MD&A performed a major inspection and scheduled repairs of a Toshiba® 130 MW steam turbine. During this planned outage, along with a LP turbine inspection, the combined main stop/control valve (MSV/CV) was replaced, as well as the L-0 and L-1 buckets.
Replacement of the combined main stop / control valve (MSV/CV) was requested by the customer in response to a technical memo issued by the OEM relating to a material deficiency. The valve’s original body was a casting, which is prone to stress fatigue and cracking. As a result, the OEM recommended that the valve be replaced with one that has a forged body.
MD&A’s experts completely replaced the combined main stop and control valve assembly. The team provided engineering services for the MSV/CV replacement and outlet pipe modification work to accommodate the new valve assembly.
A new monorail beam was installed to facilitate future CV actuator removal.
After installation, MD&A’s technicians performed several tests and inspections on both main stop and control valves to verify proper installation and assembly. They also performed HP shell arm loading tests before and after the valve assembly was replaced. Radiography inspections were also conducted after the valve casing was installed, revealing some deficiencies that were remedied immediately.
Old MSV/ CV body
New Valve Casing in place
LP Rotor Inspection, Bucket Replacement, and Related Repairs
As part of planned work for this outage, MD&A's experts removed and shipped the steam turbine LP rotor to MD&A’s Turbine-Generator Repair Facility for inspection and bucket replacement (which had been previously recommended by MD&A’s major inspection of the unit in 2020). The team performed visual inspection, blast cleaning, dimensional inspections, and NDE inspection of the entire rotor. The rotor was found to be in very good condition overall. Steampath inspection revealed minor FOD, minor moisture erosion, and minor rubs on packing seal lands.
MD&A’s experts installed new buckets for rows L-1 and L-0 rows, according to the moment weight chart provided with the buckets. They required replacement due to wet steam erosion and OEM TIL recommendations.
Rather than replacing them with conventional components, our Advanced Continuous Cover Blades (CCB) were utilized. These blades are constructed using a mono-block blade structure, leaving fewer locations for corrosive deposits. They are less susceptible to stress corrosion cracking and demonstrate excellent vibration characteristics. These long blades provide up to 8% stage efficiency increase, without requiring diaphragm replacement. As part of their installation, MD&A’s technicians reamed all dovetail pinholes, and installed new pins.
After installation, covers for both stages were final machined as required to meet the stated requirements. The team also conducted minor repairs for stages 13 TE & GE to resolve FOD/impact airfoil damage.
New buckets for rows L-1 and L-0
Upon completion of the work, a high-speed balance of the rotor was performed at our Repairs Facility.
Once the LP inner casing was removed, NDE inspection was performed on the struts located in the center flow area to verify the strut repairs from a previous outage. The LP inner casing horizontal joint was also inspected, and minor erosion was found on the upper half. During reassembly, high temperature sealant was used in the eroded area.
IP & LP Admission Control and Stop Valves were also disassembled and inspected during the outage.
Lastly, at startup, a vibration analysis was performed and the vibration levels were found to be low and met the requirements for acceptable operation.
CV and IP Admission Actuator Repairs
As part of the planned outage, MD&A’s team removed one Rexroth® Extraction CV actuator, two Mafag® IP admission valve actuators, and two Mafag® LP admission valve actuators. They were shipped to MD&A’s Bearing, Seals and Hydraulics facility for disassembly, inspection, repair, reassembly, and testing.
[Cylinder & Spring Can]
For the CV actuator, our experts rebuilt the servo, and tested, flushed, reinstalled the poppets, and replaced shaft seals and O-rings. All other main components of the actuator were found to be in good condition and reused.
New CV Actuator
For the IP and LP admission valve actuators, our technicians performed various repairs including chroming and grounding two of the shafts, polishing two of the cylinders, replacing a poppet valve on one unit, and installed new RVDT and packing glands on all.
Upon completion of reassembly, all actuators were tested and found to be properly functioning and free of leaks. The actuators were pressure tested at 110% and stroked and tripped several times.
Bearing, Seals and Hydraulics experts also repaired the T4 bearing because onsite the upper half bearing showed indications of lack of babbitt bonding at the horizontal joint. They blended some babbitt and additional PT was performed with no indications found.
Controls
MD&A’s technicians performed a wiring inventory of the DEHC and distributed IO channels. Several observations were made including old wiring that should have previously been removed, and issues with wiring that was not wired to the manufacturer’s documented specifications. The shields for four RVDT position feedback triad cables were also not landed at the EHC cabinet. MD&A’s technicians worked with the on-site electrician to resolve these issues.
The team also noted that the CV junction box did not have a properly connected ground cable. Further, LVDT jumper settings in the EHC cabinet were found in to be in “as-shipped configuration”, and therefore not properly configured. MD&A’s team resolved the issues by adjusting the settings to match the manufacturer’s drawings.
Summary
The extensive scope and successful completion of this engagement demonstrate MD&A’s ability to provide expert service on a wide range of steam turbine systems and components. From inspection and routine repairs, to more extensive work, such as bucket and MSV/CV assembly replacements, MD&A’s technicians completed the work on time and to the customer’s satisfaction. This case perfectly demonstrates why MD&A is respected as a full-service, one-stop source for turbine operators worldwide. Call our us at (518) 399-3616.
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