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.

Our approach

We isolate the water box and get to the tube sheet face, then blast it back to clean, sound metal so the repair has something to bond to. We rebuild the eroded and recessed metal around the tube ends with Belzona 1000 Series composites, bringing the face back to profile without any hot work near the tubes. Once the face is rebuilt, we apply a Belzona 5000 Series barrier coating across the tube sheet and into the tube ends to put 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 mapWe open the water box, inspect the tube sheet and tube ends, and map where galvanic and erosive attack have taken the metal so the repair is scoped correctly.
2. Surface preparationWe abrasive blast the tube sheet face to a clean, anchored profile and clear corrosion product from around the tube ends.
3. Rebuild the tube endsWe rebuild the eroded and recessed metal at the tube ends and across the face with 1000 Series composites, working cold with no hot work near the tubes.
4. Coat and isolate the metalsWe apply a 5000 Series barrier coating 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 serviceWe confirm cure and coating continuity, then hand the condenser back for the water box to be closed up and the unit returned to service.