MACHINING & MACHINERY
FAST ROTOR REPAIR
SULZER
CRACKED STEAM TURBINE ROTOR
REPAIRED AND REINSTALLED WITH 8%
IMPROVEMENT ON PERFORMANCE
When a damaged steam turbine rotor
needed to be repaired, a power generation
plant in Indonesia turned to Sulzer for an
expert service. Rather than wait for at least
a year for a new rotor from the original
equipment manufacturer (OEM), the plant
opted for a repair that took only sixteen
weeks. This swift and effective repair also
managed to achieve an 8% improvement
in efficiency.
The Indonesian geothermal power plant
had been experiencing some issues with
one of its 60 MW steam turbines. During
the previous two years, the pre-existing
maintenance provider had repeatedly tried
to repair the turbine, but the vibration issue
had persisted. Despite several attempts
to low speed balance the rotor at their
premises, it still exhibited high vibration
levels.
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INITIAL INVESTIGATION
During one of these off-site balancing
procedures, the plant engineers discovered
deep cracks that were suspected to have
been caused by a previous repair by
another service company. As well-known
experts in the repair of steam turbines,
Sulzer was called in to resolve the problem.
Sulzer’s initial inspection revealed that
the rotor had cracks on the radius section
between the last stage disk and the gland
seal area located on both the governor
and the generator sides. In addition, there
was considerable evidence of erosion
on the blades, the disks and the balance
correction holes.
REPAIR RE-EVALUATION
The initial plan was to machine out the
material until the cracks were removed and
then rebuild the shaft using submerged
arc welding before machining it to nominal
dimensions. However, after comprehensive
inspection at Sulzer, the crack propagation
already had a spiral shape through the
center of the shaft, making it impossible
to machine out the crack area only. Sulzer
then came up with a repair proposal that
involved designing a stub shaft that would
be used to join the two pieces together
before the shaft was rebuilt to its nominal
dimensions.
Andrianto Hapsoro, Head of Engineering,
Sulzer Indonesia, explains: “There was
always a customer representative in the
workshop, which helped maintain excellent
communications and keep them up to date
with progress. Any rotor repair is time-
critical, with lost revenue making every day
count in this project.”