Pressure relief valves (PRVs) are critical safety and equipment protection devices to prevent overpressure conditions. They need ongoing maintenance to assure that they operate as designed for their intended applications.
In a Valve magazine article, Lifecycle Management of Pressure Relief Valves, Emerson’s Kevin Simmons and Marcelo Dultra describe considerations for effective and efficient PRV sizing, selection, installation and maintenance across their useful lives.
Effective lifecycle management of PRVs can significantly improve operational efficiency ensuring safety, reducing maintenance costs, and increasing plant reliability.
PRVs come in many types:
- Weight-Loaded PRV
- Conventional Direct Spring-Loaded PRV (ASME recognized)
- Balanced Direct Spring-Loaded PRV (ASME recognized)
- Pilot Operated PRV (ASME recognized)
Unlike other safety devices connected with safety instrumented systems or other control systems:
PRVs are mostly self-operated mechanical equipment that do not depend on any control system or electrical instrumented system to function.
This standalone nature precludes them from sending diagnostic information to control or safety systems. They require:
Preventive maintenance with pre-scheduled inspection and testing…
Design and specification is a critical activity and requires experienced engineers to make sure the PRV is sized to properly alleviate the overpressure condition in a safe manner.
PRVs are designed, sized, selected and manufactured to meet requirements of specific codes and standards and are of special interest to the many jurisdictions charged with enforcement of local laws and regulations.
The American Society of Mechanical Engineers (ASME) have codes and standards for the PRVs based on their application, such as in direct-fired boilers and unfired vessels. Organizations such as the National Board of Boiler and Pressure Vessel Inspectors (NBBI) provide:
…certification for and operated their own certified lab for capacity certification of new PRV products. In addition, these labs are used for the re-certification of ASME manufacturers and assemblers as well as VR [Valve Repair] repair certificate holders.
The total cost of ownership for PRVs is much greater than the initial purchase and installation costs. Lifecycle costs also include:
…direct PRV repair labor, PRV repair parts, administrative, record keeping and other transactional activities, transportation, inventory administration, rigging/scaffolding/pipefitting, etc. Deeper yet is the cost of non-conformance such as unplanned outages, late delivery of repair valves, misapplication of PRVs, emissions, inventory utilization and incorrect maintenance intervals.
Kevin and Marcelo note that PRV suppliers play an important role across the lifecycle—design & selection, commissioning, operation & maintenance, optimization and decommissioning by:
…providing the correct product support at every stage in the cycle can costs be minimized while still maintaining the integrity of the PRV program. By optimizing and coordinating these activities, total lifecycle costs can be reduced.
Read the article for more on proper sizing, impacts of improper installation and benefits of effective valve asset management.
Also, join us at the October 1-5 Emerson Exchange conference in San Antonio, Texas for pressure relief valve focused sessions including: