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Journal & Thrust Bearings
Both the journal bearing and thrust bearing pads were found okay with slight rubbing marks on babbit surface. The lining/rubbing marks on bearing surface was observed as a result of contaminated oil. To rectify this the bearings were disassembled and the surface was cleaned off with a scotch brite.
The rotor was cleaned off at BYCO workshop and the dirt particles were removed from it. Rotor was found worn at sealing areas due to compressor seizure. In order to rectify this, grinding and polishing was suggested and it was sent to United Engineering workshop for grinding and polishing and then to Turbo Machinery Services workshop for shop balancing. The rotor was balanced with the coupling and the lock nut installed. Balancing certificate is attached in annexures.
Floating Seals Installation
O-rings were installed on the floating seal housing after applying Molykote. Seal housing was installed followed by installation of inner floating seal in the housing. Tangential cut ring was then installed and the outer floating ring was installed following the tangential cut ring. The position of the rings and dovel pins was confirmed with WEIR representative.
Rotor Axial Float & Free Rotation Check
The rotor was rotated by hand to check free rotation and confirm proper installation of parts. Free rotation check was done in presence of BYCO technician. Rotor cold float was checked using a dial gauge. The rotor was moved from the DE and float was recorded by a dial gauge mounted on the Non Drive End. The axial float value recorded was 0.36mm. The data recorded is mentioned in the clearances data in the report
Turbine Rear/Exhaust End
Rear end pedestal upper half disassembled. Journal bearing disassembled and upper half removed followed by as-found clearance check which was found on higher side. Bearing also showed wear and discolored surface with slight rubbing marks. Therefore, it was replaced with the bearing that was locally refurbished. Oil seals disassembled and found Ok but having carbon deposit which was cleaned.
Turbine and generator rotors uncoupled and coupling gear removed. It is a rigid fixed type coupling. All coupling bolts, nuts and both flanges marked to ensure proper installation during box up to avoid unbalance. Shaft journal and seal surfaces cleaned, polished and their OD dimensions were recorded and found within limits. There were certain bolts with burs on threads which were rectified.
Turbine Rear End
Turbine rear end bearing replaced with the available spare and its clearance recorded which was found within OEM recommended limits. Clearance was verified with plastigauge. Bearing contact checked and about 80% shaft to bearing contact observed. Oil seals assembled after cleaning and polishing. Coupling installed according to the match marks and pedestal installed to finalize turbine rear end assembly.
Turbine Rotor Axial Float
Upon completion of turbine journal bearings assembly, the rotor axial float was checked. It was out of the OEM recommended limits and shims size was calculated to bring the axial float to optimum value. The shims were installed in the thrust bearing and axial float of turbine was checked again which was now found within OEM recommended limits at an optimum value. All clearance data is available in section 5 of this report.
Services of 3rd party were hired for alignment check and perform alignment if required. The field service rep. of the 3rd party acquired the alignment data using the laser alignment tool and upon analysis recommended that machine is within tolerance limits for alignment and further alignment is not necessary. Turbine and generator were coupled after verification of machine alignment.
Lube Oil Flushing & Turning Gear
Lube oil flushing started on August 17th and turbine barring started on turning gear. A noise issue was observed on the turbine front/governor end. The axial displacement readings also showed an erratic behavior. Upon inspection through the inspection window at the front end, the pinion gear flange was found having burs around the threaded holes. These burs were ground, polished and the gear reassembled. The lube oil flushing was continued and turbine barring started once again, the noise issue and axial thrust probes erratic behavior problems were resolved. The oil filters were inspected on regular intervals and cotton cloth replaced after each inspection, foreign debris including babbitt material observed on filter cloth upon inspection.
Rotor as found centering was checked at rear end with casing and pedestal. The recorded centering data is available in section 6.
|Babbitt deposit on journal surface|
|Rear end journal bearing|
Rear end journal bearing disassembled. Babbitt material deposit observed on bearing and shaft journal surface. Bearing as found clearance was recorded. VEX recommended to replace this bearing.
Rear end coupling shim pack removed. Coupling as found stretch was recorded and coupling was removed.
Front end disassembly started with removal of the pedestal upper half.
Rotor as found centering was checked at front end with casing and pedestal. The recorded centering data is available in section 6.
the casing collar was stuck with gland seal collar at turbine front end. It was heated with gas cutters and set free with thermal expansion of casing collar. This caused an unforeseen delay of one day in the overhaul progress. Casing was then initially lifted up with jacking bolts and then with manual hoist and crane. Casing was removed and set aside. Note the orientation and position of leveling washers on the casing at this stage.
Upper Half Diaphragms
Diaphragms upper halves were removed after recording their as found clearances. Note the orientation and position of leveling washers placed between upper and lower half diaphragms. Heavy deposit observed on exhaust stage nozzle and rotor blades. A sample of the deposit was sent to lab for analysis which will be useful in the future.
Rotor removed from the diaphragms using the lifting bar arrangement and secured on the rotor stand.
Lower Half Diaphragms
Lower half diaphragms as found clearances recorded and diaphragms removed from casing for cleaning and inspection. Alignment keys secured. Note the orientation and positions of leveling washers.
|Rotor visual inspection after cleaning|
|Nozzles visual inspection after cleaning|
Rotor and diaphragm blades cleaned up with hydro jetting, steam jetting and chemical cleaning for maximum possible removal of the deposits. Turbine rotor and diaphragms did not show any damage upon visual inspection. VEX recommended to use Aluminum Oxide blasting for fast and effective cleaning of rotor blades and diaphragms nozzles. Procedure attached in annexure for future reference.
VEX recommended to carry out DPT of rotor and all diaphragms to identify any surface cracks to these parts. However, all these parts were not tested due to time limitation. The last two stage nozzles of the bleed off section only were tested with DPT. The test indicated no damage to these nozzles.
|Penetrant applied after cleaning nozzles|
|Inspection of nozzles for cracks etc., after applying developer|
|Penetrant cleaned after settling time|
Rotor was placed on the diaphragms using its lifting bar arrangement and carefully rigging with crane and chain hoist. All rotor clearances taken and recorded
All bearings were assembled after placing the rotor. Journal bearings clearances recorded and compared to as found and reference data. Thrust bearing axial clearance was checked with rotor float and compared to reference and as found data.