See general note G24 to Table 1A of Section II Part D.
The allowable stress values tabulated in Section II Part D already account for the joint efficiency of welded pipes and tubes. Thus when determining the required wall thickness (as based on circumferential stress) of the cylindrical component the joint efficiency is taken as 1.0.
When determining the allowable longitudinal stress of this material the tabulated allowable stress may be divided by 0.85 and the actual joint efficiency of the circumferential weld applied.
