ASME B16.9 Lap Joint Stub End Dimensions

This article is a comprehensive, technically accurate reference for the standard dimensions of Lap Joint Stub Ends (Type A and Type B) as defined in ASME B16.9.

What is Lap Joint Stub End?

Lap joint stub end is a popular fitting used with Lap Joint Flange to form a rotatable, low-cost flanged joint. The stub end is butt-welded to the pipe, while the loose backing flange provides bolting.

ASME B16.9 has two main types:

Type A: Designed for use with standard lap joint flanges. Requires a specific radius and lap thickness to match the flange.

Type B: Designed for use with slip-on flanges. Slightly different radius and lap configuration.

MSS SP-43 additionally defines short pattern stub ends, commonly used in lighter-weight stainless systems, but this article focuses exclusively on ASME B16.9 Long Pattern Type A and Type B.

ASME B16.9 Lap Joint Stub End Parameters

The standard specifies the following critical dimensions:

NPS – Nominal Pipe Size (½″ through 48″).

Outside Diameter of Barrel (G)—Two tolerances: ±1.6 mm for NPS ≤ 18″, ±3.2 mm for NPS ≥ 20″.

Overall Length (F)—Long Pattern length (varies by size and schedule).

Lap Diameter (G)—The raised face diameter that contacts the backing flange.

Radius of Lap (R)—Type A: 0.8 mm (1/32″); Type B: 3.2 mm (1/8″) typical.

Lap Thickness (T)—Minimum thickness before welding.

Fillet Radius (r)—On the ID at the weld end.

ASME B16.9 Lap Joint Stub End Dimensions

Nominal Pipe  Size(NPS)	DN	Outside Diameter of Barrel		Long Pattern Length, F [Notes (3), (4)]	Short Pattern Length, F [Notes (3), (4)]	Radius of Fillet, R  [Note (5)]	Diameter of Lap, G  [Note (6)]
		Max.	Min.
1/2	15	22.8	20.5	76	51	3	35
3/4	20	28.1	25.9	76	51	3	43
1	25	35.0	32.6	102	51	3	51
1 1/4	32	43.6	41.4	102	51	5	64
1 1/2	40	49.9	47.5	102	51	6	73
2	50	62.4	59.5	152	64	8	92
2 1/2	65	75.3	72.2	152	64	8	106
3	80	91.3	88.1	152	64	10	127
3 1/2	90	104.0	100.8	152	76	10	140
4	100	116.7	113.5	152	76	11	157
5	125	144.3	140.5	203	76	11	185
6	150	171.3	167.5	203	89	13	218
8	200	222.1	218.3	203	102	13	270
10	250	277.2	272.3	254	127	13	324
12	300	328.0	323.1	254	152	13	381
14	350	359.9	354.8	305	152	13	413
16	400	411.0	405.6	305	152	13	470
18	450	462	456	305	152	13	533
20	500	514	507	305	152	13	584
22	550	565	558	305	152	13	641
24	600	616	609	305	152	13	692

GENERAL NOTES: All dimensions are in millimeters.

Service conditions and joint construction often dictate stub end length requirements. Therefore, the purchaser must specify long or short pattern fitting when ordering.

NOTES:

Gasket face finish shall be in accordance with ASME B16.5 for raised face flanges.

The lap thickness T shall not be less than nominal pipe wall thickness.

When short pattern stub ends are used with larger flanges in Classes 300 and 600, (PN50 & PN110) and with most sizes in Classes 900 (PN150) and higher, and when long pattern stub ends are used with larger flanges in Classes 1500 and 2500, (PN260 AND PN420) it may be necessary to increase the length of the stub ends in order to avoid covering the weld with the flange. Such increases in length shall be a matter of agreement between the manufacturer and purchaser.

When special facings such as tongue and groove, male and female, etc., are employed, additional lap thickness must be provided and such additional thickness shall be in addition to (not included in) the basic length F.

These dimensions conform to the radius established for lap joint flanges in ASME B16.5, Pipe Flanges and Flanged Fittings.

This dimension conforms to standard machined facings shown in ASME B16.5. The back face of the lap shall be machined to conform to the surface on which it seats. Where ring joint facings are to be applied, use dimension K as given in ASME B16.5.

ASME B16.9 Lap Joint Stub End Dimensions – Long Pattern

NPS	OD of Barrel (G)	Length F (Type A & B)	Lap Diameter G (approx.)	Thickness T (min)	Radius R (Type A)	Radius R (Type B)	Fillet Radius r
1/2	21.3	76	35	3.7	0.8	3.2	3
3/4	26.7	76	43	3.9	0.8	3.2	3
1	33.4	102	51	4.6	0.8	3.2	3
1¼	42.2	102	64	4.9	0.8	3.2	5
1½	48.3	102	73	5.1	0.8	3.2	6
2	60.3	152	92	5.6	0.8	3.2	8
2½	73.0	152	105	7.0	0.8	3.2	8
3	88.9	152	127	7.6	0.8	3.2	10
4	114.3	152	157	8.6	0.8	3.2	11
5	141.3	203	186	9.7	0.8	3.2	11
6	168.3	203	216	10.9	0.8	3.2	13
8	219.1	203	270	12.7	0.8	3.2	13
10	273.0	254	324	12.7	0.8	3.2	13
12	323.8	254	381	12.7	0.8	3.2	13
14	355.6	305	413	12.7	0.8	3.2	13
16	406.4	305	470	12.7	0.8	3.2	13
18	457.0	305	533	12.7	0.8	3.2	13
20	508.0	305	584	12.7	0.8	3.2	13
24	610.0	305	692	12.7	0.8	3.2	13

Notes:

Dimensions are in millimeters (converted and rounded from original inch values as published).

Length F is the same for both Type A and Type B in the long pattern.

Wall thickness of the stub end barrel must match the connecting pipe schedule (Sch 5s, 10s, 40s, 80s, 160, XXS, etc.).

For NPS 26″ and larger, dimensions are covered by ASME B16.9 Section 12 (custom or engineered).

Material Grades Commonly We Supplied

Stainless Steel: 304/304L, 316/316L, 317L, 321, 347, 310S.

Duplex & Super Duplex: UNS S31803, S32205, S32750, S32760.

Nickel Alloys: Inconel 600, 625, 718; Incoloy 800/800H/825; Monel 400; Hastelloy C276, C22; Alloy 20.

ASME B16.9 Tolerances

Outside diameter at bevel: ±1.6 mm (NPS ≤18), ±3.2 mm (NPS ≥20).

Lap diameter: ±1.6 mm.

Lap thickness before welding: Not less than 87.5 % of nominal pipe wall.

Overall length F: ±3.2 mm.

Wall thickness: Minimum 87.5 % of pipe schedule.

Conclusion

Understanding exact ASME B16.9 Lap Joint Stub End dimensions is critical for correct flange selection. Always specify Type A or Type B depending on the flange standard you are mating with, and verify the schedule matches the pipe wall.

For quotations on stainless, duplex, or nickel alloy lap joint stub ends manufactured strictly to ASME B16.9, please contact our sales team.

We maintain ex-stock availability of most sizes in 316/316L, Duplex 2205, and Super Duplex 2507 long pattern stub ends, with rapid delivery worldwide.