Pressure Protection by Mechanical Relief Devices versus Pressure Protection by Systems and Flare-Related Safety Issues

摘要

Pressure relief by mechanical devices; e.g. pressure safety valves (PSVs), is the most common form of protecting equipment against excessive pressures. Safety of pressure vessels is treated in codes such as the European Union's Pressure Equipment Directive (97/23/EC) and ASME. For a non-fire case and protection by a single device (PSV), they universally limit the maximum pressure to which a pressure vessel can be subjected to 110 percent of the design pressure or i 10 percent of the maximum allowable working pressure (MAWP). Prior to 1996 ASME stipulated that pressure protection could only be provided by means of PSVs and/or bursting disks. In 1996 ASME approved its Code Case 2211 that allows for overpressure protection by safety instrumented systems (SIS). SIS in a pressure protection application are often called HIPPS or HIPS, for high-integrity (pressure) protection systems. The new API Standard 521 (2007) allows the use of H1PPS to eliminate certain overpressure scenarios. A wide application of HIPPS increases the frequency of having to deal with an undersized flare. Undersized flares create extremely hazardous situations. Inadequate process safety management in combination with HIPPS constitutes a major safety challenge to the process industry these days.