High Temperature Creep, Carbon Steel 1

[mshimko]

I haven't had a need to evaluate HT creep since I studied it in grad school, many years ago, and today I was asked a question regarding high temperature creep of carbon steel. The application is a steam plant, and the question pertains to installing carbon steel by mistake.

Any suggestions on where I might be able to locate any data on HT creep of carbon steel? My "standard desktop references" mention the topic, but provide no specifics.

Thanks for any suggestions.

 

[MrMyers]

Have a look in API-579-1/ASME FFS-1 2007 Part 10 and Annex F.

Most material classifications are listed in there.

Best of luck.

 

[davefitz]

Carbon steel tubes mistakenly installed within the boiler setting : ASME sect I rules govern the material selection, and section I will allow some carbon steels up to a 900 F metal temp. The tubes are more likely to fail by embrittlement if they are operating in the range of 950-1000 F, and creep is more likely above 1000 F. If iti is a tube within the setting , it is more an availability issue than a safety issue.

For pipes , they are covered by the rules of B31.1 in power plants. Failure of a pipe is a definite safety issue, including piping "within the boiler setting". B31.1 rules will not permit carbon steel to be used above 800 F, and if that mistake was made , you need to fix it. In my opinion, embrittlement by graphitization is a safety issue after about 1 year service over 800 F- you really have to change out the pipe within that first year.

Typical locations where this error is made is spray attemporator water piping close to the spray nozzle, steam piping immediately downstream of a spray nozzle, cold reheater ( HP turbine exhaust) piping, and primary superheater outlet headers and piping. In particular, if the spary water flow is much larger than predictes ( as with duct firing or change of fuels ) this PSH O/L header will run hot and can fail from graphitization.

 

[metengr]

mshimko;
What exactly do you need regarding creep data? Where was the installation of carbon steel? Piping, boiler trim, boiler tubing, etc?

Carbon steel will creep above 700 deg F. However, as mentioned above carbon steel at prolonged exposure above 700 deg F will be subjected to spheroidization and possibly graphitization, depending on service temperature and stress. When I hear material installation mistakes in stea plants my ears perk up.

 

[mshimko]

Thanks for the feedback, folks.

To answer metengr - that has been no erroneous installations of carbon steel (at least nothing that triggered this question); this is merely a hypothetical what-if analysis that I'm on the outskirts of.