Hi Thomas
No, unless the installation is subjected to an unusual environment. I have literally hundreds of stainless valves in carbon steel lines. The stainless will not deteriorate. However there is a catch; if you have say one carbon steel valve or small spool in a predominantly stainless line then I would expect the carbon steel fitting to corrode faster than if the entire line was carbon steel. Depends very much on the application. Normally the smaller the anodic (sacrificial, less noble, more corrodible) area in relation to the cathodic area, the more intense the corrosion of the weaker metal. Stainless is a little strange as the oxide layer acts like a paint. If the layer remains intact there is very little corrosive action. However if it is broken by erosion, rubbing etc, things can get out of hand very quickly. Normally not a problem in conjunction with carbon steel as the least noble constituent of stainless is (carbonish) steel. Am no corrosion expert though and welcome corrective opinion.
Ignore Geoffs caustic comment; he is just pissed off because us Kiwis are on vacation today (Queens birthday) and the Ockers have to work (and we won the Super 12). Nobody ask me a question next monday, however, when the situation is reversed.
Cheers
Steve McKenzie
-----Original Message-----
From: Geoff Stone DD&D Australia [mailto:blenrayaust@yahoo.co.uk]
Sent: Monday, June 02, 2003 9:25 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Galvanic Isolation
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
--- Thomas Laupa <tlaupa@frii.com> wrote:
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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Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Received on Mon Jun 02 01:42:00 2003
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