Gas line pressure test

smcmurrey · 07-01-2008, 11:10 PM

I ran black iron gas line in the house I'm building and need to know if the pressure test I did is valid. I used a 0-150psi gauge and put 100psi on the system for two days. There was about a 5psi drop over the two days. I've been over all fittings with a squirt bottle of soapy water but didn't find any. Is this good enough or should I keep looking?

edit: I forgot to add that there are no inspections where I'm building.

TIA,
Stan.

mstplumber · 07-01-2008, 11:24 PM

Did the pressure ever stabilize? It is possible that the pressure fluctuated due to temperature changes but if not, a leak is a leak. I had a similar situation on my last house and could not find a problem with soapy water. I bought a bottle of the stuff (mine was green) that is actually designed to check for leaks and found my problem, which was a very slow leak on a fitting. Even though most places only require a 30 PSI test on gas piping, you don't want even a slight leak on a gas line. I'd get some real leak detector and check it one more time.

smcmurrey · 07-02-2008, 08:23 AM

Thanks, I'll look for some of the leak finder at the local plumbing supply.

**Termite** · 07-02-2008, 11:52 AM

Even a small temperature change will cause a 5% change in pressure in your lines.

100psi is a unnecessary amount of pressure to subject a threaded system to, and I'm surprised it didn't actually cause a leak. Even welded lines only have to be tested at 60psi. Most jurisdictions require a 10psi test for 15 minutes, from my experience. Considering that the highest system pressure you can even have in a residence is 2psi, and most systems are 1/2 psi, your pressure test was overkill!

If you're concerned, test it again. But test it at 20 pounds or so, give it an hour, and if it hasn't moved you're in good shape.

Doesn't the leak detector stuff check for gas, not air? I thought it was for use on gas-charged systems that are thought to be leaking. I haven't used it myself. Soapy water does the trick for me.

JDC · 07-02-2008, 11:28 PM

The leak detector will check for leaks with either a gas or an air charged system (or nitrogen, argon, etc, etc, etc) and does detect leaks that regular soap and water may miss. Here in Cincinnati, we test gaslines at 30psi although testing at 100psi wont harm the system. I'd go over the joints with the leak detector with the system charged at 30psi. If nothing bubbles, call it in for inspection.

smcmurrey · 07-03-2008, 10:59 AM

I'm not worried about causing a leak at 100psi, black iron is recommended for compressed air around a shop so it can handle the pressure. I checked again last night and had about a 2lb drop. I don't think it will leak at 2lb but will go over it again this weekend.

Marlin · 07-03-2008, 10:17 PM

Black pipe can handle 100psi just fine. We test lines below 10psi though. And yes, temperature changes will affect pressure and may cause you to think you have a leak when their really isn't one.

**Termite** · 07-04-2008, 12:11 AM

I commented on 100 psi being excessive just because it is excessive, not because it will cause the pipe to fail. I was just trying to say that if there were a leak, it would be easy to identify at 100 psi.