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I read that the elimination of pressure in a propane line will destroy the pipe sealing compound at the treads, causing leaks. That is the reason a propane seller will require a leak test if the tank is allowed to run out.

During normal usage, a propane plumbing system is at a constant pressure. This means that as long as the tank has gas and is supplying the system with propane, a constant pressure is exerted on the piping and the pipe joint compound. The pipe joint compound will expand during normal pressurized usage and will retract if the system loses pressure. This loss of gas pressure may cause leaks to form because of the expansion and retraction of the piping compound within the propane plumbing system.

http://www.propane101.com/leaktest.htm

Will allowing the pressure to drop to zero also destroy a pipe joint seal where Teflon tape was used? I am currently using small portable tanks connected to gas logs by a 1/2 steel line where I used Teflon tape on the joints.

  • Side note - there is yellow teflon tape that is made for gas connections. Here is a question about it. – JPhi1618 Mar 20 at 15:53
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    @isherwood, here is one source. I think it might be one of those cya precautions since already having a leak is a good way to get an empty tank, and there's no telling how long it's been leaky/empty ? Related: if my water company has to turn off the water, they can't turn it back on unless they see zero water usage (no leaks) even if it was just shut off for a day. – JPhi1618 Mar 20 at 16:02
  • Looking around on the net, it seems to be common knowledge that "If an appliance valve or a gas line is left open when the propane supply runs out, a leak could occur when the system is recharged with propane.", but I can't find an explanation for it. Now I'm super interested. Cause a leak as in now your pilot lights are "leaks"? – JPhi1618 Mar 20 at 16:12
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    It's interesting to note that the pressure is allowed to drop to 0 in propane appliances (BBQ, space heater) when the tank is swapped. The same happens in an RV when the propane supply runs out or the tanks are swapped. I expect it might be standard practice to shut off the propane supply at a seasonally-used remote cabin, too. In the first two cases (single appliances and RV systems) there isn't any way to prevent the system piping pressure dropping to 0 when the propane tank is changed. – Greg Hill Mar 20 at 16:59
  • I find that description a little questionable. It's talking about "constant pressure from the gas", but we're talking about 1 psi of pressure, maybe. I'd have to see a lot more evidence... Imagine if gas piping really was that fragile? – JPhi1618 Mar 20 at 17:59
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I've been a gas fitter for over 20 years and worked with it much of my childhood before that. That is a completely false statement. I think it's just an excuse to get a tech in your house to see if they can generate a sale. You can almost blow with your mouth the amount of pressure that a propane system will see. After the second stage regulator the pressure is commonly 11" water column. Can you blow water up a 12" straw? Probably. Then you can blow more pressure then what's in your piping system. If a leak were to develop after "losing pressure" then it was extremely loose to begin with and wouldn't have passed the original 15 psi pressue test. 15 psi is 420" water column.

What about when the temperature changes in the house? The expansion and contraction of the fittings would be greatly more significant than a 11" pressure drop. What if you bump into the pipe? Also pipe dope is primarily a anti-seize agent not a leak sealant. It does effectively help seal poorly made threaded connections but that's not its job.

  • Thanks for the word of experience. I felt like gas piping was a little more secure than a pair of Chinese finger cuffs. I can see some reasons for doing a leak test on an empty system, but spontaneous leaks because of pressure loss just isn't one of them. – JPhi1618 Mar 21 at 14:58

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