What is this material?

[Lon Henderson]

I see this about once a year. I have never confirmed what this gray metal tubing is.
3116131162

Please, tell me what this stuff is?

[Mark Reinmiller]

Looks like tinned copper. Never saw it before.

[Lon Henderson]

Looks like tinned copper. Never saw it before.

I can't find any examples of copper tubing tinned on the exterior, but I agree that that's what it looks like. Interesting that no one else has commented, which indicates that it may be very rare.

[Steven Turetsky]

When sweating copper, the pipe is wiped off to remove the excess flux, otherwise the area will green. If there is also excess solder it will adhere. I think this plumber was on a mission (or was smoking pot).

I have seen exposed copper tinned in order to change the appearance.