M00044717
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API RP 5C8 Care, Maintenance, and Inspection of Coiled Tubing, First Edition
standard by American Petroleum Institute, 01/01/2017
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API RECOMMENDED PRACTICE 5C8 FIRST EDITION, JANUARY 2017
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Users of this recommended practice should not rely exclusively on the information contained in this document. Sound business, scientific, engineering, and safety judgment should be used in employing the information contained herein.
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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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Scope 1
Normative References 1
Terms, Definitions, Acronyms, and Abbreviations 1
Terms and Definitions 1
Acronyms and Abbreviations 5
General Information 6
Applications of Coiled Tubing 6
Responsibility of the Purchaser 7
Naturally Occurring Radioactive Materials (NORMs) 7
Properties of Coiled Tubing 8
Welding Coiled Tubing 8
General 8
Type of Welds Used in CT Products 8
Welding Processes 9
Welding Procedure and Qualification 9
Tube-to-Tube Weld Procedure Specification 11
Tube to End-fitting WPS 12
Qualifying Weld Procedure Specifications 13
Welder and Welding Operator Qualification 14
Inspection of Coiled Tubular Welds 16
Field Management of Coiled Tubular Welds 17
Welds in CT Product for Sour Service 18
Butt Welds and Fittings 18
Corrosion—Effects and Mitigation in Steel Coiled Tubing 19
General 19
General Comments 19
Corrosion and Environmental Cracking (EC) of Coiled Tubing 19
Effects of Corrosion on Coiled Tubing Serviceability 21
Corrosive Fluids in Coiled Tubing Service 22
Environmental Cracking 22
Specific Guidelines to Reduce the Risk of Coiled Tubing Environmental Cracking
Failures in Wet Sour Wells 24
Corrosion Related to Inserts 25
String Protection 25
Protection for Coiled Tubing 25
Coiled Tubular Reel Dimension Effects 26
Inspection 27
Used Coiled Tubulars 27
Drifting of Used Coiled Tubing 28
Drift Ball Standoff for Flash-free Coiled Tubing (SR,O) 29
Pressure Testing of Used Strings 30
Imperfections in Coiled Tubing 30
Mechanical Testing Procedures for Used Coiled Tubing 36
Nondestructive Inspection and Testing of Used Coiled Tubing 37
General 37
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Test Equipment 38
Qualification of Nondestructive Inspection Personnel 39
Light Levels 39
Visual and Dimensional Inspection 40
Length 41
Wall Thickness Measurement Using Ultrasonic Compression Waves 41
Wall Thickness Measurement Using Electromagnetic and Gamma Ray Methods 43
Transverse Imperfection Detection by Electromagnetic Methods 44
Longitudinal Imperfection Detection 45
Ovality Measurement 46
Prove-up of Indications 46
Magnetic Particle Inspection 47
X-radiography of Tube-to-Tube Welds or Other Sections 48
Radiographic Procedures 49
Ultrasonic Inspection of Tube Welds and Other Tube Sections 50
Ultrasonic Inspection of Seam Weld Area 51
Ultrasonic Inspection of Skelp-end Welds 51
Ultrasonic Inspection of Tube-to-Tube and Pipe-to-Pipe Butt Welds 51
Liquid Penetrant Inspection 52
Removal of Surface Imperfections 52
Assessment of Coiled Tubing 53
General 53
Fatigue Life and Fatigue Management of Coiled Tubing 53
Theoretical Calculated Fatigue Life 54
Review of String Records 54
Examples of Effective Repair on Coiled Tubing 54
Record Keeping 55
Coil Tubing Fatigue Testing and Equipment 56
Objectives of Full-scale Coiled Tubing Fatigue Testing 56
Recommended Standard Fatigue Testing Machine 56
Recommended Testing Matrices 61
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
SSC Zoning (Excluding Tube-to-Tube Welds) 24
Drift-ball Standoff in Perfectly Round Coiled Tubing 29
Drift-ball in Ovaled Coiled Tubing 30
Cycles to Failure for CT-100 (1.25 in. × 0.109 in.) 53
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The Standard Bending Machine Concept 57
Profile of the Straight and Curved Mandrels 57
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
Pitting that Occurred from Acid During Storage (Transversely Oriented Fatigue Cracks in
Base of Pitting Inside Tubing at Location of Storage Corrosion) 81
Mild and Deeper Corrosion Occurring at the Lowest Point on the ID of Stored Tubing 82
Corrosion Pit on ID with Fatigue Cracks 83
Carbon Dioxide Pitting in Hang-off Tubing 83
Microbial Corrosion Pitting Inside Tubing 84
Example of Sulphide Stress Cracking 84
Hydrogen-induced Cracking 85
Stress-oriented Hydrogen-induced Cracking 85
Fatigue Pinhole 86
Fatigue Crack Originating with High Pressure Inside the Tubing 86
Fatigue Break at a Factory Skelp-end Weld 86
Ductile Tensile Fracture (Showing “Necking” and a 45° Shear Lip) 87
Tensile Failures with Brittle Fractures 87
Separation Caused by Tensile Overload Under Flexure 88
Relatively Shallow Plough Marks on the Outer Surface of Coiled Tubing 88
Deep Plough Marks Resulting in Fatigue Cracks 89
Transversely Oriented “Chatter” (“Fish-scale”) Marks That Generally Accompany “Plough” Marks 90 D.19 Longitudinal Gouge 90
Gouges with Transverse Orientation 91
Elongated Gouges with Chatter Marks 92
Gouges with Large Transverse Component 92
Longitudinal Scratches 93
Scoring Marks on the Tube Outside Diameter 93
Wall Thinning on the Outside Diameter (left) and Internal Erosion from Sand (right) 94
Erosion of the Inside Surface from Sand That Can Result in Serious Wall Loss 94
Wear with Galling 95
Impingement Erosion 95
Burst at Thin Wall Area in Tubing 96
Burst Failures at Seam Weld (Possibly from a “Cold Weld”) 96
Examples of Dents 97
Examples of Dimple Dents 98
Example of Multiple Types of Dents 98
Laboratory-manufactured Dent with Fatigue Cracks 99
Elongated Dent 99
Buckled Tubing 100
Collapse in Two and Three Directions (One Node Is the Seam Weld) due to
Tension and High External Pressure 101
Gripper Marks 102
Gripper Block Mark with Fatigue Crack 102
Injector Ring Damage 103
Example Form for Visual and Dimensional Inspection Report 104
Page
Example Form for Electromagnetic NDT Report (Part 1) 105
Example Form for Electromagnetic NDT Inspection Report (Part 2) 106
Example Form for Preservation of Coiled Tubing Checklist 107
Example Form for Preservation of Coiled Tubing Equipment Offshore 108
Example Form for Fatigue Testing Data Collection Sheet 109
Tables
Welds with Filler Metal (Tube-to-Tube Weld) 8
Recommended Maximum Intervals Between Recalibration/Recertification 38
Actual Sample Radius of Curvature on a Standard Bending Form 58
Collapse Values for API 5ST Coiled Tubing Grades 67
Coiled Tubing Collapse Pressure Factors for Various Amounts of Utilization 73
Values for Coiled Tubing Calculations on Wall Thickness and Capabilities 75
Coiled Tubing Gauge Parameters 78
Dimensions for Yield Radius, Reel, and Guide Arch 80
Care, Maintenance, and Inspection of Coiled Tubing
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.).
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.
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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