Why the hub matters
A weld neck flange's tapered hub spreads the transition in stiffness between the rigid flange body and the pipe wall over a length, rather than concentrating it at a single weld line. Combined with a full-penetration butt weld, this makes it the flange type best suited to high pressure, high temperature, thermal cycling and other fatigue-prone service — exactly the conditions where an orifice flange set, carrying both the process pressure and the pressure-tap connections, benefits most from the extra margin.
Weld neck vs. the alternatives
| Type | Trade-off vs. weld neck |
|---|---|
| Slip-on | Faster to fit and align, but the double fillet weld carries roughly a third the fatigue strength of a full weld-neck joint — a lower-pressure, less cyclic-duty choice |
| Socket weld | Good for smaller bores where a butt weld is impractical, but the socket's crevice gap is a stress riser and a corrosion/crack initiation point weld neck doesn't have |
| Threaded | No welding at all, so it's fast and useful where welding isn't permitted or practical, at the cost of the joint's pressure and fatigue rating |
A fuller comparison, including ring-type-joint (RTJ) facing, slip-on and socket-weld and threaded types, is covered in our Orifice Flange Types post on the blog.
Dimensions
Weld neck orifice flange body dimensions and bolting follow the same pressure-class series as standard weld neck flanges, per ASME B16.36, with the tap holes and (optionally) jack-screw holes added.