The hub is the whole idea. A weld neck flange does not end at the pipe wall; it tapers gradually from the flange thickness down to the pipe wall thickness, so the joint sees a smooth stress path under pressure, bending and thermal cycling. The bore is machined to the inside diameter of the connecting pipe, which is why a weld neck order is incomplete without the pipe schedule — a Class 300 NPS 6 flange bored for Schedule 40 will not match a Schedule 80 line.
Weld neck flanges are the standard choice for high pressure, high or low temperature, and any service with vibration, bending loads or frequent thermal cycles — refinery, petrochemical, power and offshore piping. Our guide weld neck vs slip-on sets out where the cheaper slip-on is and is not an acceptable substitute.
| Item | Range / Options |
|---|---|
| Standards | ASME B16.5; large diameters ASME B16.47 Series A |
| Size range | Catalogue executions include NPS 2 executions (the Sch 40 listed to SABS / DIN patterns; the Sch 160 listed to ASME B16.5) and a 60 inch Class 150 execution (B16.47 Series A); other sizes confirmed per product at enquiry |
| Pressure classes | Catalogue executions: Class 150; further classes confirmed per product at enquiry |
| Faces | Raised face (RF) and ring-type joint (RTJ) in catalogue executions |
| Bore | Machined to the pipe schedule stated on the order — Sch 40 and Sch 160 in catalogue executions |
| Materials | Carbon steel ASTM A105 and low-temperature ASTM A350 LF2 in the catalogue executions referenced on this site; further grades are assessed against your enquiry for the specific product |
Forged, Machined, Drilled
Each flange starts as a forging in the specified grade. The hub taper and bore are turned, the face finished — serrated for RF, grooved for RTJ rings — and the bolt holes drilled on the class bolt circle. Because the bore and hub are machined from one forging, concentricity between bore and bolt circle is held the way the standard intends. The third common facing form, flat face, belongs to joints against cast iron and other brittle mating flanges — our flange face guide explains where each form belongs.
Low-Temperature and Stainless Executions
For cold service, A350 LF2 weld neck flanges (including large B16.47 Series A sizes, for example a 60 inch Class 150 execution listed in our catalogue) carry impact-tested material. For corrosive service, no stainless weld neck execution is among the catalogue executions referenced on this site: name the grade, the service temperature and the medium on the enquiry, and the execution will be assessed for the specific product before order.
Ordering
Six items define a weld neck flange: type, NPS, class, facing, grade, and bore schedule. Add quantity and any special requirements — RTJ groove form, hub length specials, or NACE material — and the quotation covers the rest.
Frequently Asked Questions
Why do you need my pipe schedule for a weld neck flange?
The flange bore is machined to the pipe's inside diameter so the weld is flush and full strength. The bore follows from NPS plus schedule. Without the schedule the bore cannot be finished — it is the single most common cause of flange order delays.
When should I choose weld neck over slip-on?
For high pressure, high or low temperature, cyclic or vibrating service, and hazardous media, weld neck is the correct default. Slip-on suits low-pressure, non-critical utility lines. Our comparison guide works through the differences in detail.
Can weld neck flanges be supplied with RTJ faces?
A Class 600 RTJ weld neck execution appears in the catalogue. State the class and facing on the enquiry and the execution will be confirmed for the specific product.
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Send Your Specification
Tell us the size, schedule or pressure class, material grade and quantity for the weld neck flanges you need. MOQ and lead time are confirmed in the quotation for your exact specification.