Manufacturing of duplex steel heat exchangers

Composite? Veneers? It’s too professional; could you explain it again?

The outer tube sheet uses a composite tube sheet (the composite layer is made of duplex steel while the base layer is 16Mn forged); the connection method for the outer tube sheet can be expansion bonding combined with strength welding； The inner tube sheet is made of 20MnMo forgings; hydraulic expansion is used to enhance its strength, with the expansion process being repeated twice. Once leakage is detected, manual mechanical expansion is employed for repair. It is best to prepare expansion joint specimens in advance to determine the expansion joint design. It’s a problem if the inner tube sheet of a double-tube-sheet heat exchanger cannot be held in place.

You must have built such heat exchangers before; we made one where the outer tube sheet was made of pure 2205, while the inner tube sheet was made of 16MnIII. This is a bit different from what you mentioned. But I lean more toward your opinion. My question is: 1. For the outer tube sheet, duplex steel can be replaced with composite steel, is this due to the need for strong welds, with the aspect of bonding being a secondary consideration? 2. The inner tube sheet is made of 20MnMo, as this material takes strength expansion issues into full consideration. What problems might arise if a 16MnIII tube sheet were used, during manufacturing or in subsequent use?

We once built a similar heat exchanger, with both the inner and outer tube sheets made of 16Mn forgings, and the tubes being of 2205 material with a diameter of Φ12×1.2. During hydraulic expansion tests, expansion was possible at sufficient strength, and both the pull-out force test and the sealing test passed. However, in actual expansion processes, there were always tubes that could not be expanded; even if expansion was successful at first, leaks occurred when trying to expand other tubes. In the end, there was no other choice but to scrap the entire device; it was a painful lesson. Later, the inner tube sheet was changed to 20MnMo, and only then was it expanded. Experience: The strength of 2205 pipes is higher than that of 16Mn forged pipes, and they exhibit severe work hardening, especially in thin-walled pipes. If there are no reliable process control measures, the most secure design approach should be adopted; there is no need to take risks by shifting the responsibility to the processing techniques. In fact, manufacturers capable of producing double-shell heat exchangers should have extensive experience in expansion jointing, as the main challenge in manufacturing such heat exchangers lies in the quality of the expansion joining of the inner shell. The process methods employed are all designed to ensure the best possible quality for this expansion joining. Therefore, when it comes to expansion joining, each company has its own techniques; in this regard, one can draw on the experience of other manufacturers, but cannot simply copy their methods. Therefore, when designing the inner tube sheet, it is necessary to consider not only factors such as strength but also the company’s manufacturing capabilities and experience, in order to arrive at the most reliable solution.

Our heat exchange tubes are Φ57x2.5, so they might be more expandable than the Φ12×1.2 you mentioned.

Below is the tube sheet material section of the tube expansion procedure

In a double-shell and plate heat exchanger, the inner shell and plate can only be joined by expansion fitting; therefore, the hardness of the tubes must be less than that of the shell and plate, otherwise there is a definite risk of leakage

There will definitely be problems. Do you have any experience with similar equipment leaks? Tube sheet 16MnIII, tubes 2205.