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Process Automation

Monitor And Detect PRV Malfunctions To Stay In Environmental Compliance

January 5, 2021

Local and national environmental regulations, with regards to Pressure Relief Valves (PRVs), are becoming more stringent as they not only apply to normal operation but also to startup/shutdown periods.

These startup/shutdown periods are often where process upsets are most likely to occur, so compliance with new regulations can be very demanding.

The more stringent rules can be generalized with three simple requirements:

Provide indication and location where a PRV event occurs through electronic monitoring

Measure the time and duration of the PRV event for recording and reporting.

Notify the operator of the event so corrective action can occur.
PRV monitoring is necessary for environmental protection compliance and can avoid expensive fines, and possible process unit or plant shutdowns.  Monitoring also prevents waste of costly material and energy, and avoids bad publicity.  Historically, Pressure Relief Valves (PRVs) have been difficult to monitor because they are simple mechanical devices by design.  Monitoring methods typically have included manual inspections of tell-tale signs.  Plants can monitor PRVs by observing process pressure, but when the system pressure is close to the operating limit, the peaks and valleys makes it difficult to determine when the PRV actually opened or closed.  For these reasons, pressure measurements are susceptible to false positives and inaccuracies and provide no real-time insight into the health and status of the individual PRVs.  Monitoring how many times PRVs activate and how long each was releasing product helps plant personnel understand processes better, but does not give visibility on leakages caused by PRV malfunction. 


When the process pressure fluctuates around the PSV setpoint value, the blocking disc will lift to allow the chamber to fill and lift the stem.  

The process fluid vents to the discharge pipe, reducing the pressure, but not opening the valve completely.  This occurrence is called simmering.  Simmering can also cause material buildup on the disc seating and create stem misalignment, which prevents the valve from closing completely.  The discharge caused by simmering and it’s side effects are not usually detectable by conventional monitoring methods and account for considerable emission volume and consequent economic losses, aside from fines and eventual plant shutdowns.

In addition to the challenges of compliance monitoring there are other issues to contend with, such as PRVs that leak, don’t close and reseat after an event, or have their bypass valves in the wrong position due to human error.  A significant part of the difficulty when designing and installing a comprehensive PRV monitoring system is that a typical plant will have several different PRV makes, models, sizes and operating pressures from various vendors. 

Pressure Relief Valves

Pressure Relief Valves

Whether you require complete VR repair for day-to-day maintenance or for shutdowns/ turnarounds/outages, Cornerstone can complete all of these needs either in our shop facilities or in the field.

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A very reliable, effective and economic way to monitor PRVs is to use wireless acoustic transmitters.  

Process fluid flowing through valves and orifices generates acoustic waves in a wide and complex range of frequencies and magnitudes.  A majority of the acoustic energy is in the ultrasound range, but some is in the human audible range as well.  Acoustic transmitters are able to detect ultrasound acoustic waves in the pipe wall as well as it’s temperature.  These devices are wireless, small, lightweight, and non-intrusive, so they are easily clamped on the existing piping.

An acoustic PRV monitoring system, in conjunction with a National Board VR Certified maintenance program will ensure PRV mechanical integrity along with their proper operation, providing reliable and robust protection for not only the plant’s assets but for all personnel and the environment