Reliability modeling of surface controlled subsurface safety valves

The article discusses the consequences of choosing a Weibull life distribution instead of an exponential distribution. The discussions are based on a specific data set for surface controlled subsurface safety valves (SCSSVs) used in offshore oil and gas production wells. The estimates of the mean time to failure and the mean fractional dead-time based on the stochastic censored data set, are shown to be non-robust with respect to variations of the Weibull parameters. The availability of the SCSSV as a safety barrier against blowouts is discussed in relation to risk acceptance criteria and the principle of ‘as low as reasonably practicable’. Replacement policies to balance the risk and operational cost are proposed and discussed.