (Hot Crack) 21

7. Toe Crack (Also Contains Offset) 22

8. Example Pressure Spectrum from a Liquid Pipeline 29

9. Example Histogram Resulting from Rainflow Cycle Counting 29

10. Coupling of Mechanical Fatigue with Environmental Crack Growth Mechanisms 34

11. In-line Inspection Response Methodology High-level Workflow 53

12. Result of a Magnetic Particle Inspection for Stress Corrosion Cracking 68

13. Result of a Magnetic Particle Inspection of Seam Crack 70

B.1 System Prioritization Flowchart 87

C.1 Definition of Failure Condition in Terms of Toughness Ratio (Kr) and Load Ratio (Lr) 91

1. Database Yield Strength Properties by Grade 94

2. Tensile Strength Properties by Grade 95

1. Toughness Properties for Vintage Electric Resistance Welding Pipe 96

2. Schematic Toughness Transition Curve (from Rolfe and Barsom, 1977) 98

3. Shift in Transition Temperature with Strain Rate 99

4. Effect of Charpy V-notch Specimen Size on Toughness Transition Curve 101

1. Fatigue Crack Growth Rate Parameters for Line Pipe, Various Sources 105

2. Fatigue Crack Growth Rate Parameters, Vintage Line Pipe Specimens 105

H.1 Type I—Underload Pressure Fluctuations for a) an Oil Pipeline and for b) a Gas Pipeline 106

H.4 Revised Three-stage Bathtub for Crack Growth in Near-neutral pH Environments 107

1. Type II—Mean Load Pressure Fluctuations for a) an Oil Pipeline and for b) a Gas Pipeline 107

2. Type III—Overload Pressure Fluctuations for a) an Oil Pipeline and for b) a Gas Pipeline 107

1. Effect of Loading Interactions on Crack Growth Rate 109

2. Comparison of Crack Growth Rates of the Same Pipeline Steel Tested Under Different Loading Scenarios 109

3. Effect of Loading Frequency on Crack Growth Rate Under Both Constant Amplitude Loading and Variable Amplitude Loading with Underloads and Minor Cycles 110

1. Outer Diameter Crack Detection Using a 45° Shear Wave (Referred to as Half Skip) 112

2. Inner Diameter Crack Detection Using a 45° Shear Wave (Referred to as Single or Full Skip) 112

3. Sensors Spaced Around the Circumference to Achieve Full Coverage 113

4. Sensors Are Angled in Both the Clockwise and Counterclockwise Direction 113

5. Outer Diameter Crack Detection Using a 45° Shear Wave (Referred to as One and One-half Skips) . 113

6. Inner Diameter Crack Detection Using a 45° Shear Wave (Referred to as Two Skips) 113

7. Phased Array Generation of 45° Ultrasonic Shear Waves in the Clockwise and Counterclockwise Direction as Well as Normal Beam for Wall Thickness 114

8. Electromagnetic Acoustic Transducer Ultrasonic Waves Generated Directly in the Pipe by Electromagnetic Pulse from a Coil in the Presence of a Strong Magnet 115

1. Example of a Magnetic Particle Inspection 123

2. Time-of-Flight Diffraction Head for Seam Weld Inspection 124

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3. Typical Inspection Result for 2 m of Anomaly-free Seam Weld 125

4. Typical Inspection for Two Anomalies—Requires Additional Analysis 125

5. Principle of a Sector Scan 126

6. Imaging a Crack at the Full-vee Path Using a Sector Scan 126

7. Focused Beam Can be Attained at the Three-fourths-vee Path—Entire Heat-affected

   Zone Is Assessed 126

8. Dense Overlap of Sector Scans Circumferentially Indexed by 3 mm (0.12 in.) 127

9. Example of Orthogonal Views 128

10. Example of Full Field Inversion of a Weld 128

L.1 ILI Response Protocol—Example 129

Tables

1. In-line Inspection Tools and Capabilities for Axial Cracks 50

2. Acceptable Crack Repair Methods 75

1. Simplified Stress Corrosion Cracking Susceptibility Ranking Factors—Illustrative Example

   (from Beavers [27]) 83

2. Range of Reported Average Stress Corrosion Cracking Growth Rates 84

1. Database Yield Strength (YS) Properties by Grade 93

2. Database Tensile Strength (TS) Properties by Grade 94

1. Basic Fracture Toughness Properties and Tests 97

2. Factors Promoting Favorable Toughness Properties in Steel Line Pipe 98

G.1 Survey Sampling of Line Pipe Fatigue Crack Growth Parameters 104

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Introduction

This recommended practice (RP) provides guidance to the pipeline industry for assessment and management of defects in the form of cracking, with particular emphasis on contributing threats and the applicable assessments. The RP presents detailed guidance for developing a crack management program. The crack management RP includes the following:

• selecting suitable methods for assessing the condition of the pipeline with respect to applicable forms of cracking;

  
  

• establishing response criteria for in-line inspection (ILI) results and determining a pressure reduction where the excavation is delayed beyond the intended timeline;

  
  

• determining appropriate hydrostatic test levels and duration;

  
  

• calculating the remaining lives of anomalies that may remain in the system so that reassessment can be carried out to reevaluate the anomalies and remediate if necessary;

  
  

• developing preventive and mitigative measures for cracking-related conditions in lieu of or in addition to periodic integrity assessment.

This RP is intended for use by operators in planning, implementing, and improving a pipeline crack management program.

Although the genesis and structure of this RP is the API 1160 RP for liquid hazardous pipeline managed under U.S. Department of Transportation (DOT) 49 Code of Federal Regulations (CFR) 195.452 of the U.S. federal pipeline safety regulations, this RP is written as a broadly applicable framework for both hazardous liquid and gas pipelines located in any location or under any jurisdiction. This RP augments API 1160 in aiding the development of integrity management programs that are required under U.S. federal pipeline safety regulations.

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Recommended Practice for Assessment and Management of Cracking in Pipelines

1. Scope

   This recommended practice (RP) is applicable to any pipeline system used to transport hazardous liquid or natural gas, including those defined in U.S. Title 49 Code of Federal Regulations (CFR) Parts 192 and 195.

   
   

   This RP is specifically designed to provide the operator with a description of industry-proven practices in the integrity management of cracks and threats that give rise to cracking mechanisms. The guidance is largely targeted to the line pipe along the right-of-way (ROW), but some of the processes and approaches can be applied to pipeline facilities, including pipeline stations, terminals, and delivery facilities associated with pipeline systems. Defects associated with lap-welded (LW) pipe and selective seam weld corrosion (SSWC) are not covered within this RP.

   
   

   This RP presents the pipeline industry’s understanding of pipeline cracking. Mechanisms that cause cracking are discussed, methods to estimate the failure pressure of cracks are reviewed, and methods to estimate crack growth are presented. Selection of the appropriate integrity assessment method for various types of cracking, operating conditions, and pipeline characteristics is discussed. This RP also reviews current knowledge about in-line inspection (ILI) technology and in-the-ditch (ITD) nondestructive evaluation technology. A methodology for responding to ILI indications and specific criteria for when to respond to certain results is presented. Applicable repair techniques are reviewed. Sections are included for the discussion of reassessment interval determination and the consideration of appropriate preventive and mitigative measures. Finally, some meaningful performance metrics for measuring the effectiveness of a crack management program are discussed.

   
   

   The technical discussion about crack formation, growth, and failure is to provide the knowledge needed by operators to effectively make integrity decisions about managing cracking on their pipeline systems.

   
   

2. Normative References

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

API 579-1/ASME FFS-1 1, Fitness-For-Service, June 2007

API Recommended Practice 1110, Recommended Practice for the Pressure Testing of Steel Pipelines for the Transportation of Gas, Petroleum Gas, Hazardous Liquids, Highly Volatile Liquids, or Carbon Dioxide

API Recommended Practice 1160, Managing System Integrity for Hazardous Liquid Pipelines, Second Edition ASME B31.4-2012, Pipeline Transportation Systems for Liquids and Slurries

ASME B31.8-2012, Gas Transmission and Distribution Piping Systems

ASME B31G-2012, Manual for Determining the Remaining Strength of Corroded Pipelines

BS 7910-2013 2, Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures

NACE SP0204 3, Stress Corrosion Cracking (SCC) Direct Assessment Methodology, 2008

1. ASME International, 2 Park Avenue, New York, New York 10016-5990, www.asme.org.

2. British Standards Institution, Chiswick High Road, London, W4 4AL, United Kingdom, www.bsi-global.com.

3. NACE International (formerly the National Association of Corrosion Engineers), 15835 Park Ten Place Houston, Texas 77084, www.nace.org.

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