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Do I need to paint or otherwise protect black gas pipe running outside to the meter? The existing pipe is painted gray, I imagine this is to prevent rust. If paint is needed, is there a specific kind that is recommended?

I live near Denver if that affects the answer.

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Given that you're painting metal, I would avoid latex paint (which is nearly every can of paint in the home-improvement store).

The #1 issue is paint prep, especially if there's rust. Rust is very difficult to stop if it's underway under paint. Any way you can remove it; sandblasting is not excessive.** Paints that claim you can paint over rust are lying, sure, you can do it, but the rust will punch through in short order.

Then a good anti-rust primer (I've been surprised by the performance of plain old Rustoleum 7769 Rusty-Metal Primer, especially if the rust removal is less than perfect). Then a quality oil paint.

Generally, colors will not hold up in hardware-store-priced paints, because mineral pigments like lead chromate (shudder) are illegal, and organic pigments that hold up are prohibitive ***. Fortunately carbon black is a mineral pigment not toxic to humans, so you can get cheap good black paint. And that's a fine color for a "black pipe" gas pipe.


** In fact, in extensive testing by NASA (who owns more steel structures in corrosive environments than anyone in the world), sandblasting is proven to be the only method that really works, with significant performance gains over needle-scaling and heavy sanding/grinding.

*** To give you an idea, I normally use top quality LPU over epoxy primer. I'm used to paying $160/gal. for black or white (but mind you it covers 1000 square feet). I ordered some burgundy, and it was $295/gal. because of the pigments. I do not recommend using LPU over epoxy because the cost of initially getting set up in the primers, converters and other chemicals is north of $400, a bit extreme for a small job.

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@Harper. Right on the money with surface prep. Then an etch primer immediately after surface prep (within hours - a day is too long) and for seriously heavy duty a tar epoxy. There are zinc based 'galvanising paints' available and the grey paint you describe may be one. Ignore any advice that they are self-priming, it's kinda true but a separate primer coat will always give a better and more durable result. Down side is that galvanising paint are not good in high wear areas. Do not attempt to treat or paint in damp / cold (less than 15°C) weather.

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