Externally Pressurized (X-Flex) Pipe Expansion Joint

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Externally pressurized pipe expansion joints, also known as x-flex expansion joints, are suited for piping systems that require large amounts of axial compression or extension. In externally pressurized pipe expansion joints, the bellows elements are arranged so that the media flow is on the external surface of the bellows. Externally pressurizing the bellows eliminates pressure instability as a limitation to the design and permits the absorption of large amounts of axial expansion.

Overview

Externally pressurized pipe expansion joints, also known as X-Flex bellows expansion joints, are engineered for piping systems that require large axial compression or extension. Unlike conventional designs, the bellows elements in X-Flex joints are arranged in such a way so that the media is in contact with the external surface of the bellows, eliminating pressure instability (column squirm) as a design limitation. This configuration allows our expansion bellows to absorb significantly greater axial movement without compromising system integrity. At US Bellows, our X-Flex bellows flexible designs are custom-engineered to meet demanding operational requirements across high-pressure and high-temperature industrial applications, delivering reliable performance where standard expansion joints fall short.

Data Tables

150# Single X-Flex 3 Inch through 10 Inch
150# Single X-Flex 12 Inch through 24 Inch
300# Single X-Flex 3 Inch through 10 Inch
300# Single X-Flex 12 Inch through 24 Inch
150# Double X-Flex 3 Inch through 10 Inch
150# Double X-Flex 12 Inch through 24 Inch
300# Double X-Flex 3 Inch through 10 Inch
300# Double X-Flex 12 Inch through 24 Inch

Features

Eliminates pressure instability
Good for large axial compression or extension

Technical Information

Installation & Maintenance (Metallic Expansion Joints)
Metal Bellows Material
Types of Metallic Bellows Deflections
Bellows Expansion Joint Loads
How to Look for Signs of Expansion Joint Failure
View more Technical Information

FAQs

Q: What is an externally pressurized pipe expansion joint?
A: An externally pressurized bellow expansion joint has media flowing on the external bellows surface, eliminating pressure instability and enabling large axial movement absorption.

Q: When should an X-Flex expansion joint be used?
A: X-Flex bellow expansion joints are ideal when piping systems require large amounts of axial compression or extension beyond standard expansion joint capabilities.

Q: How does external pressurization improve bellows performance?
A: Pressurizing the bellows externally removes pressure instability (column squirm) as a design limitation, allowing the expansion bellow to absorb significantly greater axial movement reliably.

Q: Are X-Flex expansion joints suitable for high-pressure applications?
A: Yes, US Bellows engineers custom bellows flexible X-Flex solutions designed to perform reliably under demanding high-pressure and high-temperature industrial operating conditions.

How to Test an Expansion Joint?

How do metallic bellows function?

How to look for signs of expansion joint failure

View More FAQS

Case Studies

4/9/24: Custom Designed Externally Pressurized Expansion Joints for a Flare Header Application at a Mississippi Refinery

9/14/21: Externally Pressurized X-Flex Expansion Joints for a Overseas Facility

10/29/18: 36″ Dia. Externally Pressurized Expansion Joints Designed for a Power Plant in Venezuela

6/12/08: Fourteen Externally Pressurized Expansion Joints

1/11/02: Externally pressurized expansion joints for steam plant in Kent, Ohio

More Reading

150# Single X-Flex 3 Inch through 10 Inch
150# Single X-Flex 12 Inch through 24 Inch
300# Single X-Flex 3 Inch through 10 Inch
300# Single X-Flex 12 Inch through 24 Inch
150# Double X-Flex 3 Inch through 10 Inch
150# Double X-Flex 12 Inch through 24 Inch
300# Double X-Flex 3 Inch through 10 Inch
300# Double X-Flex 12 Inch through 24 Inch

View PDF

Notes:

Rated life cycle at 650°F is 1000 cycles for full rated movement shown above.
To increase cycle life or movements, please refer to graph on cycle life.
Expansion joint is capable of taking 10% of rated movement as extension, with remaining 90% as axial compression.
Maximum test pressure: 1.5 X rated working pressure.
Bellows rated for 650°F: See catalog flange data for appropriate flange temperature/pressure ratings.
Maximum installation misalignment is ±1/4-inch axial and ±1/16-inch lateral.

Size	Axial Movement	Spring Rate	Overall Length	Weight		Effective Area	Shell Outside Diameter	Anchor Foot Height	Anchor Foot Type
				Weight
				Flanged Ends	Weld Ends


	in.	lb./in.	in.	lb.	lb.	in. 2	in.	in.
	mm	kg/mm	mm	kg	kg	kg/cm 2	mm	mm
3	4	140	24	81	65	30.24	8.625	Please consult factory regarding anchor foot usage on single X-flex
	102	2.5	610	37	30	195.05	219
	8	70	40	120	104	30.24	8.625
	203	1.3	1016	55	47	195.05	219
4	4	140	25	94	68	30.24	8.625
	102	2.5	635	43	31	195.05	219
	8	70	42	130	104	30.24	8.625
	203	1.3	1067	59	47	195.05	219
5	4	328	28	153	123	53.85	10.75
	102	5.9	711	70	56	347.33	273
	8	164	46	226	196	53.85	10.75
	203	2.9	1168	103	89	347.33	273
6	4	328	28	163	125	53.85	10.75
	102	5.9	711	74	57	347.33	273
	8	164	46	240	202	53.85	10.75
	203	2.9	1168	109	92	347.33	273
8	4	403	28	243	183	87.09	14
	102	7.2	711	110	83	561.73	356
	8	210	44	332	272	87.09	14
	203	3.8	1118	151	124	39.59	356
10	4	502	29	224	138	128.28	16
	102	9	737	102	63	58.31	406
	8	262	45	425	339	128.28	16
	203	4.7	1143	193	154	58.31	406

Materials
Bellows: A240-T304. Alternate materials available upon request. Refer to the materials section.
Flanges: ASTM A105.
50 lb. ANSI B16.5 RFSO.
Pipe: ASTM A53/A106. .
Shell: ASTM A53/A106; API-5L
Rings: ASTM A285-C.

View PDF

Notes:

Rated life cycle at 650°F is 1000 cycles for full rated movement shown above.
To increase cycle life or movements, please refer to graph on cycle life.
Expansion joint is capable of taking 10% of rated movement as extension, with remaining 90% as axial compression.
Maximum test pressure: 1.5 X rated working pressure.
Bellows rated for 650°F: See catalog flange data for appropriate flange temperature/pressure ratings.
Maximum installation misalignment is ±1/4-inch axial and ±1/16-inch lateral.

Size	Axial Movement	Spring Rate	Overall Length	Weight		Effective Area	Shell Outside Diameter	Anchor Foot Height	Anchor Foot Type
				Weight
				Flanged Ends	Weld Ends


	in.	lb./in.	in.	lb.	lb.	in. 2	in.	in.
	mm	kg/mm	mm	kg	kg	kg/cm 2	mm	mm
12	4	922	30	436	308	180.81	18	Please consult factory regarding anchor foot usage on single X-flex
	102	16.5	762	198	140	82.19	457
	8	461	49	611	483	180.81	18
	203	82	1245	278	220	82.19	457
14	4	1010	30	516	336	211.83	20
	102	18.1	762	235	153	96.29	508
	8	505	49	711	531	211.83	20
	203	9	1245	323	241	96.29	508
16	4	962	30	610	414	270.2	24
	102	17.2	762	277	188	122.82	610
	8	481	48	810	614	270.2	24
	203	8.6	1219	368	279	122.82	610
18	4	1080	30	661	401	331.61	24
	102	19.3	762	300	182	150.73	610
	8	540	48	877	617	331.61	24
	203	9.7	1219	399	280	150.73	610
20	4	1196	31	985	685	399.31	30
	102	21.4	787	448	311	181.5	762
	8	598	49	1240	910	399.31	30
	203	10.7	1245	564	413	181.5	762
24	4	1430	32	1074	634	553.55	30
	102	25.6	813	488	288	251.61	762
	8	725	50	1304	864	553.55	30
	203	13	1270	593	393	251.61	762

Materials
Bellows: A240-T304. Alternate materials available upon request. Refer to the materials section.
Flanges: ASTM A105.
150 lb. ANSI B16.5 RFSO.
Pipe: ASTM A53/A106.
Shell: ASTM A53/A106; API-5L.
Rings: ASTM A285-C.

View PDF

Notes:

Rated life cycle at 650°F is 1000 cycles for full rated movement shown above.
To increase cycle life or movements, please refer to graph on cycle life.
Expansion joint is capable of taking 10% of rated movement as extension, with remaining 90% as axial compression.
Maximum test pressure: 1.5 X rated working pressure.
Bellows rated for 650°F: See catalog flange data for appropriate flange temperature/pressure ratings.
Maximum installation misalignment is ±1/4-inch axial and ±1/16-inch lateral.

Size	Axial Movement	Spring Rate	Overall Length	Weight		Effective Area	Shell Outside Diameter	Anchor Foot Height	Anchor Foot Type
				Weight
				Flanged Ends	Weld Ends


	in.	lb./in.	in.	lb.	lb.	in. 2	in.	in.
	mm	kg/mm	mm	kg	kg	kg/cm 2	mm	mm
3	4	280	24	94	68	30.24	8.625	Please consult factory regarding anchor foot usage on single X-flex
	102	5	610	43	30.91	13.83	219
	8	140	40	136	110	30.42	8.625
	203	2.5	1016	62	50	13.83	219
4	4	280	25	115	71	30.42	8.625
	102	5	635	52	32.27	13.83	219
	8	140	42	154	110	30.42	8.625
	203	2.5	1067	70	50	13.83	219
5	4	662	28	186	130	54.24	10.75
	102	11.8	711	85	59.09	24.65	273
	8	331	46	266	210	54.24	10.75
	203	5.9	1168	121	95.45	24.65	273
6	4	662	28	210	132	54.24	10.75
	102	11.8	711	95	60	24.65	273
	8	331	46	294	216	54.24	10.75
	203	5.9	1168	134	98.18	24.65	273
8	4	810	28	191	307	87.58	14
	102	14.5	711	87	139.55	39.81	356
	8	423	44	403	287	87.58	14
	203	7.6	1118	183	130.45	39.81	356
10	4	931	29	408	246	128.88	16
	102	16.7	737	185	112	58.58	406
	8	504	45	527	365	128.88	16
	203	9	1143	240	166	58.58	406

Materials
Bellows: A240-T304. Alternate materials available upon request. Refer to the materials section.
Flanges: ASTM A105.
300 lb. ANSI B16.5 RFSO.
Pipe: ASTM A53/A106.
Shell: ASTM A53/A106; API-5L.
Rings: ASTM A285-C.

View PDF

Notes:

Rated life cycle at 650°F is 1000 cycles for full rated movement shown above.
To increase cycle life or movements, please refer to graph on cycle life.
Expansion joint is capable of taking 10% of rated movement as extension, with remaining 90% as axial compression.
Maximum test pressure: 1.5 X rated working pressure.
Bellows rated for 650°F: See catalog flange data for appropriate flange temperature/pressure ratings.
Maximum installation misalignment is ±1/4-inch axial and ±1/16-inch lateral.

Size	Axial Movement	Spring Rate	Overall Length	Weight		Effective Area	Shell Outside Diameter	Anchor Foot Height	Anchor Foot Type

				Flanged Ends	Weld Ends


	in.	lb./in.	in.	lb.	lb.	in. 2	in.	in.
	mm	kg/mm	mm	kg	kg	kg/cm 2	mm	mm
12	4	1854	30	563	333	181.96	18	Please consult factory regarding anchor foot usage on single X-flex
	102	33.2	762	256	151.36	82.71	457
	8	927	49	763	533	181.96	18
	203	16.6	1245	347	242.27	82.71	457
14	4	2028	30	695	365	213.07	20
	102	36.3	762	316	165.91	96.85	508
	8	1014	49	919	589	213.07	20
	203	18.1	1245	418	267.73	96.85	508
16	4	1770	30	836	456	271.6	24
	102	31.7	762	380	207.27	123.45	610
	8	885	48	1078	698	271.6	24
	203	15.8	1219	490	317.27	123.45	610
18	4	1986	26	948	448	333.16	24
	102	35.5	660	431	203.64	151.44	610
	8	993	30	1211	711	333.16	24
	203	17.8	762	550	323.18	151.44	610
20	4	2200	31	1338	708	401.01	30
	102	39.4	787	608	322	182.28	762
	8	1100	49	1645	1015	401.01	30
	203	19.7	1245	748	461	182.28	762
24	4	2630	32	1594	644	555.55	30
	102	47.1	813	725	293	252.52	762
	8	1315	50	1936	986	555.55	30
	203	23.5	1270	880	448	252.52	762

Materials
Bellows: A240-T304. Alternate materials available upon request. Refer to the materials section.
Flanges: ASTM A105.
300 lb ANSI B16.5 RFSO.
Pipe: ASTM A53/A106
Shell: ASTM A53/A106; API-5L
Rings: ASTM A285-C.

View PDF

Notes:

Rated life cycle at 650°F is 1000 cycles for full rated movement shown above.
To increase cycle life or movements, please refer to graph on cycle life.
Expansion joint is capable of taking 10% of rated movement as extension, with remaining 90% as axial compression.
Maximum test pressure: 1.5 X rated working pressure.
Bellows rated for 650°F: See catalog flange data for appropriate flange temperature/pressure ratings.
Maximum installation misalignment is ±1/4-inch axial and ±1/16-inch lateral.

Size	Axial Movement	Spring Rate	Overall Length	Weight		Effective Area	Shell Outside Diameter	Anchor Foot Height	Anchor Foot Type
				Weight
				Flanged Ends	Weld Ends


	in.	lb./in.	in.	lb.	lb.	in. 2	in.	in.
	mm	kg/mm	mm	kg	kg	kg/cm 2	mm	mm
3	4	140	40	140	124	30.24	8.625	7.313	A
	203	2.5	1016	64	56	195.05	219	186
	16	70	73	220	204	30.24	8.625	7.313
	406	1.3	1854	100	93	195.05	219	186
4	8	140	41	155	129	30.24	8.625	8.313	A
	203	2.5	1041	70	59	195.05	219	211
	16	70	74	241	215	30.24	8.625	8.313
	406	1.3	1880	110	98	195.05	219	211
5	8	312	45	257	227	53.85	10.75	9.375	B
	203	5.6	1143	117	103	347.33	273	238
	16	156	82	401	371	53.85	10.75	9.375
	406	2.8	2083	182	169	347.33	273	238
6	8	328	45	262	232	53.85	10.75	9.375	B
	203	5.9	1143	119	105	347.33	273	238
	16	164	82	418	388	53.85	10.75	9.375
	406	2.9	2083	190	176	347.33	273	238
8	8	403	45	412	352	87.09	14	11	C
	203	7.2	1143	187	160	561.73	356	279
	16	210	77	591	531	87.09	14	11
	406	3.8	1956	269	241	39.59	356	279
10	8	502	48	519	433	128.28	16	12	C
	203	9	1219	236	197	58.31	406	305
	16	262	80	738	652	128.28	16	12
	406	4.7	2032	335	296	58.31	406	305

Materials
Bellows: A240-T304. Alternate materials available upon request. Refer to the materials section.
Flanges: ASTM A105.
150 lb ANSI B16.5 RFSO.
Pipe: ASTM A53/A106.
Shell: ASTM A53/A106; API-5L
Rings: ASTM A285-C.

View PDF

Notes:

Rated life cycle at 650°F is 1000 cycles for full rated movement shown above.
To increase cycle life or movements, please refer to graph on cycle life.
Expansion joint is capable of taking 10% of rated movement as extension, with remaining 90% as axial compression.
Maximum test pressure: 1.5 X rated working pressure.
Bellows rated for 650°F: See catalog flange data for appropriate flange temperature/pressure ratings.
Maximum installation misalignment is ±1/4-inch axial and ±1/16-inch lateral.

Size	Axial	Spring Rate	Overall Length	Weight		Effective Area	Shell Outside Diameter	Anchor Foot Height	Anchor Foot Type
	Axial			Weight
	Movement			Flanged Ends	Weld Ends


	in.	lb./in.	in.	lb.	lb.	in. 2	in.	in.
	mm	kg/mm	mm	kg	kg	kg/cm 2	mm	mm
12	8	922	49	691	563	180.81	18	13	C
	203	16.5	1245	314	256	82.19	457	330
	16	461	87	1041	913	180.81	18	13
	406	8.2	2210	473	415	82.19	457	330
14	8	1010	49	792	612	211.83	20	14	C
	203	18.1	1245	360	278	96.29	508	356
	16	505	87	1180	1000	211.83	20	14
	406	9	2210	536	455	96.29	508	356
16	8	962	47	950	754	270.2	24	16	D
	203	17.2	1194	432	343	122.82	610	406
	16	481	83	1358	1162	270.2	24	16
	406	8.8	2108	617	528	122.82	610	406
18	8	1080	47	1002	742	331.61	24	16	D
	203	19.3	1194	455	337	150.73	610	406
	16	540	83	1433	1173	331.61	24	16
	406	9.7	2108	651	533	150.73	610	406
20	8	1196	49	1435	1105	399.31	30	19	D
	203	21.4	1245	652	502	181.5	762	483
	16	598	85	1947	1617	399.31	30	19
	406	10.7	2159	885	735	181.5	762	483
24	8	1430	50	1463	1023	533.55	30	19	D
	203	25.6	1270	665	465	251.61	762	483
	16	725	86	2025	1585	553.55	30	19
	406	13	2184	920	720	251.61	762	483

View PDF

Notes:

Rated life cycle at 650°F is 1000 cycles for full rated movement shown above.
To increase cycle life or movements, please refer to graph on cycle life.
Expansion joint is capable of taking 10% of rated movement as extension, with remaining 90% as axial compression.
Maximum test pressure: 1.5 X rated working pressure.
Bellows rated for 650°F: See catalog flange data for appropriate flange temperature/pressure ratings.
Maximum installation misalignment is ±1/4-inch axial and ±1/16-inch lateral.

Size	Axial Movement	Spring Rate	Overall Length	Weight		Effective Area	Shell Outside Diameter	Anchor Foot Height	Anchor Foot Type
				Weight
				Flanged Ends	Weld Ends


	in.	lb./in.	in.	lb.	lb.	in. 2	in.	in.
	mm	kg/mm	mm	kg	kg	kg/cm 2	mm	mm
3	8	280	40	156	130	30.42	8.625	7.313	A
	203	5	1016	71	59.09	13.83	219	186
	16	140	73	242	216	30.42	8.625	7.313
	406	2.5	1845	110	98.18	13.83	219	186
4	8	280	41	179	135	30.42	8.625	8.313	A
	203	5	1041	81	61.36	13.83	219	211
	16	140	74	271	227	30.42	8.625	8.313
	406	2.5	1880	123	103.16	13.83	219	211
5	8	662	45	297	241	54.24	10.75	9.375	B
	203	11.8	1143	135	109.55	24.65	273	238
	16	331	82	457	401	54.24	10.75	9.375
	406	5.9	2083	208	182.27	24.65	273	238
6	8	662	45	324	246	54.24	10.75	9.375	B
	203	11.8	1143	147	111.82	24.65	273	238
	16	331	82	494	416	54.24	10.75	9.375
	406	5.9	2083	226	189.09	24.65	273	238
8	8	810	45	484	368	87.58	14	11	C
	203	14.5	1143	220	167.27	39.81	356	279
	16	423	77	677	561	87.58	14	11
	406	7.6	1956	308	255	39.81	356	279
10	8	931	48	629	467	128.88	16	12	C
	203	16.7	1219	286	212	58.58	406	305
	16	504	80	867	705	128.88	16	12
	406	9	2032	394	320	58.58	406	305

View PDF

Notes:

Rated life cycle at 650°F is 1000 cycles for full rated movement shown above.
To increase cycle life or movements, please refer to graph on cycle life.
Expansion joint is capable of taking 10% of rated movement as extension, with remaining 90% as axial compression.
Maximum test pressure: 1.5 X rated working pressure.
Bellows rated for 650°F: See catalog flange data for appropriate flange temperature/pressure ratings.
Maximum installation misalignment is ±1/4-inch axial and ±1/16-inch lateral.

Size	Axial Movement	Spring Rate	Overall Length	Weight		Effective Area	Shell Outside Diameter	Anchor Foot Height	Anchor Foot Type
				Weight
				Flanged Ends	Weld Ends


	in.	lb./in.	in.	lb.	lb.	in. 2	in.	in.
	mm	kg/mm	mm	kg	kg	kg/cm 2	mm	mm
12	4	1854	49	843	613	181.96	18	13	C
	102	33.2	1245	383	279	82.71	457	330
	16	927	87	1243	1013	181.96	18	13
	406	16.6	2210	565	460	82.71	457	330
14	8	2028	49	1000	670	213.07	20	14	C
	203	36.3	1245	455	305	96.85	508	356
	16	1014	87	1446	1116	213.07	20	14
	406	18.1	2210	657	507	96.85	508	356
16	8	1770	47	1217	837	271.6	24	16	D
	203	31.7	1194	553	381	123.45	610	406
	16	885	83	1710	1330	271.6	24	16
	406	15.8	2108	777	605	123.45	610	406
18	8	1986	47	1335	835	333.16	24	16	D
	203	35.5	1194	607	380	151.44	610	406
	16	993	83	1861	1361	333.16	24	16
	406	17.8	2108	846	619	151.44	610	406
20	8	2200	49	1841	1211	401.01	30	19	D
	203	39.4	1245	837	550	182.28	762	483
	16	1100	85	2458	1828	401.01	30	19
	406	19.7	2159	1117	831	182.28	762	483
24	8	2630	50	2095	1145	555.55	30	19	D
	203	47.1	1270	952	520	252.52	762	483
	16	1315	86	2778	1828	555.55	30	19
	406	23.5	2184	1263	831	252.52	762	483

Materials
Bellows: A240-T304. Alternate materials available upon request. Refer to the materials section.
Flanges: ASTM A105.
300 lb ANSI B16.5 RFSO.
Pipe: ASTM A53/A106.
Shell: ASTM A53/A106; API-5L.
Rings: ASTM A285-C.

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4″ Dia. Single Expansion Joint Designed for a Chemical Facility

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Externally Pressurized (X-Flex) Pipe Expansion Joint

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