Obviously, if gaskets are the problem, why not do away with them? The answer is not as simple as the question.
A design that reduces the amount of gasketing is the semi-welded plate exchanger, in which most of the gasketing in contact with the process fluid is replaced with a laser weld. The other fluid channel is left gasketed. This construction is accomplished through the production of plate pairs, or cassettes, which are then assembled in proper number and configuration, just like a basic plate heat exchanger. There are two ring gaskets still in contact with the process fluid, but they can be PTFE-encapsulated because of their size and location. The unit can still be disassembled for mechanical cleaning on the non-process-fluid-side or for adding additional surface area.
This configuration has been very successful in applications where chemical resistance is required, or enhanced reliability in the presence of noxious fluids is desired. Use of semi-welded units is increasing in the chemical, refining and refrigeration industries.
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