Drilling & tapping an elbow for relief valve
Drilling & tapping an elbow for relief valve
(OP)
An outside entity is designing and constructing a new plant addition within the property of our existing plant. This new addition is supposed to be per B31.3 piping code. We have observed that several 4" piping elbows have been drilled and tapped in the field for 1/2" threaded thermal relief valves. I attached a photo. I've never seen this practice and suspect that it is not allowed by B31.3. Can someone confirm or deny this? If not allowed by code, where specifically is this stated in the code? Thanks for any help.





RE: Drilling & tapping an elbow for relief valve
I don't have an answer for you, but that picture is not at all what I was suspecting.
Initially I was going to suggest an elbow-let, but after seeing the picture that won't work.
RE: Drilling & tapping an elbow for relief valve
RE: Drilling & tapping an elbow for relief valve
I certainly hope that someone with the code knowledge chimes in. I flipped through my copy but nothing jumped out at me...though I am not even close to an expert on this code.
Good luck!
RE: Drilling & tapping an elbow for relief valve
What is the commodity, at what operating pressure and temperature?
RE: Drilling & tapping an elbow for relief valve
The fluid services vary from diesel fuel to mineral oil, used as emulsifiers, close to ambient temperature and 25 psi operating pressures. The blocked-in pressure must far exceed 25 psi as the temperature rises, effecting the need for thermal relief valves.
RE: Drilling & tapping an elbow for relief valve
Good luck,
Latexman
RE: Drilling & tapping an elbow for relief valve
I'd require (even if the code does allow it, I wouldn't tolerate the corrosion and leak risks) an elbow-o-let on the outer radius.
David
RE: Drilling & tapping an elbow for relief valve
But I like to play Devil's Advocate at times... I can't find a quote in B16.9, but if these were flanged elbows per B16.5, the tapped holes would be allowed:
B31.3 allows threaded plugs as noted in Interpretation 19-48. So, I would say that it may not be that big a stretch to argue that it could be in conformance with the minimum requirements of B31.3. Keep in mind that the minimum thickness for internal pressure is probably less than 10 mils on a straight pipe.
Now, before I get jumped, let me remind y'all that I don't agree that this is good practice... And I'd question where the process fluid is discharged when the PV burps.
jt
RE: Drilling & tapping an elbow for relief valve
I think the same holds here.
David
RE: Drilling & tapping an elbow for relief valve
RE: Drilling & tapping an elbow for relief valve
Medium was fuel gas at ~10 inches water.
I nearly had a heart attack, but the 'old hands' said they did it all the time.
I can't believe any code would allow it.
Mike Halloran
Pembroke Pines, FL, USA
RE: Drilling & tapping an elbow for relief valve