MACHINING & MACHINERY
SWIFT AND EFFECTIVE SERVICE
SULZER
The stub shaft was shrink-fitted to the shaft before being welded in place.
FAST ROTOR REPAIR ALSO IMPROVES EFFICIENCY
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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PECM Issue 38
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.”
With the location of the repair being so close
to the 6th disk, some additional repairs would
be needed to this disk, which would extend
the overall time to complete the project.