Pressure relief valves are supposed to protect your facility. Do you know they will perform as designed when needed, or are they just costing you money?
The problem with PRVs is that it’s difficult to know if they’re working or not. In their basic forms, they have no visible mechanism or electronic elements able to send a signal. Worse, after an over pressure incident, they might not close completely, resulting in a constant leak of product from the process, causing financial losses and possible regulatory issues.
Fortunately, there is a solution to the problem, and it’s the primary topic of our article in the April 2020 issue of Processing, Monitoring Pressure Relief Valves as Part of a Digital Ecosystem Reduces Cost and Improves Performance. The key point being: monitoring saves money, but it is difficult to do without using new technologies.
As safety devices, PRVs are mechanically self-operating without the need for any electronic components or external support to function. Consequently, they are typically off-grid with no built-in mechanism capable of reporting their condition or activity via an emergency shutdown system (ESD) or distributed control system (DCS). If operators want to know what is happening with a particular PRV, they typically rely on local inspection or monitor normal process pressure measurements for indication of operation near the PRV’s setpoint.
Operators need to know when a valve has opened due to an overpressure incident and if it has re-sealed itself after an incident.
With an enclosed system, it is often not possible to see if a valve does not fully reseat itself and close completely after an overpressure incident. The valve mechanism inside a PRV of either type could be seated incorrectly, leading to a standstill leakage. Such leakage may be so small as to be undetectable by process instrumentation, such as pressure transmitters and flow meters. For hours and perhaps days, product could be flowing to the recovery system unnecessarily, reducing production and plant profitability. How can troubleshooters determine when this is happening, and what specific PRVs are affected?
That’s the main problem—PRVs can leak—but there’s an easy way to tell when this is happening, just add a simple device to the valve to determine is open, closed, or somewhere in between. One option is . These can be mounted on any type of PRV by simply attaching it to the outlet pipe where it can listen to any noise made by a valve that’s fully open, or just simmering and passing a slow but constant leak of product. This is the insidious problem, and it can cost companies lots of money.
The importance of detecting leakage as soon as it starts is driven by the compounding effect over time. A mere 0.1% leakage, if left unaddressed for a year, equals a full release from a PRV for six hours. The effect is multiplied into a huge problem when considering the total population of PRVs in a process unit or overall plant. A study from 10,000 PRV service records presented an astonishing result indicating that 20% of installed PRVs leaked below 50% of set pressure, so many valves may have been leaking all the time. Even worse, 8% of valves surveyed leaked so excessively they did not pop correctly in the test.
Mounting a Rosemount 708 on a valve and sending its data via WirelessHART to a Plantweb Insight Pressure Relief Valve Application is the ultimate setup for a comprehensive monitoring approach at minimum cost and complexity.
So, ask yourself this: Can you account for all the product going into the collection systems from your PRVs? Is it from acknowledged overpressure incidents? Or is it always there, but without a clearly identified source? Maybe it’s from leaking PRVs, and it’s time to get a handle on the problem by monitoring what they’re doing. Now you know how to do it.
Let’s hear about your situation. Are you doing any monitoring of PRVs?
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