Dye penetrant testing was
completed to ensure the new
rotor had no flaws.
in order to save time, Sulzer proposed both
stage 6 disks would be removed and possibly
reinstated at a later date. This was then
agreed by customer.
Joining two sections of a turbine rotor
requires considerable expertise, including
computer modelling and finite element
analysis (FEA) to ensure that the proposed
design would withstand the stresses of
normal operation. The FEA was also carried
out at an overspeed of 3’600 rpm to ensure
that the centrifugal loading on the disks
would not cause any damage to the rotor
shaft after the repair. With all the necessary
analyses completed, the machine shop
started to prepare the two rotor shaft
sections for the addition of the stub shaft.
In-house precision machining enabled
the stub shaft to be shrink-fitted into the
prepared connections before the whole
joint area was preheated prior to the
welding process. Using precision-controlled,
submerged arc welding equipment, the
stub shaft was built up to a level that would
allow it to be machined back to the required
dimensions. Once the original dimensions
had been achieved, a series of non-
destructive tests (NDT) was carried out to
ensure there were no flaws in the completed
rotor assembly.
These processes were repeated to remove
the cracks in the thrust end of the rotor
as well, bringing the completed assembly
back to finished dimensions. Once all the
machining was complete, the rotor was
dynamically balanced before being shipped
back to the customer.
IMPROVING PERFORMANCE
While the repairs were being completed on
the rotor, the field service team was working
at the customer’s site to repair the diaphragm
and improve the sealing of the casing. This
work would be influential in improving the
efficiency of the steam turbine.
Prior to the project being started by Sulzer,
the turbine required 393 tonnes of steam per
hour to produce the
53.4 MW of energy. Despite one set of disks
being removed, the repair to the static and
rotor components of the turbine delivered
by Sulzer, enabled it to maintain an output
of 55.1 MW but using only 374 tonnes per
hour of steam, which is an 8% improvement
in efficiency.
When the repaired turbine rotor arrived
back on site, the field service team carried
out the installation and commissioning,
which included vibration testing at full
load. All the results were well within the
original specifications and the generator has
remained at full capacity ever since.
Andrianto concludes: “The customer was very
impressed with the results of this project. In
total, the whole repair took only 16 weeks,
which is considerably less than the estimated
lead time for a new rotor from the OEM,
which is closer to 52 weeks.”
About Sulzer
Sulzer, headquartered in Winterthur,
Switzerland, since 1834, specializes
in pumping solutions, services for
rotating equipment, and separation,
mixing, and application technology.
Sulzer provides cutting-edge
maintenance and service solutions
for rotating equipment dedicated to
improving customers’ processes and
business performance.
Precision machining was required to ensure a perfect fit.
www.sulzer.com
Issue 38 PECM
139