c. Carbon steel - Historically the most versatile and effective coating for
carbon steel runners and wicket gates has been red lead priming paint,
Federal Specification T-T-P-86 Types II and IV.
As an alternative coating to avoid lead contamination, vinyl resin, VR-3, is used
as a runner and gate coating at many facilities. The vinyl resin can be supplied
in white which greatly enhances visibility in the turbine. However when heated
the vinyl resin can generate toxic fumes and must be thoroughly removed prior
to weld repair.
Coal tar epoxy can be successful as a wicket gate coating but often loses
adhesion and peels off under high velocity flow.
Epoxy Phenolic coatings may provide better bonding, corrosion and abrasion
resistance for future runner and gate applications. At the present time
Reclamation has had insufficient experience to verify the their performance.
In units which must pass large concentrations of sand and sediment, neoprene
coatings are reported to significantly extend runner life on carbon steel and bronze
11. GUIDE BEARING REBABBITTING
The majority of turbine guide bearings in Reclamation service are oil-lubricated, split
shell, babbitted journal bearings.
Minor scratches on the babbitt can often been be adequately restored by scraping.
However, periodically due to lubrication failure or normal wear the bearing must be
rebabbitted to restore design clearances and surface finish.
The following are guidelines to be used for preparation of rebabbitting specifications:
a. Babbitt material - Unless otherwise specified by the manufacturer, we
require Type ASTM B-23, grade 2, or grade 3 tin based babbitt.
b. Casting - The babbitt is applied using centrifugal casting methods.
c. Tinning - After thorough removal of the old babbitt, the entire bonding
surface for the babbitt must be retinned. If the bearing shell is cast iron, it must
be tinned with nickel.