Digester and Clarifier Mechanism Repair

The challenge

Inside a digester and a clarifier, the rake arms and drive components sit under the sludge and the gas, where corrosion works on the steel from every side. Over time the wetted metal thins across the mechanism and the arms pit and weaken. As that steel is lost, the rake runs out of true and struggles to move solids the way it was built to, and the corrosion keeps spreading until the arms can no longer carry the load. Left untreated, the mechanism fails and the basin has to come out of service for a full set of new arms, which is costly and slow.

Our approach

We start by blasting the arms and the wetted mechanism back to clean metal so the repair has sound steel to bond to. We rebuild the pitted and thinned sections with a cold-applied composite, bringing the arms back to profile so they carry the load and run true again. Then we protect the whole assembly with a coating keyed to the digester environment, so the steel sits under one barrier against the sludge and the gas. We work cold throughout, with no hot work on the mechanism, and the rebuilt arms keep moving solids without the owner pulling the basin for new ones.

1. Assess and mapWe inspect the rake arms and drive components and map where the wetted steel has pitted and thinned across the mechanism.
2. Blast to clean metalWe grit-blast the arms and the wetted mechanism back to clean, profiled steel so the composite and the coating bond properly.
3. Rebuild with compositeWe rebuild the pitted and thinned sections cold with composite, restoring profile so the arms carry the load and turn true again.
4. Coat for the environmentWe protect the rebuilt assembly with a coating keyed to the digester environment, carrying the steel under one barrier against the sludge and the gas.
5. Return to serviceWe confirm the rebuilt and coated mechanism is sound and hand it back so the rakes keep moving solids in the basin.