Why are fittings “heavier” than mating pipe and what controls the end preparation for welding?
Fittings require reinforcement to make them as strong as seamless pipe of the same diameter, wall and material grade as designated by the marking on the fitting. In addition, forming methods or pipe availability could dictate use of heavier material to ensure adequate strength. This results in a heavier body thickness and a requirement to machine the welding ends to match the pipe. ASME B16.9 or B16.25 Figure 1 shows the maximum machining envelope for welding end transitions to comply with the B31 Piping Code requirements for matching components of unequal wall thickness. This figure provides for taper boring the ID at 18 degrees maximum, taper turning the OD at 30 degrees maximum, or a combination of both to hold the specified fitting end tolerances.
