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I'm getting new gas service (Nat. Gas, M425, 1-1/4") installed. Big Box Store doesn't sell 1-1/4" black pipe (only 1"), but they do sell 1-1/4" galvanized. Can I run galvanized for mainline (from exterior protruding nipple for meter connection, then run up and through the attic) and branch off using smaller 1" black iron pipe, manifolds, and fittings or CSST and fittings? I've heard common folklore regarding galvanized, but I'm looking for cited code violations.

I've tried to thoroughly review UPC and IRC codes, but everything seems to point to no issues using black iron, galvanized, or CSST [1], but I couldn't find anything mentioning a mix of them.

What I know so far from my research:

  1. Galvanized is no longer a risk when used with NG because modern zinc coating processes no longer cause flaking and NG composition is no longer corrosive. It can be used outside or where moisture is present.
  2. Black (iron) pipe can't be used outside or where moisture is present.
  3. CSST must be properly bonded and installed by a certified person.
  4. There is no galvanic corrosion/reaction between galvanized and black pipe because they're both made of "soft steel", galvanized is simply coated with zinc.

Code should be relevant to my locale: Snohomish County, Washington State, USA.

[1] IRC G2414.42(403.4.2), ASTM A 43/A 53M: https://up.codes/viewer/washington/irc-2015/chapter/24/fuel-gas#G2414.4.2

This specification covers seamless and welded black and hot-dipped galvanized steel pipe in NPS 1/8 to NPS 26

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    I am in Oregon haven’t installed a new gas service for quite a while I believe our states are similar, they used to frown on galvanized even on seamless , in ground we had to use vinyl coated but above ground outside black iron was ok it had to be isolated from masonry, The one thing I did find out was not all pipe is equal the big box in this case may sell a lower quality pipe it meets specs but barely. So compare not only prices but type and quality you don’t want to use sub standard material when it comes to gas and you want it to last your lifetime and beyond.
    – Ed Beal
    Aug 4, 2020 at 4:03
  • Any chance you found an answer on your own? I'm about to start building one county over (Skagit) and have the same question. Hoping to use painted black iron, myself.
    – Bungle
    Feb 8 at 9:16
  • "I couldn't find anything mentioning a mix of them" because you shouldn't. #4 needs a citation : "There is no galvanic corrosion". No inspector wants to see a mix of installed junk that was found on the floor of the truck. That fails Code #001 : "workmanlike manner".
    – Mazura
    Feb 14 at 3:25
  • I've installed mixes of "black" and galvanized steel gas piping a dozen times, inspected and passed in Washington state. Stay away from the "black" pipe at the Big Boxes, which many times just has a shoddy coat of black paint which flakes terribly, inside and out. Black pipe installed outdoors will rust quickly, whereas galvanized will remain presentable for years.
    – kreemoweet
    Feb 14 at 5:03

1 Answer 1

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Best check local codes in your area, things change over time.

When in doubt, ask the Local Authority Having Jurisdiction -- which in the US is generally the local building inspector. They're the ones who have final say on what meets local requirements.

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    When in doubt, ask the Local Authority Having Jurisdiction -- which in the US is generally the local building inspector. They're the ones who have final say on what meets local requirements.
    – keshlam
    Feb 13 at 22:36
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    This is the answer to many questions here. However, we're looking for something a bit more concrete than "check elsewhere". Something like "Yes, it should be fine but always check AHJ" or "No, never do that it'll blow up". Just "ask elsewhere" is, well, not all that helpful.
    – FreeMan
    Feb 13 at 22:51
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    It's not check elsewhere, it's ask the dude who has the authority to tell you to rip it out. Or maybe just not do it all schlocky in the first place to save four cents on a coupling.
    – Mazura
    Feb 14 at 3:23

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