Boiler operating above design temperature

[mpeck1982]

I have a water tube boiler with a superheater that is designed for 60,000 lb/hr, 650 deg F at 400-psig. I have noticed that they have operated the boiler in the past at 750 deg F. Should I have anything to worry about? The records show they have only done this once for a 6 hour period. The material is SA213 T22 which has boiler applications up to 1100 to 1200 deg F.

Is there anything to worry about when boiler is above desin temp? my load was light at 20,000 lb/hr and pressure was around 400-psig.

 

[LittleEd]

Looks to me like the stress value for that material is the same at 750 deg. as it is at 650 deg. (actually doesn't change till you get over 850 deg.), so I don't think it damaged the material. SA-213 T-22 is typcially used in hottest areas of the boiler for this purpose.

 

[metengr]

Agree with LittleEd, with the Cr-Mo superheater tube material (T22) even at 750 deg F you are not near temperature where time dependent properties (creep or stress rupture) govern.

 

[mpeck1982]

Where can I find that information? Do you have a link?

 

[metengr]

What information? If you mean the temperature for time dependent properties for T22 material, this information can be found in ASME B&PV Code, Section II, Part D.

 

[davefitz]

The asme allowable stress for SA213 T22 is 16.6 ksi from 300-850F, but one also needs to evaluate the other components downstream of the tubes, such as the header, transfer line ,valves, and the steam turbine or steam host. Also, the average steam outlet temperature does not represent the worst tubbe metal temperature in the heated zone , due to tube -to-tube temperature unbalances and heat transfer related metal temperature increases.

If the transfer pipe is SA335 P11, the allowable stress drops from 15.4 ksi at 650 F to 14.8 ksi at 750 F.

"Nobody expects the Spanish Inquisition! "

 

[chicopee]

Or the stress tables in the ASME power code I. Notice the stress/ time temperature data.

 

[chicopee]

Should be "...Notice the stress/temperature data..." Is the pressure rating being exceeded at 750 dF?