Risk Due to the Ageing of Equipment: Assessment and Management
Within the current risk assessment practice, generic failure frequencies are used although it is recognised that data related to certain equipment types (including pressurised equipment) are not updated. Public databases do not take into account the ageing of materials, the newer quality systems and the different maintenance management. Failure frequencies are used to develop fault trees, thus lack in such data may lead to questionable decisions regarding facilities' licensing, land use and emergency planning. To overcome this limit there are two complementary ways: 1) to collect new data on equipment failures, 2) to introduce corrective parameters, which balance the uncertainties induced by the use of general frequencies. The Directive Seveso III, in force since July 2015, explicitly calls for the introduction of a safe ageing management of critical facilities. To deal with this issue, managers currently adopt Risk Based Inspection (RBI) standards (ASME, API or RIMAP) based on the use of some compensatory factors, which are subjectively defined by managers. The new Directive imposes to demonstrate the appropriateness of the choices to the Control Authorities. This paper aims at verifying if the RBI procedures comply with some essential requirements of the Directive Seveso III; then guidance will be provided to auditors on how to verify the management of risk arising from plants' ageing in chemical industry.