316 fittings corrosion
316 fittings corrosion
(OP)
Guys, I’ve got a little problem with some 316L steel fittings on a 316L pipe used for an auxiliary cooling water vent line. The fluid is sea water with 5ppm sodium hypochlorite and at ambient temperature and low pressure conditions (1.5 – 6 psi).
The fittings have only been in service for just 5 months. Would appreciate if you could have a quick look at the attached pictures, and your thoughts on the apparent corrosion or surface deposits would be most welcome.
The fittings have only been in service for just 5 months. Would appreciate if you could have a quick look at the attached pictures, and your thoughts on the apparent corrosion or surface deposits would be most welcome.





RE: 316 fittings corrosion
Aaron Tanzer
www.lehightesting.com
RE: 316 fittings corrosion
The combination of seawater, chlorination, oxygen, and intermittent service assure that this will fail.
I am surprised that it lasted 5 mo.
What you see on the out side is corrosion product from the pitting on the inside.
You can probably stick an ice pick through the weld on this fitting.
Redesign the system. No threaded connections, use AL-6XN, any field welds need to be automatic orbital welds made with C-22 filler. No weld discoloration allowed, pickling is even better. You can put sections together with autogenous welds and then have them solution annealed.
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Plymouth Tube
RE: 316 fittings corrosion
RE: 316 fittings corrosion
RE: 316 fittings corrosion
RE: 316 fittings corrosion
with 316 at 16% Cr and 2.0% Mo (if your lucky they will give you 2.05%) it is often less pitting resistant than 304 with 18.5% Cr and 0.10% N.
One other factor is that the welds in 316 will often have very poor pitting resistance due to Mo segregation. In 304 the welds are not much worse than the base metal. In as welded structures 304 (specially 304LN) will significantly out perform 316L.
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Plymouth Tube
RE: 316 fittings corrosion
Aaron Tanzer
www.lehightesting.com
RE: 316 fittings corrosion
The thing to remember with PREN is that it estimates the maximum possible relative pitting resistance for a given chemistry.
I know of many ways to make material so that the actual corrosion resistance is a fraction of the optimum.
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Plymouth Tube
RE: 316 fittings corrosion