"rust" of a stainless steel tank
"rust" of a stainless steel tank
(OP)
Hi all,
I am faced with a stainless steel (316L) tank having been used in the storage of Choline chloride. This tank shows corrosion, in particular in welds and heat affected zones. Strangely enough, the corrosion products are deep "rust" coloured (reddish-brown), suggesting formation of iron oxides. I had expected greyish products, black even. In surface areas, covered with these rust stains (dripping down the wall of the tank) serious pitting is present underneath. These pits are relatively deep, and completely covered by a thin wall of stainless steel. Inside the pits, there is no corrosion product and the surface is bright metallic.
Has anyone seen this before? Especially the rust colour puzzles me.
regards
rob
I am faced with a stainless steel (316L) tank having been used in the storage of Choline chloride. This tank shows corrosion, in particular in welds and heat affected zones. Strangely enough, the corrosion products are deep "rust" coloured (reddish-brown), suggesting formation of iron oxides. I had expected greyish products, black even. In surface areas, covered with these rust stains (dripping down the wall of the tank) serious pitting is present underneath. These pits are relatively deep, and completely covered by a thin wall of stainless steel. Inside the pits, there is no corrosion product and the surface is bright metallic.
Has anyone seen this before? Especially the rust colour puzzles me.
regards
rob





RE: "rust" of a stainless steel tank
RE: "rust" of a stainless steel tank
The pits are bright because of active corrosion, this is common.
The welds and HAZ have a lot lower corrosion resistance than the base metal. This is partially due to the heating and forming problems in the microstructure (chrome carbides in the HAZ and residual delta ferrite in the welds). The other part could be improper surface condition. If there were oxides formed during welding and they were just ground off then this won't work. They would need to actually be pickled to clean them.
And what the heck is Chlorine Chloride?
Was the tank sealed? Inert gas purged? Any moisture would be fatal.
My guess is that the wetted part of the tank was pitted but not discolored until you drained it and let humid air reach it, then the corrosion products turned orange.
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P.E. Metallurgy, Plymouth Tube
RE: "rust" of a stainless steel tank
RE: "rust" of a stainless steel tank
Were you storing it pure and dry or as a solution?
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P.E. Metallurgy, Plymouth Tube
RE: "rust" of a stainless steel tank
Dik
RE: "rust" of a stainless steel tank
But this is often sold as a solution ~70%.
Lets put it this way, at pH=4 316 will only tolerate about 20ppm Cl before you have pitting attack.
A lined CS steel tank might be a better option.
If you want metal look at 2205 for construction, and remember that it is a lot stronger so you can make it a lot thinner.
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P.E. Metallurgy, Plymouth Tube
RE: "rust" of a stainless steel tank
Dik
RE: "rust" of a stainless steel tank
RE: "rust" of a stainless steel tank
It's been a few months since your original post, so I don't know whether you still need an answer. Is it still an issue?
RE: "rust" of a stainless steel tank
RE: "rust" of a stainless steel tank
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P.E. Metallurgy, Plymouth Tube