Schedule 40 P/T limits

The P/T rating of pipe depends on the pipign code it has to meet, B31.1 for steam, B31.3 for Refinery piping, B31.4 for oil pipelines, B31.8 for gas pipelines, etc, etc, etc.

So, you need to decide what code that piping has to meet and then calculate the appropriate allowable pressures and temperatures using the formulas and design factors in that code.

If you are interested in B31.3 for oil and gas services refer to API RP 14E which has a table indicated the recommended max operating pressure/temp for various A106 Gr B pipe diameters/schedules.

Thanks you guys. I'm really thinking for steam use, but you've basically answered my question . . appreciated.

Depending on the application, and the rules of whatever jurisdiction you're in, your steam line will likely fall under one of two codes - ASME B31.1 or B31.3. Even within those codes, there are local spins and exceptions, so it's always best to check with the inspection authority before going too far.

But take care that API RP 14E -as SooCS replied- is a practice for an offshore piping.