News and Information

News and Information

NEWS INFORMATION

27

2021

-

03

Key Considerations for Replacing Heat Exchange Tubes in Shell-and-Tube Heat Exchangers

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A shell-and-tube heat exchanger, also known as a tube‑bundle heat exchanger, is a type of partitioned heat exchanger that uses the walls of a bundle of tubes enclosed within a shell as the heat-transfer surface. This type of heat exchanger has a relatively simple structure, reliable operation, and can be fabricated from various materials—primarily metals—making it suitable for high‑temperature and high‑pressure applications. It is currently the most widely used heat‑exchanger design. Key considerations when replacing heat‑transfer tubes in a shell-and-tube heat exchanger: 1. The tube surfaces must be free of defects such as cracks, folds, or scale. 2. When tubes need to be joined by welding, each individual heat‑transfer tube may have no more than one weld; however, U‑shaped tubes may have up to two welds.

　　A shell-and-tube heat exchanger, also known as a tube‑bundle heat exchanger, is a type of partitioned heat exchanger that uses the walls of a bundle of tubes enclosed within a shell as the heat-transfer surface. This design is relatively simple, highly reliable, and can be fabricated from a wide range of materials—primarily metals—making it suitable for operation under high temperature and high-pressure conditions. It is currently the most widely used type of heat exchanger. Key considerations when replacing heat exchange tubes in a shell-and-tube heat exchanger are as follows:
　　1. The pipe surface shall be free from defects such as cracks, folds, and scale.
　　2. When tubes are joined by welding, each heat exchange tube may have no more than one weld (U‑bend tubes may have two welds). The minimum tube length shall not be less than 300 mm, and the bent section of a U‑tube shall be at least 50 mm long. No welded joints shall be located in the straight sections of the tube, and the misalignment at the joint shall not exceed 15% of the wall thickness, nor more than 0.5 mm.
　　3. When expansion joints are used between tubes and the tube sheet, the hardness of the tubes shall be checked; generally, the tube hardness should be 30 HB lower than that of the tube sheet. If the tube hardness exceeds or is close to that of the tube sheet, both ends of the tubes shall be annealed, with an annealing length 80–100 mm longer than the tube sheet thickness.
　　4. The ends of the tubes and the tube‑sheet holes shall be clean, free of grease and other contaminants, and shall not exhibit any through‑going longitudinal or helical grooves or other defects that could compromise the tightness of the expansion joint.
　　5. The tube ends shall extend beyond the tube sheet by a length of 4 ± 1 mm.
　　6. Hydraulic expansion is recommended for the expansion joint between the tubes and the tube sheet. Each expanded joint shall not be re‑expanded more than twice.
　　7. When tubes are welded to the tube sheet, the cut surfaces of the tubes shall be smooth and free of burrs, unevenness, cracks, delamination, and other defects; furthermore, the weld area must be free of slag, iron oxide, oil, and any other contaminants that could compromise weld quality.

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Chongqing Shuaihao Machinery Co., Ltd.

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