Re: [PipingDesign] Galvanic Isolation

From: <Pete>
Date: Sun Jun 01 2003 - 22:53:00 EDT

Geoff,
I think you missed the intent of the question from Thomas. He is asking about Galvanic corrosion. I'll put my 2 cents in. Galvanic corrosion - between two dissimilar metals will result in accelerated corrosion of the more reactive metal and less corrosion of the more stable metal. This situation is most severe in the more opposite type metals or those farther apart in galvanic series. Copper and steel would be an example of two metals that would have a problem. An insulated joint or galvanic coupling would be neccesary. This joint would electrically insulate the two different metals. In my limited experience I would guess that steel and stainless steel would not be a problem but thats where my knowledge drops off. Also undergound systems would add a level of concern too.

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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[Non-text portions of this message have been removed] Received on Sun Jun 01 22:53:00 2003

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