the project would require some of the
specialist facilities in the Edmonton Service Center, which has considerable experience in reverse engineering complex
components. With the aim of delivering
a more reliable and efficient turbine, Sulzer
instigated a metallurgical root cause failure
analysis of the damaged shaft to determine
if there were any design modifications that
could be implemented before remanufacturing began.
Even the repair of conventional steam
turbines requires a considerable amount
of high specification machine tooling and
large capacity over-head cranes as well as
a highly skilled workforce. When the repair
involves an almost unique design, the
experience and skill of the engineers really
comes to the fore.
The Edmonton Service Center special-
izes in the refurbishment and delivery of
performance upgrades for large compres-
sors and turbines. The ability to design
and create replacement parts through
reverse engineering enables the team in
Edmonton to deliver improved reliability
and extended service life for a wide range
of plant assets.
The initial investigation showed that
the material used to create the RH stub
shaft could be replaced with ASTM A470
class 7 forging, which is commonly used
in the modern turbine industry. The class
7 material has a higher nickel and chromium content, giving it a higher yield
strength and better resistance to heat and
corrosion than the original.
The new stub shaft was designed, machined, tested and inspected before it was
ready for final assembly. In the meantime,
the rotors were also refurbished with special attention paid to the steam seals which
provide a uniform pressure drop between
each turbine stage. The original seals featured an outdated design that was machined out and modified to accommodate
the common ‘J-Strip’ seal which was installed and gave a tighter clearance between each stage of just 0.010”.
Finally, the repair team turned their at-
tention to the creation of two new rotor
couplings, which connect the turbine rotors
to the generators. The couplings are installed
using a set of eight high tensile, tapered pins
and a series of large, threaded sleeves that
together ensure a uniform torque transfer.
The rotor couplings also act as a journal
bearing, supporting the overhung rotor. As
such, the couplings had to be machined to
a very tight tolerance with a high quality
surface finish to ensure the perfect fit. The
Edmonton Service Center is equipped with
modern machining technology that allowed
the high precision couplings to be manufactured on time.
Once all of the machining was com-
plete, the left and right hand rotors were
reassembled, checked for run-out and
then low speed balanced in Edmonton.
The last operation required the completed
rotors to be shipped to Sulzer’s Houston
Service Center, where the company has
its own at-speed balancing facility.
This crucial process uses vibration diagnostics to analyze the radial vibration
at the bearings and ensures that the optimum balance is achieved at operating
speed as well as minimizing the deflection
and vibration amplitudes during ramp
up and coast down.
With the balancing complete, the rotors were returned to the pulp manufacturing plant, where the field service team
assisted with the installation and commissioning of the turbine.
Rod Whittaker, Project Manager at Sulzer’s Edmonton Service Center concludes:
“Being the first time such a repair has been
attempted in North America, there were
some considerable challenges in this project, not least the precision machining of
the new couplings. Fortunately, our extensive experience and technical expertise has
ensured that the turbine refurbishment was
completed on time and the generator will
continue to provide reliable service for
many years to come.”
showed that the
material used to
create the RH
stub shaft could
be replaced with
ASTM A470 class
7 forging, which is
in the modern