Pump-Turbine Runners. A vent check should be made as discussed
above at both the turbine and pump discharge.
"Application of Braces and Strongbacks. If the amount of repair welding to a
turbine runner is such that blade distortion may occur, braces or strongbacks
should be applied on the side of the blade opposite the weld repair (i.e., usually
on the pressure side). These braces or strongbacks are typically applied near
the discharge edge. Typical examples are shown on
"Even though strongbacks and braces are temporary, proper weld procedures
for their installation are important to minimize residual stresses and metallurgical
changes in the runner material. Carbon steel weld material should be used for
carbon steel runners, and austenitic 308 material for stainless steel areas.
Preheat requirements discussed below for pitting repair also apply to application
of strongbacks and braces.
"Surface Preparation. Surface preparation should be by grinding, chipping, or
carbon arc gouging (air arcing) the damaged area to sound metal. Following
carbon arc gouging, the prepared area should be ground to bright metal.
Grinding is particularly important on martensitic stainless steel castings to assist
in controlling the heat-affected zone from the carbon arc gouging, and should
extend to 2 inches (51 mm) beyond the prepared area. For austenitic stainless
steel, chipping is not recommended because this material will tend to work
harden, making preparation more difficult.
"Preparation should extend to 1/4 inch (6 mm) to 1/2 inch (13 mm) beyond the
edge of the damaged area. For application of a weld material different from the
base material (e.g., stainless material on carbon steel), the edge of the
preparation should be square cut to avoid a feather edge at the joint of the two
"The prepared area should be visually inspected for defects. In high stressed
martensitic stainless steel) or dye penetrant (on austenitic stainless steel)
procedures should be used.
"In areas within or adjacent to stainless steel overlay where it is planned to first
build up the area with mild steel weld material, care must be taken to ensure that
all stainless steel is removed from the area to be welded. The area and depth
of stainless steel may be defined by etching with Nital or copper sulfate. Mild
steel will show the effects of etching, whereas stainless steel will not.