Safety Relief Valves. A boring topic to be sure, but it's one piece of equipment in your facility that should not be installed and forgotten. Why? Well I've always liked the phrase, "A picture is worth a thousand words."
Relief valves, the last line of defense against accidents such as these, are an important part of your facilities safety equipment. There are a number of things you should do to keep the valve ready to do its job should it become necessary.
First, have the valve tested on a periodic basis.
The National Board of Boiler and Pressure Vessel Inspectors is one of the governing bodies for the testing and/or repair of Safety Relief Valves. Within their Code, they recommend a written procedure be created for testing these type valves. You, as the owner of the valve, can test the valve, but it must be done so in accordance with the National Board Inspection Code and your state's and/or local regulations. We recommend that the test be performed by an authorized testing facility. A list of these facilities can be found here. You can also find other companies that perform this service by typing "relief valve repair" into your favorite internet search engine.
So how often should you have your valve be tested? Based on the National Board Code, which bases their inspection intervals on what type of service the valve is used for, the following intervals are suggested:
- Steam Service- Annually
- Air and Clean Dry Gas Service- Every 3 years
- Propane or Refrigerant- Every 5 years
- All others- Per inspection history
- For valves installed for liquid service, our experience suggests that these should be check annually.
Second, the valve's outlet piping should be sized so that it is at least as large in diameter as the valve's outlet. If not, the piping could form back pressure on the valve's outlet thereby causing the valve not to open properly. Also keep in mind that this piping should be oriented so that no liquid relieved through this piping can flow back and rest on the valve's outlet port. Doing so, could allow corrosion to occur within the valve's internal components and prevent the valve from opening.
Third, your maximum operating pressure, within the tank the valve is connected to, should be at least 10% below the valve's set pressure. This will prevent the valve from 'creeping' open. Relief valves are set to fully open at its 'set' pressure, but will begin to partially, or creep, open before then. This is normally 10% below its set pressure. If your valve is allowed to do this, trash and/or corrosion can set in over time which then could prevent the valve from either closing completely or from fully opening, either of which is not a flavorable solution.
Pressure relief valves are an often neglected and overlooked safety feature in your facility. Take some time to inspect them. You never know when they may called on to save your life.