Mechanical Dynamics &Analysis (MD&A) recently completed a steam turbine major inspection of an industrial Siemens® SST-600, 36-stage, 60.5 MW steam turbine including generator and related system components.
Industrial steam turbine/generators are used globally in chemical and petrochemical plants, refineries, pulp & paper mills, and mining operations. They are also used in biomass and waste-to-energy facilities, combined heat and power plants, geothermal and concentrated solar power installations, and desalination operations, including many others.
Ongoing operation of these units ensures stable, reliable use of proven technologies to convert the expansive power of steam into useful mechanical work. The processes are both fundamental and critical as the world exploits all available resources to meet its present and future needs for heat and power.
The professionals at MD&A are uniquely qualified to serve these needs by applying their deep and time-tested experience with steam turbine/generators, regardless of OEM.
For this particular industrial unit, onsite work was performed by MD&A’s Outage Services division, Generator division and our Turbine & Generator Controls division. All valves were sent to MD&A’s Turbine-Generator Repair Facility in St. Louis, MO for inspection and repair. MD&A’s Bearing, Seals and Hydraulics Division in Euclid, OH, inspected bearing assemblies, thrust pads and oil deflectors.
ST-660 Industrial Steam Turbine Major Inspection
After mobilizing, MD&A’s experts removed the upper-half shell and turbine rotor, then performed blast cleaning for complete non-destructive examination. The rotor, packing carriers and blade carriers were aligned to OEM specifications. The nozzles were blast cleaned and NDE’d in place.
Inspection revealed evidence of steam cutting that was photographed and recorded, as well as some deformed bolts. Various other specifics were recorded in the Recommendations Report.
Upper half and lower half shells were also cleaned and inspected.
A key benefit of MD&A’s inspections is written and photographic documentation of lessons learned that can assist the owner/operator in future outages. One lesson learned was on the rotor lift. For this inspection, the turnbuckles were removed and chain falls were used in their place. For future outages, two 15-ton and two 10-ton chain falls should be on hand due to minimal lift clearances.
This recording would benefit both owner/operator and contractors involved in future work.
In-depth inspections then proceeded. This included axial and radial blade clearances, rotor radial runout checks, nut rotation and tightening, thrust bearing clearances, and complete visual and NDE inspections (general, HP impulse wheel, and all 36 rotor stages).
Generator
For the Siemens® conventionally air-cooled generator (71.18 MVA), the coolers were cleaned, visually inspected and pressure tested. The field was removed and generator inspection and testing were performed.
MD&A completed major inspections of both the generator field and stator including visual, borescope and electrical testing. Minor contamination was found on the field turn windings beneath the retaining ring. Signs of field turn migration were also identified and addressed.
One field ground detection bolt was found already removed prior to the MD&A Generator Team’s arrival. It was reinstalled according to OEM specifications.
To complete electrical testing, the field winding was isolated from the brushless excitation components. Testing then proceeded on the generator field (IR with PI, DLRO and AC Impedance), rotating armature and rectifier wheel, stationary field, and stator.
At completion, field windings were reconnected to the shaft-mounted brushless excitation equipment and a final IR test was performed.
Conductive paint was applied to the affected partial discharge areas to reduce sparking effect and increase stator bar life.
With testing complete, MD&A issued a recommendation for power factor testing at yearly outage intervals to monitor health of the insulation system.
Brushless Exciter
The brushless exciter was cleaned, inspected, and realigned. The ABB Unitrol 6000 Exciter Regulator Cabinet was also cleaned and inspected.
Steam Turbine Valves
MD&A’s facility in St. Louis disassembled, cleaned and inspected the control valve, main stop valve and other valves. The emergency stop valve was also disassembled, cleaned and inspected during the outage.
For all, a final blue check was performed, 100% blue contact was achieved. New rope packing, supplied by MD&A, was installed during valve reassembly.
Other key elements
All turbine bearings were replaced due to wear. Generator bearings were NDE’d and reused. Replacement thrust bearings were installed at reassembly due to wear, New RTDs were installed at MD&A’s Bearing, Seals and Hydraulics facility.
Auxiliary system work included the lube oil tank which was drained and cleaned under MD&A supervision. MD&A performed additional cleaning of the tank and baffle plates. Two lube oil coolers were unstacked, washed and disassembled.
Alignment
Topless laser alignment was completed before startup. This method utilizes laser accuracy to eliminate the time-consuming and expensive process of reassembling a steam turbine for “Tops-On” alignment measurements, saving hundreds of man-hours labor per turbine section. This included horizontal joint measurements, bolt roundness checks, stationary component position verification, and side slip readings among others using laser equipment. Our alignment engineers have the expert knowledge needed to interpret the data.
Why MD&A?
The experts at MD&A are not only dedicated to the fundamentals of turbine and generator longevity. They apply their vast experience in all OEMs to understand and import precise lessons learned throughout the industry, then direct their knowledge and skills to the ongoing development of using steam effectively and efficiently for the long-term benefit of owner/operators throughout the world.
MD&A’s technical directors and service technicians bring decades of experience to each industrial and utility project regardless of OEM, a process now proven in more than 20 countries worldwide. Committed to both industrial and utility customers.
We invite you to discuss any steam turbine, generator or gas turbine issues with us today. Call us at (518) 399-3616.
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