Care, Maintenance, and Inspection of Coiled Tubing

API RECOMMENDED PRACTICE 5C8 FIRST EDITION, JANUARY 2017

Special Notes

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Copyright © 2017 American Petroleum Institute

Foreword

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The verbal forms used to express the provisions in this recommended practice are as follows:

• the term “shall” denotes a minimum requirement in order to conform to the recommended practice;

  
  

• the term “should” denotes a recommendation or that which is advised but not required in order to conform to the recommended practice;

  
  

• the term “may” is used to express permission or a provision that is optional; and

  
  

• the term “can” is used to express possibility or capability.

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Contents

Page

1. Scope 1

2. Normative References 1

3. Terms, Definitions, Acronyms, and Abbreviations 1

   1. Terms and Definitions 1

   2. Acronyms and Abbreviations 5

4. General Information 6

   1. Applications of Coiled Tubing 6

   2. Responsibility of the Purchaser 7

   3. Naturally Occurring Radioactive Materials (NORMs) 7

   4. Properties of Coiled Tubing 8

5. Welding Coiled Tubing 8

   1. General 8

   2. Type of Welds Used in CT Products 8

   3. Welding Processes 9

   4. Welding Procedure and Qualification 9

   5. Tube-to-Tube Weld Procedure Specification 11

   6. Tube to End-fitting WPS 12

   7. Qualifying Weld Procedure Specifications 13

   8. Welder and Welding Operator Qualification 14

   9. Inspection of Coiled Tubular Welds 16

   10. Field Management of Coiled Tubular Welds 17

   11. Welds in CT Product for Sour Service 18

   12. Butt Welds and Fittings 18

6. Corrosion—Effects and Mitigation in Steel Coiled Tubing 19

   1. General 19

   2. General Comments 19

   3. Corrosion and Environmental Cracking (EC) of Coiled Tubing 19

   4. Effects of Corrosion on Coiled Tubing Serviceability 21

   5. Corrosive Fluids in Coiled Tubing Service 22

   6. Environmental Cracking 22

   7. Specific Guidelines to Reduce the Risk of Coiled Tubing Environmental Cracking

      Failures in Wet Sour Wells 24

   8. Corrosion Related to Inserts 25

7. String Protection 25

   1. Protection for Coiled Tubing 25

   2. Coiled Tubular Reel Dimension Effects 26

8. Inspection 27

   1. Used Coiled Tubulars 27

   2. Drifting of Used Coiled Tubing 28

   3. Drift Ball Standoff for Flash-free Coiled Tubing (SR,O) 29

   4. Pressure Testing of Used Strings 30

   5. Imperfections in Coiled Tubing 30

   6. Mechanical Testing Procedures for Used Coiled Tubing 36

9. Nondestructive Inspection and Testing of Used Coiled Tubing 37

   1. General 37

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      Contents

      Page

   2. Test Equipment 38

   3. Qualification of Nondestructive Inspection Personnel 39

   4. Light Levels 39

   5. Visual and Dimensional Inspection 40

   6. Length 41

   7. Wall Thickness Measurement Using Ultrasonic Compression Waves 41

   8. Wall Thickness Measurement Using Electromagnetic and Gamma Ray Methods 43

   9. Transverse Imperfection Detection by Electromagnetic Methods 44

   10. Longitudinal Imperfection Detection 45

   11. Ovality Measurement 46

   12. Prove-up of Indications 46

   13. Magnetic Particle Inspection 47

   14. X-radiography of Tube-to-Tube Welds or Other Sections 48

   15. Radiographic Procedures 49

   16. Ultrasonic Inspection of Tube Welds and Other Tube Sections 50

   17. Ultrasonic Inspection of Seam Weld Area 51

   18. Ultrasonic Inspection of Skelp-end Welds 51

   19. Ultrasonic Inspection of Tube-to-Tube and Pipe-to-Pipe Butt Welds 51

   20. Liquid Penetrant Inspection 52

   21. Removal of Surface Imperfections 52

10. Assessment of Coiled Tubing 53

    1. General 53

    2. Fatigue Life and Fatigue Management of Coiled Tubing 53

    3. Theoretical Calculated Fatigue Life 54

    4. Review of String Records 54

    5. Examples of Effective Repair on Coiled Tubing 54

    6. Record Keeping 55

11. Coil Tubing Fatigue Testing and Equipment 56

    1. Objectives of Full-scale Coiled Tubing Fatigue Testing 56

    2. Recommended Standard Fatigue Testing Machine 56

    3. Recommended Standard Coiled Tubing Fatigue Testing Procedure 58

    4. Recommended Testing Matrices 61

    5. Final Recommendations 61

Annex A (informative) Coiled Tubing Properties 62

Annex B (informative) Collapse of Coiled Tubing 65

Annex C (informative) Reference Tables 74

Annex D (informative) In-service Imperfections Found in Coiled Tubing 81

Annex E (informative) Example Forms 104

Bibliography 110

Figures

1. SSC Zoning (Excluding Tube-to-Tube Welds) 24

2. Drift-ball Standoff in Perfectly Round Coiled Tubing 29

3. Drift-ball in Ovaled Coiled Tubing 30

4. Cycles to Failure for CT-100 (1.25 in. × 0.109 in.) 53

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   Contents

   Page

5. The Standard Bending Machine Concept 57

6. Profile of the Straight and Curved Mandrels 57

7. Curvature of a 1.75 in. Reference Tube Fully Wrapped onto a Standard Bending Form 58

A.1 Typical Measurement Locations for Coiled Tubing Outer Diameter and Wall

Thickness Measurements (OD Readings at AA, BB, CC, and DD) 63

B.1 Calculated Collapse Pressure Ratings for Various D/tmin Ratios of As-manufactured Coil Tubing . . 66 D.1 Acid Corrosion at a Butt Weld 81

1. Pitting that Occurred from Acid During Storage (Transversely Oriented Fatigue Cracks in

   Base of Pitting Inside Tubing at Location of Storage Corrosion) 81

2. Mild and Deeper Corrosion Occurring at the Lowest Point on the ID of Stored Tubing 82

3. Corrosion Pit on ID with Fatigue Cracks 83

4. Carbon Dioxide Pitting in Hang-off Tubing 83

5. Microbial Corrosion Pitting Inside Tubing 84

6. Example of Sulphide Stress Cracking 84

7. Hydrogen-induced Cracking 85

8. Stress-oriented Hydrogen-induced Cracking 85

9. Fatigue Pinhole 86

10. Fatigue Crack Originating with High Pressure Inside the Tubing 86

11. Fatigue Break at a Factory Skelp-end Weld 86

12. Ductile Tensile Fracture (Showing “Necking” and a 45° Shear Lip) 87

13. Tensile Failures with Brittle Fractures 87

14. Separation Caused by Tensile Overload Under Flexure 88

15. Relatively Shallow Plough Marks on the Outer Surface of Coiled Tubing 88

16. Deep Plough Marks Resulting in Fatigue Cracks 89

17. Transversely Oriented “Chatter” (“Fish-scale”) Marks That Generally Accompany “Plough” Marks 90 D.19 Longitudinal Gouge 90

1. Gouges with Transverse Orientation 91

2. Elongated Gouges with Chatter Marks 92

3. Gouges with Large Transverse Component 92

4. Longitudinal Scratches 93

5. Scoring Marks on the Tube Outside Diameter 93

6. Wall Thinning on the Outside Diameter (left) and Internal Erosion from Sand (right) 94

7. Erosion of the Inside Surface from Sand That Can Result in Serious Wall Loss 94

8. Wear with Galling 95

9. Impingement Erosion 95

10. Burst at Thin Wall Area in Tubing 96

11. Burst Failures at Seam Weld (Possibly from a “Cold Weld”) 96

12. Examples of Dents 97

13. Examples of Dimple Dents 98

14. Example of Multiple Types of Dents 98

15. Laboratory-manufactured Dent with Fatigue Cracks 99

16. Elongated Dent 99

17. Buckled Tubing 100

18. Collapse in Two and Three Directions (One Node Is the Seam Weld) due to

    Tension and High External Pressure 101

19. Gripper Marks 102

20. Gripper Block Mark with Fatigue Crack 102

21. Injector Ring Damage 103

1. Example Form for Visual and Dimensional Inspection Report 104

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2. Example Form for Electromagnetic NDT Report (Part 1) 105

3. Example Form for Electromagnetic NDT Inspection Report (Part 2) 106

4. Example Form for Preservation of Coiled Tubing Checklist 107

5. Example Form for Preservation of Coiled Tubing Equipment Offshore 108

6. Example Form for Fatigue Testing Data Collection Sheet 109

Tables

1. Welds with Filler Metal (Tube-to-Tube Weld) 8

2. Recommended Maximum Intervals Between Recalibration/Recertification 38

3. Actual Sample Radius of Curvature on a Standard Bending Form 58

1. Collapse Values for API 5ST Coiled Tubing Grades 67

2. Coiled Tubing Collapse Pressure Factors for Various Amounts of Utilization 73

1. Values for Coiled Tubing Calculations on Wall Thickness and Capabilities 75

2. Coiled Tubing Gauge Parameters 78

3. Dimensions for Yield Radius, Reel, and Guide Arch 80

Care, Maintenance, and Inspection of Coiled Tubing

1. Scope

   This recommended practice covers the care, maintenance, and inspection of used low alloy carbon steel coiled tubing. Commonly manufactured coiled tubing outside diameters range from 25.4 mm (1.000 in.) to 88.9 mm (3.5 in.).

   
   

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 Specification 5ST, Specification for Coiled Tubing

   ASTM A370 1, Standard Test Methods and Definitions for Mechanical Testing of Steel Products

   H. Haga, K. Aoki, and T. Sato (1980a), Welding Phenomena and Welding Mechanisms in High Frequency Electric Resistance Welding—1st Report, Welding Journal 59(7), pp. 208–212

   
   

   H. Haga, K. Aoki, and T. Sato (1980b), The Mechanisms of Formation of Weld Defects in High-Frequency Electric Resistance Welds, Welding Journal 59(7), pp. 103s–109s

   
   

   For a list of other documents associated with this standard, see the Bibliography.

   
   

3. Terms, Definitions, Acronyms, and Abbreviations

3.1 Terms and Definitions

For the purpose of this document, the following definitions apply.

3.1.1

Bauschinger Effect

A phenomenon that occurs in polycrystalline metals (including steel), that results in a decrease of the yield strength in one direction due to plastic deformation in another direction such as is caused by service loads, coiling, or straightening.

3.1.2

bed wrap

The wraps of coiled tubing that are adjacent to the cylindrical core of the shipping or usage reel.

3.1.3

cold work

Plastic deformation at such temperatures and rates that substantial increases occur in the strength and hardness of the metal.

NOTE Visible structural changes include changes in grain shape and, in some instances, mechanical twinning or banding.

3.1.4

critical weld(s)

Primary connections in coiled tubing where failure would jeopardize the safety of personnel or equipment and/or be detrimental to the integrity of the coiled tubing string or operation.

NOTE Critical welds include, but are not necessarily limited to, tube-to-tube girth joints and high-pressure end-fitting welds for union connections to swivel joints on coiled tubing reels.

1 ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania 19428, www.astm.org.

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