Pressure Relief Device – A Last Line of Defense

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What is a last line of defense? It depends on the surrounding environment. For example, a levee would be the last line of defense in controlling flood and a goal keeper would be the last line of defense in a soccer game. The consequences are unacceptable in the event if the last line of defense fails. In refinery, petrochemical complex, or offshore facilities, the pressure relief system, in particular, pressure relief devices are the last line of defense if all other safety device or controls fail. Inadequate pressure relief system was the major cause of undesirable events in the last two decades in the oil and gas industry. Occupation Safety and Health Administration (OSHA) promulgated C.F.R. § 1910.119 regulation, the Process Safety Management (PSM) standard, in 1992 in response to a series of incidents involving the improper management of hazardous chemicals with specific emphasis on pressure relief system design and design basis.

The pressure relief devices are used to relieve excess fluid from equipment to limit the equipment pressure below its Maximum Allowable Working Pressure (MAWP). A pressure relief device is not connected to any power supply, plant utilities (air, steam, etc.) or control schemes. Therefore, pressure relief device is a key asset in any refinery, petrochemical complex, or offshore facility. It is a self-contained mechanical device that is under pressure. A pressure relief device and associated system such as sub-headers flare headers, knock-out drums, and flare stacks safeguard the operating facility, its workers, and the environment. Hence, accurate analysis, documentation, and management of the pressure relief device and associated system are critical for the operating facility. In addition, a systematic pressure relief system analysis helps determine the safe operating limit of a unit from a relief system perspective. This information further helps the plant management in making debottlenecking business decisions.