Special cases of connections between tubes and tube sheet

In manufacturing heat exchangers with the highest operational parameters, channels in the holes of the tube sheet are often used; after the expansion of the tubes, these play the role of a labyrinth seal. Nevertheless, the use of such channels makes it necessary to increase the length of the expansion, which in such cases is done in one or two stages, depending on the length.

the expansion of the tubes

Expanded tube connections made with a straight expander with an integrated feed assembly

The current designs of turbine condensers, which are a compromise between efficiency, reliability, and cost, are a big challenge for the companies charged with the assembly of tubes. It is necessary to expand a relatively hard, thin-walled (0.3-0.5 mm) seamed tube in a soft, flexible, stainless steel tube sheet.

The use of straight expanders with an integrated feed assembly allows for precise expanded connections, with ± 1% of replicability of the extent of expansion, to be achieved. This result can be obtained after performing tests on a sample tube sheet and setting an optimum torque of the expander drive.

This solution prevents the distortion of ligaments. This is impossible when using a self-feeding expander.

expanded tube connections made with a straight expander with an integrated feed assembly

Hydraulic expansion of tubes in exchangers with the highest operational parameters

The continuous increase of operational parameters of heat exchangers, especially in the power industry, the chemical industry, and in utilization equipment, makes it necessary to use very thick tube sheets.

Hydraulic expansion is currently the only technique that guarantees the tightness of the contact between the tube wall and the surface of the hole in the tube sheet. The process of expansion is slow and fully controlled by a measurement and control system.

The most important outcome of the process is the preservation of the structure of the tube; using a mechanical expander would inevitably lead to a change of the structure.

hydraulic expansion of tubes

Orbital welding of tubes to the tube sheets

Thanks to the rapid development of welding technologies, it is possible today to make precise and reliable welded connections between tubes and tube sheets. Significantly better results can be achieved by using a mix of typical expansion techniques and welding techniques, i.e. "expansion + welding", "forcing through + welding", or, in the case of exchangers with the highest operational parameters, "channels in the hole + forcing through + expansion + welding".

In addition to typical expansion and forcing through, we offer a connection of these technologies with orbital welding of tubes to the tube sheet using Polysoude welding machines.

orbital welding of tubes to the tube sheets

Other techniques to make connections between tubes and the tube sheet, such as soldering, gluing, and packing glands, are used rather rarely and not in pressure vessels.