bearing shoes must be poured. Regardless of the method used to rebabbit the
bearings, ultrasonic testing should be performed to verify the integrity of the babbitt
to steel bond and the absence of porosity. A babbitt to steel bond of no less than 85
percent should be specified.
The bearing journals and thrust runner should also be inspected for any damage.
The journals should be checked for any scoring or other damage. Damage is rare,
but in most cases scratches or scoring can be adequately repaired by s6ning to
remove any high spots. More severe damage may require machining. The thrust
runner should be checked for scoring on the bearing surface and for any fretting
corrosion damage between the runner and the thrust block. If fretting corrosion is
severe, check the contact area between the runner and the thrust block. If less than
70 percent, machining may be necessary. If machining is required, choose a machine
shop carefully, as it is critical that the thrust runner surface be perfectly
perpendicular to the shaft. Tolerances for thrust runners are usually in the 10-
4.2 Turbine runner
In most cases, the repair of cavitation damage can be accomplished much more effectively
with the runner removed from the turbine pit, as the runner can be positioned for easier
access. An overhaul is an excellent opportunity to restore the runner to like new condition,
or in some instances, better than new condition.
describes techniques and procedures for repairing turbine runners.
4.3 Wicket gates
The wicket gate bushing and packing journals should be measured and checked to drawing
tolerances. The wicket gate shaft should be checked for straightness. The top and bottom
sealing surfaces should also be checked for wear or cavitation damage. The heel-to-toe seal
areas should be checked for straightness and to verify that the seal surfaces are parallel to
the gate shaft.
Worn or corroded journals that operate in greased bronze wicket gate bushings
should be built up by welding with a 309 stainless steel and machined back to
original diameters. The repair to the top and bottom sealing surfaces will depend on
the damage and on the facing plate material. If the damage is obviously from
misaligned or misadjusted wicket gates with no apparent galling, and the materials of
the gate and facing plates are not prone to galling, weld repair with a material similar
to the gate material should be sufficient. If galling is present, a galling resistant
material should be used to overlay the top and bottom surfaces. If the facing plate is
a bronze, a stainless steel or Nitronic 60 stainless steel weld overlay would be
recommended. If the facing plates are stainless steel or steel. Nitronic 60 or nickel