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Up Topic Welders and Inspectors / Education & Training / Pasivating stainless steel
- - By gyadon (**) Date 05-14-2004 17:05
I need some help. We are building a cooling tower with a stainless steel floor. It will be welded with flux core SS wire dual sheild base metal 304. One of the engineers ask my customer if they were going to blast or pasivate the welds? I have had some experience with pickle and paste method, but this has been ten years ago. A welding supply salesman gave me an article that was very informative on this subject but as I said that was ten years ago and of course I have lost the article.
One big question of course is it necessary? If so what is the best way? and so on. I should add that this is rather large, will hold all the water, and be the roof. Any help out there?

GYADON, CWI
Parent - - By G.S.Crisi (****) Date 05-14-2004 20:36
I'll give you a completely different an answer than you expect.
Why a stainless steel floor in a cooling tower? Isn't that an unnecessary luxury?
Of course, the problem is corrosion, but the water circulating through a cooling tower is never that corrosive so as to need a stainless steel basin, unless your case is a very very special one. In this case, and just for information and to learn something new, I'd like to know what it consist of.
It's not uncommon that cooling towers suffer corrosion problems, but they can be overcome using far less sophisticated and expensive materials.
On Power magazine, September 2001 issue, page 24, it is explained how the corrosion problem in a cooling tower in Austin, TX, was solved by applying a polyurethane coating made by Bayer Chemical Corp. of Pittsburgh. The name of the product is Baytec SPR.
If you want more information, contact www.bayer.com
Giovanni S. Crisi
Sao Paulo - Brazil

Parent - - By gyadon (**) Date 05-17-2004 18:59
I don't design, I inspect what they give me.
Parent - By G.S.Crisi (****) Date 05-17-2004 20:46
If that's the point, on one of the last issues of Welding Journal magazine it appeared an article on how to passivate s.s. welds.
I don't remember exactly which issue it was, but it shouldn't be very difficult to find it out on the section dedicated to the magazine in this same site.
Giovanni S. Crisi
Parent - By jamesrodr (*) Date 05-20-2004 18:12
hi Gyadon ,

If you want to pickle the plates this may help you. Use nitric and hydrofluoric acid mix. the common formula is 5 to 25% of 65% strength nitric acid and 1 to 3 % of 50% hydrofluoric acid. This is usually done for about 15 minutes at 50 degrees centigrade . The final stage is always rinsing with water at about pH 6-7.

Regards

James
Parent - By jamesrodr (*) Date 05-20-2004 18:20
hi Gyadon ,

If you want to pickle the plates this may help you. Use nitric and hydrofluoric acid mix. the common formula is 5 to 25% of 65% strength nitric acid and 1 to 3 % of 50% hydrofluoric acid. This is usually done for about 15 minutes at 50 degrees centigrade . The final stage is always rinsing with water at about pH 6-7. Passivation for annealed or cold worked non reflective surface is nitric acid 67% strength 20-50% volume .

Regards

James
Up Topic Welders and Inspectors / Education & Training / Pasivating stainless steel

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