SA-335 Grade P12 and P22 3

[SaeidNorouzi]

hi all,

what is the main practical difference between these two alloys:
1- SA-335 Grade P12 (USA / ASME) Cr(0.8-1.2) Mo(0.44-0.65)
2- SA-335 Grade P22 (USA / ASME) Cr(1.9-2.6) Mo(0.8-1.1)

Is it possible to substitute the second item with first one?
We are going to use them in boilers?

thanks a million

 

[heathot]

The main difference between these alloys is the allowable stress values, per ASME Section II, Part D;
Grade P22 has generally, at high temperature, an higher allowable stress compare with P12. In general you cannot simply substitute a pipe in grade P22 with an identical one in grade P12.
It's maily depending from the design temperature.

 

[davefitz]

Other differences are cost, welding procedure, thermal conductivity.

If you are buildig an enire boiler, there may be cost savings by substituting T23 for all t22, t11, t12 and other light alloy tubes, as one scheduled furnace run by the mill for a single large T23 order may be cheaper than the smaller mill runs for the other alloys.

 

[stanweld]

One would almost never substitute P12 for P22 due to the greater design allowable stress at temperature of the P22. P11 and P12 are essentially interchangeable.

 

[blacksmith37]

As Stan points out the allowable stress/temperatures are significantly different. Also the ASME PREheat/PWHT are different. Also there is some difference in resistance to high temperature hydrogen attack, if that is a consideration. In my experiece P12 was unusual, P11 more common. These alloys; 1 1/4 Cr; 1/2 Mo and 2 1/4 Cr ;1 Mo are the workhorses of the petroleum/hydrotreating industry.