secondary super heater

[zuhair2000]

thanks for help
the problem we have that the secondary super heater coils were
manufactured from different alloys 213T22,213T12,213T13(in the same coil loop)
and for convienace we are arranging to manufacture the
coils from SA213T22 only so if any one can advice if its
ok or not?

 

[saplanti]

You need to check the design temperatures and allowable stresses for each section material. If they are the same you can use T22 tubes for the others. I do not have the code with me to answer completely, sometimes the lower grade materials have higher allowables at lower temperatures.

 

[boilerone]

I checked ASME Section IID, only for lower than 300F that T22 has slightly lower allowable stress values than that of T12. Since 2nd superheater is always higher than 300F so you can safely use the T22 to replace T12 and keep the same thicknesses that is used for T12 right now. I do not have data for T13 but it is likely the same case.

Nevertheless, since you are changing materials, you no longer qualify 'replacement-in-kind' so you still have to provide a calculation plus a lot more paper work for the inspector and meet code requirements for 'alteration'.

 

[metengr]

zuhair2000;
I would not recommend you proceed down the path of attempting to optimize the SSH into one alloy on your own. Why? Because you have not presented any information as to why you a replacing the existing SSH and because you don’t have enough materials experience to attempt a re-design. Have a boiler OEM look at this for you.