Relief Valve Vent Stack - Testing Pressure? 1

[jcampb21]

Hey guys,

I have a relief valve acting as a form of over pressure protection before a meter station. I am currenty fabricating the discharge piping. Does the outlet piping need to be pressure tested? To what pressure? It it ANSI 600 inlet but ANSI 150 outlet. It is venting to atmosphere, has a set point of 1480psig, and needs to dishcarge 60MMSFCD.

thanks for any replys

 

[BigInch]

I've never hydrotested relief valve vent to atm piping.

Independent events are seldomly independent.

 

[LittleInch]

I've always tested relief piping before now and essntially the test pressure depends what the process conditions are and what is listed on the line list. There will be some positive pressure on the line d/s of the relif valve and what you test it to depends on how long the relief piping is and whether other valves relieve into the same line. Normally the key issue is design temperature and whether the material is good for the duty. 60 MMSCFD is quite a lot of gas and if its at ambinet when it goes in, it will be minus 30 C or so when it comes out. if the discharge fpgoes on for any length of time the piping will get very cold and you don't want it to fail and vent gas direct from the relief valve :-( If there is no pressure listed on the line list then test to the flange rating (#150) or the pipe rating once you back calculate, what ever the lowest is. You may need to weld on a cap or flange to the free end and then cut it off after the test. Very serious incidents and explosions have occurred when relief piping has failed and sent gas all over the site instead of up the stack / vent and relief piping design and testing is sadly not always given the respect and attention it deserves. What you always need to think is what would happen if this pipe broke / ruptured / cracked when a relief valve is going off. Unless there is a very good reason not to, testing is always good and relieves the fabricator of some level of liability in the event of failure.

 

[BigInch]

Usually, as I have assumed, a relief valve at a meter station is nothing more than a simple, very short stack immediately above the valve that exits directly to atmosphere, no more than 1 meters long or so, as I think the OP implied, ie. not venting to a header - to relief line - to flare or other longer pipe system. That would be very much indeed a completely different type of system and I would then agree with my little brother in that case and test the line.

I sincerely hope that any confusion over what was posted and what I thought was implied will not cause anybody any undue grief.

Independent events are seldomly independent.

 

[dcasto]

First off If there is enough back pressure to make the piping covered then you are in violation of all standards unless you have a pilot operated valve. I again remind people that under b 31.3 the testing is to confirm mechanical joints are secure and not a strength test. So unless you propose welding a cap on the relief vent in order to test the flange or threaded outlet and then cut the cap off.

An open ended line and even a pressure vessel require no testing. What's next hydro testing your 100 foot tall flare stack

 

[LittleInch]

Dcasto, With respect there are many simple spring pressure relief valves on systems that are connected to a header. I appreciate the point, but on high pressure pipelines there is usually a big pressure difference from one side to the other - as here - when whatever pressure a relief piping gets to is v small compared to the high presusre side and hence has no real impact on the lift pressure, but certainly for lower presusre systems back pressure from the relief system is sometimes over looked. jcampb21 - How about giving us a few more details such as size and length of your relief line. At 60 MMSCFD my guess is it would need to be quite a long way from the relief valve itself to safely vent. To be fair to my bigger brother, a simple 2 to 3m long relief line would not be hydrotested, but anything more complex or longer than that should be tested and yes it should include the 100 foot flare stack. 31.3 does refer to its testing as a leak test "to ensure tightness". This can be many things to many people, but at a test pressure of 1.5 times operating pressure works as a strength test of the piping including the mechanical joints to me. If you don't test, how do you ensure "tightness"?