Why are yellow gas appliance connectors single-use?

Question

I am looking for an explanation why yellow gas appliance connectors are single-use. What is it that makes them not reusable? Does it wear and reshape sympathetically so that it can't form another joint without gaps and leaks?

Answer 1

The most likely answer that's not just "liability insurance CYA" [which is certainly a possible answer] would be the use of a metal-to-metal seal where one part is a fully annealed but work-hardenable metal, such as a copper alloy.

That would be soft and easily deformed to make the seal the first time it was used, and the deformation would work-harden it so it would not be as soft and easily deformed the next time, so it might not seal properly.

Such seals are common in ultra-high vacuum work. I do not know if gas connectors (now) use such seals in some manner, as all direct knowledge I have of fuel gas for homes is decades out of date, and was mostly propane anyway.