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:


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