A condenser shell may be fitted with an expansion joint if the:

The installation of an expansion joint in a condenser shell is advised when the condenser tubes are expanded into the tube sheets. This scenario is significant because the tubes must accommodate thermal expansion and contraction due to temperature changes during operation. When the tubes are tightly fit into the tube sheets, any movement caused by thermal expansion can create stress concentrations that may lead to damage or failure of the condenser.

An expansion joint allows for movement between the shell and the fixed points of the tube sheets, thereby minimizing stress and accommodating changes in length of the tubes as they heat and cool. This consideration is critical for maintaining the integrity and efficiency of the condenser over its operational lifespan.

Considering the other options, they do not directly relate to the need for an expansion joint. For example, temperature differentials are indeed important in assessing thermal expansion but do not dictate the necessity for an expansion joint as clearly as the relationship between tube expansion and tube sheet constraints. The configuration of U-shaped tubes or the method of construction may affect the overall design and performance, but they do not inherently necessitate the use of an expansion joint like the expansion of tubes into the tube sheets does.