There is sometimes confusion about the joint efficiency when you compare the ASME B31.1 and the ASME B31.3. The joint efficiency for the ASME B31.1 (2020) are included in the allowable stress values of Table A-1 (US Customary units). Be careful, because some tables are also available is SI or metric units.
For reference from ASME B31.1:
104.1.2
SE or SF = maximum allowable stress in material due
to internal pressure and joint efficiency (or
casting quality factor) at the design
temperature, psi (MPa). The value of SE
or SF shall not exceed that given in
Mandatory Appendix A for listed materials
or as determined per para. 123.1.2(b) for
unlisted materials, for the respective material
and design temperature. These values
include the weld joint efficiency, E, or the
casting factor, F.
Table A-1
A587 under column 'E or F': 0.85
For reference: A106 seamless pipe under column 'E or F': 1.0