ASME SA249 TP316L Stainless Steel U Bend Heat Exchanger Tube
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Why does the U-bend area often become the most failure-prone section in high-spec heat exchanger projects? Ensuring dimensional accuracy, structural integrity, and long-term reliability after bending is a critical concern for both procurement and engineering teams.
Our ASME SA249 TP316L Stainless Steel U Bend Heat Exchanger Tube is specifically designed for high-performance heat exchange systems, effectively addressing common issues such as cracking in the bend area, insufficient wall thickness, difficult installation, weld leakage, and reduced heat transfer efficiency.
To control wall thinning in the TP316L bend area, we apply a precise bending process, maintaining the thinning rate within ≤10% to ensure that pressure-bearing capacity remains unaffected. After bending, all U-tubes undergo stress relieving heat treatment (Stress Relieving / Solution Annealing), which effectively releases residual stresses, restores corrosion resistance, and prevents stress corrosion cracking during service.
In terms of critical geometric control, the ovality in the bend area is maintained within ≤8%, ensuring proper fit with tube sheets and support structures while avoiding assembly interference. Overall dimensional tolerances strictly comply with ASME SA249 and relevant standards, ensuring accurate parallelism and center distance of both tube ends, thereby improving installation efficiency.
Regarding internal cleanliness, our TP316L U-bend heat exchanger tubes undergo a full-process cleaning and degreasing treatment to ensure that the inner surface is free from oxide scale, oil, and foreign particles. This meets the stringent cleanliness requirements of heat exchangers and helps reduce fouling during operation.
ASME SA249 TP316L Stainless Steel U Bend Boiler Tube Specifications
| Sizes / Thickness | OD: 0.25"- 6" ; W.T: 0.02" - 0.5" or as required by clients | ||||
| Manufacture | Shall be made by the seamless or welded process with no filler metal added. | ||||
| Heat Treatment |
For seamless tubes, as an alternate to final heat treatment in a continuous furnace or batch-type furnace, immediately following hot forming while the temperature of the tubes is not less than the specified minimum solution treatment temperature, tubes may be individually quenched in water or rapidly cooled by other means. S32205---(1020-1100℃) Quench:rapid cooling in air water |
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| Length | As required by clients | ||||
| Surface Condition |
All tubes shall be free of excessive mill scale, suitable for inspection. A slight amount of oxidation will not be considered as scale. |
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| Bending Radius | From 1.5*OD(Outside Diameter) To 1500mm, ≤1.5*OD,necessary To agree precision of geometrics | ||||
| Straight Tubes | max length 35000mm | ||||
U-Tube Specifications: Minimum Bending Radius
| MINIMUM BENDING RADIUS IN MM | |||||||||||
| Outside Diameter | Wall Thickness | ||||||||||
| inch | 0.035 | 0.039 | 0.049 | 0.059 | 0.065 | 0.079 | 0.083 | 0.095 | 0.109 | ||
| mm | 0.89 | 1.1 | 1.24 | 1.5 | 1.65 | 2 | 2.11 | 2.41 | 2.77 | ||
| BWG | 20 | 18 | 16 | 14 | 13 | 12 | |||||
| inch | mm | ||||||||||
| 0.625 | 15.9 | 40 | 32 | 24 | 24 | 24 | 32 | ||||
| 0.63 | 16 | 40 | 32 | 24 | 24 | 24 | 32 | ||||
| 0.75 | 19.05 | 38 | 28.5 | 28.5 | 28.5 | 28.5 | 28.5 | 38 | |||
| 0.787 | 20 | 40 | 30 | 30.3 | 30 | 30 | 30.5 | 35 | |||
| 0.839 | 21.3 | 42.5 | 32 | 32 | 32 | 32 | 32 | ||||
| 0.984 | 25 | 50 | 38 | 38 | 38 | 38 | 50 | ||||
| 1 | 25.4 | 51 | 38 | 38 | 38 | 38 | 51 | ||||
| 1.181 | 30 | 60 | 45 | 45 | 45 | 45 | 60 | ||||
| 1.252 | 31.8 | 65 | 48 | 48 | 48 | 48 | 65 | ||||
| Initial Length:Maximum Lengths of 22 m can be supplied on request | |||||||||||
| Bending Radius: Maximum 1000mm | |||||||||||
| The above sizes are those most frequently used,other sizes can be produced upon request. | |||||||||||
Weight Chart for Heat Exchangers Tube& Condensers Tube & Boilier Tube
| Outside Diameter | Stainless Steel Tube Weight (kg/m) | ||||||
| Birmingham wire Gauge Conversion from BWG to mm | |||||||
| 20 BWG | 18 BWG | 16 BWG | 14 BWG | 12 BWG | 10 BWG | ||
| mm | inch | 0.89 mm | 1.24 mm | 1.65 mm | 2.11 mm | 2.77 mm | 3.4 mm |
| 6.35 | 1/4 | 0.121 | 0.158 | 0.193 | - | - | - |
| 9.53 | 3/8 | 0.192 | 0.256 | 0.324 | 0.39 | 0.466 | - |
| 12.7 | 1/2 | 0.262 | 0.354 | 0.454 | 0.557 | 0.685 | 0.788 |
| 15.88 | 5/8 | 0.332 | 0.452 | 0.585 | 0.724 | 0.905 | 1.057 |
| 19.05 | 3/4 | 0.403 | 0.55 | 0.715 | 0.89 | 1.123 | 1.325 |
| 25.4 | 1 | 0.543 | 0.746 | 0.976 | 1.224 | 1.561 | 1.863 |
| 31.75 | 1 1/4 | 0.684 | 0.942 | 1.237 | 1.558 | 2 | 2.401 |
| 38.1 | 1 1/2 | - | 1.139 | 1.498 | 1.892 | 2.438 | 2.939 |
| 44.5 | 1 3/4 | - | 1.336 | 1.761 | 2.228 | 2.879 | 3.481 |
| 50.8 | 2 | - | 1.531 | 2.02 | 2.559 | 3.314 | 4.014 |
| 63.5 | 2 1/2 | - | - | 2.542 | 3.227 | 4.19 | 5.09 |
| 76.2 | 3 | - | - | 3.064 | 3.894 | 5.067 | 6.166 |
| 88.9 | 3 1/2 | - | - | 3.586 | 4.562 | 5.943 | 7.241 |
| 101.6 | 4 | - | - | 4.108 | 5.229 | 6.819 | 8.317 |
| 114.3 | 4 1/2 | - | - | - | 5.897 | 7.696 | 9.393 |
Non-Destructive Testing and Pressure Testing
Compliance of the straight pipe section does not guarantee compliance after bending, as the bending process may induce micro-cracks.
Hydrostatic Testing: Typically, a 100% hydrostatic test is required upon completion of the bending process; the test pressure is usually higher than that applied to the straight pipe section to verify the integrity and leak-tightness of the bend area.
Air Tightness Testing: For more demanding service conditions, the pipe is required to be pressurized internally with high-pressure air and submerged in a water tank for inspection.
Penetrant Testing (PT): For small-radius bends (those with a small bend radius/R-value), PT inspection of the outer surface of the bend is required to confirm the absence of micro-cracks.
Packaging and Support
Due to their unique shape and susceptibility to deformation, U-tubes cannot be adequately secured using standard bundling methods.
Layered Separation: Each layer of U-tubes must be separated by wooden slats or foam boards.
Secure Bracing: The interior of the crate must be fitted with a bracing frame to prevent the "long legs" of the U-tubes from shifting or deforming during transit.
Specialized Wooden Crates: Fully enclosed wooden crates are mandatory; the length of the crate must be custom-sized to accommodate the longest tube leg.
FAQ
Q: Why do the bent sections of U-tubes typically require an additional stress-relieving heat treatment?
A: The bending of U-tubes involves a process of severe cold deformation, which leaves significant residual stresses within the bend radius (R-zone). If these stresses are not relieved, the TP316L material becomes highly susceptible to Stress Corrosion Cracking (SCC) when exposed to environments containing chloride ions or specific chemical media.
Q: How does the tolerance on the center-to-center distance (pitch) of U-tubes affect installation?
A: If the deviation in the center-to-center distance (the spacing between the two legs) is excessive, the tubes will fail to align with the corresponding holes in the tube sheet. This can result in induced stresses caused by forced installation, or-in severe cases-render assembly impossible.
Tolerance Requirement: For tubes with a bend radius (R) of less than 500 mm, the tolerance on the center-to-center distance is typically required to be within ±1.5 mm.
Q: For SA249 U-tubes, where should the weld seam be positioned within the bent section?
A: Requirement: During loading onto the bending machine, the weld seam must be positioned to avoid the outermost side (the tension zone) and the innermost side (the compression zone)-areas subject to the highest stress during bending. Typically, the seam is placed along the neutral axis-specifically, at the 90° lateral position. This practice effectively mitigates the risk of weld cracking during the bending process.
