Background to the derivation of partial safety factors for BS 7910 and API 579

The background to the derivation of partial safety factors (PSFs) given in two standards, BS 7910 and API 579, is described. In both cases, PSFs are provided to achieve selected target reliability levels against the failure modes of fracture and plastic collapse in structural components. The recommended PSFs in the two standards are compared in order to investigate differences. Example fitness for service assessments are also conducted in order to explore the potential impact of differences on the output of an assessment. Work being carried out to review and update the current partial safety factors for the next revision of BS 7910 is discussed.