Pressure Safety Valves (PSV) and Spares

Some indication of the country of operation would be valuable.

Roll up. Roll up. PSVs available by mail-order. Just fell off the back of a space shuttle....<splutter>

I assume you are talking about pressure relief valves. If so, you should always provide a spare as an "option only" if your client requests a "spares list". For high pressure applications, its best to design a bypass circuit with an additional pressure relief valve should the primary fail. Needless to say, the results could be catastrophic if a pressure relief valve fails-HAVE A PLAN! For both steam and hydraulic systems, the relief valve should dump (when the device activates due to excess pressure) to a reservoir the capture the fluid. Air pressure is easy-the releif valve can dump to atmosphere. There is no standard for the provision of spares. It is up to the designer however, to insure that there is at least a bypass circuit in the event that one of the valves malfunctions.

thank you for your thorough response

during P&ID generation for the plant which my colleagues and I are designing, by pass circuit have been provided for all PSVs. but no spare has been provided for them. there were not any request from client side to consider spare for them. but as I said in previous text, I have heared that for those PSVs will be sized based on fire case, spare psv should be provided. but I do'nt know is this ture and is there any standard to force us to follow this concept?

I have given more consideration to your issue. I Checked with ISO 4126, CSA B51, ASME Sections I,IV and VIII and can find no requirements for spares. If you have a backup circuit that also contains a Pressure Safety Valve, you have a spare. (i.e. if one device fails-the bypass circuit with an additional PSV will releive the pressure). Most of the specifications (mentioned above) state that the designer should include maintenance procedures or periodic checks on the PSV's to insure operational stability. It is then, incumbant upon the Client, to specifically request "spares for 1 or two years of operation"-in the Contract. I would suggest that you do the following:

1. Make sure you have a by-pass circuit with an additional PSV,

2. Ask the client if he/she would like to place an order for Spares,

3. Make sure you have a scheduled maintenance/test procedure for the PSVs