LAP JOINT FLANGE

Lap joint flanges feature a flat face and are always used in conjunction with a stub end.

Lap joint flanges resemble, in shape, slip-on flanges except for the radius at the crossing of the flange face and the bore to accommodate the flanged portion of the stub end.

A lap joint flange slips over the pipe and seats on the back of the stub end and the two are kept together by the pressure of the bolts.

The use of lap joint flanges in combination with stub ends is a cost-effective solution for stainless steel or nickel alloy pipelines, as the material of the lap joint flange can be of a lower grade (generally carbon steel) than the material of the stub end (which has to match the pipe grade, as in contact with the conveyed fluid).

Lap flange is having two components, a stub end, and a loose backing flange. Stub end is butt-welded to the pipe and Backing flange freely moves over the pipe. The backing flange can be of a different material than stub material and normally of the carbon steel to save the cost. Lap flange is used where frequent dismantling is required, and space is constrained.

The backing flange can be of a different material than stub material and normally of the carbon steel to save the cost.
This flange provides better joining due to butt-weld as compared to a socket and threaded type flanges
Not suitable for small size, Costly components, and fabrication as compared to threaded, slip-on, and socket flange.
Lap flange provides connection flexibility as you can freely rotate the flange on the pipe. It is used where frequent dismantling is required, and space is constrained.

Lap Flange Cross section with weld detail

Lap Joint flange dimensions are covered in ASME B16.5 – which covers Pipe Flanges and Flanged Fittings for size NPS ½” to 24” for above NPS 26” to 60” it should be as per ASME B16.47.

During a dimensional inspection of a lap flange, you should check for

Outer & Inner Diameter of body
Bolt Circle & Bolt hole Diameter
Length of the Hub
Straightness and alignment of the bolt hole

Class 150 Lap Joint Flange Dimensions

Size in Inch	Size in mm	Outer Dia.	Flange Thick.	RF Dia.	RF Height	PCD	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
		A	B	C	D	E
1/2	15	135	30.2	34.9	7	88.9	4	3/4	120	7/8	M20	3.2
3/4	20	140	31.8	42.9	7	95.2	4	3/4	125	7/8	M20	3.7
1	25	160	35	50.8	7	108	4	7/8	140	1	M24	5
1 1/4	32	185	38.1	63.5	7	130.2	4	1	150	1 1/8	M27	7.8
1 1/2	40	205	44.5	73	7	146	4	1 1/8	170	1 1/4	M30	10.5
2	50	235	50.9	92.1	7	171.4	8	1	180	1 1/8	M27	18
2 1/2	65	265	57.2	104.8	7	196.8	8	1 1/8	195	1 1/4	M30	25.5
3	80	305	66.7	127	7	228.6	8	1 1/4	220	1 3/8	M33	39
4	100	355	76.2	157.2	7	273	8	1 1/2	255	1 5/8	M39	61.5
5	125	420	92.1	185.7	7	323.8	8	1 3/4	300	1 7/8	M45	102
6	150	485	108	215.9	7	368.3	8	2	345	2 1/8	M52	157
8	200	550	127	269.9	7	438.2	12	2	380	2 1/8	M52	241
10	250	675	165.1	323.8	7	539.8	12	2 1/2	490	2 5/8	M64	470
12	300	760	184.2	381	7	619.1	12	2 3/4	540	2 7/8	M72	575

Class 300 Lap Joint Flange Dimensions

Size in Inch	Size in mm	Outer Diameter	Flange Thick.	Lapped Thick.	Lapped ID	PCD	Lapped Thick.	Lapped Radius	No of Bolts	Bolt Size UNC	Machine Bolt Length	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
		A	B	C	D	E	G
1/2	15	95	38	22	22.9	66.7	14.3	3	4	1/2	55	65	5/8	M14	1.2
3/4	20	115	48	25	28.2	82.6	15.9	3	4	5/8	65	75	3/4	M16	1.4
1	25	125	54	27	34.9	88.9	17.5	3	4	5/8	65	75	3/4	M16	1.4
1 1/4	32	135	64	27	43.7	98.4	19.1	5	4	5/8	70	85	3/4	M16	1.8
1 1/2	40	155	70	30	50	114.3	20.7	6	4	3/4	75	90	7/8	M20	2.7
2	50	165	84	33	62.5	127	22.3	8	8	5/8	75	90	3/4	M16	3.2
2 1/2	65	190	100	38	75.4	149.2	25.4	8	8	3/4	85	100	7/8	M20	4.6
3	80	210	117	43	91.4	168.3	28.6	10	8	3/4	90	110	7/8	M20	5.9
3 1/2	90	230	133	44	104.1	184.2	30.2	11	8	3/4	95	110	7/8	M20	7.7
4	100	255	146	48	116.8	200	31.8	11	8	3/4	95	115	7/8	M20	10
5	125	280	178	51	144.4	235	35	11	8	3/4	110	120	7/8	M20	12.7
6	150	320	206	52	171.4	269.9	36.6	13	12	3/4	110	120	7/8	M20	17.7
8	200	380	260	62	222.2	330.2	41.3	13	12	7/8	120	140	1	M24	26
10	250	445	321	95	277.4	387.4	47.7	13	16	1	140	160	1 1/8	M27	36
12	300	520	375	102	328.2	450.8	50.8	13	16	1 1/8	145	170	1 1/4	M30	52
14	350	585	425	111	360.2	514.4	54	13	20	1 1/8	160	180	1 1/4	M30	75
16	400	650	483	121	411.2	571.5	57.2	13	20	1 1/4	165	190	1 3/8	M33	86
18	450	710	533	130	462.3	628.6	60.4	13	24	1 1/4	170	195	1 3/8	M33	113
20	500	775	587	140	514.4	685.8	63.5	13	24	1 1/4	185	205	1 3/8	M33	143
24	600	915	702	153	616	812.8	69.9	13	24	1 1/2	205	230	1 5/8	M39	216

Class 400 Lap Joint Flange Dimensions

Size in Inch	Size in mm	Outer Diameter	Flange Thick.	Lapped Thick.	Lapped ID	PCD	Lapped Thick.	Lapped Radius	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
		A	B	C	D	E	G
1/2	15	95	38	22	22.9	66.7	14.3	3	4	1/2	75	5/8	M14	1.3
3/4	20	115	48	25	28.2	82.6	15.9	3	4	5/8	90	3/4	M16	1.5
1	25	125	54	27	34.9	88.9	17.5	3	4	5/8	90	3/4	M16	1.8
1 1/4	32	135	64	29	43.7	98.4	20.7	5	4	5/8	95	3/4	M16	2.3
1 1/2	40	155	70	32	50	114.3	22.3	6	4	3/4	110	7/8	M20	3.2
2	50	165	84	37	62.5	127	25.4	8	8	5/8	110	3/4	M16	4.1
2 1/2	65	190	100	41	75.4	149.2	28.6	8	8	3/4	120	7/8	M20	5.9
3	80	210	117	46	91.4	168.3	31.8	10	8	3/4	125	7/8	M20	7.3
3 1/2	90	230	133	49	104.1	184.2	35	10	8	7/8	140	1	M24	9.6
4	100	255	146	51	116.8	200	35	11	8	7/8	140	1	M24	11.8
5	125	280	178	54	144.5	235	38.1	11	8	7/8	145	1	M24	14.1
6	150	320	206	57	171.4	269.9	41.3	13	12	7/8	150	1	M24	20
8	200	380	260	68	222.2	330	47.7	13	12	1	170	1 1/8	M27	31
10	250	445	321	102	277.4	387.4	54	13	16	1 1/8	190	1 1/4	M30	42
12	300	520	375	108	328.2	450.8	57.2	13	16	1 1/4	205	1 3/8	M33	59
14	350	585	425	117	360.2	514.4	60.4	13	20	1 1/4	210	1 3/8	M33	82
16	400	650	483	127	411.2	571.5	63.5	13	20	1 3/8	220	1 1/2	M36	107
18	450	710	533	137	462.3	628.6	66.7	13	24	1 3/8	230	1 1/2	M36	130
20	500	775	587	146	514.4	685.8	69.9	13	24	1 1/2	240	1 3/4	M39	157
24	600	915	702	159	616	812.8	76.2	13	24	1 3/4	265	1 7/8	M45	232

Class 600 Lap Joint Flange Dimensions

Size in Inch	Size in mm	Outer Diameter	Flange Thick.	Lapped Thick.	Lapped ID	PCD	Lapped Thick.	Lapped Radius	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
		A	B	C	D	E	G
1/2	15	95	38	22	22.9	66.7	14.3	3	4	1/2	75	5/8	M14	1.3
3/4	20	115	48	25	28.2	82.6	15.9	3	4	5/8	90	3/4	M16	1.4
1	25	125	54	27	34.9	88.9	17.5	3	4	5/8	90	3/4	M16	1.8
1 1/4	32	135	64	29	43.7	98.4	20.7	5	4	5/8	95	3/4	M16	2.3
1 1/2	40	155	70	32	50	114.3	22.3	6	4	3/4	110	7/8	M20	3.2
2	50	165	84	37	62.5	127	25.4	8	8	5/8	110	3/4	M16	4.1
2 1/2	65	190	100	41	75.4	149.2	28.6	8	8	3/4	120	7/8	M20	5.9
3	80	210	117	46	91.4	168.3	31.8	10	8	3/4	125	7/8	M20	7.3
3 1/2	90	230	133	49	104.1	184.2	35	11	8	7/8	140	1	M24	9.6
4	100	275	152	54	116.8	215.9	38.1	11	8	7/8	145	1	M24	16.8
5	125	330	189	60	144.4	266.7	44.5	11	8	1	165	1 1/8	M27	29
6	150	355	222	67	171.4	292.1	47.7	13	12	1	170	1 1/8	M27	36
8	200	420	273	76	222.2	349.2	55.6	13	12	1 1/8	190	1 1/4	M30	52
10	250	510	343	111	277.4	431.8	63.5	13	16	1 1/4	215	1 3/8	M33	77
12	300	560	400	117	328.2	489	66.7	13	20	1 1/4	220	1 3/8	M33	91
14	350	605	432	127	360.2	527	69.9	13	20	1 3/8	235	1 1/2	M36	105
16	400	685	495	140	411.2	603.2	76.2	13	20	1 1/2	255	1 5/8	M39	150
18	450	745	546	152	462.3	654	82.6	13	20	1 5/8	275	1 3/4	M42	182
20	500	815	610	165	514.4	723.9	88.9	13	24	1 5/8	285	1 3/4	M42	232
24	600	940	718	184	616	838.2	101.6	13	24	1 7/8	330	2	M48	332

Class 900 Lap Joint Flange Dimensions

Size in Inch	Size in mm	Outer Diameter	Flange Thick.	Lapped Thick.	Lapped ID	PCD	Lapped Thick.	Lapped Radius	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
		A	B	C	D	E	G
1/2	15	120	38	32	22.9	82.6	22.3	3	4	3/4	110	7/8	M20	1.8
3/4	20	130	44	35	28.2	88.9	25.4	3	4	3/4	115	7/8	M20	2.3
1	25	150	52	41	34.9	101.6	28.6	3	4	7/8	125	1	M24	3.6
1 1/4	32	160	64	41	43.7	111.1	28.6	5	4	7/8	125	1	M24	4.1
1 1/2	40	180	70	44	50	123.8	31.8	6	4	1	140	1 1/8	M27	5.5
2	50	215	105	57	62.5	165.1	38.1	8	8	7/8	145	1	M24	11.5
2 1/2	65	245	124	64	75.4	190.5	41.3	8	8	1	160	1 1/8	M27	16.5
3	80	240	127	54	91.4	190.5	38.1	10	8	7/8	145	1	M24	12
4	100	290	159	70	116.8	235	44.5	11	8	1 1/8	170	1 1/4	M30	24
5	125	350	190	79	144.4	279.4	50.8	11	8	1 1/4	190	1 3/8	M33	38
6	150	380	235	86	171.4	317.5	55.6	13	12	1 1/8	190	1 1/4	M30	50
8	200	470	298	114	222.2	393.7	63.5	13	12	1 3/8	220	1 1/2	M36	78
10	250	545	368	127	277.4	469.9	69.9	13	16	1 3/8	235	1 1/2	M36	112
12	300	610	419	143	328.2	533.4	79.4	13	20	1 3/8	255	1 1/2	M36	148
14	350	640	451	156	360.2	558.8	85.8	13	20	1 1/2	275	1 5/8	M39	182
16	400	705	508	165	411.2	616	88.9	13	20	1 5/8	285	1 3/4	M42	193
18	450	785	565	190	462.3	685.8	101.6	13	20	1 7/8	325	2	M48	258
20	500	855	622	210	514.4	749.3	108	13	20	2	350	2 1/8	M52	317
24	600	1040	749	267	616	901.7	139.7	13	20	2 1/2	440	2 5/8	M64	608

Class 1500 Lap Joint Flange Dimensions

Size in Inch	Size in mm	Outer Diameter	Flange Thick.	Lapped Thick.	Lapped ID	PCD	Lapped Thick.	Lapped Radius	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
		A	B	C	D	E	G
1/2	15	120	38	32	22.9	82.6	22.3	3	4	3/4	110	7/8	M20	1.8
3/4	20	130	44	35	28.2	88.9	25.4	3	4	3/4	115	7/8	M20	2.3
1	25	150	52	41	34.9	101.6	28.6	3	4	7/8	125	1	M24	3.7
1 1/4	32	160	64	41	43.7	111.1	28.6	5	4	7/8	125	1	M24	4.1
1 1/2	40	180	70	44	50	123.8	31.8	6	4	1	140	1 1/8	M27	5.5
2	50	215	105	57	62.5	165.1	38.1	8	8	7/8	145	1	M24	9.8
2 1/2	65	245	124	64	75.4	190.5	41.3	8	8	1	160	1 1/8	M27	16.4
3	80	265	133	73	91.4	203.2	47.7	10	8	1 1/8	180	1 1/4	M30	21.8
4	100	310	162	90	116.8	241.3	54	11	8	1 1/4	195	1 3/8	M33	33
5	125	375	197	105	144.4	292.1	73.1	11	8	1 1/2	250	1 5/8	M39	59
6	150	395	229	119	171.4	317.5	82.6	13	12	1 3/8	260	1 1/2	M36	75
8	200	485	292	143	222.2	393.7	92.1	13	12	1 5/8	290	1 3/4	M42	118
10	250	585	368	178	277.4	482.6	108	13	12	1 7/8	335	2	M48	198
12	300	675	451	219	328.2	571.5	123.9	13	16	2	375	2 1/8	M52	264
14	350	750	495	241	360.2	635	133.4	13	16	2 1/4	405	2 3/8	M56	341
16	400	825	552	260	411.2	704.8	146.1	13	16	2 1/2	445	2 5/8	M64	454
18	450	915	597	276	462.3	774.7	162	13	16	2 3/4	495	2 7/8	M72	590
20	500	985	641	292	514.4	831.8	177.8	13	16	3	540	3 1/8	M76	792
24	600	1170	762	330	616	990.6	203.2	13	16	3 1/2	615	3 5/8	M90	1248

Class 2500 Lap Joint Flange Dimensions

Size in Inch	Size in mm	Outer Diameter	Flange Thick.	Lapped Thick.	Lapped ID	PCD	Lapped Thick.	Lapped Radius	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
		A	B	C	D	E	G
1/2	15	135	43	40	22.9	88.9	30.2	3	4	3/4	120	7/8	M20	3.2
3/4	20	140	51	43	28.2	95.2	31.8	3	4	3/4	125	7/8	M20	3.7
1	25	160	57	48	34.9	108	35	3	4	7/8	140	1	M24	5
1 1/4	32	185	73	52	43.7	130.2	38.1	5	4	1	150	1 1/8	M27	7.5
1 1/2	40	205	79	60	50	146	44.5	6	4	1 1/8	170	1 1/4	M30	10
2	50	235	95	70	62.5	171.4	50.9	8	8	1	180	1 1/8	M27	17.5
2 1/2	65	265	114	79	75.4	196.8	57.2	8	8	1 1/8	195	1 1/4	M30	23
3	80	305	133	92	91.4	228.6	66.7	10	8	1 1/4	220	1 3/8	M33	37.8
4	100	355	165	108	116.8	273	76.2	11	8	1 1/2	255	1 5/8	M39	57
5	125	420	203	130	144.4	323.8	92.1	11	8	1 3/4	300	1 7/8	M45	95
6	150	485	235	152	171.4	368.3	108	13	8	2	345	2 1/8	M52	148
8	200	550	305	178	222.2	438.2	127	13	12	2	380	2 1/8	M52	221
10	250	675	375	229	277.4	539.8	165.1	13	12	2 1/2	490	2 5/8	M64	425
12	300	760	441	254	328.2	619.1	184.2	13	12	2 3/4	540	2 7/8	M72	500