An Operator performed an uprating assessment to determine whether the affected section of the Installation would be acceptable for the higher pressure. The study identified an outstanding action to investigate whether sufficient mitigation of fatigue failures would be provided by the original hydrostatic pressure test. In particular there was a requirement to show that the likelihood of failure would be acceptably low during pressure-raising and that the likelihood would remain acceptably low for a period of operation at the increased pressure for at least two years.
The Operator therefore commissioned AFAA to undertake a fitness-for-purpose assessment to investigate whether the above requirements would be met.
AFAA carried out a fitness-for-purpose study based on Structural Reliability Analysis (SRA). Structural Reliability Analysis is used to determine the probability of failure due to identified failure modes, taking account of uncertainty in key parameters, and also taking account of the effects of mitigating measures.
AFAA were able to demonstrate to the Operator that overall installation failure probability would be acceptable during pressure-raising and for continued operation at the uprated pressure for at least 2 years.