Expansion of Tube to tubesheet joint

1) when & why expansion is necessary?

Expansion is necessary in all cases because the tube hole in the tube sheet is slightly higher than the tube OD. So if we do not expand it will cause crevice and ultimately tends to leakage.

 2) Difference between contact(light) & heavy expansion and what its range.

For Heavy expansion, normally grooves shall be provided in the tube sheet as per TEMA RB-7.24. Tubes will be expanded in such a way that it will flow in these grooves. In Heavy expansion normally 5% thinning of tube thickness occurs.

 3) For strength, a weld is an expansion necessary.

For strength welded tube to tube sheet joints, contact expansion is necessary as explained in (1) above.

 4) what are the applications to expand the tube?

Tubes are expanded using standard roller expander or sometimes using a hydraulic expander.