Pressure vessel nozzles need three things: a neck of the right wall, a flange face at the end of it, and enough length for the shell weld and any reinforcement pad. A standard weld neck flange gives a short hub and expects pipe behind it. The long weld neck (LWN) forges the neck and flange as one piece with a straight barrel, so the vessel shop welds one circumferential joint instead of assembling neck-plus-flange from separate parts — fewer welds, full forging quality through the neck, and a bore that runs true from shell to face.
The flange end of an LWN follows the same dimensional pattern as a standard weld neck flange of its class, with the barrel length and bore specified on the order. They are standard equipment on columns, separators, heat exchangers and tankage in refinery and chemical service.
| Item | Range / Options |
|---|---|
| Standards | Barrel length and bore stated on the order; flange end dimensions confirmed per product at enquiry |
| Size range | Confirmed per product at enquiry |
| Pressure classes | Confirmed per product at enquiry |
| Barrel length | Stated on the order — confirmed per product at enquiry |
| Faces | Per the mating flange — confirmed per product at enquiry |
| Materials | Confirmed per product at enquiry |
Why One Forging Beats an Assembly
The alternative to an LWN is a piece of pipe welded to a standard weld neck flange, welded again into the shell — two joints and a pipe material that must match the neck duty. The single forging removes one weld, keeps grain flow through the neck, and gives the vessel designer a known, uniform barrel for reinforcement calculations. On repeated vessel designs, it also makes nozzles a catalogue item instead of a fabrication.
The company's official website publishes the works equipment on its company tour — flange forming machines, vertical machines and drilling machines among the production equipment shown.
Heavy Wall and Bore Options
The barrel wall and bore follow the nozzle design: state the finished bore clearly on the order. Where the nozzle carries an internal lining, refractory or a dip pipe, that bore is what the barrel is machined to — before it ever reaches the vessel.
Ordering
Define: NPS, class, facing, grade, overall barrel length, and bore (or wall). If the LWN is for a coded vessel, add the material test and documentation requirements at enquiry stage so they are built into the order, not chased after delivery.
Frequently Asked Questions
What barrel lengths are standard for long weld neck flanges?
The barrel is part of the forging, so its length is set at manufacture, not cut down on site: state the overall length on the order and it is confirmed for the specific product at enquiry.
Are LWN flanges part of ASME B16.5?
The long weld neck is an extended weld neck pattern rather than a standard flange type in its own right. The flange-end dimensions of a specific product are confirmed against the mating flange at enquiry; the extended barrel is specified by length and bore on the order.
Can long weld neck flanges be supplied in A350 LF2?
LF2 is not among the executions recorded for this flange type on this site — the LF2 records elsewhere on this site belong to other flange types and do not transfer. If your specification calls for A350 LF2, state the design temperature and any impact-test documentation requirement on the enquiry and the execution will be assessed for the specific product before order.
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Send Your Specification
Tell us the size, schedule or pressure class, material grade and quantity for the long weld neck flanges you need. MOQ and lead time are confirmed in the quotation for your exact specification.