A Fixed Tube Sheet heat exchanger is the most common type of heat exchanger in all Industries. Mostly used in higher-pressure and Higher Temperature applications.
Fixed tube Sheet heat exchangers are the one that are very much used in process chemical industries and refinery services, as there is absolutely no chance for intermixing of fluids. This type of heat exchanger is employed where even slightest intermixing of fluids cannot be tolerated. A fixed-tubesheet heat exchanger has straight tubes that are secured at both ends to tube sheets welded to the shell. The construction may have removable channel covers, bonnet-type channel covers, or integral tube sheets. The principal advantage of the fixed-tubesheet construction is its low cost because of its simple construction. In fact, the fixed tube sheet is the least expensive construction type, as long as no expansion joint is required.
Other advantages are that the tubes can be cleaned mechanically after removal of the channel cover or bonnet, and that leakage of the shell side fluid is minimized since there're no triangled joints. A disadvantage of this design is that since the bundle is fixed to the shell and cannot be removed, the outsides of the tubes cannot be cleaned mechanically. Thus, its application is limited to clean services on the shell side. However, if a satisfactory chemical cleaning program can be employed, fixed-tubesheet construction may be selected for fouling services on the shell side. In the event of a large differential temperature between the tubes and the shell, the tube sheets will be unable to absorb the differential stress, thereby making it necessary to incorporate an expansion joint. This takes away the advantage of low cost to a significant extent