Is heat treatment necessary?
Thread Content
It is a low-alloy steel heat exchanger unit; the fluid flowing inside the tubes is highly hazardous, while the cooling water flows on the shell side. The thickness of the tube sheet is 40 mm, and it is made of material Q345R. The heat exchange tubes are made of 20-grade steel. Is stress-relief heat treatment necessary for the shell side?
GB150.4 Clause 8.2.2.3: Carbon steel and low-alloy steel vessels used to contain media with an extremely high or high degree of toxicity shall undergo post-weld heat treatment. The parts in contact with the tube side medium include the tube sheet and the heat exchange tubes. If the shell and tube sheet are connected by flanges, the tube side can be heat-treated separately. For fixed-tube-sheet heat exchangers, overall heat treatment after all the tube and shell side welds have been completed should be considered, or local heat treatment of the final welds and the tube-to-tube-sheet weld joints.
According to standard and regulatory requirements, stress-relief heat treatment is necessary. The specific method to be used depends on the actual structure of the heat exchanger; if the tube side and shell side can be separated, such as in the case of extractable U-tube heat exchangers, stuffing box heat exchangers, or floating-head heat exchangers, then the heat treatment is carried out only on the tube side. For fixed-tube-sheet heat exchangers, attention must be paid during heat treatment to the thermal expansion differences between the heat exchange tubes and the material of the shell side cylinder, and heat treatment specifications should be established.
The tube side is highly hazardous; why is heat treatment required for the shell side?
The second floor explained it in quite detail; time to learn!
Heat treatment is necessary; heat exchange equipment may develop certain structural stresses during manufacturing. Similarly, during operation, differences in temperature across its various components can exacerbate these structural stresses, leading to stress corrosion cracks in the welds. Since such equipment is used in highly hazardous environments, it is essential to eliminate any potential risks inherent in the heat exchanger itself. Heat treatment is required in accordance with the specifications set out in the equipment manufacturing standards.
The shell components related to the pipe train also need heat treatment