Two case studies are presented that review the design, execution, and results of chemical cleaning on utility once-through generating units. OT was first introduced into the U.S. in 1991. The OT application was successfully demonstrated on a number of utility once-through generating units. Many in the utility industry quickly made the transition from all-volatile treatment (AVT) to OT based on these successful applications. Prior to OT, once-through generating units were chemical cleaned on a preventive maintenance basis (which ranged from 18-36 months). With the advent of OT in the United States, it was touted in the utility industry that chemical cleaning would no longer be required on once-through generating units. Operator experience has shown that chemical cleaning of once-through generating units cannot be avoided but that the frequency rate can be extended out to beyond 8 years.
Keywords" All-Volatile Treatment (AVT), Oxygen Treatment (OT), Hydroxyacetic/Formic Acid (HAF), Ammonium Bifluoride (ABF), Diammonium EDTA, Corrosion Inhibitor