Carbon Steel High temperature oxidation query

[robsalv]

Hi folks.

I've had a good look around for info on the kinetics, degradation or otherwise of carbon steel exposed to highish temperatures to no luck. There's heaps of stuff about what alloying will provide better high temp properties, but this is a different issue.

I'm trying to get a clearer picture of the types of degradation and degradation rate I can expect in cyclically exposing a plain carbon steel furnace stack to temperatures around 740DegC.

The service is a small gas regeneration heater burning essentially natural gas.

Higher regen gas temperatures are required and firing harder to a stack temperature of 740DegC [1364F] will get it. For 45+ years the max stack temperature was 660DegC /1220 F.

At this sort of temperature, I'm wondering whether there might be some unexpected high temperature oxidation issues or metallurgical structure issues if operating often above the 1333F /723C transition temperature.

I've already recommended a shorter inspection interval - especially for the damper which was on it's last legs anyways...

Any thoughts, link resources or words of wisdom would be appreciated.

Thanks in advance.

Rob

 

[metengr]

The two major issues I see with using carbon steel in this application is exposure to oxidation and creep deformation. The creep deformation at these metal temperatures is highly dependent on stress, which I gather might be very low for the stack - other than wind loading.

I would be more concerned with oxide exfoliation from thermal cycling, and subsequent loss of wall thickness that at some point would result in barreling of the lower shell courses or rings that support the stack. I would definitely keep an eye on the lower shell course thickness because at some point you will waste away and the carbon steel shell wall will become paper thin.

 

[robsalv]

Metengr

Very good point!!!

*smacks own forehead hard* Why didn't I think of that!!

Will update the inspection plan to recognise the thinning risk.

Cheers

Rob