How a stub end joint works

The stub end is a short length of pipe with a flared lap at one end. It is welded to the pipe, and a lap joint flange slides over it and rests behind the lap. The gasket seals against the lap face, and the bolted flange clamps the two laps together. Because the flange is loose, it rotates freely, which makes bolt-hole alignment easy during installation, and it can be removed for maintenance. The flange does not touch the process fluid, so it can be carbon steel, coated or galvanised, even when the pipe and stub end are stainless steel, duplex or a nickel alloy.

Long and short pattern

Long pattern stub ends to ASME B16.9 have a longer barrel, which leaves room for the flange to slide back during fit-up and for the butt weld to be made and inspected away from the flange. Short pattern stub ends to MSS SP-43 are more compact and economical, and are widely used in light-wall stainless piping (Sch 5S and 10S). The length for each size is given in the respective standard.

MSS SP-43 Type A, B and C

• Type A – forged or formed with a machined lap face and a fillet radius that matches standard lap joint flanges. The most common type.
• Type B – with a smaller fillet radius, for use with standard slip-on flanges as backing flanges.
• Type C – fabricated from pipe by flaring or by welding a ring to the pipe end, usable with either lap joint or slip-on flanges.

Specifications

Materials

• Stainless steel – ASTM A403 WP304L, WP316L, WP321.
• Carbon steel – ASTM A234 WPB, A420 WPL6.
• Alloy steel – ASTM A234 WP11, WP22, WP91.
• Duplex and super duplex – ASTM A815.
• Inconel and other nickel alloys – ASTM B366.

Backing flanges are supplied in carbon steel, galvanised or coated, or in the same material as the stub end where external corrosion is a concern. All fittings are on the pipe fittings page.

How we manufacture stub ends

Seamless stub ends are formed from pipe by hot or cold flaring of the lap, or machined from forgings for heavy walls. Welded stub ends are made from plate or welded pipe. After forming, stub ends are heat treated as the material standard requires, the lap face is machined to the specified finish, and the weld end is bevelled. Each stub end is marked with material, size, schedule and heat number and checked for dimensions and lap-face finish.

Where stub ends are used

Stub ends with lap joint flanges are used in stainless steel water and process piping, duplex and super duplex seawater systems, titanium and nickel alloy piping, plastic-lined piping, and any system that must be dismantled often for cleaning or inspection. They are especially economical in large sizes and in costly alloys, where a solid alloy flange would be expensive. They are less suitable for high-pressure, cyclic or high bending-load service, where weld neck flanges are preferred.

Ordering stub ends

Please give the material, size, schedule, long or short pattern (and MSS type for short pattern), lap-face finish, quantity, and whether matching backing flanges are needed. Dimensions are in the butt-weld fitting dimensions chart and the standards.