Why is the tube sheet of the evaporator not welded?
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Why isn’t the tube sheet of the evaporator welded? At Zhangjiagang Chemical Machinery Factory, during the inspection, it was observed that the tube sheet of the heat exchanger was only expanded and joined, without being welded； In what situations is welding not used?
There is no definitive answer, just as there is no clear choice between expanding first and then welding, or welding first and then expanding. No welding is used; only expansion joining is employed, and it must be a strength-based expansion join. A strength-based expansion join requires very high processing standards and operates under fairly stringent conditions. For specific provisions, refer to GB151-2014 Heat Exchangers. Strength expansion joining is mainly suitable for designs with a pressure of less than or equal to 4.0 MPa ； Design temperature ≤ 300°C ； In situations where there is no severe vibration, no significant temperature fluctuations, and no obvious stress corrosion during operation.
When the pressure i is very low, strength expansion joining can also be used alone
Is it severe vibration but with low pressure? Is it recommended to only inflate rather than weld?
I have dealt with this before: in gas-filled environments, heat exchangers are not allowed to be welded; only expansion joining is permitted.
Because expanding first and then welding can lead to welding defects, such as pores and sand holes, GB151 has updated the requirements regarding the expansion-welding process, stipulating that welding should take place after full expansion; this addresses the issue of welding defects. However, the reason for carrying out only expansion without welding is likely a design-related issue, and a combination of seal welding and strength expansion could be used
I don’t understand what is meant by the 6th floor – why don’t pores form when welding is carried out after it’s fully expanded?
Is expansion joining achieved through the tight connection resulting from the thermal expansion of the workpiece after it is heated?