1. 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

2. Potential Risks

3. 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

4. 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

5. 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

6. Failure Mechanisms

7. 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

8. 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

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

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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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