Corrosion in NPT threads vs pure Acetic Acid

[Euphellow]

On a pilot plant to be built in short time we have lot of vessels with NPT female instr conn`s. Fluid is 100% liquid acetic acid. We suspect -in time- that NPT thread will corrode with the result that instr can`t be taken from the vessel and the vessel is ruined and we get a major claim. How good idea is use of NPT and this fluid. Is there any one who can advise.

thanks in advance!
Note1esign p&T in range of max 20 barg & 250C and 2 barg & 150C type vessels.
Note2: Due to small sizing of vessels flanges wont`t work.

 

[eromlignod]

Is stainless steel an option?

Don
Kansas City

 

[Euphellow]

Don

I forgot to mention that all material, vessels and instrumentation and tubing /piping is already AISI 316 including bite ring fittings.

rgds
Henjo

 

[MikeHalloran]

By "instr conn's" you mean... what?

Half couplings welded to the shell?

If so, you can have them made from billet or high pressure fittings, giving you an arbitrarily thick wall... e.g., thick enough to be bored out and tapped to a larger size should repair be necessary.

If they're already made, and thin, just use a lot of teflon tape... and older pipefitters.





Mike Halloran
Pembroke Pines, FL, USA

 

[Euphellow]

Exactly Mike, half couplings and full couplings it is ; all 316 SS joining to NPT SS 316 connectors and NPT instruments. So any thought about pure acetic acid and NPT corrosion?

rgds

Henjo

 

[MikeHalloran]

It seems you've got the right material:

http://www.millenniumchem.com/NR/rd...iumMaterialHandlingGuideAceticAcidEnglish.pdf

You have to use an anti-seize or ptfe tape or _some_ kind of pipe thread sealant on pipe threads in order to prevent galling on assembly. Enough of the sealant usually remains to allow disassembly by ordinary means.

An MSDS has this to say:
"Corrosivity:
Highly corrosive in presence of stainless steel(304).
Slightly corrosive in presence of aluminum, of copper.
Non-corrosive in presence of stainless steel(316)."

So I'm not sure that I understand your concern, unless you're worried that you may have some misidentifed 304 stainless in the system.





Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

We have numerous 40# acid eggs with threaded connections fabricated from 316L, circa 1960 with max carbon 0.0350, that are in use with Glacial Acidic Acid on a 24/7/365 basis. The acid is quite pure, almost reagent grade. The max temperature is 150F. The only problems we have had is when operations decided to use the eggs as a mixing pot.
I can recall no problem with the threads other than they are extremely hard to break if required. Any new make require the use of Teflon tape or paste.