U-Shaped Heat Exchanger Tubes : Seamless Tubes For High-performance Boilers And Heat Exchangers

U-Shaped Heat Exchanger Tubes are seamless or welded tubes bent into a U-shape, designed to optimize heat transfer in heat exchanger tubes and boiler tubes. Conforming to standards like ASTM A179, A192, A213, and JIS G3462, these tubes are essential for industries such as petrochemical, power generation, chemical processing, and HVAC systems. Their corrosion resistance and function as a thermal expansion absorber enhance pipeline durability in high-temperature and high-pressure environments.

Manufactured through cold-drawing or hot-rolling processes, U-Shaped Heat Exchanger Tubes feature 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 project requirements. Post-bending heat treatments, such as stress relief annealing (650-720°C for carbon and alloy steel) or solution annealing (1010-1193°C for stainless steel), ensure optimal mechanical properties and prevent cracking. Surface treatments like pickling, passivation, or 3LPE coating improve corrosion resistance, while capped ends protect tubes during transport.

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 325 MPa (carbon steel) to 620 MPa (alloy steel) and yield strengths from 180 MPa to 440 MPa, they are designed for temperatures up to 650°C and pressures up to 10 MPa. The U-shaped design minimizes thermal stress, eliminates the need for expansion joints, and reduces installation costs, making them ideal for compact heat exchanger systems.

Available in materials like carbon steel (ASTM A179, A192), low-alloy steel (ASTM A213 T11, T91), and stainless steel (304, 316), U-Shaped Heat Exchanger Tubes offer versatility for various applications. Carbon steel tubes excel in low-to-medium temperature systems, while alloy and stainless steel grades provide superior corrosion resistance and creep strength for high-temperature environments. The seamless construction ensures leak-free performance, and their ability to handle corrosive fluids makes them suitable for chemical processing and pneumatic conveying systems.

Addressing challenges like pipeline wear, corrosion, and thermal stress, U-Shaped Heat Exchanger Tubes provide a reliable solution for engineers seeking efficient boiler tubes and heat exchanger tubes. Their high thermal conductivity, durability, and low maintenance requirements make them a preferred choice for critical applications in demanding industrial settings, ensuring long-term performance and efficiency.

The bend side is free-floating and this helps in thermal expansion without requiring expansion joints. U-tube heat exchangers have a simple structure which makes them easy to manufacture and maintain. They are commonly used in shell and U-tube heat exchangers.

U bent heat exchanger tubes are used in various industrial applications for heat transfer between fluids, such as in boilers and condensers. U bent heat exchanger tubes are made from a variety of materials including stainless steel, titanium, and copper alloys depending on the application and environmental factors. They are typically designed to withstand high temperatures and pressures and are used in both liquid and gas applications.

Both ends of the U-tube are fixed on the same tube plate, and the shell and heat exchange tubes are separated. This allows the tube bundle to freely expand and contract without generating temperature difference stress, which is a problem that can occur in other types of heat exchangers.

U-shaped heat exchanger tubes have a simple structure which makes them easy to manufacture and maintain. They are commonly used in shell and U-tube heat exchangers, which consist of a cylindrical shell with U-shaped tubes inside. The U-tube design allows for better heat transfer efficiency, and the compact size of the U-shaped tubes means that the heat exchanger can be very powerful despite its small footprint.

Overall, U-shaped heat exchanger tubes are a popular choice for many industrial applications due to their simplicity, efficiency, and compact size.

U-tubes are made of precision straight tubes. These precision straight tubes are completed after cold rolling and bright annealing. In order to meet the technical conditions of our customers, every step of the process is strictly controlled.

U-tubes are mainly divided into two categories according to materials: stainless steel U-tubes and alloy steel U-tube

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.