F22 is going to fall either under an A182 or A336 Standard; UNS K21590. Both are P5A materials, 2.25% Chrome, !% Moly. Not exactly sure what the poster means by "seal welds." I mean, of course I know what a seal weld is but am not sure what thickness he's working with, etc., etc., etc., Told him before in an identical thread he'd need to give us more information in order to give a proper answer. On my site, we have a 200C MINIMUM maintained preheat but his might have different requirements. Likely as not, he's working with a B31.3 Code, which requires a 350F (177C) minimum regardless of preheat. Poster: if this is the correct code, see Table 330.1.1.