Everything you should know about U bend tube

 Murphy can make U bend tube in our factory according to customer requirements. The elbow is heat treated according to the customer’s requirements, and then hydrostatic pressure test and dye penetration test are performed as needed.

U-shaped elbows are widely used in heat exchanger systems. Heat exchanger equipment based on stainless steel U bend tube plays an important role in the nuclear industry and petrochemical machinery manufacturing.

U bend tube heat exchangers are specially designed for high temperature applications, especially steam condensing or hot oil systems. When the differential expansion makes the fixed tube-sheet heat exchanger unsuitable, and in some cases the floating head type (HPF) cannot be selected, the U bend tube heat exchanger will be selected.

The surface of the finished U-shaped elbow should be free from scale and scratches after bending.

Dimensional tolerance U-bend pipes are in accordance with relevant regulations of TEMA R.C.B. and ASTM A566 and ASTM A688

U bend tube diameter

In the bending part of the U bend tube with R = 2×D or larger, the main diameter and the secondary diameter of the pipe shall not deviate from the nominal diameter by more than 10% before bending.

If the specified value is less than 2×D, the tolerance may be larger, which requires the customer to confirm before ordering.

Wall thickness of U bend tube curved part

The wall thickness of the tube in the U-shaped bend shall not be less than the value determined by the following formula:

 

Tf wall thickness after bending, inch [mm],
T specified minimum pipe wall thickness, unit: [mm]
R centerline bending radius, inch [mm]
D Nominal outside diameter pipe diameter, inches [mm].

U bend tube leg length

For U-shaped tubes, the distance from the tangent point of the bend and the tube leg to the end of the tube leg, the length of the leg should not be less than the specified value, but it can exceed the specified value as follows:

Leg length [mm]

Up to 6000 mm: -0 / +3.2 mm
Over 6000 mm to 9000 (inclusive): -0 / +4.0 mm
More than 9000 -0 / + 4.8 mm

Difference in leg length

Unless otherwise specified, the difference in the length of the pins of the U-shaped elbow shall not exceed 1⁄8 inch = 3.2 mm.

Tube end: right angle
The end of any tube shall not deviate from the square by more than:

0.25 mm, suitable for tubes up to 5/8″ [15.9 mm]
0.40 mm [15.9 mm] for pipes higher than 5/8 inches

Leg spacing

The distance between the legs measured between the tangent point of the bend and the distance between the legs should be no more than 1⁄16 inch [1.5 mm] from the value (2 R-specified outside diameter of the pipe), where R is the centerline bend radius.

 Curvature of the curved part

The curvature of the curved portion of the U-tube should be substantially uniform and must not exceed 6 1⁄16 inches (1.5 mm) of the nominal centerline radius.

Deviation from the plane of bend

The allowable deviation from the bending plane must not exceed 1⁄16 inch [1.5 mm], for example measured from a tangential angle.

The dimensions of special grade heat exchanger tubes may differ from the above dimensions.

Basic testing and processing:

1. High-pressure hydrostatic test: minimum: 10 Mpa-25Mpa.
2. Underwater air test after bending
3. U-tube wall thickness test
4. Eddy current test before U-shaped bend is formed
5. Ultrasonic test before U-shaped bend is formed
6. Heat treatment can relieve stress

Other details of U bend tube:

a. Cut all the pipes to the specified leg length, and use air for internal cleaning and deburring.
b. Before packaging, both ends of the U-shaped elbow are covered with plastic covers.
C. Vertical separator for each radius.
d. Each plywood box is equipped with a packing list covered with plastic to facilitate identification of order details, including an accurate list of internal radius and length.

 For more information, contact us!