Rolled vs Seal-Welded Tube Joints

U-Tube Heat Exchangers For

Rolled vs Seal-Welded Tube Joints
U-Tube Duty

The tube-to-tubesheet joint is where most exchanger leaks start. Choosing how to make it is a decision about pressure, cycling, cleanability and whether you ever intend to retube.

Rolled (expanded). The tube end is expanded mechanically into the tubesheet hole, which usually carries annular grooves that the tube material flows into. It is fast, economical, and it can be drilled out later so the tube is replaceable. The limitation is the crevice at the back of the joint where tube and tubesheet are in contact but not bonded.

Seal welded. A weld at the tubesheet face closes the front of the joint. The roll still carries the mechanical load; the weld provides the seal and eliminates the crevice at the wetted face. This is the standard arrangement on sanitary duty, where a crevice no cleaning cycle reaches is unacceptable.

The Crevice Problem. Behind a rolled-only joint, tube and tubesheet touch without being bonded. That gap is microscopic and it is enough. Process fluid enters, sits stagnant, concentrates and attacks. On sanitary duty it is a place cleaning agents never reach.

A seal weld at the face closes it from the wetted side. That is why sanitary and pharmaceutical specifications require seal welding regardless of the pressure, where an industrial specification at the same pressure might accept a rolled joint quite happily.