It depends on how long you want the exhaust pipe to last and the thickness of the pipe. Carbon steel exhausts used to be the rule but short life expectancy was expected. For longer serviceslife, type 409 ferritic stainless steel is often used.
Well it was originally schedule 40. However, they installed schedule 10 and I was asked to verify the stresses at the supports for the new thickness. Schedule 10 fails and stiffening is required. B31.1 does not even show an allowable for that temperature. Is there any other source that we can use to detemrine the allowable if any left at that temperature?
Right of a single bar falls under the discourage category. Right of a double bar is prohibited.
B31.3-2006 is all I have handy, and it's just a single bar at 800 with no double bar to be found.
So, I still stand by my "does not prohibit" statement.
If sigma needs anything more comprehensive than a hint to go look at B31.3 or Sec2... well, a free message board probably isn't the place to get it. Even us burned out rock stars turned engineers need some business nowadays.