Reverse engineering improvements Precision manufacturing
The Edmonton Service Center specializes
in the refurbishment and delivery
of performance upgrades for large
compressors and turbines. Finally, the repair team turned their
attention 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 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 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.
At-speed balancing
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. Once all of the machining was complete,
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.
The original seals featured an outdated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". 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."