A.Mike Casey, a licensed plumber in Connecticut and California and co-author of Code Check Plumbing, responds: Although black iron pipe is a bit less expensive, galvanized pipe offers better corrosion resistance. In my experience, both types of piping work fine, and the IRC and the National Fuel Gas Code allow both — along with corrugated stainless steel tubing (CSST) and copper tubing (with some limitations) — to be used for natural gas distribution piping.
But you’re right: Some municipalities, particularly in the Northeast, still allow only black iron for natural gas piping. This is probably because the quality of natural gas once varied more widely than it does now, and local contaminants like hydrogen sulfide could cause problems with certain types of piping.
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