Where Are Long Weld Neck (LWN) Flanges Used?

A long weld neck flange is a weld neck flange with an extended hub. That extension turns the part from a flange into a short nozzle body.

How it differs from a standard WN

A standard weld neck hub gives a gradual transition between pipe and weld. In an LWN the hub is extended to the length of a pipe section, and the bore is often machined from full body thickness. As a result:

• Fewer welds; the nozzle is a single piece
• It can be welded directly to a vessel shell
• Stress distribution improves at high pressure
• The bore can be machined independently of the line schedule

Where it is used

• Vessel and tank nozzles: A one piece nozzle welded into the shell
• High pressure lines: From Class 900 upwards, to reduce stress concentration
• Orifice measurement sets: Provides enough wall for the pressure tappings
• Compressor and pump connections: Where vibration is high

When ordering

Three extra pieces of information are needed compared with a standard WN: hub length, bore (to line schedule or special) and outside profile. Without them the maker assumes, and the part will not match the vessel design.

Material grade, pressure class, face type and certificate level are stated as usual. LWN flanges usually come from production rather than stock, so allow for lead time.

See our services page for our fabrication scope and the flange page for dimensions.

FAQ

Is an LWN flange the same as a nozzle?
It acts as a short nozzle body, welded directly into the shell and removing the need for a separate pipe section.

How is the bore determined?
Either to the line schedule or to the project design; it must be stated on the order.

Is it available from stock?
Common sizes may be, but most combinations are produced to order.