P91 pipe welded to SA-516-70 ASME Pressure Vessel

[EJWhite]

I'm having an issue installing a P91 pipe into a SA-516-70 Pressure vessel. It seems I have to transition from P91 to P22 and then to SA-516-70. With that said, I'm assuming I have to place a P22 sleeve around the P91 pipe prior to installing it into the tank. Is anyone familiar with this course of action? Is there another alternative?

 

[metengr]

No. You need an actual transition with the nozzle material. So, you would be having the P91 pipe butt welded to a P22 nozzle which is welded to the carbon steel shell as a transition nozzle. The transition nozzle should first be fabricated with Grade 91 pipe welded to the P22 nozzle material so that PWHT can be done before installing it in the carbon steel vessel.

 

[MJCronin]

So.... what is the max operating temperature at the transition of this strange system ?

Is the temperature >1100F, for which P91 piping material was developed or is it less than 750F, where ASME allows use of carbon steel materials such as SA 516-70?

What, exactly is the problem with a piping flange at this tank to piping joint..????

Something does not seem right.....

MJCronin
Sr. Process Engineer

 

[EJWhite]

Vessel is a Steam Turbine Blowdown Vessel. ASME Design is 50 PSIG at 750° F. Client asked for a few P91 nozzles which I can not weld directly to SA-516-70. I believe I will follow the earlier suggestion and utilize a P22 transition piece.

 

[metengr]

I can see the reason for the Grade 91 based on erosion, however, I would not consider Grade 91 just because of the weldability concerns, although at 750 deg F this is a sweet spot for Grade 91.