Tube to Tubesheet Joint – Expansion before or after welding???

A very common question arises while deciding the sequence of welding and expansion of Tube to Tubesheet Joint.

The preferred and the recommeded sequence is welding before expansion:

The reasons as mentioned below;

1.Welding shall be performed in an atmosphere where welding gases can escape; welding after expansion will surely result in bad tube-to-tubesheet joints having porosity or weld inclusions by lubricants (if cleaning not done properly)

2.Welding after expansion would cause adverse effects on expansion (can get loosened) due to welding heat. Such tubes would be requiring re-rolling.

On the other hand, the demerits are;

a. No foolproof check would be in place for leak tightness of expansion done.

b. Chance of welding getting damaged during expansion process. The later can be overcome by increasing the starting distance of expansion towards shell side (recommended is > 12 mm from the toe of the weld joint, used by manufacturers.

PS. For Titanium & Zirconium, mouth expansion prior to welding is recommended to avoid/minimize root oxidation.

Reference: Scribed article posted by Dries Vandezande

Keep reading, happy welding

KP Bhatt

Know about MLP in Tube #Tubesheet joint

MLP – Minimum Leak Path

Concept – while designing the heat exchanger, critical and potential leak path of the fluid is tube to tubesheet joint. Thus, T#TS joint design become more important. It has to be decided whether to go for expansion joint, seal weld or strength weld or combination of strength weld and expansion.

Definition – Minimum Leak Path for the strength weld joint is the minimum distance required by a fluid from root side of the weld to get leaked from face side i.e. Tubesheet side.

Generally, requirement of MLP is same as the tube thickness.

Above sketch represents the T#TS joint, where “b” is measured as Minimum Leak Path.