Pete,
I clearly understood the question. Stainless steel is protected by a thin layer of chromium dioxide that has a different potential to carbon steel. If there is an electrolyte present there will be a galvanic cell created and corrosion of the less noble metal will occur. In addition to this there may be instances of stress concentration and given the right environment this can be accelerated.
Most installations are dry or when wetted do not remain moist and hence the opportunity for corrosion is reduced. Stainless steel is named that because it "stains" "less" than carbon steel. There are many instances of type 304 ss corroding, although it tends not too corrode as fast as carbon steel.
Geoff
Geoff Stone
--- Pete Burns <peteburn@optonline.net> wrote:
Pete
Thomas,
In a dry environment there will not be corrosion. In a wet or moist environment
there will be. Generally where it rains and then dries out the corrosion will be minimal. In a salt water environment the corrosion would be severe.
Sydney Water go to the extreme of requiring insulating gaskets and washers under bolt heads in such environments where dissimilar metals occcur.
I do not know of any code requirement covering this matter. Generally the requirement is set out in company standards.
I would have thought someone employed by Nalco would know these facts! The discussion appears in the books published on corrosion by Nalco. So the question sounds a bit of a "Dorothy Dixer" to me. (for those not familiar with
the colloquial expressions of the English and Australian parliaments the latter
term covers the questions put by one's own side. The intent being to allow a colleague to spruke on about a matter that would in the normal course of events
never have been raised.)
Geoff Stone
Gentlemen:
involved with installation of carbon steel and stainless steel piping. piping is 150# class, and line sizes are 4 thru 10 inches. is there a need for galvanic isolation between dissimilar spools?
thank you for your help.
Thomas G Laupa PE
Senior Engineer - Ondeo Nalco Applied Services
Office Address: One Ondeo Nalco Center, Naperville, IL, 60563
Courier Address: 1003 Remington, Fort Collins, CO, 80524
970-227-5127
800-493-5009 fax
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