This paper describes utility experience with a tube sleeving technique used for extending the remaining life of two heaters that have been rapidly degrading.
Waterside Unit 80 experienced numerous forced outages and de-rating incidents due to tube leaks in the two Heaters #81E and 82W. Root cause analysis was performed using eddy current testing and remote video inspections. The tube leaks were attributed to Stress Corrosion Cracking (SCC) of the Alloy 400 tubing in two specific locations: (1) the tubesheet area, and (2) the U-bends.
The sleeves (thin-walled tubes) were inserted and hydraulically expanded on the inside surface of the tube in the tubesheet area. The nine-inch long sleeves had covered the specific location where the tubes were susceptible to SCC. Sleeves were installed as a preventive measure in tubes that have not yet cracked. As a result of the sleeving, the parent tube metal in that area no longer experienced the chemical environment of the feedwater. This prevented crack initiation in that area. Additionally, a few tubes having pinhole leaks were also sleeved and returned to service instead of the usual practice of plugging the leaking tubes.