The tube to tube sheet joint is the most critical joint in a heat exchanger. The applicable code of construction specifies some of the standard tube to tube sheet weld joint configurations and various tests to be performed primarily from the mechanical design considerations. For example, as per ASME Sec VIII Div-2, following are the design considerations for a typical tube to tubesheet joint in case of a heat exchanger.

1. Tubes used in the construction of heat exchangers may be considered to act as stays which support or contribute to the strength of the tube sheet
2. Tube to tube sheet joint shall be capable of transferring the applied tube loads.
3. The design of tube to tube sheet joint depends on type of joint, degree of examination, and shear load tests, if performed

In a tube to tube sheet joint, Mechanical design is usually based on the shear strength of the joint and the tube thickness is based on the thermal design. Hence, tube to tube sheet is a perfect example of trade-off between thermal and mechanical design principles. Some of the conventional types of tube to tube sheet joints used in manufacturing of heat exchangers are shown in Figure 4.8.3.