I have some confusion regarding metallurgical limits.

ASME II-D 2015 § 2-110 defines allowable stress as the least of:

• 1/3 Specified Minimum Tensile Strength @ room temp
• 1/3 Tensile strength @ temp
• 2/3 specified minimum yield strength @ room temp
• 2/3 of the yield strength @ temp (with exception to some stainless steels and alloys)

ASME B31.3 2014 § 302.3.2.d defines allowable stress as the least of:

• lower of 1/3 of St and 1/3 tensile strength @ temp
• lower of 2/3 of Sy and 2/3 of yield strength @ temp, (with exception for some stainless steels and alloys)

These definitions appear identical. However, when you look at tabulated data in the appendices, we have different results for at least some materials. Example: A-53 Gr B has 3 different curves.
B31.3 is highest, with II-D having 2 curves spanning 4 options.

Does anyone have an idea for the reason of this disconnect between ASME divisions?

Thanks.

I think for A53 Gr B Seamless (S/B) there aren't differences between values Table 2A and B31.3, except value at 700F, which is "value based on successful experience in service".
However, the scope of 2A (basically components of some classes of Section III) and B31.3 scope are different. This explains why 2A includes A53 GR B as limited for temperature up to 700F SPT- supports only.
In fact I think we don't need to compare them, maybe just to appease the curiosity on similarity of safety factors.