Persistent leaks on high pressure fittings (thread sealant)?
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    Default Persistent leaks on high pressure fittings (thread sealant)?

    Does this sound familiar to anyone: G 1/8" fittings on stainless steel pressure gauge manifold (or distribution block). Assembled with Loctite thread sealant.
    Stubborn small leaks under high pressure (500 to 1000 bar)

    I have assembled and disassembled the damn thing at least five times, washing everything with brake cleaner and ultrasonic cleaner every time.
    And yet there is microscopic leak in more than one of the fittings!
    Some of them seal ok and but there is always more than one leaker.

    Leaks are always really small, like 1 drop of oil in 10 minutes under 1000 bar pressure but they ruin my day totally.

    Zinc plating on the pressure gauge fittings?
    Air getting mixed in the adhesive because the threaded fittings are on the side of round bar?
    Distribution block deforming too much under pressure?

    Loctite thread sealant has been 100% fool proof until now for me and now I am stumbled with this stupid pressure manifold.

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    I am not familiar with "G" fittings. Are these flared, ferrule (like Swage Lock), solid with just threaded connector or what? Thanks.

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    How about teflon tape and sealant

    Peter

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    At 500 - 1000 bar (7,350 - 14,700 psig) you could be getting the threaded components themselves distorting (I know it won't be much, but neither is your leak??) .......or again possibly ???? the sealant itself breaking down under such high pressures

    What pressure is the grade of Loctite good for?

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    Are the leaks clearly through the threads, or possibly elsewhere like through porosity in the manifold stock? Are the threads NPT, NPTF, other?

    Picture would help allow a guess about possible distortion....Or you could set one up against a dial indicator as you pressurize.

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    Quote Originally Posted by crossthread View Post
    I am not familiar with "G" fittings. Are these flared, ferrule (like Swage Lock), solid with just threaded connector or what? Thanks.
    Straigth 1/8” british pipe thread.

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    Quote Originally Posted by MattiJ View Post
    Does this sound familiar to anyone: G 1/8" fittings on stainless steel pressure gauge manifold (or distribution block). Assembled with Loctite thread sealant.
    Stubborn small leaks under high pressure (500 to 1000 bar)

    Zinc plating on the pressure gauge fittings?
    Air getting mixed in the adhesive because the threaded fittings are on the side of round bar?
    Distribution block deforming too much under pressure?
    The Swagelock catalog section on precision pipe fittings shows a maximum working pressure of 9400 psi for a 1/8 316 stainless steel male fitting and 6100 psi for the female fitting. The maximum pressure is limited by the female pipe fitting. The larger diameter of the female fitting would require a thicker wall in order to match the maximum working pressure of the male fitting. These are safe working pressures based on 1/4 the ultimate tensile strength. The deformation of the assembly may be providing a clue that you are exceeding the safe operating pressure.

    A pressure gauge filled with glycerin will hide peak pressures that exceed what is being displayed.

    The distribution block design may be responsible for the leak.

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    There are several types of thread sealants. I was just reading on the net. I used to use type 565 Loctite and when I assembled the pipe into a pump outlet and didn't let it dry overnight it leaked. But never leaked if I let it dry overnight. I see they have a version called 567 for higher pressure.

    loctite pipe sealant 567 - Bing video

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    Wait, shouldn't straight british pipe be sealed with a copper washer or bonded washer?

    threads shouldn't be an issue

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    Quote Originally Posted by gustafson View Post
    Wait, shouldn't straight british pipe be sealed with a copper washer or bonded washer?

    threads shouldn't be an issue
    Mostly it is sealed with face seal as you say. So far I have had good luck also with adhesive sealing on thread but maybe I'm pushing my luck too far this time with the pressure and the adhesive..

    I'll have to check the adhesive type. (I tried also high strength thread lock but it wasn't better or worse than the "real" stuff.)

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    Quote Originally Posted by Limy Sami View Post
    At 500 - 1000 bar (7,350 - 14,700 psig) you could be getting the threaded components themselves distorting (I know it won't be much, but neither is your leak??) .......or again possibly ???? the sealant itself breaking down under such high pressures

    What pressure is the grade of Loctite good for?
    Both possible I guess. Pressure distribution manifold is a 25 mm stainless bar with 4 mm through hole, five 1/8" BSPP(G) thread ports on the side of the bar. Ports separated more than 50mm from each other Seems plentifull compared to say 10k psi rated fittings. (1/8" BSPP is 9.7mm or so on top of the threads, leaving me with ~7.5mm wall thickness.)

    Leakage actually started already below 300 bar as I had 300 bar pressure meter connected at the time. Yet it holds 1000 bar with no bigger drama, just leaks proportionally more?

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    I am pretty sure you want to spot face the tube to make a space for a washer and that will take care of your problem

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    Quote Originally Posted by Peter from Holland View Post
    How about teflon tape and sealant

    Peter
    That is how the professional installer do it. I would say at least 6 turns of tape followed by sealant.

    Is better to have brass threads on a gauge turning into female brass or harder material. The OP has plated threads going into stainless. I would think that brass would
    deform at the critical points and hold more pressure (if you really do a torque job). Just an opinion.

    7252-14504 PSI (500 - 1000 bar) is this what compression fittings are for?

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    The picture shown..to me, look like taper threads. No way a straight threat would seal that way..needs a o-ring or washer and a sealing face..just like Gustafson pointed out.

    Stuart

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    Are all of the components actually G thread? Usually they are already machined to except the o-rings.

    If I recall correctly there is a Japanese version of BSPP that will accept the G threads but does not have the o-ring chamfer and the thread profile is slightly different. I have seen these get mixed in with things and cause head scratching problems.

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    Quote Originally Posted by MattiJ View Post
    If you send this to Parker customer support they could help you out. Probably recommend replacement fittings for such high pressures.

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    First off, 2000 psi is not high pressure. I made hundreds of connections in field conditions at those sorts of pressure with 3/8" od and 1/2" od pipe when I was in the site test section at work. Leaks were just not permitted.

    G thread is BSPP and the titting must seal against a flat face. Spot face the manifold and use a Dowty seal for each one. Very little torque is requited.

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    Quote Originally Posted by MattiJ View Post
    Straigth 1/8” british pipe thread.
    With thanks to Mark Rand and others

    Now we have the answer -( I think ) ..........you are using the correct mounting ''female'' fitting

    Because IME pressure gauges with straight threads are sealed on the end face with a washer (copper / fibre / bonded seal etc etc) and not on the threads - which are only there to provide the clamping force for the sealing face.

    If it's leaking past the threads it means the face seal isn't working.

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    Quote Originally Posted by Mark Rand View Post
    First off, 2000 psi is not high pressure. I made hundreds of connections in field conditions at those sorts of pressure with 3/8" od and 1/2" od pipe when I was in the site test section at work. Leaks were just not permitted.

    G thread is BSPP and the titting must seal against a flat face. Spot face the manifold and use a Dowty seal for each one. Very little torque is requited.
    It's not 200psi Mark it's 1000 bar


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