Resumen de Safety life cycle analysis applied to the engineering of pressure relief valves in process plants
José Basco Montia
Chemical plants and other industrial installations process and store hazardous materials, which represent a certain risk to people, equipment and the environment. Overpressure is one of the most common upsets in process plants and relief devices (pressure relief valves, rupture discs, overpressure-vacuum valves) are required on process equipment to prevent internal pressures from rising to levels, which could cause catastrophic equipment failure. They are the ultimate line of protection against equipment rupture and are therefore extremely critical safety elements. However, this criticality is not always accounted for in existing plants and in the engineering of new ones, as a lot of pressure relief systems audits performed recently, especially in US, have demonstrated. As an example, a 2014 report from Siemens Energy, Inc. of Houston, pointed out that, after performing 1,197 pressure relief systems audits between 2005 and 2014, consisting of 174,943 pieces of equipment and 80,372 pressure relief devices, 47% of the relief devices had a deficiency, e.g. 13,4% were undersized. In another statistical study focused on the maintenance process of pressure relief valves conducted in 1995 and based on 13,000 items inspected in the workshop, it was found that 18% of the valves only opened at a pressure higher than 110% of the set pressure and 3% did not open at a pressure of twice the set pressure. Therefore, it is clear that a methodology for increasing the reliability of pressure relief devices would be very useful. A new methodology has been developed in this thesis based on an extension of the safety life cycle concept developed for the safety instrumented systems, according to the IEC 61511. This new methodology covers all the steps of the life cycle of a pressure relief valve: a) risk analysis; b) safety requirements specification; c) design; d) reception, installation and checking; e) operation, maintenance and revision; f) management of change; g) decommissioning h) verification and i) documentation and technical audits. This methodology has been applied to three existing petrochemical plants, obtaining results that validate it as a useful tool in the target of increasing the reliability of pressure relief valves.
