Replace & Recertify relief valves at the right intervals
The most important appurtenances on any pressurized system are the pressure relief devices (PRDs) provided for overpressure protection of that system (NBIC Part 2, 2.5.1 a). Relief valves are the last line of defense in the protection of pressurized systems. As such, it is imperative the valves be properly installed and are functional.
Benefits of replacing and recertifying your relief valves:
- Protect your pressurized systems
- Ensure employee safety
- Minimize property loss
- Comply with NBIC Part 2 Section 2.5.8
The NBIC Section 2.5.8 recommends inspection and test frequencies for pressure relief devices on the following intervals:
- Power Boilers < 400-psig – Manual check every 6 months; pressure test annually
- Power Boilers > 400-psig – every 3 years
- High Temperature Hot Water Boilers – annually
- LP Steam Boilers – Manual check quarterly; pressure test annually
- Hot Water Heating Boilers – Manual check quarterly; pressure test annually
- Air and Dry Gases – every 3 years
- Refrigeration Relief Valves – every 5 years
- Vessels and Piping – depends on the service/history
To aid in managing the safety/relief valve program, an asset register (listing) of all valves in the facility with service dates should be compiled. Information, including relief valve set pressure, type (service), inlet and outlet size and capacity, can be included to ease ordering and replacement of valves.
An installation SOP should be created for relief valves and personnel trained on proper installation.
Key Areas of the SOP
Some of the items included on the SOP should be:
- The valve should be installed in the proper position. Most valves are required by the manufacturer to be installed in the vertical position. Valve position should be verified prior to installation.
- The valve should be installed as close to the vessel as possible.
- Bolts must pass completely through the nuts and should be torqued properly. Under-tightening results in blowing the gasket or seal out while over-tightening pinches the gasket or seal, also resulting in leakage.
- Ensure the relief valve inlet and outlet piping is not reduced at any point. The piping inlet/outlet inside diameter must be as large (or larger) than the valve inlet/outlet inside diameter. Reduction in piping results in a reduction of the flow through the valve and thus decreases the valve capacity rating.
- Relief piping must not be supported by the valve and must terminate at a safe point of discharge.
- Block valves are allowed to be utilized for ASME Section VIII-1 pressure vessels per Mandatory Appendix M, however, they must be of a straight-through design and locked or sealed in the “open” position. If a lock is used in lieu of a seal, access to the keys used for “block valves,” if installed, should be controlled and audited.
- Block valves should only be applied following a formal MoC procedure. Once again, the block valve cannot restrict flow through the relief valve.
- Tamper seals must be in place on the plugs covering the valve-setting ring and on the top cap (if applicable). A damaged seal requires testing of the valve by a VR or T/O Certificate Holder. Care should be taken during installation to ensure the seals are not broken.
- Body drain plugs shall be removed on all steam systems and drain piping directed away from personnel travel paths.
- Body drain plugs should be removed on nonhazardous systems, particularly those where moisture could remain on the valve seat and corrode the disc and seat. The discharge stream from this port should be evaluated and routed to a safe point if necessary.
- Upward discharge piping should have provisions for draining, especially on those valves not equipped with body drain plugs.
- Wrenches should never be used on the body of a valve. This could distort the body and cause the valve to bind and may hinder the operation of the valve.
- Threaded relief valves are equipped with a wrench point – never use a pipe wrench.
- Data plates must be intact and legible. The set pressure of the valve must typically be no higher than the MAWP of the vessel/boiler and the capacity of the valve must relieve all possible energy to the vessel/boiler under any circumstance.
- Gags, shipping ties, plastic, etc., must be removed from the valve at installation. These items could restrict the valve from opening, resulting in an over-pressure condition and possible failure.
- Calibration/test data reports should be filed for reference. Certified shops (VR) shall perform repairs and recertification; (T/O) may do recertification.
*This is not an all-encompassing list.
*This is only a guidance for relief maintenance and installation. The jurisdictional codes apply (including local) and should always be referenced.
Our Experience with Pressure Vessel Inspections
TÜV SÜD ARISE Incorporated (ARISE) holds accreditation through the American Society of Mechanical Engineers (ASME) and the National Board of Boiler Pressure Vessel Inspectors to conduct third-party inspections of boilers, pressure vessels, and components. You can be confident in our team’s expertise to replace and recertify relief valves, so your pressurized systems are protected.