HELP!! Stainless Steel Pipe, Threaded Joints & Leaks 2

[eng256]

Firstly, I am completely out of my depth here so I need advise.
I have an installation with a lot of SS piping (various dia 4" to 1¼". Many of the joints are threaded. We are planning to seal them and I was proposing loctite 567. Any one have experiences and procedures as to how to undertake this task and what to look out for? Piping is used for De-ionized water with Glycol for a colling plant.

Thanks for your input.

 

[EdStainless]

Fact of life: Threaded pipe joints are designed to leak.

Why not use automatic orbital welding? You have a more reliable system.
Yes, you can use Loctite. I haven't done this in years so I am not up on the specific products. You need to know how clean the threads will need to be and you will need to control the amount of sealant used. Either too much or too little and you will not get acceptable results.

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[eng256]

We have considered welding. The location of most of the leaks is in a cooling heat exchanger. Problem I see with welding is getting the expertise to this work (the locale is very remote).
We were considering loctite as we should be able to proceduralize the work and have it done by local contractors.

 

[unclesyd]

As stated above threaded SS pipe is designed to leak.
Here is a product that you might want to checkout if it is compatible with the process fluids.

http://www.xpando.com/pjc.html

 

[EdStainless]

You would be better off transporting one welder and his equipment to site.
Any thread seal will work for a while, but with temperature cycling and chemical interactions I don't see it being a permanent solution.

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Rust never sleeps
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[unclesyd]

We expressly prohibit welding of threaded SS fittings for sealing purposes. A seal weld normally leaves a few threads exposed at the toe of the weld and we have found that this area if primary source of fatigue failure, both mechanical and thermal.
We have a storied history of both threaded and socket welded SS fittings. We have found that additional time and expense of butt welded fittings more than pays for itself over time.

 

[eng256]

I really appreciate this discource. I have just contact EXPAND for information.

My greatest concern is the interation of this product with the fluid and any contamination that it may intoduce in the network, also its ability to handle the wide temperature swings.

 

[EdStainless]

Yes Syd, butt weld only. Don't ever weld over a threaded joint. It can cause too many problems to mention.

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Rust never sleeps
Neither should your protection

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[eng256]

Any thought on using Loctite? (my reference was for Loctite #567)
I have talked with XPANDO and looks like an interesting product. I am also checking with site if butt-weling is a possibility.

 

[MikeHalloran]

I like Loctite. Not over butt welding, but if you must have threads, that's my usual choice as a sealant. I use the PST/567 as a general purpose threadlocker, too.

Loctite used to sell a special PST for stainless pipe, but I don't know what was really different about it, and I haven't seen it in a while.

All the help you could want from Loctite is just a phone call away. The local reps have always been quick to respond, and extremely helpful, even if you'll never ever buy a truckload of product.





Mike Halloran
Pembroke Pines, FL, USA

 

[eng256]

Thanks all for your input.
I will draft out proceedures for my customer's approval using the guides you all have provided.

 

[dik]

Can you use T-Tape? or does that only leak in the long term, too?

Dik

 

[eng256]

We used t-tape on the first installation (about 2 years ago), and then everything was stripped down, cleaned and re-fitted last year.
I want this next outage to be the last one for this reason.

 

[Compositepro]

Threaded joints are not "designed to leak". They are designed to be sealed in order not to leak. There is definitely a leak path in the thread that has to be sealed. there are many sealants on the market. You have to select an appropriate sealant and also apply it correctly. If your pipe goes through a lot of thermocycling you need a sealant that does not expand an contract a lot. This means filled with metal or ceramic particles. Teflon tape can be stripped off while screwing the joint together and, being an unfilled polymer, will expand and contract more than the steel. This will lead to leaks.

 

[EdStainless]

Male and female pipe threads have the same taper and the thread profile on the male is truncated. It is not possible for an unfilled pipe thread to seal. We get away with it in most fluids because we either use dope, or debris in the fluid plugs the leak path. You never use pipe threads in high purity gases or in vacuum, it just won't work.

eng256, If you are going to all of the trouble to dismantle, clean and reassemble that is a lot of work. I see why you don't want to do it again.
If go with butt welding make sure that there are requirements on the purging gas and the resulting color of the welds (inside and out).

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm