Weld joint efficiency (E) does not change calculated stress. E is used to increase the required (pressure) wall thickness where the weld quality is uncertain. But this E is not used in setting the allowable stresses for EXP, SUS & OCC.
B31.1 and B31.3 handle this E differently. The allowable stress tables in B31.3 hold the material basic allowable stress. In B31.1, the allowable stress table holds SE, not just S.
In CAESAR II, if you enter E for a B31.1 model, the program will divide the entered allowable stresses (SC, SH1,...,SH9) by this E - thus increasing the allowable stress (since E<1). This will also reduce the (calculated stress/allowable stress) ratio.
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Dave Diehl