Galvanized pipe threaded to 304 fitting

[springwaterbr]

Hello all,

As per a client requirement, certain treated water and instrument air lines have stainless steel lines that branch off to galvanized steel pipe, which are threaded in accordance with our pipe spec.

In specing SS threaded half-couplings and threadolets for these branch connections I'm worrying about the possibility of galvanic corrosion significant enough to warrant special attention, especially given the threads.

Service temperature is ambient, the pipes aren't shrouded and the atmosphere is industrial (fertilizer plant with sulfuric acid, ammonia and phosphoric acid units), so I believe rainwater might be the bigger culprit in the event of serious corrosion, in which case the threaded connection wouldn't play as significant a part in the damage.

The alternative I have in mind would be welded stainless steel branching fittings and subsequent flanged connections where the spec transition occurs.

Do any of you have any experience with this situtation? Thank you.

 

[mk3223]

I don't think it's an issue of the galvanic corrosion for the instrument air pipe. It's common to have SS instrument valve or tubing connecting to the IA supply of the galvanized pipe. But, it could be an issue for the water pipe depending on the property of the treated water.
Suggest to search similar topics in this forum or google.

 

[Dhurjati Sen]

Dear springwaterbr,

This is not an uncommon situation. Normally the galvanizing goes off. This happens due to poor quality, galvanic corrosion between CS & Zn and lastly that between SS & Zn.

Regards.

DHURJATI SEN
Kolkata, India