316 S.S. Threaded Fittings

[Greg9]

Has anyone had any experience with Stainless Steel threaded fittings for 1/2" dia piping used in Breathing Air Service (non toxic).

I have heard that S.S. is susceptible to galling making it impossible to seal correctly. Any help would be appreciated. Thanks

 

[dbaird]

I always used an anti-seize compond on instruments/pipe fittings that was suspect to gall.
Checkout:

http://www.texacone.com/easeoff.htm

David Baird
mrbaird@hotmail.com

Sr Controls Engineer

EET degree.

Journeyman Electrician.

 

[Montemayor]

Greg:

Stainless Steel is not only "susceptible to galling", it will gall - and make life miserable for you and your piping crew. But why use threaded joints on stainless? If you are using fitting under an inch in size, use tubing instead. And if you are talking about 1 inch and above, then just weld the joints (SW of SO depending on the pressure). Dealing with trying to cut threads and then mechanically screw the fittings can be frustrating when the inevitable subsequent leaks develop. It's frustrating to use a quality material and watch it fail to do what is normally a mundane job of sealing. The stuff galls; and no better "quality" of SS is going to stop that. It's the nature of the beast and an expected tradeoff in light of the positive qualities you inherit with it.

 

[Cockroach]

No, I've never seen galling in a sweet application.

Your concern is probably more manufacturing than design. Stainless will give thread pickup if not properly machined, i.e. feather edge(s) on flanks of threading. The pins should be wire brushed or at least cut with an appropriate insert that breaks the sharp edges.

"dbaird" also has a valid point. Threads should never been run dry, possibly galling was the result of dry make-up, over tightening or simply a fitting put into service with history. I have found teflon based greases to be problematic, those copper based are better. You could also tape the thread, this is a typical old practice.

Good luck with it.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[unclesyd]

There are very stringent requirements on a breathing air distribution system for particulates, metals, and whatever. The only way we were able to get around the cleanliness requirements were with socket welds and screwed fittings. We used only properly applied Teflon Tape. If anything can get into the piping stay away from it.

 

[moltenmetal]

Breathing air means anaerobic pipethread sealants are a no-no. Since fitting SS 150# cast fittings and stainless screwed pipe to a leak-tight fit-up with just teflon tape requires a great deal of pipefitting skill, I'd steer you toward compression fittings and tubing. 3/4" OD tubing has a similar ID to 1/2" pipe. Though compression fittings cost considerably more than 150# cast threaded fittings, they take less labour and less skill to install. And you're guaranteed a clean fit-up- no sealants required.