Stainless U bend tubes : High-performance Tubes For Efficient Thermal Transfer

Stainless U-Bend Tubes are seamless or welded stainless steel tubes bent into a U-shape, designed to redirect fluid flow in heat exchanger tubes and ensure efficient thermal expansion absorber performance. Widely used in industries such as petrochemical, power generation, food processing, and pharmaceuticals, these tubes are critical for applications requiring corrosion resistance and high-temperature durability. Conforming to standards like ASTM A213, A269, A688, and ASME SA213, they are engineered for seamless integration into boilers, condensers, and superheaters.

Manufactured through cold-drawing or hot-rolling processes, Stainless U-Bend Tubes are typically made from grades like 304, 304L, 316, 316L, or 321 stainless steel, offering excellent resistance to pitting, crevice corrosion, and oxidation. The U-shape design allows for compact layouts, reducing the need for additional fittings and minimizing thermal stress in pipeline durability. Available in outer diameters from 9.53mm to 50.8mm and wall thicknesses from 0.8mm to 3.0mm, these tubes can be customized for leg lengths up to 12 meters and bend radii of 1.5D to 10D, meeting diverse project requirements.

The U-Shaped Tubing undergoes solution annealing post-bending to relieve residual stresses and enhance corrosion resistance, followed by rigorous testing, including hydrostatic, pneumatic, and dye penetrant tests, to ensure compliance with ASTM A688/A688M or TEMA standards. The tubes are mandrel-bent to maintain a uniform cross-section, preventing wrinkles or ovality, which ensures optimal flow and heat transfer efficiency. Surface treatments like pickling, passivation, or polishing further enhance durability, while capped ends prevent contamination during transport and installation.

Compared to straight tubes, Stainless U-Bend Tubes offer superior thermal compensation, allowing free expansion and contraction without the need for expansion joints, which reduces costs. Their high chromium (18-20%) and nickel (8-12%) content in grades like 304/316L ensures resistance to corrosive fluids, making them ideal for harsh environments like refineries or chemical plants. The tubes are also suitable for hygienic applications, such as food and beverage processing, due to their smooth, crevice-free surfaces that meet AS 1528.1 standards for cleanliness.

The Stainless U-Bend Tubes address challenges like pipeline wear, corrosion, and thermal stress in demanding systems. Their versatility, combined with easy maintenance and long service life, makes them a preferred choice for engineers seeking reliable heat exchanger tubes for critical applications in extreme conditions. Whether used in nuclear power plants or pharmaceutical processing, these tubes deliver unmatched performance and safety.

Heat exchanger equipment on the basis of stainless steel U-tube is essential in strategically important and critical fields nuclear and petrochemical machine building.

Surface condition Finished U Bend Tube shall be free of scale, without scratches after bending

Heat exchanger tubes can also be delivered as U-bent tube / U bend pipe, manufactured according to the common heat exchanger standards. Our basic specification for u bend pipes is ASTM A213/A213M, ASTM A 312/312M, EN 10216-5, and we can also follow various specifications on customers' requests.

Stainless U bends in the tube help to change the direction of the flow of the medium being transported, which helps to reduce the need for additional piping that would otherwise be required to accomplish the same effect. These tubes are often used in industries where cleanliness and hygiene are critical, such as food and beverage processing, pharmaceuticals, and chemical processes, because stainless steel is non-corrosive and resistant to high temperatures and pressure.

304L Stainless Steel U Bend Tubing

Engineered for durability and corrosion resistance in demanding industrial applications.

304L stainless steel tubing provides great durability by combining excellent physical properties with resistance to corrosive agents found in automotive exhaust emissions. This 304L tubing is made in the USA and is mandrel bent to provide smooth bends to ensure maximum flow. Burns' high standards ensure constant cross sections minimizing labor costs for fabricators.

U Bend Tubing made of 304L stainless steel is a type of tubing that is bent in the shape of a U. It is commonly used in various industries, including oil and gas plants, chemical and petrochemical plants, power generation plants, refineries, and boiler heat exchangers.

304L stainless steel is a specific grade of stainless steel known for its durability and resistance to corrosive agents. It combines excellent physical properties with a remarkable resistance to corrosion. The material is commonly used in applications where resistance to corrosion is essential, such as in harsh environments or when dealing with corrosive substances.

Austenitic & Martensitic Stainless Steel U Bent Tube

With strong wood structure box packing by containers loading and shipping.

Stainless Steel U-Bent Tube Standards & Material Grades
Standard	Material Grade	Application (U-Tube Bundles For)
ASTM A213	TP304/304L, TP316/316L, TP310S	Boiler, Condensers, Super Heaters, Heat Exchangers, Coolers/Inter-coolers, Chiller
ASTM/ASME A/SA268	TP405, TP409, TP410, TP430, TP439, TP444	Ferritic and Martensitic Stainless Steel Seamless U-Tube bundles
ASTM/ASME A/SA213	TP304/304L, TP304H, TP316/316L, TP347/347H, TP316Ti, TP321/321H, TP310S	Seamless Austenitic Stainless Steel U-Tube bundles
ASTM A249	TP304/304L, TP304H, TP316/316L, TP347/347H, TP316Ti, TP321/321H, TP310S	Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser U-Tube bundles; Boiler, Condensers, Super Heaters, Heat Exchangers, Coolers/Inter-coolers, Chiller
ASTM A269	TP304/304L, TP316/316L	Stainless Steel U-Bend Heat Exchanger Tube, Boiler Tubing bundles
-	Monel400, UNS N06600, UNS N06625, Incoloy800/800H, Incoloy825, Hastelloy	U-Tube bundles; U-Bend tubes
-	Duplex UNS S31803/32205, UNS S32750, Super Duplex	U-Bend tubes for Heat Exchanger, Boiler, Condensers, Super Heaters, Coolers/Inter-coolers, Chiller

FAQs of Stainless U bend tubes

Engineered to meet diverse industrial needs with robust materials and versatile designs.

Stainless U-Bend Tubes are seamless or welded stainless steel tubes bent into a U-shape, used in heat exchangers to redirect fluid flow and absorb thermal expansion.

They are used in heat exchangers, boilers, condensers, and superheaters in industries like petrochemical, power generation, food processing, and pharmaceuticals.

Common grades include 304, 304L, 316, 316L, and 321 stainless steel, with optional coatings like pickling or passivation for enhanced corrosion resistance.

For stainless steel 304: - Carbon (C): ≤0.08% - Manganese (Mn): ≤2.00% - Phosphorus (P): ≤0.045% - Sulfur (S): ≤0.030% - Silicon (Si): ≤1.00% - Chromium (Cr): 18.0-20.0% - Nickel (Ni): 8.0-12.0%

For stainless steel 304: - Tensile Strength: ≥515 MPa - Yield Strength: ≥205 MPa - Elongation: ≥40% (Longitudinal), ≥30% (Transverse) - Hardness: ≤201 HBW

Outer diameters range from 9.53mm to 50.8mm, wall thicknesses from 0.8mm to 3.0mm, with bend radii of 1.5D to 10D. Tolerances follow ASTM A688, with ovality ≤10% and wall thinning per TEMA standards.

Produced via cold-drawing or hot-rolling, followed by mandrel bending and solution annealing to relieve stresses and enhance corrosion resistance.

Tests include hydrostatic, pneumatic, dye penetrant, and dimensional inspections to ensure compliance with ASTM A213, A688, or TEMA standards.

Tubes are installed in heat exchanger tube sheets with welded or expanded ends, with capped ends to prevent contamination during transport and setup.

U-Bend tubes allow for compact layouts and thermal expansion compensation without additional joints, unlike straight tubes, which may require expansion joints, increasing costs.

Stainless U bend tubes Standard Specifications

Chemical Composition of Stainless Hollow Sections (Grades 304, 304L, 316, 316L per ASTM A554/A312)
Grade	C (% max)	Mn (% max)	Si (% max)	P (% max)	S (% max)	Cr (%)	Ni (%)	Mo (%)	N (% max)
304	0.08	2.00	1.00	0.045	0.030	18.0-20.0	8.0-11.0	-	0.10
304L	0.03	2.00	1.00	0.045	0.030	18.0-20.0	8.0-12.0	-	0.10
316	0.08	2.00	1.00	0.045	0.030	16.0-18.0	10.0-14.0	2.0-3.0	0.10
316L	0.03	2.00	1.00	0.045	0.030	16.0-18.0	10.0-14.0	2.0-3.0	0.10

The low carbon content in 304L and 316L enhances weldability, while molybdenum in 316 and 316L improves resistance to pitting and crevice corrosion, making Stainless U bend tubes ideal for harsh environments.

Mechanical Properties of Stainless Hollow Sections (Grades 304, 304L, 316, 316L per ASTM A554/A312)
Grade	Tensile Strength (min, MPa)	Yield Strength (min, MPa)	Elongation (min, %)	Hardness (max, HB)	Hardness (max, HRB)
304	515	205	40	201	92
304L	485	170	40	201	92
316	515	205	40	217	95
316L	485	170	40	217	95

These mechanical properties make Stainless U bend tubes suitable for applications requiring high strength and corrosion resistance, such as architectural structures, marine environments, and chemical processing.

Comparison table of stainless steel brands of various countries

In order to solve the cumbersome and difficult to remember stainless steel grades, improve the practicability of the brand representation, and the contrast with the international standard grades, China has formulated the "Universal Code System for Steel and Alloy Grades", such as 06Cr19Ni10, corresponding to 304. Different grades of stainless steel have different ingredients, but they all have a national standard. The standards of each country are also different.

Stainless Steel Grade Equivalents Across Standards
No	China (GB)		Japan (JIS)	American		Korea (KS)	EU (BS EN)	India (IS)	Australia (AS)	Taiwan (CNS)
No	Old	New (07.10)	SUS	ASTM	UNS	STS	EN	IS	AS	CNS
Austenitic Stainless Steel
1	1Cr17Mn6Ni5N	12Cr17Mn6Ni5N	SUS201	201	S20100	STS201	1.4372	10Cr17Mn6Ni4N20	201-2	201
2	1Cr18Mn8Ni5N	12Cr18Mn9Ni5N	SUS202	202	S20200	STS202	1.4373	—	—	202
3	1Cr17Ni7	12Cr17Ni7	SUS301	301	S30100	STS301	1.4319	10Cr17Ni7	301	301
4	0Cr18Ni9	06Cr19Ni10	SUS304	304	S30400	STS304	1.4301	07Cr18Ni9	304	304
5	00Cr19Ni10	022Cr19Ni10	SUS304L	304L	S30403	STS304L	1.4306	02Cr18Ni11	304L	304L
6	0Cr19Ni9N	06Cr19Ni10N	SUS304N1	304N	S30451	STS304N1	1.4315	—	304N1	304N1
7	0Cr19Ni10NbN	06Cr19Ni9NbN	SUS304N2	XM21	S30452	STS304N2	—	—	304N2	304N2
8	00Cr18Ni10N	022Cr19Ni10N	SUS304LN	304LN	S30453	STS304LN	—	—	304LN	304LN
9	1Cr18Ni12	10Cr18Ni12	SUS305	305	S30500	STS305	1.4303	—	305	305
10	0Cr23Ni13	06Cr23Ni13	SUS309S	309S	S30908	STS309S	1.4833	—	309S	309S
11	0Cr25Ni20	06Cr25Ni20	SUS310S	310S	S31008	STS310S	1.4845	—	310S	310S
12	0Cr17Ni12Mo2	06Cr17Ni12Mo2	SUS316	316	S31600	STS316	1.4401	04Cr17Ni12Mo2	316	316
13	0Cr18Ni12Mo3Ti	06Cr17Ni12Mo2Ti	SUS316Ti	316Ti	S31635	—	1.4571	04Cr17Ni12MoTi20	316Ti	316Ti
14	00Cr17Ni14Mo2	022Cr17Ni12Mo2	SUS316L	316L	S31603	STS316L	1.4404	02Cr17Ni12Mo2	316L	316L
15	0Cr17Ni12Mo2N	06Cr17Ni12Mo2N	SUS316N	316N	S31651	STS316N	—	—	316N	316N
16	00Cr17Ni13Mo2N	022Cr17Ni13Mo2N	SUS316LN	316LN	S31653	STS316LN	1.4429	—	316LN	316LN
17	0Cr18Ni12Mo2Cu2	06Cr18Ni12Mo2Cu2	SUS316J1	—	—	STS316J1	—	—	316J1	316J1
18	00Cr18Ni14Mo2Cu2	022Cr18Ni14Mo2Cu2	SUS316J1L	—	—	STS316J1L	—	—	—	316J1L
19	0Cr19Ni13Mo3	06Cr19Ni13Mo3	SUS317	317	S31700	STS317	—	—	317	317
20	00Cr19Ni13Mo3	022Cr19Ni13Mo3	SUS317L	317L	S31703	STS317L	1.4438	—	317L	317L
21	0Cr18Ni10Ti	06Cr18Ni11Ti	SUS321	321	S32100	STS321	1.4541	04Cr18Ni10Ti20	321	321
22	0Cr18Ni11Nb	06Cr18Ni11Nb	SUS347	347	S34700	STS347	1.4550	04Cr18Ni10Nb40	347	347
Austenitic-Ferritic Stainless Steel (Duplex)
23	0Cr26Ni5Mo2	—	SUS329J1	329	S32900	STS329J1	1.4477	—	329J1	329J1
24	00Cr18Ni5Mo3Si2	022Cr19Ni5Mo3Si2N	SUS329J3L	—	S31803	STS329J3L	1.4462	—	329J3L	329J3L
Ferritic Stainless Steel
25	0Cr13Al	06Cr13Al	SUS405	405	S40500	STS405	1.4002	04Cr13	405	405
26	—	022Cr11Ti	SUH409	409	S40900	STS409	1.4512	—	409L	409L
27	00Cr12	022Cr12	SUS410L	—	—	STS410L	—	—	410L	410L
28	1Cr17	10Cr17	SUS430	430	S43000	STS430	1.4016	05Cr17	430	430
29	1Cr17Mo	10Cr17Mo	SUS434	434	S43400	STS434	1.4113	—	434	434
30	—	022Cr18NbTi	—	—	S43940	—	1.4509	—	439	439
31	00Cr18Mo2	019Cr19Mo2NbTi	SUS444	444	S44400	STS444	1.4521	—	444	444
Martensitic Stainless Steel
32	1Cr12	12Cr12	SUS403	403	S40300	STS403	—	—	403	403
33	1Cr13	12Cr13	SUS410	410	S41000	STS410	1.4006	12Cr13	410	410
34	2Cr13	20Cr13	SUS420J1	420	S42000	STS420J1	1.4021	20Cr13	420	420J1
35	3Cr13	30Cr13	SUS420J2	—	—	STS420J2	1.4028	30Cr13	420J2	420J2
36	7Cr17	68Cr17	SUS440A	440A	S44002	STS440A	—	—	440A	440A

U-Bend Fabrication Tolerances

U-bend tubes are widely used in heat-exchanger systems. Heat-exchanger equipment on the basis of seamless stainless U-tubes is essential in strategically important and critical fields — nuclear and petrochemical machine building.

U-tube explanation

a...................The difference in length between two straight pipe sections
c..............The tangent spacing of the outer wall of the elbow
Da............nominal steel pipe outer diameter
E..............The distance between the outer diameters of the two straight ends
f...............the distance between the ends of the two straight ends
l............... straight tube length
Lg............. straight pipe section plus total length of pipe
Rm...........nominal bending radius
S.............nominal wall thickness
Smin.......The minimum wall thickness at the back of the elbow
t...............the bend deviates from the horizontal distance
So...........Standard minimum wall thickness

Tube Bending Tolerance Specifications
Item	Condition (when)	Tolerance
Ovality	Nominal bend radius ≤ 2 x nominal OD	less than or equal to 12%
	2 x nominal OD < Nominal bend radius ≤ 4 x nominal OD	less than or equal to 10%
	Nominal bend radius > 4 x nominal OD	less than or equal to 5%
	Nominal bend radius ≤ 2 x nominal OD	0.75 x nominal wall
Minimum wall thickness	2 x nominal OD < Nominal bend radius ≤ 4 x nominal OD	0.8 x nominal wall
	Nominal bend radius > 4 x nominal OD	0.9 x nominal wall
	Nominal bend radius ≤ 8" (200mm)	+/-3/64"(1mm)
Bending Radius	8" (200mm) < Nominal bend radius ≤ 16" (400mm)	+/-1/16"(1mm)
Bending Radius	Nominal bend radius >16" (400mm)	+/-5/64"(1mm)
Distance between legs	-	Max 1/16"(1.5mm)
Wall thinning of bending area	-	Max 17%
Difference between leg lengths at the ends	Leg length ≤ 16' (4.88m)	+1/8"(3mm)
Difference between leg lengths at the ends	Leg length > 16' (4.88m)	+3/16"(5mm)
Deviation from plane of bend	-	≤ 3/16"(1.5mm)
Flattening on bend	-	≤ 10% nominal diameter
Straight leg length	≤5m	+1/8"(3mm)
Straight leg length	>5m	+3/16"(5mm)
Total tube length including radius	≤6m	+3/16"(5mm)
Total tube length including radius	>6m	+5/16"(8mm)

U-Tube heat exchanger Pros and Cons

U-Tube heat exchangers are known for their distinctive U-shaped tubes that offer several advantages and also come with certain limitations.

Pros:

The U-tube heat exchanger features a single tubesheet with both ends of the tubes secured to it. This design allows the tubes to expand and contract freely, avoiding thermal stress and offering excellent thermal compensation. A double tube pass is utilized, providing a lengthy process path, high flow rates, and superior heat transfer performance with robust pressure resistance. The tube bundle is removable from the shell for convenient maintenance and cleaning, presenting a simple structure and low cost.

Cons:

Limitations imposed by the elbow's curvature radius restrict the arrangement of heat exchange tubes. This results in a larger inner tube spacing within the tube bundle and a lower utilization rate of the tube sheet. The shell-side fluid is prone to short-circuiting, which can impede heat transfer. When a tube leaks or sustains damage, only the U-shaped tubes on the outer part of the bundle can be readily replaced. Damage to the inner heat exchange tubes is not as easily repairable and may require blocking off. Furthermore, the damage to a single U-shaped tube equates to the loss of two tubes, leading to a higher scrap rate.

Uses of U-Bend Tube

U-bend tubes are used to transfer heat between fluids.

Heat Transfer

Transfers heat between fluids, allowing return flow at 180° in a compact space.

Industrial Applications

Used in heat exchangers, chemical & petrochemical, food processing, and refrigeration industries.

Oil & Gas Plants

Applied in heat exchangers at Oil & Gas, petrochemical plants, refineries, and power plants.

Corrosive Medium Handling

Handles aggressive fluids like sodium hydroxide + sodium hypochlorite safely.

Expansion Compensation

Allows pipeline expansion without buckling; flexible or sliding options available.

Finned Tube Applications

Enhances heat transfer when the outside coefficient is lower than the inside, improving efficiency.