Condenser Tube Sheet Galvanic Protection

The challenge

A turbine condenser puts a tube sheet and a bank of tubes of a different metal in constant contact with cooling water, and that joint of dissimilar metals sets up galvanic attack. The corrosion concentrates at the tube ends and across the tube sheet face, and the cooling water adds an erosive scour on top of it. Metal is lost where the tubes meet the sheet, the inlet ends start to thin and recess, and the seal at the tube-to-tubesheet joint is put at risk. Left unchecked, the loss spreads, leaks develop between the water and steam sides, and the condenser is pulled for an unplanned repair that takes a unit off the grid.

The Belzona approach

The water box is isolated to reach the tube sheet face, which is then blasted back to clean, sound metal so the repair has something to bond to. Belzona 1000 Series composites rebuild the eroded and recessed metal around the tube ends, bringing the face back to profile without any hot work near the tubes. Once the face is rebuilt, a Belzona 5000 Series barrier coating goes across the tube sheet and into the tube ends, putting a continuous, non-conductive layer between the two dissimilar metals and the cooling water. That barrier is what breaks the galvanic couple, so the attack that started the whole problem has nothing to act on.

1. Assess and mapThe water box is opened, the tube sheet and tube ends inspected, and the galvanic and erosive attack mapped so the repair is scoped correctly.
2. Surface preparationAbrasive blasting takes the tube sheet face to a clean, anchored profile and clears corrosion product from around the tube ends.
3. Rebuild the tube ends1000 Series composites rebuild the eroded and recessed metal at the tube ends and across the face, applied cold with no hot work near the tubes.
4. Coat and isolate the metalsA 5000 Series barrier coating goes over the rebuilt face and into the tube ends to separate the dissimilar metals from the cooling water and break the galvanic couple.
5. Cure and return to serviceCure and coating continuity are confirmed, then the condenser goes back for the water box to be closed up and the unit returned to service.