Although various material combinations are possible the most successful combination
for general service has been:
Stationary ring: Nickel Aluminum Bronze, UNS C95500
Rotating Ring: Austenitic Stainless Steel, UNS S30400
Due to their dimensional stability, single-piece castings or ring-rolled forgings have
proven to be most successful in resisting premature failure due to fatigue of the rings
or the fasteners holding them in place.
A variety of stationary seal ring designs common in Reclamation powerplants have
provided trouble free service. The basic features of these designs are:
1. A thin single piece cast bronze alloy ring shrunk in place in a steel retainer.
2. Thin bronze alloy ring segments factory welded and machined to form a
single piece fabricated ring and shrunk in place.
3. A cast bronze alloy single piece integral ring and retainer.
4. A cast bronze alloy integral ring and retainer cast and assembled in four 90
5. A weld overlay of bronze alloy on the inside diameter of an existing steel
When procuring new stainless steel runners, Reclamation practice is to specify seal
ring surfaces integral with the runner bands instead of providing separate replaceable
seal rings. The surfaces are specified to have sufficient thickness and strength to allow
a cleanup cut during future overhauls in which a stationary ring with a smaller inside
diameter would be installed to close the seal clearances.
WHEN BORING STATIONARY SEAL RINGS, THE UNIT CENTERLINE MUST BE
ACCURATELY DETERMINED. Usually this can be accomplished by hanging a single
tight wire through the unit and locating centering points at several elevations through
the turbine and draft tube to insure the boring bar is set plumb and concentric with the
turbine bearing and the generator stator. Generally stationary seal rings are bored to
be concentric with each other and the centerline of the unit to within 0.1 multiplied by
the diametrical seal ring clearance.