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Posted by Pete Petrossian on January 09, 2002 at 12:38:05:
In Reply to: Re: Galvanized Pipe in Blowoff-Blowdown Systems posted by Craig on May 31, 2001 at 13:02:29:
: : : : What is the reason that galvanized pipe is not permitted in Boiler Blowoff and Blowdown systems ?
: : : : (See ASME B31.1 "Power Piping Code" para. 122.1.4 )
: : : : Is the reason because the zinc coating will pose a health hazard as it degrades due to high temperature or is there another reason ?
: : : : Thanks in advance !!
: : : : MJC
: : I believe the reason has to do with electrolysis. The two dissimilar metals set up a galvanic
: : reaction, and the galvanized pipe is slowly eaten away, reducing the strength. I don't know if that
: : is the reason the code people have, but is what I was told by an inspector about
: : 20 years ago. There may be other reasons. Here in California, the only place you can use
: : galvanized pipe is for the makeup water line to the feedwater tank. Every other pipe has
: : to be black iron.
: : :
: : : I'm not sure about the galvanized restriction, but you will need scd 80 pipe up to the second BB valve.
: The above is correct. The electrolytic action that it sets up causes an advanced corrosion rate. Also, most Galvanized pipe is not "code material". BB piping must be SCH80 with a heat treat number and "code material", the piping must be ran full size to the point of discharge. The installation is governed by ASME code section 1 for high pressure boilers.
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