A safety relief valve is designed to protect the pressurized system to which it is connected, and it should also protect personnel and other equipment in the event of system failure. Proper installation, maintenance and operation of pressure relief valves are critical in an overpressure event. Excessive actuation of a pressure relief valve may indicate a problem with the operation or design of the system.
Our recommendations are general and based upon standard industry practices. It is the responsibility of owners and users to assure that these guidelines are followed, in addition to meeting all applicable ASME codes, military specifications, and local jurisdictional requirements.
- Only trained, qualified personnel should install pressure relief valves.
- Using information from the nameplate, confirm the following:
- Verify that the valve being installed is the correct valve for the intended service media, set pressure, and temperature.
- Verify that the system operating pressure does not exceed the maximum operating pressure of the valve. In most cases, that pressure is between 75% and 90% of the relief valve’s set pressure.
- Valves should be mounted so the stem is in a vertical position.
- Check threads for burrs or foreign material before installation.
- Minimize thread sealant and Teflon® tape. Excessive sealant or tape may loosen and lodge itself on the valve seating surface, causing a leak or preventing proper operation.
- Clear away any restrictions or foreign material in the inlet piping.
- Make sure that any gaskets are properly positioned and do not restrict the flow-path.
- When tightening the valve to its inlet, use only wrench or hex flats that are provided on the valve. Do not tighten the valve by using a wrench on the valve body.
- Do not use excessive force or torque.
- If using a block valve upstream of the pressure relief valve, use a full-bore device with locking mechanism and assure that the minimum area of the block valve is at least that of the inlet area of the pressure relief valve.
- Check for leaks at all connections, and correct all prior to system operation.
- Adequate supports should be provided in both the inlet and discharge piping systems to prevent excessive loads and bending moments during valve discharge. If binding or excessive loading is imposed on a pressure relief valve as a result of its installation or operation, failure or leakage may occur.
- If a bellows valve is installed, do not plug the bonnet vent as this could cause the valve to malfunction.
- If insulation is being used, assure it does not plug any valve openings or restrict the movement of components that are intended to move.
- Vibration can be the source of major pressure relief valve problems. System dynamics as well as placement of pressure relief valves or other components should be considered to minimize vibration and its effects.
- Additional information on pressure relief valve piping design is given in ASME Section VIII, Appendix M and ANSI/ASME B31.1 Power Piping Code, Non-Mandatory Appendix II.
- Piping from the source to the valve inlet should have the same minimum opening area as the inlet opening area of the pressure relief valve.
- The pressure relief valve should be located as close as possible to the pressure source or vessel being protected.
- The inlet piping system for a pressure relief valve should be designed so that restrictions and sources of pressure drops such as reducing flanges, elbows, and sharp edges are minimized.
- Discharge piping should be at least the size of the valve outlet, equivalent in pressure class, and the piping should be as short and direct as possible from the valve to the point of discharge.
- The discharge should be piped upward or into a manifold to prevent the loosening of fittings or components during the relief operation.
- Consideration should be made in design to minimize the effects of back pressure. Back pressure buildup in the discharge of a pressure relief valve may affect its set pressure and opening operation.
- The discharge, or outlet, of a pressure relief valve must be drained to prevent the buildup of liquid, ice, or hydrate.
- Drains or vent openings should not be plugged, restricted, or pressurized from unrelated pressure sources.
- Consideration should be made to minimize the effects of high noise levels resulting from media discharge by abatement, piping to a safe area, or both.
- Discharge piping should be piped to a safe area to prevent discharge of high pressure fluids from causing harm to personnel or equipment.
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