Publicised catastrophic failures of forged materials in deepwater applications have called into question the structural integrity of such products and focused industry attention on the need for carefully-managed ‘integrity management’ of key components.
Errors in material selection at the design stage, the use of incorrect heat treatment techniques and inconsistent mechanical testing regimes, often involving test pieces not taken from the actual components, can lead to product failures during operation, typically resulting in significant environmental, safety and financial costs.
With suppliers to the oil & gas and marine industries appreciating the need for integrity management of deep sea components to prevent expensive failures or prolonged shutdowns, Yorkshire-based independent heat treatment and metallurgical testing specialist Keighley Laboratories is experiencing an upturn in demand for first article inspection of pre-production components.
It is a preventative measure that the company believes could be adopted more widely, especially with the life expectancy of products extending from ten years to 25 years or more, often in extremely harsh and corrosive environments.
Leonard Stott, customer support manager for Keighley Labs’ Technical Services division, said: “More than ever there is a definite requirement for proven product reliability and fitness-for-purpose, as well as a need for consistent mechanical and corrosion properties that can only be achieved by applying the correct processing and heat treatment techniques. Also, product testing procedures need to be accurate, not least the correct positioning and orientation of test sample pieces, to ensure optimum and consistent test values.
“It would be costly for suppliers to set up the necessary in-house procedures to ensure critical mistakes don’t happen, so it is worthwhile sub-contracting the metallurgical testing of components to independent experts like ourselves.”
Keighley is a specialist in the analysis, testing and heat treatment of metals, holding many leading quality accreditations relevant to various industry sectors.
It was the catastrophic failure of a mooring shackle in the Gulf of Mexico and a second incident involving two sockets in another mooring system, which highlighted faults in the original heat treatment process as a likely cause. A subsequent report by the US Department of the Interior’s Minerals Management Service (MMS) concluded that defective heat treatment during component processing resulted in a metal unable to meet Charpy impact test requirements for material toughness and that testing parameters were either not followed or not adequate to ensure specifications were met.
The MMS recommended that operators should revise their specifications to make sure that testing and manufacturing produces a satisfactory product, which will meet future usage demands. It also commented that operators should review their requirements for both destructive and non-destructive testing of critical elements, as well as ensuring that test coupons, or pieces, are properly representative.
It was later found that the test pieces were not samples taken from the actual product and subsequent research indicated the importance of sample positioning in achieving representative and consistent toughness values. Thus, while energy absorption in a longitudinal orientation achieved a satisfactory 70-80 joules, the same test in the transverse direction recorded a disastrously low 4 joules. It was also easier for a smaller test piece of 2” cross-section to pass the impact test, rather than a larger, more representative section.