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High Precision Stainless Steel U-Bend Seamless Tube for Industrial Heat Exchangers
Yuhong Group Co., Ltd. specializes in the engineering and supply of heat transfer components for shell-and-tube heat exchangers, pressure vessels, and air coolers. Our product portfolio includes U-bend tubes, tube bundles, finned tubes, and heat exchanger fittings such as tubesheets, baffles, and channel covers. With over 25 years in thermal equipment manufacturing and certifications including ASME U Stamp, TEMA, ABS, DNV, GL, PED, and ISO 9001, we supply stainless steel seamless U-bend tubing engineered to meet the dimensional and metallurgical demands of industrial heat transfer applications.
Product Overview
The High Precision Stainless Steel Seamless U-Bend Tubing is manufactured in accordance with ASME SA213 / ASTM A213 - the standard specification for seamless ferritic and austenitic steel boiler, superheater, and heat-exchanger tubes. The U-bending process is performed via cold working, with bending radius, center-to-center distance, and straight leg length executed per customer drawings. Post-bend heat treatment (stress relieving or solution annealing) is applied to the bend area plus 300 mm of each leg beyond the tangent point to eliminate residual stresses. Inert gas (argon) purging during bending prevents internal oxidation.
Bend radius: min. 1.5 × OD up to 1500 mm; Max. straight length before bending: 26 m - 35 m
Additional grades including duplex (S31803, S32205, S32750), super duplex, nickel alloys (Inconel, Monel, Incoloy), and titanium are available upon agreement.
OD, wall thickness, ovality, bending radius, leg length
Cotton Ball Test
--
Internal diameter cleanliness verification
Flattening / Flaring Test
ASME SA213
Confirms tube can be U-bent and expanded into tubesheet
Each tube is pickled, dried, marked, and packed following TEMA "C" and ASTM A688 requirements. Ovality in the bend area is controlled to ≤10% of nominal OD; wall thinning is maintained within ≤10% of nominal wall thickness.
Application Scenarios
These U-bend seamless tubes are engineered for U-tube bundle shell-and-tube heat exchangers, where differential thermal expansion between tubes and shell makes fixed tubesheet designs unsuitable. Primary applications include:
Oil & Gas Plants - process heat exchangers, condensers, reboilers
Chemical & Petrochemical Facilities - corrosive media heat transfer
Power Generation - feedwater heaters, superheaters, boiler tubing
Food Processing & Refrigeration - sanitary heat transfer
The U-bend configuration allows each tube to expand and contract independently, eliminating the need for expansion joints and simplifying bundle removal for maintenance.
Technical Advantages and Customization
Precision Bending Control: Cold-working process with controlled bending parameters ensures consistent bend radius and minimizes wall thinning (≤10%). Ovality is maintained within ≤10% of nominal OD.
Post-Bend Heat Treatment: The bend area plus 300 mm of each leg undergoes stress relieving or solution annealing (1040-1120°C), restoring corrosion resistance and preventing stress corrosion cracking.
Oxidation Prevention: Argon gas purging during bending prevents internal oxidation and maintains ID cleanliness.
Dimensional Flexibility: Customizable bending radius (min. 1.5 × OD to 1500 mm), leg length, and overall tube length per customer drawings.
Material Versatility: Austenitic stainless steels, duplex, super duplex, nickel alloys, and titanium - all available upon agreement.
Certification Support: Tubes supplied with EN 10204 Type 3.1 or 3.2 mill test certificates, third-party inspection available.
Frequently Asked Questions
Q: What is the minimum bending radius for ASME SA213 stainless steel U-bend tubes?
A: The minimum recommended bending radius is 1.5 × the tube outside diameter. Radii smaller than this require agreement on geometric precision.
Q: Why is post-bend heat treatment necessary for stainless steel U-bends?
A: Cold bending introduces residual stresses that can lead to stress corrosion cracking (SCC) in service. Solution annealing (1040-1120°C followed by rapid cooling) relieves these stresses and restores the material's corrosion resistance.
Q: What is the allowable wall thinning in the bend area?
A: Wall thinning on the outer arc of the bend is typically limited to ≤10% of nominal wall thickness for critical service applications.
Q: How is ovality controlled in U-bent sections?
A: Ovality (out-of-roundness) at the bend shall not exceed 10% of the nominal tube outside diameter for bend radii up to 2 × OD, and ≤12% for smaller radii.
Q: What standards apply to ASME SA213 U-bend tubes?
A: Straight tubes are manufactured to ASME SA213 / ASTM A213. U-bending and inspection follow TEMA RCB-2.31 (9th Edition) and applicable sections of ASME Section VIII.
For detailed specifications, custom bending requirements, or third-party inspection arrangements, please contact Yuhong Group Co., Ltd. at vladimir@steelseamlesspipe.com.
