I agree with metengr. I assume you're concerned with welding these materials. As you know the P1 material is .5 Mo, and should be readily weldable, P12 and P22 are Cr Mo alloys and they do require a higher preheat. In my experience most welders tend to skimp on preheat and maintenance of the proper interpass temperatures. Preheats need to be through wall and extend past the welding area on all sides an amount sufficient to slow the weld cooling, typically several times the wall thickness, say a minimum of 2". The best way I know of to ensure proper preheat is to use temperature controlled heating elements. What wall thickness are we talking about?