Precautions for heat exchange tubes of shell and tube heat exchangers

A shell and tube heat exchanger, also known as a tube heat exchanger, is a type of wall heat exchanger in which the wall surface of the tube bundle is enclosed in a shell as a heat transfer surface. This heat exchanger has simple structure and reliable operation. It can be made of various structural materials (mainly metal materials), and can be used under high temperature and high pressure. It is currently the most widely used type.

Precautions for heat exchange tubes of shell and tube heat exchangers:

1. The surface of the pipe should be free from cracks, wrinkles, thick skin and other defects.

2. When splicing is required, the same heat exchange tube can only have one welded joint (the U-shaped tube can have two welded joints). The length of the shortest pipe shall not be less than 300mm, and the length of the curved part of the U-shaped pipe shall be at least 50mm. Long straight pipe sections shall not have joint welding. Butt misalignment shall not exceed 15% of the pipe wall thickness, and shall not be greater than 0.5 mm.

3. The hardness of the tube should be checked when the tube and tube sheet are expanded. Generally, the hardness of the tube should be 30HB lower than that of the tube sheet. When the hardness of the test tube is higher than or close to the hardness of the test tube plate, the two ends of the test tube should be annealed, and the annealing length should be 80-100mm longer than the thickness of the test tube plate.

4. Both ends of the pipe and the hole of the pipe plate should be clean, free of grease and other dirt, and there should be no longitudinal or spiral marks that affect expansion and sealing.

5. Both ends of the tube should protrude from the tube plate with a length of 4±1mm.

6. The expansion joints between pipes and plates should be hydraulically expanded. Each bump should be re-inflated no more than twice.

7. When the pipe and the tube plate are welded, the cutting surface of the pipe should be flat and free of burrs, bruises, cracks, interlayers, etc., and there must be no slag, iron oxide, grease and other sundries that affect the welding quality.