design header wall thickness required by para. 403.1.2. For welded pipe, when the branchdoes not intersect the longitudinal or helical seam weld of the header, the allowable stressvalue for seamless pipe of comparable grade may be used in determining th for the purposeof reinforcement calculations only. When the branch does intersect the longitudinal or helicalseam weld of the header, the allowable stress value, S, of the header shall be used in thecalculation. The allowable stress value, S, of the branch shall be used in calculating tb.