How Potrero Utililized Flush Patches to Manage Localized Under Deposit Corrosion Damage in Waterwall Tubes

Flush Patch repair of boiler tubes, in which a circular section of tube is replaced to repair an isolated flaw, is typically considered to be a temporary repair. This paper reviews the successful flush patch repair program at the Potrero Power Plant in San Francisco. Over an 11-year period, a total of 294 flush patch repairs were utilized to repair isolated locations of under deposit corrosion in high flux areas of the water wall tubes. In this time period, three patches were replaced due to leaks found in hydro testing. Most of the repairs were performed in the early part of a decade when the unit was on line for an average of over 7,100 hours a year.