Passivation of Super Duplex Stainless Steel

niumec, Hello. I have worked with a lot of this in utility world with various alloys. We had chloride exposure etc. I have had to pickle & passivate huge ductwork high in the air collecting in bladders running to a frac tank with AVESTA Red. No fun. Anyhow, I have seen some effects (actually a lot) from alloy that has not had this treatment. Usually, the big culprit is embedded iron from tooling etc. There is a spray called Ferroxyl (spelling?) that turns blue when it encounters iron on alloy. It's a good check. Proper tooling that works with this alloy is a must. Secondly, the AVESTA gel works pretty well with high heat. It will not remove all heat tint. There is a color guide from the nickel institute that shows the variations. The big thing is that when you apply heat like from a welding torch or plasma, you are removing the outer protective layer from the SS. It needs passivated to restore this. I would check the Nickel Institutes specs for other suggestions, most of this comes from going through it. Hopefully this helps.

tipenergy,

thanx a lot.

We get something called K2 Paste here in India which we used for passivation. The following is the website of the product:

http://www.surfaceinnovators.com/aboutk2/index.htm

Would you be kind enough and go through it and suggest if it will work for super duplex?

Like welding, machining removes the surface layer that forms as the stainless steel is rolled. It is this outer oxide layer that gives stainless steel its corrosion resistance, so passivation is commonly done after machining.

Paste passivation is one way to do it, although nitric acid passivation is equally as common. There is also a citric acid passivation that works well in the food and pharmaceutical industries. Any of these methods should work for you.

PDEF is right. My experience is that when we tried citric acid, we used coupons and had them tested as well, that it didn't work well enough. Maybe with the food industry where you are seeing different types of "attacks" on the protective chromium oxide layer, it may work well. For us, we had to use the AVESTA, and that still wasn't perfect. A 3M flapper wheel will take out aggressive bluing and heat tint etc, but I would still use the pickling and passivation. WARNING: This is nasty stuff! Do not inhale, do not let it get on your skin. It will go through the skin and attack the calcium in your bones. They make a paste that neutralizes it if it does come in contact. If you feel that you don't want to mess with it, there might be another manufacturer in your area that has tanks that are made for this. I will see if I can find the link for the Nickel Institute paper etc shortly.

It looks like the K2 product line has a comparable product, even though they don't list concentrations. Note: there is the pickling and then the passivation, make sure you do both. If it isn't working well, heat can help sometimes. I have seen the results of ferritic contamination and weld area. Corrosion cells can set up pretty well in about 6 weeks and have nasty results under the right conditions. It is prudent what you are doing. Good luck.

niumec Avesta has a book out that provides details for working with Duplex Stainless. Check out their website.

Thanx everyone.

Appreciate your suggestions.