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Old 05-07-2010, 08:22 AM   #1
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Gas Pressure Test - What is good enough


I've had my gas piping worked on while my major house reno is getting ready for a rough-in inspection. Plumber has fixed numerous leaks in the gas pipe, but its still leaking. Right now the pipe is holding 15 PSI with about a 1/2-3/4 PSI drop after 24 hours. Is this the best I can expect or should I push for this thing to be holding for a straight 24 hours with no leaks. Most pressure tests I've been able to find reference to online only ask for pressure to hold for 15 min or so, which the system I'm sure would pass. I just want to do whats best for my family, but not beat up the plumber by holding his work to an unreasonable/impossible standard.

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BRENT
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Old 05-07-2010, 08:49 AM   #2
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Gas Pressure Test - What is good enough


24 hr @ 15 Psi should be fine, working pressure is not even a 1\2 Psi it's generally around 0.7 W.C (Water Column) pressure on most 250,000 BTU residential meters.

Although I would soap test the joints and fittings, especially Black iron fittings from China, they are sand molded and have a tendency to leave perforations in the fittings
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Old 05-07-2010, 09:03 AM   #3
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Start with your gauge. 99% of our leaks come from the gauge itself, and not from the joints in the gas line.

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Old 05-07-2010, 09:05 AM   #4
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Gas Pressure Test - What is good enough


Did he test the system with the appliances connected? or did he valve off or cap off the individual feeds to each appliance before testing the main line? According to NFPA 54, the national fuel gas code, he's only required to pressure test the line at 1.5 times the working pressure or no less than 3 psi. I find it unlikely your operating pressure is 10 psi, most residential pressures after the meter are 1/2 psi or less like bob said. The test duration of a single family house is a minimum of 10 minutes, not to exceed 24 hours. It sounds like the plumber went above and beyond what pressure he was required to test at and the duration of the test, so you should be fine.
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Old 05-07-2010, 10:59 AM   #5
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Gas Pressure Test - What is good enough


Clearly the gas will run at a PSI much much lower than what is tested. All ends are capped as we are still in a rough-in phase. He did also check his meter for leaks and all is well. I think I'm going to go shoot some soapy water on the joints after work and see what comes up. If I can't find anything else I'm going to let him go. Its to code, and technically thats all he really needs to accomplish.
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Old 05-07-2010, 12:39 PM   #6
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Gas Pressure Test - What is good enough


When it comes to gas and water, I want ZERO leakage. Even a small gas leak over time (especially if it happens to be in a confined space) can evenually build up into something dangerous.

Now that said, 1/2 to 3/4 PSI pressure differential after 24 hours could be just a change in the temperature. The real question is whether or not the pressure continues to drop (remember that old school formula... PV=nRT ?)
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Old 05-07-2010, 12:49 PM   #7
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When it comes to gas and water, I want ZERO leakage. Even a small gas leak over time (especially if it happens to be in a confined space) can evenually build up into something dangerous.

Now that said, 1/2 to 3/4 PSI pressure differential after 24 hours could be just a change in the temperature. The real question is whether or not the pressure continues to drop (remember that old school formula... PV=nRT ?)
http://en.wikipedia.org/wiki/Zero-risk_bias
Since the public is horrified of gas explosions and all the spin doctors in the world cannot reassure them in this case, the standards probably assure public safety to the same level as helicopter reliability. . .99.9999% safe, 'six nines' reliability.
But, I cannot find anything on the Web to back this up. A number like "residential gas explosions per 100,00 homes per year" would be useful.
Hwy deaths in the US and residential house fires are 40,000 per yr. With 100M homes in the US the chance of yours catching fire is 1 in 2500 per year, and gas explosions must be way less frequent than this. 60 people per year in the US get hit by lightning and this makes news, but I can't remember ever reading about a resi. gas explosion in any local newspaper where I've lived.

Last edited by Yoyizit; 05-07-2010 at 01:19 PM.
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Old 05-07-2010, 01:56 PM   #8
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Gas Pressure Test - What is good enough


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http://en.wikipedia.org/wiki/Zero-risk_bias
Since the public is horrified of gas explosions and all the spin doctors in the world cannot reassure them in this case, the standards probably assure public safety to the same level as helicopter reliability. . .99.9999% safe, 'six nines' reliability.
But, I cannot find anything on the Web to back this up. A number like "residential gas explosions per 100,00 homes per year" would be useful.
Hwy deaths in the US and residential house fires are 40,000 per yr. With 100M homes in the US the chance of yours catching fire is 1 in 2500 per year, and gas explosions must be way less frequent than this. 60 people per year in the US get hit by lightning and this makes news, but I can't remember ever reading about a resi. gas explosion in any local newspaper where I've lived.
I though I had recently read something that indicated gas lines should be able to maintain pressure indefinitly... i.e. no leaks. That doesn't sound like something that is impossible to acheive.

And when it comes to plumbing... the same thing seems to hold. I don't think someone would find it acceptable if a water line in their house dripped a drop of water inside a wall once every hour. If it did, over time you would get water damage. And this seems to be the case. I've got probably over 100 joints in the copper tubing supplying my house with water. It is really that much to ask that NONE of these joints leak?

And if we can acheive that with water lines at 50 PSI, it seems like it should be pretty simple to achieve that same thing with a 2 PSI gas line (except it's more difficult to find a gas leak).
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Old 05-07-2010, 03:11 PM   #9
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Gas Pressure Test - What is good enough


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That doesn't sound like something that is impossible to acheive.
I don't think someone would find it acceptable if a water line in their house dripped a drop of water inside a wall once every hour.

I've got probably over 100 joints in the copper tubing supplying my house with water. It is really that much to ask that NONE of these joints leak?
If the water evaporated as fast as it dripped, no problem. And if the gas dissipated so it always stays below an explosive or asphyxiating or a stinky level, I guess no problem.

The standard is probably set so that a gas fitter of "ordinary skill & diligence" will have X gas leaks in his/her working lifetime. To have X equal to zero is probably impossible to achieve and exponentially time consuming.

Of these leaks, what percent result in a complaint of a gas smell? How 'bout an explosion?

Come to think of it, I've never seen plaintiff's attorneys on TV asking me to call them because my health has been damaged, possibly due to long term exposure to low levels of NG. Does this mean no leaks, or no harm due to the leaks that are out there?

With 100 joints and no leaks [at present, that you know of] you've got better than 99% reliability. My reliability at soldering joints is 90% but I'm not a plumber.

Since water leaks don't usually kill people, and assuming as many water pipes as gas pipes are installed, the standards for gas pipe fitters is probably higher. I guess this would be reflected in the amount of training and the skill level of the people entering the field.

Last edited by Yoyizit; 05-07-2010 at 03:28 PM.
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Old 05-07-2010, 03:29 PM   #10
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Gas Pressure Test - What is good enough


Nat gas code: piping must hold 2 1/2 times working pressure forever. NO LEAKS
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Old 05-07-2010, 06:34 PM   #11
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Gas Pressure Test - What is good enough


Have him test @ 3lbs with a 5lb max gauge, this will give you a quicker indication of the extent of leaks if any. This is how we are required to test in my area.
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Old 05-07-2010, 06:46 PM   #12
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This is how we are required to test in my area.
What sensitivity is req'd? 10 PPM?
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Old 05-07-2010, 08:45 PM   #13
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Gas Pressure Test - What is good enough


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Have him test @ 3lbs with a 5lb max gauge, this will give you a quicker indication of the extent of leaks if any. This is how we are required to test in my area.
A gauge shall not have a range of more than twice the test pressure applied to the system.

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Old 05-08-2010, 09:25 AM   #14
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Most inspectors are going to want to see something like a Rogers gauge. They are about a hundred bucks.
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Old 05-19-2010, 08:46 AM   #15
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And if we can acheive that with water lines at 50 PSI, it seems like it should be pretty simple to achieve that same thing with a 2 PSI gas line (except it's more difficult to find a gas leak).
Just a thought, water is nearly in solid state at room temperature and is more dense than natural gas at the same temp. and would not leak given the same pressure and same size hole in a pipe. If you turn water into a gas (steam), you would see more leaks than in liquid form.
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