That would just make a jet fire. Which may eventually result in the catastrophic failure of the pipe but if you really want to see a house jump cut a slot. Much more area for gases to mix. It's only 1psi probably so a hole may not be enough.

My understanding is that it doesn't really depend on the metal much. It's just the blackbody radiation associated with that temperature. So basically anything glowing red from heat is probably over 500°C.

"As the object increases in temperature to about 500 °C (773 K; 932 °F), the emission spectrum gets stronger and extends into the human visual range, and the object appears dull red."

https://en.wikipedia.org/wiki/Black-body_radiation

there could even be a leak…

Autoignition here is referring to the temperature at which it will ignite immediately upon mixing with oxygen. Below that temperature, they can mix and not burn (like what happens with a gas leak).