National Academies of Sciences Workshop on Subsea Bolt Performance

1. National Academies of Sciences Workshop on Subsea Bolt Performance Session I - SUBSEA FASTENER DESIGN REGULATIONSPart 1 – Fastener Systems in Use in Critical Equipment and the Diverse Environments in Subsea Oil and Gas Drilling and Production Khlefa A. Esaklul Corrosion and Materials Advisor Asset Integrity – Worldwide Engineering & Operation Occidental Oil and Gas Corporation Chair of NACE International Technical Coordination Committee

2. Introduction • Deepwater and subsea operation continue to be the future of the oil and gas production to meet the growing energy needs • As the demand for oil and gas increases, exploration in deepwater increased and extended to higher water depths, higher pressure, higher temperature and more aggressive environments • This resulted in more complex operation and demand for higher thickness, higher strength and cracking resistant materials for the various components in these operations • A decade ago the depth was < 7000 ft., today it is exceeding 10,000 ft. of water depth (Pacific Santa Ana vessel can operate at 12000 ft.)

3. Deepwater Drilling Complexity

4. Deepwater Drilling Complexity - Large structures with multiple connections

5. Deepwater Production Subsea System Complexity EXPORT LINES EXPORT LINES EXPORT LINES

6. Subsea Trees & Jumpers

7. Background • Flanged connections are still an integral part of any offshore developments with fasteners being one of the primary means for assembly. • Development of deepwater reservoirs with higher reservoir pressure and temperature requires a class of materials with optimum combined properties that exceed the commonly used subsea materials. • Costly intervention and the demand for higher safety and environmental protection increased the need for inherent design reliability and highly reliable and proven performance parts. • Fasteners of all types and sizes are integral part of these components • Fasteners with diameters that exceed 2.5 inch (100 mm) are increasingly becoming more common.

8. Examples of Subsea Flanged Connection Riser Flange Flexible flowlines BOP Configuration Wellhead components

9. Example of the number of fasteners in use in various systems CP Anodes

10. Common Application of High Strength Fasteners US Bolt Website • Drilling risers • Connectors • Blowout preventers (BOP) • Subsea assemblies • Trees and wellheads • Risers, flowlines and pipelines tie point flanges • Internal assembly bolts for valves, connectors, etc.

11. Mechanical Properties - Strength - Toughness Corrosion Resistance - General Corrosion - Galvanic Corrosion - Localized Corrosion (Pitting, Crevice, etc.) Resistance to Environmental Assisted Cracking - Stress Corrosion Cracking - Hydrogen Embrittlement - Sustained Load Cracking Fasteners Materials Selection Criteria

12. Challenges • Loading conditions • Static (weight, fluids column, pressure, etc.) • Dynamic (ocean current, wave action, Vortex Induced Vibration, etc.) • Environmental conditions • External (salt water, temperature, CP interaction, stray current etc.) • Internal (drilling fluids, produced fluids, etc.) • Limited or difficult monitoring • Inaccessibility • For inspection • For maintenance

13. Materials Options for Subsea Fasteners

14. Materials Options for Subsea Fasteners

15. High strength steel are susceptible to SCC and HE when cathodically protected and their susceptibility increases with increasing YS. Steels with YS < 120 ksi are generally resistant to SCC and HE. Steels with YS > 120 ksi, the resistance decreases with increase in strength. Typical KISCC is 50 – 75 ksi-in for steels with YS = 145 ksi. Typical KIC for this steel is 200 ksi.in . NASA showed that in the absence of CP, AISI 4340 is resistant to SCC up to tensile strength of 180 ksi (40 HRC) ~ 155 ksi YS. SCC and HE Resistance

16. KISCC as a Function of Yield Strength for 4340 Alloy Steel Atlas of Stress Corrosion Cracking data, ASM International, 1984

17. KISCC as a Function of Yield Strength Ref 17 in An Introduction to the Design and Behavior of Bolted Joints by John BickfordY. Chung Threshold preload levels for avoiding stress corrosion cracking in high strength bolts Tech Report 1984

18. Historically alloy steel fasteners were limited to ASTM A320 L7M and ASTM A193 B7M grades with a maximum hardness of 22 HRC, i.e., the specified limit for sour service applications per NACE MR0175/ISO 15156. Studies have shown that limiting sub-sea steel fasteners to the sour service requirements (22 HRC) is overly conservative. Instead subsea steel fasteners exposed to CP can be used to a maximum hardness of 34 HRC per ISO/DIS 13628-1 recommended practice. API 17D and Norsok Standard limit the hardness to HRC 35 for steel. For Corrosion Resistant Alloys (CRAs) materials, limits are per NACE MR0175/ISO 15156 Strength Limit with CP

19. In view of the limited data, selection of subsea fasteners applications still relies on qualification testing for the specific application. HE testing can be by slow strain rate tests, C-ring, U-bends, notched bars or fracture mechanics tests. Most of the experimental data suggest that many materials are prone to hydrogen embrittlement based on accelerated testing but until recently there have been limited reported failures in the field. The challenge has been in how to establish reliable test methods for materials qualification and asses the risk to HE. Qualification Testing

20. Materials Susceptibility to HE

21. Materials Susceptibility to HE

22. Subsea High Strength Fasteners in Use • High strength steels • AISI 4140 and 4340 for 125 ksi YS • AISI 4340 for >135 ksi YS • PH Nickel alloys • 718, 725, 945HS, 946 and 625HS for > 135 ksi YS • 718, 725, 925, 945, 625HS for 125 ksi YS • PH Stainless steel • A286 UNS 06660 for 105 – 125 ksi YS • Titanium alloys (Ti-6-4 ELI used in Heidrun drilling riser)

23. Corrosion Control • For above water and in the splash zone, coating and encapsulation are used with good success. • For subsea, cathodic protection works well such that no coating is required. Coating is used to protect fasteners prior to installation. • Cathodic protection potential can vary and could exceed -1100 mV in some areas near anodes or systems where both impressed current and anodes could co-exist or possible stray current.

24. Fasteners Coating • Electroplating Temperature Limit • Cadmium electroplating 608 ◦F • Zinc and Zinc Nickel electroplating 788 ◦F • Hot dip Coating • Hot dip galvanizing 800 ◦F • Hot Dip-spun galvanizing 800 ◦F • Mechanical plating • Zinc and aluminum plating (+ phosphating) 800◦F • Phosphating • Zinc Phosphate Ambient • Organic Coating • Xylan (PTFE) 450◦F • Xylar 1000 ◦F • Teflon or PTFE 450 ◦F • Electroless nickel 1600 ◦F

25. Most Widely Used Coatings for Subsea Applications • Zinc Electrplating • Dip galvanizing • Zylan • Zinc Phosphate

26. Low operating stress - Design stresses are at 66% YS. Design based on worst-case conditions that include too extreme loading conditions (100 Year Storm) applied stress ~ 70 – 80% UTS. Fasteners are shielded from CP system via Isolation and grease packing. The severity of the tests used to qualify the materials for these applications. Recent failures suggest these conditions may have changed and/or co-existed as drilling extended to higher water depths Why there are Less failures than Predicted?

27. Why did the recent failures occur? • 3 ¼ inch diameter bolts with a range of hardness measured in one lot used for drilling riser applications over a decade ago exceeded the 34 HRC limit with no failures. • Is it the load?, the material? or the environmental conditions? • Data appears to suggest that a combination of the above are the likely cause • Loading conditions could be under estimated (wave action, ocean current, depth, etc.) • HE susceptibility increases with stress level particularly at stresses approaching yield strength for most if not all materials • Quality assurance may not be sufficient to control strength, microstructure, hydrogen ingress, etc. • CP overprotection may have increased either through over design or unaccounted for conditions (Zn coating, anode and impressed current, low temperature, etc.)

28. Materials Specifications and Quality Assurance • High strength alloys for subsea applications must adhere to specifications mainly heat treatment, degree of cold work and maximum hardness to ensure sufficient resistance to EAC. • Tighter specifications are needed to ensure adequate resistance to HE.

29. For large diameter (> 2 ½ inch) fasteners with yield strength of 150 ksi, the options are limited to the following alloys: - Alloy steels (AISI 4340) - Alloy 718 - Alloy 725 - Alloy 945 - Alloy 946 HS - MP 159 - Ti Alloys MP 35N, 17-4PH H1100, Alloy A286, Alloy 925, Rene 41, Alloy 625, Alloy 686 and Be-Cu alloys do not meet the strength / size requirements Materials Options

30. Summary • Several materials options are available to meet the needs of the industry in high strength fasteners. • These materials require more characterization of their limits to HE and effect of sacrificial coatings where used • There is a need for better monitoring systems to measure the level of CP in subsea systems and any potential interference. • Tighter specifications and quality control are needed to ensure materials are within specified limits (e.g. hardness) to ensure adequate resistance to HE. • Effect of thread cutting rolling vs. machining is still unresolved • On line monitoring of loads in drilling risers are needed to determine the effect of ocean currents, VIV, etc.