Relief Valve Discharge Pressure Testing

[Paul Guilford]

I am currently designing to ASME B31.3 and have been asked about pressure testing Relief Valve Discharge Pipes.
ASME states that Vents and drains need not be pressure tested post the last valve but as they are covered under the PED and classed as being in the scope of PED if the discharge pressure is >0.5Barg (Guidline 1/42 we have asked our installation contractor to pressure test these lines to 1.5 times design as per B31.3. Not a problem up to now.
However as we have a weep hole in the discharge pipe to remove condensation etc. so effectively we have two open ends the installation contractor is asking if he does need to pressure test the line.
I have looked in all the docs I can find but this situation doesn't appear to be documented anywhere.
Anyone out there come across this and had an acceptable solution.
I was thinking we could pressure test before putting the weep hole in thereby proving the strength on the pipe. But is this really necessary.
All comments would be appreciated.

 

[mk3223]

If the discharge vent pipe needs a hydro test per the project requirement and also a weep hole for drain, it needs to specify the correct work sequence in the work spec, i.e. do the test first, and then drilled the weep hole.

P.S. what's the guideline 1/42?

 

[Paul Guilford]

Thanks for that I agree the pressure test should have been done before the weep hole was put in to strength test the pipe.
The Guideline 1/42 is from the Pressure Equipment Directive Guideline Number 1/42.
Link:

https://ec.europa.eu/growth/sectors/pressure-gas/pressure-equipment/guidelines_en

Its basically a set of questions and answers for clarification of the PED. The reason this one is significant is that it classes the discharge pipe of a relief valve as within the PED therefore must be proof tested. Where as the ASME B31.3 would not require a test as the pipe is open ended so can be a visual inspection only.
If we just did that the pipe would not comply with the PED directives.
That's my interpretation of it anyway.

 

[XL83NL]

What PED category has the line been classified to? That determines what is necessary (please note Im not talking about what should be checked as a minimum safety requirement - just wthat's required under the PED)
- If the line is classifed category 0 aka SEP, I would only check if the line can handle the pressure which can be seen after the relief valve at a discharge case, and do no hydrotest, unless the hydrotest can be easily facilitated.
- If the line is classifed a category > I, I would have the line be hydrotested.

In the cases I ran into this, this normally wasnt an issue, as our specs have all been designed to be flange limited, and we normally only engineer small(er) linesizes, typically up to 8". The spool under question would then have been foreseen by a temporary cap which would have been cut after hydrotest.

 

[mk3223]

Thanks for the PED guidelines.
If correctly required to follow the PED guideline, you may weld a temporary cap on the weep hole for the testing.
IMO, for the testing pressure of 1.5x of the design pressure, it can be based on the actual discharge pressure of the relief flow.