Under pressure

Owen Stephens, safety relief valve specialist for Nacional Safety Valves UK, discusses the importance of correctly sizing, selecting and maintaining a safety relief valve The primary reason to use a safety relief valve is to prevent a pressurised vessel or system from over pressurising. It is there to protect life, property and the environment and is the last line of defence should other safety systems fail. As the last line of defence, the accuracy and quality of a safety relief valve is paramount in ensuring an overpressure situation is avoided. Overpressure scenarios can be defined as a situation resulting from the internal pressure within piping or vessels exceeding the maximum allowable working pressure (MAWP). HOW CAN AN OVERPRESSURE SITUATION OCCUR? API Standard 521 Part I details common causes that may result in a need for overpressure protection: Closed outlets/blocked discharge Overfilling Thermal expansion Chemical reaction Exposure to external fire (fire case) Cooling system failure Each of the aforementioned overpressure scenarios could happen independently from one another or more than one could happen simultaneously. It is important that the user...