Carbon steel pipe in high temp application

[Cogenengineer]

A plant we operate uses carbon steel, 8" seamless pipe ASTM A106 schedule 20, 1020 carbon steel for an internal combustion engine exhaust. The gas temp runs around 1150F consistantly. The pressure the pipe sees is less than 1 psig. There are concerns about the prolonged intergrity of the piping as most of it is totally insulated. I have access to ASME B31.1 and see on App A Table A-1 on note 3 that carbon steel is not recommened for application of constant temp above 775 F. I do not have access to ASME BPVC IID that probably has the answer I'm looking for. The question is can this piping sustain it's integrity with this exposure? It should also be noted that the engines run about 12 hours per day and do not operate at night so there is some regular temperature cycling of the system.
I have seen many plants get away with using steel pipe , but not when it is insulated. Any thoughts on the material used and recommended alternatives is appreciated.

 

[metengr]

In your application, the carbon steel piping will deteriorate mostly from exposure to cyclic, high temperature oxidation. At 1150 deg F, the carbon steel pipe will also deform under its own weight from creep. Eventually, you will corrode enough of the wall thickness that the exhaust pipe will fail from a loss in structural integrity.

As far as mechanical properties, carbon steel looses significant strength at sustained temperatures above approximately 950 deg F. In your application, since you do not contain internal pressure because the exhaust pipe acts like a vent, allowable stresses do not play a significant role. Premature failure will occur from loss of material and poor strength.

I would replace the carbon steel exhaust pipe with a ferritic stainless steel, like AISI Type 409 SS. This material is used in car exhaust systems.