Tubes may be:
- packed at both ends
- expanded at the inlet end and packed at the other
- expanded at both ends.
In all cases, the water inlet end of the tube has a flared entry which can be obtained by using a ferrule or expanding and bell mouthing the tube.
Freedom for thermal expansion of the tube is arranged at the water outlet end of the tube. Where the tube is expanded at both ends, a tube plate is arranged to move, and the tube plates, in this case, are stayed to their respective water box doors. An expansion bellows piece fitted between the shell and the tube plate allows the tube plate to move but some form of external support is required to take the weight of the water box and tube plate.
Flared entry:- This is to reduce turbulence just inside the inlet end of the tube by streamlining the flow. Turbulence has an erosion-corrosion effect which leads to leaks. Rubberized inserts are sometimes used in the inlet ends for protection.
Recent investigations have shown that bad entry conditions are a more likely cause for inlet end tube erosion.
Flow across the tube plate can cause breakaway at the inlet of the tube resulting in eddying and erosion.
