Optimizing Pressure Relief Valve Lifecycle Management

Emerson's Kevin Simmons

Emerson's Marcelo Dultra

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.

Valve magazine: Lifecycle Management of Pressure Relief ValvesKevin and Marcelo open noting:

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:

Posted Friday, September 21st, 2018 under Regulator, Safety.

One comment so far

  1. Jonas Berge says:

    I agree PRVs are mostly self-operated and do not depend on instrumentation to function. So I agree, the challenge has always been that it is not possible to review relief event history or access online diagnostic information for improvements, and thus preventive maintenance and testing is mandated.

    But it is getting better. Many plants have started to instrument their PRVs as part of digitalization of how the plant is run and maintained, to achieve operational excellence. They are not instrumenting the PRV’s safety release function – that remains mechanical. They are instrumenting the PRVs for passive monitoring with wireless position or acoustic sensors. This gives them the possibility to capture and review the sought-after relief event history and access some diagnostic information online. With a sensor in place on the PRV they get a positive indication of valve lift; release, simmering, stuck-open, or even passing (internal leak due to not seating back properly). This is integrated with the historian software or DCS for indication to operators, but you also get the history log which is useful to safety officers and energy managers etc. For PRVs with rupture disk a wireless pressure transmitter is added to detect pin-hole leaks. That is, the instrument is not taking the place of PRV proof test, but if there is an overpressure event they can positively see if the PRV lifted or not without having to infer from line pressure. Periodic test still required as explained in the article. Moreover, for plants that have a flare reduction program to cut losses due to flare/vent, to meet the clean air act, or simply be a good corporate citizen etc. – they can’t inspect all their PRV for passing or being stuck open sufficiently frequently. It’s not practical, because there are too many, and they are often mounted high in inconvenient locations. This is digital transformation; changing from manual and paper-based tasks, to new automatic, digital, software-based, and data-driven ways of working. You get accurate timestamp of release duration so you can more accurately compute and prove release volume if needed for reporting, not worst-case as in the case with “sock”. When you see flaring, you know positively which of maybe a hundred PRVs on the same flare header which is releasing or passing. Having an exact time-stamp of release allows process engineers to better do “forensics” to figure out what event caused the overpressure, and possibly change the process accordingly to prevent it from happening again, reducing future losses etc. Passing PRVs can be overhauled sooner than originally scheduled to stop the losses. Because instrumenting PRV reduces losses and cost, it is easy to justify the investment. The more valuable the product the more you save – so on hydrogen lines you save even more than on hydrocarbon lines). For this reason, many digitization efforts start with energy efficiency projects like PRV and steam traps, because they pay for the infrastructure very quickly. That same digital infrastructure is then used to improve reliability and reduce maintenance cost etc. Learn more what other plants are doing from this essay:

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