PWHT time ASME 1 versus B31.1

[ijzer]

According ASME 1 the minimum PWHT time for materials P15E (like SA-335 P91) with thickness over 5 inch is 5 hours.
For ASME B31.1 the minimum 5 hours is required already over 2 inch thickness.
Does anybody know why this difference or could this be a typo in B31.1?

 

[metengr]

ASME Section I has had the 5 inch lower thickness limit soak time (versus 2" or less and 2" to 5" soak times) for P-No 5 B materials in 2006, and when the CSEF steels were reclassified as P-No 15E Group 1 in the 2009 addendum. There are technical differences between B31.1 and Section I because they are two different standards committees and sometimes they do not synchronize with each other.

If there is a typo, it is normally caught early and an errata is issued.