Pressure/Safety relief valves (PRV/SRV) are still used in the same capacity as they have been for the past fifty years, to protect you in the event a vessel reaches or exceeds its rated pressure. When a PRV/SRV opens, the liquid/vapor is discharged into an engineered vent line, to be released to the atmosphere in a controlled manner. There are two items to alert you that a vessel has reached its pressure rating, one item is a rupture discs that mounts under the relief valve and the second is a vent line ammonia sensor tied to an alarm.
As a rule, there can be many PRV/SRVs connected to one vent line header, so the rupture discs are a good tool to let you know which one has lifted. Another general rule is that PRV/SRVs do not completely reseat after they open, requiring a replacement of the offending PRV/SRV. This is a great reason to install the three way manifold offered by all relief valve manufacturers. This manifold allows for the isolation of a lifted relief valve after correcting the issue that caused the relief valve to lift while putting another relief valve in service so the vessel is back in operation under protection of an operational PRV/SRV.
There is some maintenance required for PRV/SRVs. All PRV/SRVs should be checked at the minimum annually to ensure they are undamaged and free of rust and debris. OSHA also requires all PRV/SRVs to be changed every 5 years or the existing valve to be re certified. These requirements should be scheduled in your PSM program’s mechanical integrity component and in your facilities maintenance program.
Some challenges everyone seems to run into are your current pressure relief valve is no longer available or made or a similar valve from another manufacturer cannot replace your obsolete valve without some engineering being done first. At the bare minimum, a Management of Change (MOC) must be completed. What normally happens is the new relief valve relieves at a different release rate and your vent line header may no longer be compliant with the code changes of the last ten years. Your existing relief header may have been grandfathered before the code modification in the 2000’s, but when you change to a different PRV/SRV, it will no longer be under the grandfather clause. The end result may require the relief header to be updated to the new codes.
As you can tell, there are many components to the relief valve and their code requirements. Take a few minutes and ensure you are keeping up with the code requirements. If we can be of any assistance, please do not hesitate to contact us.