All-welded plate exchangers
Eliminating gaskets entirely by developing fully welded plate exchangers further enhances the reliability as well as the temperature and pressure limits of the plate exchanger. While all have internals made of thin, pressed alloy sheet, the exchangers may be quite different in appearance and performance, depending on the manufacturers' design, specifications and materials of construction.
Temperature limits at the low end range from -200 degrees Celsius for certain all-stainless-steel designs, to -40 degrees Celsius. At the high end, the limits range from 250 degrees Celsius, to above 800 degrees Celsius. Sizes range from units small enough to fit on top of a desk, to those more than 15 m in length.
Because they have no tube-tubesheet joints, welded plate exchangers do not suffer from internal vibration and are mechanically reliable. Construction is of corrosion-resistant alloy. The high reliability and reduced maintenance costs, as well as the low installation costs are factors that heavily favor these heat exchangers.
However, there are a number of features that distinguish the construction of welded units and can determine the final choice of equipment. For example, exchangers that are welded in all three directions should be used primarily for continuous operations, as cyclic services can cause thermal fatigue unless baffles are built into the design.
Some units have no gaskets. However, others use them for the covers, shells or heads for the final sealing of the vessel from the environment.
It is important to note that welded plate exchangers, unlike gasketed and semi-welded models, can neither be expanded in surface area nor can they be cleaned readily by mechanical methods. If cleaning is expected to be necessary, it is best to provide for the ability to clean chemically when laying out the equipment design.
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