Can you weld SS304 to zinc-plated ASTM A53 without corrosion?

IMHO either welding or brazing to Zn plated steel would be a mistake.
Both Zn and Carbon steel are pretty far from Austenitic stainless grades on the Galvanic chart, and unless you are operating in pure non-conductive water, you will get the zinc acting pretty fast as a sacrificial anode to the more cathodic 304. (Which of course is the purpose of Zn galvanizing in the first place)
304 is about the cheapest SS made, and most metals that are compatible w. 304 are a little more expensive than carbon steel.
Without knowing the loads on your assembly, it's hard to make a recommendation. Have you looked at plastic?

Harry, Thanks for the reply. Plastic wouldn't work because the product is used in the fire industry and standards require the pressure retaining elements of the assembly to be metallic. The assembly must withstand a burst pressure of 875 psi. Asssembly has to pass a salt spray corrosion test (20% NaCl fog/spray at 95 degrees F for 10 days with no evidence of incipient corrosion). Bill

Much better information. You could braze the joint, but I would recommend that the assembly (at least the Zn plated section) be painted after braze with a Polyurethane paint, with the paint extending about 1 inch past the braze joint . Powder coating is best and I'm pretty sure that you can get PU powder coating done pretty inexpensively. (Polyurethane BTW works better outdoors than other paints because it chalks less).

Bill:
I agree with Mr. Andreas, but for another reason.
Either welding or brazing of zinc plated stainless steel is a very, very bad idea. Once the zinc melts it quickly will cause liquid metal embrittlement and grain (crystal) boundary cracking of the stainless steel.
Tell the manufacturer who suggested a zinc plated steel to go look up some of the discusions resulting from the 1974 Flixborough disaster. (Perhaps he/she was not alive back then?) For example, see: Also, for welding the stainless steel tube and reducer probably should be 304L, or a stabilized grade.
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