National Academies of Sciences Workshop on Subsea Bolt

National Academies of Sciences Workshop on Subsea Bolt Performance Session I - SUBSEA FASTENER DESIGN REGULATIONS Part 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

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. )

Deepwater Drilling Complexity

Deepwater Drilling Complexity - Large structures with multiple connections

Deepwater Production Subsea System Complexity EXPORT LINES

Subsea Trees & Jumpers

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.

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

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

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.

Fasteners Materials Selection Criteria • 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

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

Materials Options for Subsea Fasteners

SCC and HE Resistance • 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.

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

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

Strength Limit with CP • Historically alloy steel fasteners were limited to ASTM A 320 L 7 M and ASTM A 193 B 7 M grades with a maximum hardness of 22 HRC, i. e. , the specified limit for sour service applications per NACE MR 0175/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 17 D and Norsok Standard limit the hardness to HRC 35 for steel. • For Corrosion Resistant Alloys (CRAs) materials, limits are per NACE MR 0175/ISO 15156

Qualification Testing • 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.

Materials Susceptibility to HE Alloy / Condition HE Susceptibility Comments AISI 4340 and 4130 > 120 ksi Sys Susceptible for hardness > 34 HRC at potential of - 950 m. V or more negative Based on lab testing and field experience Grade L 7 ASTM A 320 Susceptible for hardness > 34 HRC at potential of - 950 m. VSCE or more negative Based on lab testing and field experience SAF 2507 Slight or some effect of cathodic protection Crack growth tests 254 SMO No or very little effect of cathodic protection Crack growth tests Ferralium 255 Susceptible at potential of -1000 m. VSCE Based on slow strain rate tests Alloy 286 (solution treated and aged) Resistant Based on SST, C-ring, tensile and fracture mechanics tests K-500 All conditions Susceptible at potential of - 850 m. V or more negative Based on field experience and slow strain rate tests Marinel Beryllium Copper No or very little effect of CP Resistant Crack growth tests Based on slow strain rate tests

Materials Susceptibility to HE Alloy / Condition HE Susceptibility Comments Susceptible at potential of - 1000 m. V or more negative Susceptible at potential of - 1250 m. V Based on field experience and slow strain rate tests Based on slow strain rate tests Crack growth tests Alloy 725 (solution treated and dual aged) Slight or some effect of cathodic protection Susceptible at potential of - 850 m. V or more negative Resistant Alloy 945 Susceptible at 5 m. A/cm 2 CP current Based on notch tensile tests Alloy 946 Susceptible at 5 m. A/cm 2 CP current Based on notch tensile tests Alloy X-750 Alloy 925 (solution treated &dual aged) Alloy 625 Alloy 718 (solution treated &dual aged) Based on slow strain rate tests Based on CT tests Based on slow strain rate tests Ti-6 Al-4 V (solution Variable susceptibility treated annealed) Based on slow strain rate tests, notched bars, U-bends. Ti-5111 (as forged) Based on slow strain rate tests and fracture toughness Resistant

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, 945 HS, 946 and 625 HS for > 135 ksi YS – 718, 725, 945, 625 HS for 125 ksi YS • PH Stainless steel – A 286 UNS 06660 for 105 – 125 ksi YS • Titanium alloys (Ti-6 -4 ELI used in Heidrun drilling riser)

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 m. V in some areas near anodes or systems where both impressed current and anodes could co-exist or possible stray current.

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

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

Why there are Less failures than Predicted? • 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 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. )

Materials Specifications and Quality Assurance n 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. n Tighter specifications are needed to ensure adequate resistance to HE.

Materials Options • • 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 946 HS - MP 159 - Ti Alloys MP 35 N, 17 -4 PH H 1100, Alloy A 286, Alloy 925, Rene 41, Alloy 625, Alloy 686 and Be-Cu alloys do not meet the strength / size requirements

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.