Possible small gas leak in black iron pipes

WillK · 01-17-2012, 09:51 PM

Okay, I consider myself capable of making good connections in gas pipe, I put in new pipe for our water heater and gas stove before we moved in to our current house, prior to that I had assembled a pipe line to a pool heater.

This past weekend, I needed to put in new pipes to the gas stove so they would be routed around a structural beam I'm soon to install. I applied Rectorseal on all joints, and after pressurizing the system when completed, I checked everything with Harvey leak detection fluid and I found no signs of leakage.

Now, this is in Michigan, and most of the work is in our crawlspace, the crawlspace accesses aren't exactly air tight. The pipe actually comes through the floor in the closet behind the kitchen because there is 5" of flooring in the kitchen, and in this room my wife (who has more sensitve smell senses than I) smells gas or dead rats. I don't smell anything, and I am not finding any dead rats.

Anyway.. My point about this being in Michigan is that being that it's winter, I have not openned up windows to air this out as I might otherwise do after a project like this. This particular room is home to my son's fish, it's in a tank that isn't heated, and moving it poses 2 problems - little bit of a pain, and I don't have an alternate location where it wouldn't be disturbed by the cat and/or dog... So moving it is bad for the fish's health, openning a window is bad for the fish's health.

When I openned the pipes to change them, I could smell that so I know I can smell a larger leak.

I've seen what a leak looks like with leak detector fluid.. I've seen it do what happens in this video:
http://www.youtube.com/watch?v=qoCqj...eature=related

I am certain I don't have that kind of leak..

Here's my questions:
1) The video probably shows completely missing sealant, will a small leak look like that anyway or is there something smaller I might miss? This area of crawlspace is tight and not well lit.

2) Is it possible for the gas smell to linger, and I really don't have a leak - just lingering gas?

The issue is having the time and energy to reassemble these pipes. It's probably a 4 hour job, just because of how confined the space is, and having to go in and out so I can set the pipes on clean floor instead of dirt so I don't get another bad joint from dirt contamination. I'm not saying I have a dirt contaminated joint, I never set any new pipes on dirt, but right now I don't know what joint is leaking....

My options tonight are to turn off the gas to the water heater and stove. I have a shutoff valve that shuts off the branch serving those 2 appliances so I can do so without shutting off the furnace. I'll probably do that since it needs to be done regardless, then see how far I can get tonight rebuilding the pipe assembly - if I can't get through that, I could borrow the cap off the drip leg so I can have hot water for the shower in the morning.

hvac benny · 01-17-2012, 10:27 PM

There's more to installing gas than threading pipe together and checking for bubbles. For instance, sizing pipe (did you do that?) and pressure testing the completed work. Since you didn't do that, what you need to do now is disconnect the piping from any pressure regulators or appliances and cap/plug any open pipe, then attach a gauge to the gas line and pump it up to a minimum of 15psi for 15 minutes, although 30 psi for 24 hours is better. If the pressure drops during the test, you have a leak.

WillK · 01-17-2012, 11:07 PM

The pipe is all 3/4". Nothing is more than 20' to the meter.

After going through with the leak fluid starting from the last joint working towards the union fitting I'd need to start with, I found the leak this time right at the union. So the hardest thing about fixing this leak will be relighting the water heater and getting to my shutoff valve for the branch.

GirlWithWrench · 01-17-2012, 11:24 PM

Glad you found your leak! Remember to hold that pilot button down for, ummm, ever to get the water heater relit. Doesn't sound like you need it, but I did just post a video on YouTube last night on lighting a water heater pilot. Here's alink for kicks: http://youtu.be/PZDUDVkZ5sE Happy Plumbing!

Live Free, Work Hard

WillK · 01-18-2012, 12:07 AM

Yeah... Actually, being that I'm tired, I was about to head to bed having forgotten to restart the water heater.

What I came back to say is that in retrospect, I think I realized what went wrong. I put the wrench on the wrong side of the union when I tightened it the first time. It probably is worth its own thread, but as I said - I need to get to bed, so I'll be brief.

Unions are handy things, they let you make a joint where the pipes don't have to spin.

But suppose you tighten the nut and don't hold anything else. One side will tend to tighten, the other side will tend to loosen. While tightening the nut, you should hold the side with another wrench which otherwise would loosen.

My mistake was that I put my second wrench on the other side. So the one side of the fitting probably loosened a little without me noticing. I should've caught it when I leak tested, but it was a pin-point leak as I found during my last testing. Once I new where the exact point was that was leaking I could get the leak detector to bubble, but it was possible to make a swipe that missed that point.

5 minute fix, 30 minutes of cleanup.