Leaky Joints - Compressed Air

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Old 03-02-16, 12:56 PM
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Leaky Joints - Compressed Air

I installed some 1/2" rigid metal pipe a couple years ago to run compressed air to my work shop and up to my driveway. I initially used paste to seal all the joints but several of the joints leaked at higher pressures (80 PSI+), so I disassembled everything and used Loctite 542. However, I still have leaks at several of the joints, and the pipes are as tight as I can get them. What's the deal? Should I not use any sealant at all? Is there some type of sealant I can apply without removing all of the joints (big PITA)?
 
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Old 03-02-16, 01:22 PM
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I installed some 1/2" rigid metal pipe
What kind of "rigid metal pipe". Steel? Threaded joints?
 
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Old 03-02-16, 01:39 PM
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Galvanized steel with tapered threaded joints.
 
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Old 03-02-16, 01:44 PM
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If they are steel pipe I have have run into some that just would not seal. I blame it on cheap imports and the manufacturers taps and dies were worn out since no amount of tightening could get them to seal. 542 is recommended for fine threads so it's not really intended for coarse NPT threads but I don't know what else you could try. I'd consider getting new pipe or fittings.
 
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Old 03-02-16, 01:48 PM
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I'm not positive I used 542. It may have been another version of Loctite. I remember researching a couple different types and 542 was listed for all types of pipe up to 2" in diameter if I remember correctly. I'll check tonight when I get home. Regardless, I ordered a stick of Loctite 561 PST and will give that a try before resorting to more drastic measures. If that doesn't work, then I'll consider replacing the piping with 1/2" aluminum. McMaster has pipe rated to 150 psi, which is plenty enough for my system. A little pricey though, but I only need about 12 feet of pipe and six fittings.
 
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Old 03-02-16, 04:17 PM
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Likely Pilot is correct and it is because of poor quality threads. Unfortunately, at this point you have likely stretched the fittings (internal threads) as well and nothing will cause it to seal.

I would use new fittings and this time use Permatex Number 1 joint compound. Permatex Number 1 is a hard setting compound so make sure you have the arrangement correct when you do it.

Gasket Sealants : Permatex® Form-A-Gasket® No. 1 Sealant
 
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Old 03-03-16, 10:44 AM
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Only going that far wouldn't copper with flared fittings work better?
 
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Old 03-03-16, 12:43 PM
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When you dry fit the fittings how many turns are you getting. Should be able to go 3 revolutions by hand. I have never had any problem with threaded pipe. We dont use galv. for comp air. we use carbon steel.
 
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Old 02-22-18, 09:55 AM
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Only going that far wouldn't copper with flared fittings work better?
I need to re-route my air line now that I have a garage. I'm thinking of going with copper. The length of piping from my compressor to the regulator in my garage will be about 25'. I've never used copper compression fittings. Is this the way to go, or should I solder? I'd really like to avoid soldering if possible. I have experience soldering, but I don't particularly enjoy it, for obvious reasons. Also, would there be any noticeable improvement if I go with 3/4" as opposed to 1/2"? I wouldn't think so for such a short run.
 
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Old 02-22-18, 01:27 PM
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I just found that the crimping tool for the copper fittings is a couple thousand dollars. Scratch that idea. Guess I'll be using black iron pipe or sweating copper.
 
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Old 02-22-18, 05:50 PM
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Only going that far wouldn't copper with flared fittings work better?

Just use copper and soldered fittings, works great!
 
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Old 02-23-18, 07:59 AM
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Just use copper and soldered fittings, works great!
That's likely what I'll end up doing.
 
 

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