15 Cr 25 Ni austenitic weld material and an overlay of a 50 percent
cobalt-containing alloy will result in a repair with good physical and
cavitation resistant properties without post-weld heat treatment. It should
be cautioned that experience with this procedure is limited.
Austenitic Stainless Steel Materials (including overlay). The damaged
areas should be repaired with 308 austenitic weld material.
"Weld Process. Two processes are used for cavitation repair welds:
Gas metal arc welding (GMAW) or MIG welding
Shielded metal arc welding (SMAW) or stick electrode
"The GMAW process has the following advantages:
More rapid application of weld metal.
Lower heat input; therefore the increased rate of weld material
application should not increase the possibility of blade distortion.
If applied correctly, weld quality should be better, with no slag inclusion
and reduced excess weld.
"There are, however, a number of disadvantages with this process, which
would favor the SMAW method.
For applications of small amounts of weld (less than about 30 lb [14 kg]),
the increased set-up time of the SMAW process will offset savings in time
for application of the weld.
Overhead weldings is (sic) difficult with the GMAW process; therefore,
this process is less suited for repairs on the underside of propeller and
Kaplan runner blades.
The GMAW process is not suitable for areas such as the junction of the
runner bucket to the band.
With GMAW process, special care in ventilation is necessary because
excessive air movement will disperse the gas shield. However, insufficient
ventilation will result in an accumulation of Argon gas in the work area
creating a hazard to personnel. Air-supplied hoods are recommended for