Are allowable stress in B31.1 and Sec II D the same? 1

You are aware that Section II, Part D contains allowable stresses (among other things) for multiple Codes, including Section VIII, Divisions 1 and 2, Section III, and Section I? All of which have different design margins as described in the Appendices of Part D.

Care to restate your question?

I understand B31.3 uses slightly different allowable stress than B31.1 because of the different methods used to determine allowable stress.

I am wondering if B31.1 uses the same method as Section II D to determine allowable stress?

I found my answer (Yes, with exception)

ASME B31.1 102.3.1 (C)

(C) The basis for establishing the allowable stress values
in this Code Section are the same as those in the
ASME Boiler and Pressure Vessel Code, Section II,
Part D, Appendix 1; except that allowable stresses for
cast iron and ductile iron are in accordance with
Section VIII, Division I, Appendix P for Tables UCI-23
and UCD-23, respectively.