"Research is being done by the CEA on the use of the pulsed arc method of field
repair with the gas metal arc welding process. This technique can provide more
stable overhead and vertical welding when compared to the older spray transfer
"When selecting a weld process, the preference and experience of the welder
should be considered. With the GMAW process in particular, lack of experience
may offset any advantages of this process.
"Repair Procedures. The procedures developed for cavitation repairs are site
specific because of the many factors involved. It is recommended that
procedures be established for each repair program to maintain a consistent
approach, to monitor the results and to avoid excessive costs in any one area
of the program.
"These procedures should be modified to incorporate any changes which could
benefit subsequent repairs. The items discussed below illustrate some of the
important points which should be covered by the procedures.
"Initial Dimensional Checks. Prior to the start of cavitation repairs to a turbine
runner, dimensional checks should be made. These will serve as a basis for
determining whether or not weld distortion has occurred and also to establish
whether or not any measures are necessary to correct distortion which may have
occurred during a previous repair or during initial runner manufacture.
Propeller and Kaplan Runners. The pitch angle of each blade should be
recorded, using the bottom ring elevation of the top of the draft tube liner
as a datum (
Vent checks of the discharge area of the runner should also be made.
This check is made by measuring the closest distance between adjacent
blades, at the discharge edge.
Francis Runners. A vent check should be made as mentioned above for
propeller and Kaplan turbines (
measurements, the average opening between each pair of blades, the
overall average opening, and a variance from average of each opening
can be calculated. Corrective action should be taken if there is large
variation in vent openings, particularly if oversize vent openings are
grouped together on one side.