High-strength Tubes For High-temperature Applications
Alloy steel u-tubes provide superior strength and corrosion resistance for heat exchangers and boilers.
High-strength Tubes For High-temperature Applications
Alloy steel u-tubes provide superior strength and corrosion resistance for heat exchangers and boilers. designed for high-temperature and high-pressure environments, they ensure durable pipeline performance.
Alloy Steel U-Tubes are seamless or welded tubes made from alloy steel, bent into a U-shape for use in heat exchanger tubes and boiler tubes. Conforming to standards like ASTM A213 (T5, T9, T11, T22, T91) and JIS G3462, these tubes are designed for high-temperature and high-pressure applications in industries such as petrochemical, power generation, oil and gas, and chemical processing. Their corrosion resistance and role as a thermal expansion absorber make them ideal for enhancing pipeline durability in harsh environments.
Manufactured through cold-drawing or hot-rolling, Alloy Steel U-Tubes offer outer diameters from 6.35mm to 50.8mm, wall thicknesses from 0.8mm to 6mm, and bend radii from 1.5D to 1500mm, customizable to meet project specifications. Post-bending heat treatments, such as stress relief annealing (650-720°C) or normalizing (850-950°C), optimize mechanical properties and prevent cracking. Surface treatments like pickling, passivation, or 3LPE coating enhance corrosion resistance, while capped ends protect tubes during transport and installation.
These tubes undergo rigorous testing, including hydrostatic, eddy current, flaring, flattening, and hardness tests, to comply with ASTM A450/A450M and TEMA standards. With tensile strengths ranging from 415 MPa (T11) to 620 MPa (T91) and yield strengths from 205 MPa to 440 MPa, they are engineered for temperatures up to 650°C and pressures up to 10 MPa. The U-bend design reduces thermal stress and eliminates the need for expansion joints, making them cost-effective and space-efficient for heat exchanger tubes.
The alloy steel composition, typically containing 1-9% chromium (Cr) and 0.5-1% molybdenum (Mo), offers superior creep strength and corrosion resistance compared to carbon steel, while being more economical than stainless steel. Grades like T11 and T22 are ideal for boiler superheaters, while T91 excels in high-temperature applications like power plant reheaters. The seamless construction ensures leak-free performance, and their ability to handle abrasive fluids makes them suitable for pneumatic conveying systems.
Addressing challenges like pipeline wear, corrosion, and thermal stress, Alloy Steel U-Tubes provide a reliable solution for engineers seeking durable boiler tubes and heat exchanger tubes. Their high strength, durability, and low maintenance requirements make them a preferred choice for critical applications in demanding industrial environments, ensuring long-term performance and efficiency.
Alloy steel U tubes are typically constructed from materials containing varying proportions of alloying elements like chromium (Cr), molybdenum (Mo), nickel (Ni), and others. These alloys offer exceptional heat resistance, corrosion resistance, and mechanical strength.
Alloy Steel U-tube heat exchanger tubes are bent into a U-shaped tube, the fluid inlet and outlet were installed in the same side on both sides of the head with partitions into two rooms, each tube is free to expand and retract to solve the heat Compensation problem.
The U tube is an important part of the U tube heat exchanger.
The main structure of the U type tube heat exchanger includes the tube box, the barrel, the head, the heat exchange tube, the nozzle, the baffle plate, the punching plate and the guide tube, the short circuit structure, the support and other accessories.
Alloy Steel U tubes used for heat transfer tubes is usually used for heat transfer tubes and ordinary cold drawn tubes. The former is suitable for non phase transition heat transfer and vibration prone situations, and the latter is suitable for reboiling, condensing heat transfer and non vibration general situations.
Alloy Steel U tubes has a variety of forms, smooth tube is the most traditional form, because it has the advantages of easy manufacturing and low unit length cost, which is the most common in the current application. The pipe should be able to withstand certain temperature and stress. When the tube and shell side fluid are corrosive, the pipe should also have corrosion resistance.
The material of Alloy Steel U tubes：T5, T11, T12, T22, T9, T91, etc.
The U-shaped configuration of these tubes significantly enhances their heat transfer capabilities. This design increases the surface area available for heat exchange, resulting in improved efficiency in heat exchangers and condenser systems.
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.05-0.15 |
| Manganese (Mn) | 0.30-0.60 |
| Phosphorus (P) | ≤0.025 |
| Sulfur (S) | ≤0.025 |
| Silicon (Si) | 0.50-1.00 |
| Chromium (Cr) | 1.00-1.50 |
| Molybdenum (Mo) | 0.44-0.65 |
| Property | Value |
|---|---|
| Tensile Strength, min (MPa) | 415 |
| Yield Strength, min (MPa) | 205 |
| Elongation, min (%) | 30 |
| Hardness, max (HBW) | 163 |
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.08-0.12 |
| Manganese (Mn) | 0.30-0.60 |
| Phosphorus (P) | ≤0.020 |
| Sulfur (S) | ≤0.010 |
| Silicon (Si) | 0.20-0.50 |
| Chromium (Cr) | 8.00-9.50 |
| Molybdenum (Mo) | 0.85-1.05 |
| Vanadium (V) | 0.18-0.25 |
| Niobium (Nb) | 0.06-0.10 |
| Property | Value |
|---|---|
| Tensile Strength, min (MPa) | 620 |
| Yield Strength, min (MPa) | 440 |
| Elongation, min (%) | 20 |
| Hardness, max (HBW) | 250 |
Engineered to meet diverse industrial needs with robust materials and versatile designs.
| Element | ASTM A213 T11 | ASTM A213 T91 |
|---|---|---|
| Carbon (C) | 0.05-0.15 | 0.08-0.12 |
| Manganese (Mn) | 0.30-0.60 | 0.30-0.60 |
| Phosphorus (P) | ≤0.025 | ≤0.020 |
| Sulfur (S) | ≤0.025 | ≤0.010 |
| Silicon (Si) | 0.50-1.00 | 0.20-0.50 |
| Chromium (Cr) | 1.00-1.50 | 8.00-9.50 |
| Molybdenum (Mo) | 0.44-0.65 | 0.85-1.05 |
| Vanadium (V) | - | 0.18-0.25 |
| Niobium (Nb) | - | 0.06-0.10 |
| Standard & Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HBW) |
|---|---|---|---|---|
| ASTM A213 T11 | ≥415 | ≥205 | ≥30 | ≤163 |
| ASTM A213 T91 | ≥620 | ≥440 | ≥20 | ≤250 |
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.
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
| 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) |
| 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) |
| 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) |
| >5m | +3/16"(5mm) | |
| Total tube length including radius | ≤6m | +3/16"(5mm) |
| >6m | +5/16"(8mm) |
U-Tube heat exchangers are known for their distinctive U-shaped tubes that offer several advantages and also come with certain limitations.
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.
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.
U-bend tubes are used to transfer heat between fluids.
Transfers heat between fluids, allowing return flow at 180° in a compact space.
Used in heat exchangers, chemical & petrochemical, food processing, and refrigeration industries.
Applied in heat exchangers at Oil & Gas, petrochemical plants, refineries, and power plants.
Handles aggressive fluids like sodium hydroxide + sodium hypochlorite safely.
Allows pipeline expansion without buckling; flexible or sliding options available.
Enhances heat transfer when the outside coefficient is lower than the inside, improving efficiency.
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