Thermal Sleeve

[32001]

Hai,

I have a question on mud drum in a boiler where we are going to introduce steam coil heater. The boier design pressure is 400 psi. And the coil heater is 300 psi@ sat. My question is does the nozzle require thermal sleeve. Or what temp diefferential does the ASME Section I code allows not to have one.

 

[davefitz]

The ASME code requires a thermal sleeve on the feedwater connection to a steam drum whose design pressure is above (???) psig. This implies that the thermal fatigue associated with a temperature diference between Tsat at (???) psig and 80 F is marginally acceptable- a larger temp differential would be unacceptable unless a thermal sleeve is provided. The same logic could be applied as a rule of thumb for the case of the steam coil connections to the mud drum,but it is not a ASME section I code requirement.

You can find other rules of thumb for use of thermal sleeves from condenser mfr's- I believe they assume the plant is base loaded and they will require a thermal sleeve if the incoming steam dump is more than 300F hotter than the condenser normal casing temp ( perhaps 120 F + 300 F). Yuo shuld use a smaller temp diff if the unit is cycled.

A more sophisticated method of determining if the sleeve is required is conduct a fatigue analysis , using either ASME sect VIII div 2 or the EU PED codes.