Potential Risks, Limitations, And Failure Mechanisms Arising From Fastener Design, Manufacture, Material, And Coating Selection Prepared for the National Academy of Sciences Workshop on Subsea Bolt Performance 10 April 2017 Tim Haeberle Chief Consulting Engineer – Materials and Processes GE Oil & Gas

Potential Risks

Potential Risks From Failure Of Threaded Fasteners On Subsea Drill Through Equipment Equipment with critical threaded fastener systems includes: Marine drilling riser - bolted designs Lower marine riser package (LMRP) Blow out preventer (BOP) stack The potential risks vary depending on: The type of equipment The specific fastener(s) on the equipment The stage of drilling operations

Potential Risks From Failure Of Threaded Fasteners On Subsea Drill Through Equipment The potential risks include: Difficulty in control of the well The need for an LMRP pull to the surface and subsequent repair The need for a BOP stack pull to the surface and subsequent repair Loss of containment Minor leakage of drilling mud, with quick control More leakage of drilling mud, but limited by available volume Minor leakage of hydraulic fluid, with quick control More leakage of hydraulic fluid, but limited by available volume Minor leakage of oil or gas, with quick control Significant leakage of oil or gas, with delayed control In general, the risk of significant loss of containment of oil or gas with a delay in maintaining control increases the closer to the wellhead a threaded fastener failure occurs

Potential Risks From Failure Of Threaded Fasteners On Subsea Drill Through Equipment Flex Loops Choke & Kill Connector LMRP Connector Annular BOP Subsea BOP stacks are designed to minimize risk with: Redundant control systems Two independent control pods and hydraulic systems connected to the drill ship via the riser An acoustic control pod and pressurized hydraulic fluid reservoir on BOP if the two primary control systems fail Ability to operate BOPs mechanically with a remotely operated vehicle (ROV) if the two primary systems and the acoustic pod system fail Multiple annular BOPs and multiple ram BOPs The hydraulic connector under the BOP is the most critical location since it connects the BOP to the wellhead Annular BOP Wellhead Connector Choke & Kill Valves LMRP Mandrel Ram BOP Ram BOP Ram BOP

Failure Mechanisms

Failure Mechanisms Associated With Threaded Fasteners The API Multi-Segment Task Group on Bolting was formed in early 2015, to consider issues raised in the BSEE QC- FIT report The API Multi-Segment Task Group on Bolting released a report in early 2016 that includes: Detailed mapping of potential failure mechanisms Identification of existing API specs and industry standards intended to mitigate the risk of specific failure mechanisms Recommended actions for API and ASTM committees that will further mitigate the risk of specific failure mechanisms The API report was submitted to BSEE in February of 2016

API Specifications Provide Requirements To Reduce Risks The API Multi-Segment Bolt Task Group Report was not the start of API specifying bolting requirements API product specs such as API 6A, API 16A, and API 17D have contained bolting requirements for decades ASTM bolt spec normative references Maximum design stress limits Quality control requirements API 17D 1st Edition was issued in 1992, with a 35 HRC maximum for low alloy steel bolting API spec 20E for low alloy steel bolting, 1st Edition issued in 2012, with 34 HRC maximum for bolting API Spec 20F 1st Edition for CRA bolting issued in 2015

Conditions Required For Environmentally Assisted Cracking Susceptible Material Environment Tensile Stress EAC

Prevention of EAC Susceptible Material Environment Susceptible Tensile Stress Susceptible Material Environment Tensile Stress Susceptible Material Environment Tensile Stress

H-embrittlement is a key issue Bolting with high strength & hardness has been a problem The development of the over-arching document is in progress Zinc plating is being eliminated as an option

These failure mechanisms are not prevalent There are a number of existing mitigating factors API to add cautionary note on ASTM A453 Type 660 Grade D Control of applied tensile stresses is important

Proper material selection is a key factor Fit for purpose material properties is also a key factor Requirements in API product specs, API Spec 20E and API Spec 20F need to be followed

Low temperature brittle fracture is more of a problem for oil & gas equipment used on land or on platforms, where temperatures can reach as low as -75F or -60C For subsea applications, it has not been seen as an issue

Liquid metal embrittlement is included It can be a concern both in manufacturing processes and in bolt lubrication practices It is not a common issue for subsea applications The recommendations need to be implemented as we are currently lacking mitigating factors

Fatigue should not be a problem in a properly designed and torqued threaded fastener, operated within the design limits Some bolts are torqued in by the manufacturer while others are torqued in the field by the customer Proper torque practices are necessary

API issued API Spec 20E in 2012 and API Spec 20F in 2015 Developed in recognition of the fact that ASTM bolting specs were not sufficient for insuring quality and fit for purpose bolting materials However, adoption these new API bolting specs by the API product committees has been slower than desirable, but is now underway

Tensile overload is a concern, but there are a number of mitigating factors in place Over torqueing remains a concern Better monitoring & recording of the stresses on risers, including pull tension, water velocity, & VIV would be helpful

Summary The failure of threaded fasteners on subsea equipment can result in various issues, ranging from minor to significant, including loss of control or loss of containment The API CSOEM Multi-Segment Bolt Task Group issued a report in 2016 that identifies: Potential failure mechanisms Existing mitigating factors Recommendations for further API TG actions where mitigating factors do not currently exist or are deemed to be insufficient API has numerous Task Groups working to implement the recommendations, but some testing is needed to better define the limitations of specific alloys The industry is committed to protecting the environment and its workers, so recommendations from the National Academy of Sciences Bolt Group for additional mitigations are welcome