What is the difference between welding first and then expanding, and expanding first and then welding?/

Process difference: Mechanical expansion generally involves welding first and then expanding, to ensure welding quality； Hydraulic expansion is also acceptable. Currently, welding is done first followed by expansion; in applications with strict sealing requirements, the welding+expansion+welding process is employed.

The GBl5l—1999 standard specifies that hybrid expansion-welding structures are widely used because they can effectively dampen the vibrations of the tube bundle, thereby preventing damage to the weld seams and avoiding gap corrosion; in addition, they offer higher strength and sealing performance compared to expansion welding or pure welding alone. Currently, for conventional heat exchange tubes, the \"flattening expansion + strength welding\" method is commonly used ； For important heat exchangers or those operating under severe conditions, the \"strength expansion + sealing welding\" method is required. The expansion-welding combined structure can be divided into two types based on the sequence of expansion and welding in the manufacturing process: expansion first followed by welding, and welding first followed by expansion. Strength expansion fitting is suitable for design pressure~

In most cases, welding first and then expanding is the more common approach, as it ensures better welding quality!

When ordering the heat exchanger, I specified in the technical agreement that the expansion-welding-expansion process should be used.

What does the heat exchanger refer to, as mentioned by a friend upstairs?

What was said on the third floor is very clear. To be honest, in actual processing, if the heat exchange tubes are thin, expansion jointing is used; when the tubes are thicker and stricter requirements apply, welding is employed. The effect of welding combined with expansion jointing isn’t very satisfactory

In practice, welding is carried out first followed by expansion, which helps to avoid the impact of residual oil in the expanded tubes on the weld seam.

Strength welding + expansion bonding and strength expansion + sealing welding are two different processes for connecting tubes to tube sheets in heat exchanger manufacturing. If everything is done exactly as required, the results are excellent! It ensures that there are no gaps at the junctions between the heat exchanger tubes and the tube sheet, thereby preventing corrosion of the tubes and tube sheet by the medium and residual impurities, and it also guarantees that the seal between the tubes in the heat exchanger bundle and the tube sheet is leak-free.

I also think that in most cases, welding first and then expanding is the more common approach, as welding inevitably causes some deformation; by welding first and then expanding, the quality of the weld can be ensured!