White Rust Corrosion/Condenser Tube

An ammonia evaporative condenser tube was received for failure analysis. The tube material was SA-178 A zinc galvanized carbon steel. It had been in service for 3 years. The sample was removed from the top row of the north condenser, near the inlet, presumably the hottest surface.

The condenser was receiving service about 2 months after startup. Therefore, for the first couple of months, it had been run with no water treatment or passivation. A significant amount of corrosion (including white, yellow and brown deposits) had developed and covered approximately 30-50% of the tube surface. It was indicated that there were tubercles everywhere in the basin but they were especially bad at the point where the water inlet had been. A phosphate passivation procedure was immediately performed on the condenser bundles and then a routine water treatment program was initiated.

The pH was controlled with carbon dioxide injection. The condenser had its own small sump beneath the ammonia tubes and water was recirculated over the tubes to condense the ammonia inside the tubes as a part of ammonia refrigeration system. All the water recirculation lines are made from copper and a substantial amount soluble copper was detected in the water when ammonia leaks were present.

 

 

Severe corrosion was observed on the tube OD.

Significant pitting as well as several corrosive deposits (white, yellow and brown colored) were noted.

The ID exhibited minor corrosion.