Stub End: Types & Sizes (ASME B16.9)

Quick Reference

Stub ends + lap joint flanges = cost-effective alternative to weld neck flanges for high-grade materials (SS, duplex, nickel alloy). Types: A (long tapered hub), B (squared lap), C (separate collar). Patterns: MSS (short), ASA/ANSI (long). Standards: ASME B16.9, MSS SP-43. Sizes: up to 80”.

Stub End

What Is a Stub End?

A stub end is a short length of pipe with one flared end, used together with a lap joint flange to create a flanged pipe connection. The flared end seats against the flange face while the plain end butt-welds to the pipeline. The lap joint flange slides freely over the stub end and does not need to be welded, so the flange can be removed for maintenance or system modifications without cutting any welds.

This two-piece arrangement has expanded well beyond low-pressure service. Modern stub end assemblies now handle high-pressure applications across process, offshore, and power piping.

The flared end profile matches the facing of the lap joint flange, giving a smooth, continuous sealing surface. This end receives the butt weld to the pipe. The plain (unflarred) end has an OD that matches the flange bore, sliding through the lap joint flange with a close fit. Stub ends are produced in carbon steel, stainless steel, duplex, super duplex, and nickel alloys to match whatever the pipeline carries.

Stub ends come in three types (A, B, and C), each with a different hub geometry and lap profile. The differences are covered in detail below.

The stub end and lap joint flange combination delivers three practical benefits in the field:

Benefit	How It Works
Easy assembly and disassembly	The flange slips off without cutting welds, saving hours during turnarounds and cleaning cycles in process plants.
Lower material cost	Only the stub end must match the pipe alloy. The flange never contacts process fluid, so it can be plain carbon steel.
Free bolt-hole alignment	The lap joint flange rotates freely around the stub end, eliminating the alignment headaches common with fixed weld neck flanges.

During installation, the stub end is butt-welded to the pipe using standard WPS-qualified procedures. A gasket seals the interface between the flared end and the mating flange face. All three components (stub end, lap joint flange, and pipe) must share compatible NPS, schedule, and end-prep dimensions.

Stub End with Lap Joint Flange

A stub end paired with a lap joint flange replaces a weld neck flange for flanged connections. Two parts do the work:

• The Stub End is a pipe section with one end flared outward by a flaring machine, then trimmed to length. The opposite end butt-welds to a pipe of the same NPS, material, and wall thickness.

• The Lap Joint Flange slips loosely over the stub end. When bolted to the mating flange, it compresses the flared end against the opposing flange face, forming the seal.

This assembly provides alignment flexibility, easy access for inspection or modification, and compatibility with lined or non-metallic pipe. It is a practical choice wherever frequent disassembly is expected.

Benefits of Using Lap Joint Stub Ends

Two benefits drive most stub end selections over weld neck flanges:

1. Lower total cost of the flanged joint. The lap joint flange can be a lower grade than the stub end and pipe, cutting the total weight of high-grade alloy in the joint.

Example:

For an SS316 pipe, instead of a full 316 welding neck flange, a combination of an SS316 stub end and a carbon steel lap joint flange does the same job. The total weight of SS316 drops, and so does the cost.

Stub ends minimize high-grade material weight across stainless, duplex, and nickel alloy piping. The larger the diameter and pressure class, the greater the savings.

2. Easier flange installation. The lap joint flange rotates freely on the pipe, simplifying bolt-hole alignment with the mating flange.

Beyond these two primary reasons, the stub end / lap joint arrangement offers additional practical gains:

Advantage	Detail
Simplified maintenance	The flange slips off without cutting pipe. No hot work permit needed just to remove a flange for inspection, saving time and labor.
Weight reduction	Stub ends weigh less than weld neck flanges of the same NPS and class, a real factor on offshore platforms, pipe racks, and suspended systems.
Material match at the seal face	The sealing surface is the same alloy as the pipe, so corrosion resistance at the gasket contact zone matches the rest of the system.
Thermal expansion tolerance	The lap joint flange can slide slightly over the stub end, absorbing pipe movement without concentrating stress at the joint.
Reduced leak risk	Because the seal face alloy matches the pipe, gasket compatibility and corrosion resistance stay consistent across the joint.

Applicable Specifications

Stub ends are manufactured and inspected against several overlapping codes and standards:

ASME Standards

ASME B16.9 covers factory-made wrought buttwelding fittings from NPS 1/2 through NPS 48 (DN 15 through DN 1200). It defines dimensions, tolerances, and material requirements for stub ends. ASME B16.5, while focused on flanges, includes provisions for stub end use with lap joint flanges across pressure classes.

MSS Standards

MSS SP-43, “Wrought and Fabricated Butt-Welding Fittings for Low Pressure, Corrosion Resistant Applications,” supplements the ASME standards. It details dimensions and requirements for stainless steel and alloy stub ends in Types A, B, and C, aimed at corrosion-resistant, lower-pressure service.

International Standards

ISO 15590-3 covers fittings for petroleum and natural gas pipeline transportation systems, including stub ends.

Industry-Specific Standards

Petroleum, chemical, and pharmaceutical sectors often impose project specifications that go beyond the general codes, particularly for exotic alloys, elevated temperatures, or cyclic-pressure service.

ASA/ANSI VS. MSS Stub Ends

ASA (American Standards Association) was the predecessor of ANSI (American National Standards Institute). The term ASA still appears in legacy specifications, but both refer to the same lineage of standards.

ASA (ANSI) Stub Ends

ASA (ANSI) stub ends follow the dimensional requirements of ANSI B16.9 for factory-made wrought buttwelding fittings. They cover both seamless and welded construction, in multiple materials and sizes, for use with lap joint flanges. These are the general-purpose stub ends found across most piping systems.

MSS Stub Ends

MSS stub ends follow MSS SP-43, which focuses on lightweight stainless steel buttwelding fittings. SP-43 defines Types A, B, and C, with an emphasis on corrosion-resistant service at moderate pressures.

Key Differences

Aspect	ASA/ANSI Stub Ends	MSS Stub Ends
Scope	Broad: multiple industries, materials, and pressure ratings	Focused on stainless steel and alloys for corrosion-resistant, lower-pressure service
Type designations	Covers a range of designs without explicit A/B/C type labels	Explicitly defines Types A, B, and C with distinct geometry for each
Typical selection driver	Standard piping systems, higher-pressure service	Corrosion resistance, lighter wall thickness, cost optimization on alloy piping

The choice between ASA/ANSI and MSS stub ends depends on the piping specification, required material, pressure-temperature rating, and project code compliance.

Stub End Types

Stub ends are available in three types, named “A”, “B”, and “C”.

Each type has a distinct hub and lap geometry that suits different piping conditions.

Stub End “Type A”

Type A is the most common stub end configuration and handles the widest range of service conditions.

The hub has a long, tapered profile with a curved radius matching the pipe bore. This gradual transition minimizes turbulence and erosion at the joint. The taper accommodates a range of pipe wall thicknesses, and the overall geometry closely mimics the flow path through a weld neck flange.

Type A stub ends are manufactured in carbon steel, stainless steel, duplex, and nickel alloys to match pipeline requirements. Dimensions follow ASME B16.9, guaranteeing compatibility with standard lap joint flanges.

During installation, the straight end of the stub end is butt-welded to the pipe with the flared end (the lap) precisely aligned to the pipe terminus. The lap joint flange then slips over and seats against the back of the flare. When bolted to the mating flange, the assembly compresses the flare to create the seal.

Characteristic	Type A Detail
Flow path	Smooth tapered transition, comparable to a weld neck flange
Flange rotation	Full 360-degree rotation for bolt-hole alignment
Maintenance access	Flange removes without cutting welds
Cost position	Economical when the flange can be a lower-grade material
Pressure range	Suitable for both low- and high-pressure service

Stub End “Type B” (MSS SP-43 Type B)

Type B has a squared-off lap instead of a tapered hub. The flat lap face sits flush against the back face of the lap joint flange, and the OD of the lap matches the pipe OD directly.

The welding end of a Type B stub end typically has a thinner wall than a Type A, because Type B targets lighter pipe schedules (Sch 5S, 10S). Dimensions follow MSS SP-43. Materials include carbon steel, stainless steel, and alloys, selected to match the pipeline.

Installation mirrors Type A: the stub end is butt-welded to the pipe with the squared lap facing outward, then the lap joint flange slides over and bolts up.

Characteristic	Type B Detail
Lap geometry	Squared-off, flush face
Wall thickness	Thinner, matched to lighter pipe schedules
Fabrication	Simpler geometry, lower manufacturing cost
Typical service	Lower pressure and temperature, water treatment, chemical processing, general industrial
Pressure/temperature limits	Not suited for demanding high-pressure or high-temperature service

Verify that the stub end material and dimensions are compatible with both the pipe schedule and the process fluid before specifying Type B.

Stub End “Type C” (Lap-Joint/Slip-On Flanges)

Type C uses a separate lap collar that is independent of the stub end body. The stub end itself has a straight-cut terminus where the collar sits. This two-piece construction allows the collar position to be adjusted along the stub end length before final assembly.

Materials follow the same options as Types A and B. Because of the adjustable collar, dimensions can be tailored to non-standard piping layouts.

Installation follows the same butt-weld procedure for the stub end body. The separate collar is then slid into position, and the lap joint flange seats against it. When bolted, the flange compresses the collar to form the seal.

Characteristic	Type C Detail
Collar	Separate piece, adjustable position
Best use case	Systems requiring precise alignment or non-standard configurations
Maintenance	Same easy disassembly as Types A and B
Customization	Collar and stub end can be tailored independently
Lead time and cost	Typically longer lead time and higher cost than Types A or B due to the two-piece construction

Confirm that the collar and stub end are fully compatible with the lap joint flange dimensions and meet the applicable project specification.

Differences Between Stub End Type A, B, C

The main differences between stub end Type A, B, and C revolve around their design features, compatibility with various flange types, and specific applications:

Feature	Type A	Type B	Type C
Geometry	Long tapered hub; smooth flow transition	Squared-off lap; aligns with backing flange face	Separate lap/collar; adjustable fit
Flange Compatibility	Wide range of flange sizes	Lap joint flanges for lighter pipe schedules	Adjustable with lap joint flanges for unique configurations
Application	Versatile; various industries and piping schedules	Lighter pipes; less demanding conditions	Precise alignment; challenging piping configurations
Installation	Tapered hub accommodates a range of piping schedules	Simplified fabrication; specific dimensional compatibility	Lap collar positioned independently for alignment flexibility
Pipe Schedules	Wide range of wall thicknesses	Lighter schedules	Customizable

Short vs. Long Pattern Stub Ends

Short pattern and long pattern stub ends differ in overall length, which affects flow transition and the types of systems they fit.

Short pattern (MSS) and long pattern stub ends (ASA)

Short Pattern (MSS)

Short pattern stub ends have a compact body length. They pair with standard lap joint flanges and work well where axial space is tight. The shorter hub does not provide the same gradual flow transition as the long pattern, so they are most common in moderate-pressure, moderate-temperature service with slip-on or lap joint flanges.

Long Pattern (ASA/ANSI)

Long pattern stub ends have an extended hub that creates a smoother flow transition from pipe to flange face, closely approximating the hydraulic profile of a weld neck flange. This makes them the better choice for high-pressure, high-temperature, or erosion-sensitive service. They pair with lap joint flanges where the system needs the alignment flexibility of a lap joint but the flow performance of a welding neck.

Selection Guidance

Factor	Short Pattern (MSS)	Long Pattern (ASA/ANSI)
Available space	Tight layouts, close-coupled flanges	Standard or generous layout spacing
Flow sensitivity	Moderate; acceptable turbulence at the joint	Low turbulence, smooth transition
Pressure/temperature	Low to moderate	Moderate to high
Maintenance frequency	Either pattern allows equal flange access	Either pattern allows equal flange access

Choose the pattern based on the project piping specification, available space, and the pressure-temperature-erosion demands of the service.

End Types for Stub Ends

Stub ends can be ordered with different end finishes depending on the connection method:

Beveled Ends

Beveled ends have an angled cut (typically 30 or 37.5 degrees) at the welding end, matching the pipe bevel for full-penetration butt welds. This is the standard end type for most piping systems, especially in high-pressure service where weld integrity matters most.

Squared Ends

Squared ends are cut flat across, creating a perpendicular face. They are used where the stub end butts against a flat surface or another squared end. This simpler preparation works for socket-type or fillet-weld connections and for lighter-duty fabrication.

Flanged Ends

Flanged end stub ends have an integral flange forged or machined as part of the fitting, allowing a bolted connection without a separate lap joint flange. This configuration suits systems requiring frequent dismantling for inspection or cleaning.

Grooved Ends

Grooved ends have a machined circumferential groove that accepts a grooved coupling or gasket. These stub ends connect into grooved piping systems, providing fast assembly and disassembly at moderate pressures. Fire protection systems and commercial HVAC installations commonly use this end type.

Threaded Ends (Male Only)

Threaded end stub ends carry male threads for engagement with female-threaded valves, fittings, or pipe. They allow assembly and disassembly without welding and suit low- to moderate-pressure systems where threaded connections are specified.

Stub End Materials

The buttweld fittings material specifications apply also to stub ends.

The table summarizes the most common carbon, stainless, duplex, and nickel-alloy grades. Note that other materials may be used to manufacture stub ends, namely Cupronickel, Titanium, and Copper.

For details about the chemical composition and mechanical properties of BW fittings, please consult this article.

ASTM Materials for Stub Ends	Grade	UNS Equivalent
Carbon Steel[ASTM A234 WPB]	WPA/WPB/WPC	K03006
Stainless Steel[ASTM A403]	304/304L	S30403
	304H	S30409
	316/316L	S31603
	316H	S31609
	317L	S31703
	904L	N08904
	309S/H	S30908
	310S	S31008
	321	S32100
	6XN	N08367
	20CB	N08020
	347	S34709
	254SMO	S31254
Duplex /Super Duplex[ASTM A815]	2205	S31803/S32205
	Zeron 100	S32760
	2507	S32750
	410	S41000
Nickel Alloys[ASTM A366 - replaced by ASTM A462]	HC22	N06022
	HB-3	N10675
	HG3	N06985
	HX	N06002
	HC2000	N06200
	HC276	N10276
	NCI	N06600
	NC	N04400
	N	N02200
	NL	N02201
	NCMC	N06625
	NICMC	N08825
	NIC10	N08810
	NIC11	N08811

Stub Ends Dimensions

The charts below show the MSS and ANSI stub end dimensions in inches.

Stub End Length and Lap Dimensions

NPS	MSS Stub End	ANSI Stub End	Pipe OD	Lap OD	Radius
1/2	2	3	0.84	1.35-1.38	1/8
3/4	2	3	1.05	1.66-1.69	1/8
1	2	4	1.315	1.7-2	1/8
1 1/4	2	4	1.66	2.47-2.5	3/16
1 1/2	2	4	1.9	2.85-2.88	1/4
2	2.5	6	2.375	3.59-3.62	5/16
2 1/2	2.5	6	2.875	3.9-4.12	5/16
3	2.5	6	3.5	4.97-5	3/8
3 1/2	3	6	4	5.47-5.5	3/8
4	3	6	4.5	6.16-6.19	7/16
5	3	8	5.563	7.28-7.31	7/16
6	3.5	8	6.625	8.47-8.5	1/2
8	4	8	8.625	10.59-10.62	1/2
10	5	10	10.75	12.69-12.75	1/2
12	6	10	12.75	14.94-15	1/2
14	6	12	14	16.19-16.25	1/2
16	6	12	16	18.44-18.5	1/2
18	6	12	18	20.94-21	1/2
20	6	12	20	22.94-23	1/2
24	6	12	24	27.19-27.25	1/2
26	6	12	26	29.19-29.25	1/2
28	6	12	28	31.69-31.75	1/2
30	6	12	30	33.69-33.75	1/2
32	6	12	32	35.94-36	1/2
34	6	12	34	37.94-38	1/2
36	6	12	36	40.19-40.25	1/2
38	6	12	38	42.69-42.75	1/2
40	6	12	40	44.69-44.75	1/2
42	6	12	42	46.94-47	1/2
44	6	12	44	49.19-49.25	1/2
46	6	12	46	51.19-51.25	1/2
48	6	12	48	53.19-53.25	1/2
50	6	12	50	55.19-55.25	1/2
52	6	12	52	57.19-57.25	1/2
54	6	12	54	59.44-59.5	1/2
60	6	12	60	65.44-65.5	1/2

Pipe Wall Thickness and Flange Thickness by Schedule

NPS	Sch	Pipe WT (Nom)	Flange thk (Min-Max)
1/2	05S	0.065	0.065-0.127
1/2	10S	0.083	0.083-0.145
1/2	40S	0.109	0.109-0.171
1/2	80S	0.147	0.147-0.209
3/4	05S	0.065	0.065-0.127
3/4	10S	0.083	0.083-0.145
3/4	40S	0.113	0.113-0.175
3/4	80S	0.154	0.154-0.216
1	05S	0.065	0.065-0.127
1	10S	0.109	0.109-0.171
1	40S	0.133	0.133-0.195
1	80S	0.179	0.179-0.241
1 1/4	05S	0.065	0.065-0.127
1 1/4	10S	0.109	0.109-0.171
1 1/4	40S	0.14	0.14-0.202
1 1/4	80S	0.191	0.191-0.253
1 1/2	05S	0.065	0.065-0.127
1 1/2	10S	0.109	0.109-0.171
1 1/2	40S	0.145	0.145-0.207
1 1/2	80S	0.2	0.2-0.262
2	05S	0.065	0.065-0.127
2	10S	0.109	0.109-0.171
2	40S	0.154	0.154-0.216
2	80S	0.218	0.218-0.28
2 1/2	05S	0.083	0.083-0.145
2 1/2	10S	0.12	0.12-0.182
2 1/2	40S	0.203	0.203-0.265
2 1/2	80S	0.276	0.276-0.338
3	05S	0.083	0.083-0.145
3	10S	0.12	0.12-0.182
3	40S	0.216	0.216-0.278
3	80S	0.3	0.3-0.362
3 1/2	05S	0.083	0.083-0.145
3 1/2	10S	0.12	0.12-0.182
3 1/2	40S	0.226	0.226-0.238
3 1/2	80S	0.318	0.318-0.38
4	05S	0.083	0.083-0.145
4	10S	0.12	0.12-0.182
4	40S	0.237	0.237-0.299
4	80S	0.337	0.337-0.399
5	05S	0.109	0.109-0.171
5	10S	0.134	0.134-0.196
5	40S	0.258	0.258-0.32
5	80S	0.375	0.375-0.437
6	05S	0.109	0.109-0.171
6	10S	0.134	0.134-0.196
6	40S	0.28	0.28-0.342
6	80S	0.432	0.432-0.494
8	05S	0.109	0.109-0.171
8	10S	0.148	0.148-0.21
8	40S	0.322	0.322-0.384
8	80S	0.5	0.5-0.562
10	05S	0.134	0.134-0.196
10	10S	0.165	0.165-0.227
10	40S	0.365	0.365-0.427
10	80S	0.5	0.5-0.562
12	05S	0.156	0.156-0.218
12	10S	0.18	0.18-0.242
12	40S	0.375	0.375-0.437
12	80S	0.5	0.5-0.562
14	05S	0.156	0.156-0.218
14	10S	0.188	0.188-0.25
14	40S	0.375	0.375-0.437
14	80S	0.5	0.5-0.562
16	05S	0.165	0.165-0.227
16	10S	0.188	0.188-0.25
16	40S	0.375	0.375-0.437
16	80S	0.5	0.5-0.562
18	05S	0.165	0.165-0.227
18	10S	0.188	0.188-0.25
18	40S	0.375	0.375-0.437
18	80S	0.5	0.5-0.562
20	05S	0.188	0.188-0.25
20	10S	0.218	0.218-0.28
20	40S	0.375	0.375-0.437
20	80S	0.5	0.5-0.562
24	05S	0.218	0.218-0.28
24	10S	0.25	0.25-0.312
24	40S	0.375	0.375-0.437
24	80S	0.5	0.5-0.562
26-60	40S	0.375	0.375-0.437
26-60	80S	0.5	0.5-0.562

Pro Tip

For duplex and super duplex piping, stub ends with lap joint flanges can cut material costs by 40-60% compared to full duplex weld neck flanges. The lap joint flange never contacts the process fluid, so it can be carbon steel or standard stainless. The cost savings scale with flange size and pressure class.

Common Mistake

Using stub ends without verifying the lap joint flange bore is compatible. Lap joint flanges are available in different bore sizes (Schedule 10, Schedule 40, etc.) - if the flange bore is too small for the stub end’s OD, the flange won’t slide over it. Check both the stub end OD and flange bore before ordering.

Field Note

When rotating lap joint flanges to align bolt holes, support the pipe weight independently. The stub end alone shouldn’t carry the hanging load of the piping - the stub-end-to-flange interface isn’t designed for shear stress. Use temporary supports or pipe stands during alignment, then tighten bolts evenly.

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