of galvanic corrosion in the confined area under the overlay. Such damage can be
minimized by achieving good quality repair welding.
"All repair welding should be given a thorough visual inspection. Dye penetrant
examination should be 'conducted on any areas where the weld quality is fair to
poor. If the plant owner is experiencing continual problems with voids forming below
holes or defects in overlay, the complete overlay should be inspected with dye
"Other areas where non-destructive testing should be used during cavitation
When a cavitation repair is completed over a crack repair, dye penetrant
examination of the final surface should be performed.
At the base of the prepared surface where the cavitation damage is in highly
stressed areas, magnetic particle or dye penetrant examination should be
When making weld repairs with stainless steel plate, dye penetrant
examination of the weld should be performed.
"Removal of Braces and Strongbacks. Immediately prior to and after removal of
braces and strongbacks, reference measurements should be made to verify that the
blades do not spring out of shape once the braces or strongbacks are removed.
These measurements can include reference of the propeller or Kaplan runner blade
to a fixed point on the discharge range or on a Francis turbine, a dial indicator
mounted on the draft tube liner, runner band, or runner crown.
"Final Dimensional Checks. Final dimensional checks should include a repeat of
those dimensions measured prior to the start of repairs. If templates are available
or have been made, the template checks should also be made.
"If the power developed by the turbine is not to be decreased, then the vent opening
after the repair should be equal to or greater than that measured prior to the repair.
A tolerance of -0 to + 3 percent of total vent is recommended.
"On propeller and Kaplan runners, the blade angle should also be unchanged. A
tolerance of -0 to + 1/2 degree is recommended.
"Repair of Discharge Minus (Propeller and Kaplan Turbines). Repair of cavitation
damage on a propeller or Kaplan turbine discharge ring is a time consuming and