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Stub end

Stubend geometry

The Stub End, which essentially a short length of pipe, which has one end that is flared outwards and the other end prepared to be welded to pipe of the same Nominal Pipe Size (NPS), material and of a similar wall thickness. The Lap Joint Flange, which is a ring backing Flange and it is very similar in geometry to the Slip-on Flange.

Stub ends are mechanical joints that comprises of two components.

This type of flanged connection was also referred to as “Van Stone” or “Vanstone flare laps”, however this is an historic terminology and very rarely used technically or commercially.

公称通径 外径尺寸 高度F 翻边直径G 倒角半径R
NPS DN OD Mss ANSI Nominal&max Nominal&min A Max B Max
1/2 15 21.3 50.8 76.2 35 34 3 0.8
3/4 20 26.7 50.8 76.2 43 42 3 0.8
1 25 33.4 50.8 101.6 51 50 3 0.8
11/4 32 42.4 50.8 101.6 64 63 4.8 0.8
11/2 40 48.3 50.8 101.6 73 72 6.4 0.8
2 50 60.3 63.5 152.4 92 91 7.9 0.8
21/2 65 73 63.5 152.4 105 104 7.9 0.8
3 80 88.9 63.5 152.4 127 126 9.6 0.8
31/2 90 101.6 76.2 152.4 140 139 9.6 0.8
4 100 114.3 76.2 152.4 157 156 11.2 0.8
5 125 141.3 76.2 203.2 186 185 11.2 1.6
6 150 168.3 88.9 203.2 216 215 12.7 1.6
8 200 219.1 101.6 203.2 270 269 12.7 1.6
10 250 273.1 127 254 324 322 12.7 1.6
12 300 323.9 152.4 254 381 379 12.7 1.6
14 350 355.6 152.4 304.8 413 411 12.7 1.6
16 400 406.4 152.4 304.8 470 468 12.7 1.6
18 450 457.2 152.4 304.8 533 531 12.7 1.6
20 500 508 152.4 304.8 584 582 12.7 1.6
22 550 559 152.4 304.8 641 639 12.7 1.6
24 600 610 152.4 304.8 692 690 12.7 1.6

The combination of stub ends and backing flanges is an alternative way to join pipes compared to the use of standard flanges.

This solution is used in these typical scenarios:


Stub ends are manufactured in three different types and two standard length.

Type “A”: this type is produced and machined to fit lap joint flanges.The mating surfaces of the stub end and the lap joint flange have a matching profile and surface. The lap thickness of type A stub ends is > = the minimum wall thickness of the connected pipe. The outside the stub end and the lap joint flange have a matching profile and surface. The lap thickness of type A stub ends is > = the minimum wall thickness of the connected pipe. The outside corner of type A has a radius to accommodate the lap join flange, whereas the inside corner is squared.

Type “B”: this type of stub ends is suited for standard slip-on flanges acting as lap-joint flanges. The lap thickness of type B stub ends is >= the minimum WT of the connecting pipe. The lap of these type of stub ends has generally a serrated face. To ensure tight joints, chamfers on the ID side of the flange are required.

Type “C”: this last type can be used both with lap joint and slip-on backing flanges and are fabricated out of pipes. The lap of C-type stub ends is flared over and the lap thickness is 75% of the connecting pipe WT. Type C has a short fillet outer radius able to host any back up flange.

Type “CS”: this type is similar to “C” with the difference that the lap face has concentric serrations machined during the manufacturing process.


Dimensions and manufacturing tolerances are covered in ASME B16.9 - Butt Weld Fittings and MSS-SP-43 (JIS B2312, JIS B2313 may also apply).

Carbon steel stub end
Long pattern stub ends
Stainless steel stub end
Short pattern stub ends

Stub End come in three standard lengths, MSS SP43 or ANSI B16.9 short and long pattern. Short pattern stub ends are mostly used for flanges from class 300 to class 600 and above. Besides these standard types, End-Users and contractors can require stub ends with non-standard lengths to suit specific project’s requirement. This will of course come at an additional cost.

Ends/Face lap finishing


The following types of ends may be ordered:

Material for Stub Ends

Stub Ends are available in numerous ASTM and other international recognized materials, to match pipe specifications, as low alloy, stainless steel, austenitic-ferritic, high alloy steels (nickel alloy such as Inconel, Incoloy 800, Monel, Hastelloy C276), non-ferrous materials (copper, cupronickel 90 /10 and cupronickel 70 / 30) and titanium / zirconium / tantalum.

Lap-joint flanges are most commonly available in carbon steel and low temperature carbon steel, because it is a lower cost than the Stub End that will be wetted by the service and it must be of a suitable grade of steel. If orientation and alignment of bolt holes is the only issue, then for standardization, then the Stub End and the Lap Joint Flange can be of the same material.

The most common material grade for stub end is the ASTM A403 / ASME SA403 (stainless steel stub ends). With reference to EU materials, the most common grades are DIN 1.4301, DIN1.4306, DIN 1.4401, DIN 1.4404.

Stub Ends assembly

Stub ends and lap joint flanges can be assembled following this process:

It can also be mated to a fabricated plate Flange with compatible, bolting dimensions.

Why use Stub Ends?

Commercial benefits
Commercial advantages are that the Stub End, will be wetted and it must be made of a grade of material that meets the process design and service conditions of the pipeline. However, the Lap Flange is un-wetted and it can be made of a lower grade of material as long as it meets
the mechanical strength requirements of the piping systems.

This means that instead of:
Duplex Stub End and a Duplex Lap Joint, you could have Duplex Stub End and Carbon Steel Lap Flange.
Or you could have Stainless Stub End and Carbon Steel Lap Flange. There are other bimetallic combinations that result in a flange assembly that is commercially cheaper.

During recent years the price differential between Duplex/Stainless Steel and Carbon Steel has narrowed and this practice on large Projects has become less common, however a cost difference always exists (the higher the NPS and the length of the pipeline / piping system, the higher the saving). On the other hand, the warehousing cost of one single component, i.e. a Weld Neck Flange, requires less shelf space than the cost of warehousing a Lap Joint and a Stub End. End Users and Contractors shall determine the actual convenience of using stub ends, considering all these factors and generally the commercial advantage is still valid and it may suit certain situation, especially in “brownfield” modifications.

Installation benefits
The “loose” Flange concept of a Lap Joint, is very beneficial during field installation of piping systems. If two spools are to be mated up in the field, having one Flange that can be rotated is very advantageous when aligning the bolt holes, prior to the introduction of the Stub bolt and the accompanying nuts. The facility of easier orientation and alignment of bolt holes, is of particular use it there is a spool that
has to be removed frequently, if positive isolation is a process requirement.

Stub Ends limitations
A Lap Joint consists of two independent components that are not integrated with a weld and like for like in size/pressure class/material it lacks the mechanical strength and capabilities to withstand fatigue, like a one piece Weld Neck Flange or a welded together Slip On or Socket Weld Flanges. In cyclic services, collars EN 1092-1 type 35 PN 16-25-40 are used instead of stub ends (especially to close pumps and compressors). If carefully consideration is given to Process Design condition, the service and the final application, then a Lap Joint Flange mechanical connection are a valid and cheaper method for installing piping systems compared to the use of standard flanges.

How to order a Stub Ends

The following information shall be provided to order a stub end:

Lap Joint Flanges

Lap Joint Flanges (LJ Flanges) are used on piping fitted with lapped pipe or with lap joint stub ends the combined initial cost of the two items being approximately one-third higher than that of comparable welding neck flanges.

Lap joint flange Standards, Dimensions & Weight

Standards: ANSI, MSS, API, AWWA, DIN, JIS, BS and GB.

More Products related to fittings:

Fitting specification, Standard and identification

There are different varieties of pipe fittings made of various materials and available in various shapes and sizes.

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