P number quandry: 1 vs 3 ? 2

[montec]

We're planning construction of a non-code pressure vessel for REMOTE testing of reactive chemistry. (OK, explosions). Nevertheless, I refer to the BPV code for guidance in welding and optimizing the strength of this reusable vessel. It consists simply of a 36 in OD pipe x 0.6 wall alloy API 5LX65. Slip on flanges of A694F65 welded at pipe ends and dome closures of A51670N with same mating flanges. Domes have center thru-bosses of A572Gr50.

QUESTION: My initial take on these 4 alloys shows all are P#1. I found no chromium values on vendor sites. Yet, when I look at the mill test certs, API5Lx65 shows chromium at 0.02(%) and A516-70N shows chromium at 0.08(5). So, does this report make the two alloys as P#3? Am I missing a minimum threshold or something??

Gratefully, Montec

 

[weldtek]

Per Sec IX API5L-X65 is P1 Gr 2

 

[metengr]

For carbon steels, there can be tramp (unspecified) elements present as a result of using scrap metal to make heats of steel versus hot metal (original blast furnace). Tramp elements are not considered part of the chemical composition for determination of P-No grouping by ASME Section IX.

 

[Guest102023]

SA-516 calls out A20 (you can use SA-20), 'General Requirements for Plate'. Table 1 gives limits for unspecified elements.

It still requires some knowledge of ferrous alloys and the ultimate application to judge which elements may be significant at, say 0.10%, and whether they were added deliberately. Cr and Ni are usually not significant at that level, Nb and V might be.