Compressed Gas Relief Devices

Pressure and temperature relief devices are required to protect storage vessels and other equipment as well as piping and instruments against pressures higher that those for which they are designed.

Pressure relief devices (PRDs) are required for most compressed gas systems and storage vessels. A PRD is intended to release pressure to prevent a rupture or burst failure.

Thermal pressure relief devices (TPRDs) are required for composite storage vessels and any other systems where the ability of a component to contain pressure may be compromised by heat or fire. A TPRD is intended to vent the contents before a cylinder or component can be weakened by heat or fire.

• Relief devices must be suitable for hydrogen service and the specific operating conditions
• Examples of relief devices include rupture disks and relief valves
  • Because of the relatively thin construction of rupture disks, they are particularly sensitive to hydrogen embrittlement failures.
  • Because relief valves are manufactured using different materials in a single valve, attention to the suitability of each material used in valves requires close attention. For example, some austenitic stainless-steel valves have stems that are made from martensitic stainless steel. Austenitic stainless steel is generally considered acceptable for hydrogen service, whereas martensitic stainless steel is not.
• Relief devices should be fire resistant and must be sized to quickly release the contents of components which they protect.

Relief device discharge piping must be properly sized and designed to withstand venting thrust forces. See Venting for more information about vent stacks. In addition, the outlet of any relief device discharge piping must be protected against rain, dirt, and insects by the use of a blow-off vent cap.