Re: Galvanized Pipe in Blowoff-Blowdown Systems

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Posted by Craig on May 31, 2001 at 13:02:29:

In Reply to: Re: Galvanized Pipe in Blowoff-Blowdown Systems posted by Vern on May 30, 2001 at 12:32:42:

: : : 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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