1. WELCOME

2. ERECTION / OVERHAULING CHECKS AND VIBRATIONS

3. CRITICAL OVERHAUL CHECKS IN LARGE TURBINE
The various checks during erection / overhauling of 120 MW, 210 MW, 250 MW and 500 MW, KWU sets are covered here.
ALIGNMENT OF ROTORS
COUPLING OF ROTORS
CATENARY OF THE MACHINE
SWING CHECK
TURBINE ROTORS
ROLL CHECK OF VARIOUS CASINGS
HORN DROP CHECKS
BEARINGS
TURBINE PEDESTALS
TURBINE CASINGS

4. CRITICAL OVERHAUL CHECKS IN LARGE TURBINE
(a) ALIGNMENT OF ROTORS
Carry out alignment of HP/IP/LP/Gen. rotors together without coupling them. This will results in avoiding the influence of coupling face error on other end of the shaft during checking of alignment.
Ensure that the checking of bearings including replacement if any has been done before start of alignment
The axial gap between two couplings during alignment should be checked with the slip gauge in place of feeler gauge and the gap should be kept between 1 to 2 m.m. in HP/IP/LP coupling after fitting of rotor in spigot.
Side pads, axial keys, thrust pads of the bearings should be removed during the alignment checks.

5. Ensure that the bearings / rotors are not getting disturbed during alignment checks due to charging of JOP lines.
It is observed that HP front end of rotor gets more frequently disturbed due to higher JOP pressure and causes un-reliable alignment reading on HP/IP coupling. Adjust just adequate JOP pressure for free rotation of rotors in all the bearings.
Ensure free movement of temporary coupling bolts during checking of alignment on each set.
Ensure free rotation of rotor in the casing during alignment checks. Preliminary roll check / bump check values may be recorded to ensure its free rotation.
Ensure that all the major weights are installed on TG deck during alignment of rotors in case of spring loaded foundation.

6. Four sets of alignment values are recorded at 0°,90°,270°,360° on each coupling and then averaging is done. The trend of the reading in each set should match otherwise it should be repeated.
Parallel axial gap in all couplings are permitted except at free ends of rotor i.e. HP/IP and Gen./Exc. couplings where 0.03/ mm. bottom opening is advisable.

7. (b) COUPLING OF ROTORS
Rotors are coupled based on the face runout of two adjoining coupling. The face runout of all rotors are checked at site before coupling and shop values are also supplied from the works.
The couple runout value is to be carefully analyse before finalizing the coupling of two rotors.
No major change in rotor CRO is permitted from initial value of free runout of rotor.
Any change in CRO from free runout value of rotor is caused either due to error in centring of two rotor or due to error of the coupling faces.
Higher CRO is not permitted and proper correction is to be carried out before proceeding further.
The swing check and CRO are the two important checks for the coupling of two rotors.The swing check is possible only on HP/Exc. end of the rotor hence the CRO is only check for various couplings.

8. (c) CATENARY OF MACHINE
Catenary of the machine is to be maintained along with the alignment of various rotors. In KWU sets it is possible to achieve both catenary and alignment values together in turbine rotors.
Much thrust has not been given to catenary values of Generator and Exciter. The catenary of turbine rotors are maintained and afterward Generator/Exciter are aligned without much bothering of the Generator/Exciter catenary.
Check catenary over the journal of the shaft by installing special fixture and water level jars.
Pedestals heights along with catenary are also to be checked for the reference in each inspection during correction of alignment.
Any major correction in catenary should be done by adjusting shims in the spring units in case of spring-loaded foundation.

9. Correction of catenary in normal foundation should be done by adjusting the shims in the bearing supports. However the height of the front and centre pedestal can be adjusted in case of sliding pedestal machine.
Catenary and alignment of rotors are to be checked together. The final catenary values are recorded after completion of alignment.
The major variation in catenary (with normal foundation) is caused due to sinking of IP/LP pedestal in most of the sites. The variation in pedestal height has been noticed up to 3.00 mm from initial grouting in pedestal nos. 3 and 4.
In case of major sinking of IP/LP pedestal (with normal foundation) the error can be distributed between bearing number 3 & 4 during correction of catenary.
Checking / correction of catenary by adjusting shims in the spring units is required during initial 1st/ 2nd inspections due to settling of spring units/foundation etc.

10. (d) SWING CHECK
In large turbines the swing check is measured on both extreme end of the rotor system i.e. on HP front end and Exciter end. In cases where machines are supplied without exciter rotor then swing check is measured only on HP front end of the rotor.
Ensure that all the coupling bolts are fully tightened / elongated to the design values during recording of the swing check. Value checked with partial coupling bolts may not give reliable reading.
Record swing check of HP rotor with LP rotor in coupled and un-coupled condition. Any influence on swing check of HP rotor caused due to coupling of LP rotor need to be corrected on LP/IP coupling.

11. Any correction in swing check value is recommended by interchanging the coupling hole position otherwise rotor face to be corrected by machining.
Cutting/scrapping of coupling faces by hand for improvement of swing check to be avoided.The face runout of two rotors to be ensured for the best position and then they should be coupled.
The maximum permissible value of the swing check has been specified by designer however the minimum swing value will result in better performance of the machine.
During replacement of HP rotor the swing check value of the rotor is to be ensured before reaming/ honing of the coupling holes. During this stage the temporary coupling bolts are to be provided in all the holes.
Ensured that HP rotor is not fouling inside the module during recording of swing check while rotating the rotor.

12. All coupling bolts are to be tightened / elongated equally in a sequential manner during recording of swing check. No in-different tightening of coupling bolts is permitted to improve the swing check value.
During checking of swing check the rotor is hanged with the slings on a babbitted half ring with chain pulley block and throw of rotor on horizontal plane is measured during rotation of rotor.
BHEL has developed a trolley for recording of the swing check for HP rotor and it is in advance stage of manufacturing. The drawing for the trolley is enclosed and the same can be procured / manufactured.

13. (e) TURBINE ROTORS
Check radial runout of rotors in each inspection at coupling, journals and between inter-stages to ensure healthiness of rotor.
Check facial runout of rotors before coupling wherever possible however no correction of coupling faces is recommended by hand scrapping.
Inspection of rotor blades by hammer test/feeler gap for any looseness and necessary re-blading.
Checking of rotor fins in glands and inter-stage area including re-finning if required.
Much thrust has not been given on re-finning of rotor during COH but these areas are to be attended.
Re-finning of rotor in gland area is possible on a lathe machine. But the re-finning in inter-stage area is possible only in a limited way unless rotor blades are removed.

14. (f) ROLL CHECK OF VARIOUS CASINGS
Roll check values are recorded initially during dismantling and after final alignment of rotors for HP/IP/LP casing.
During COH of HP Module the roll check of inner casing is also recorded.
Re-finning of rotor/casing is planned on the basis of increased in roll check values, poor heat rate of machine, leakage through casing glands and more on actual inspection of rotor / casing fins.
Radial clearances of the casing are set on the basis of roll check values of the casing and an off set in top and bottom clearances are kept as per recommendation of designer.
Improper radial clearance set during the roll check of the casing may cause barring gear jamming problem.
The roll check values are to be checked / corrected after correction of rotor alignment.

15. Increase/ change in roll check values are caused due to rubbing of fins of the casing/rotor, ovality in casing,damage to the layer of lubrite packer,change in alignment of rotors etc. during operation of the machine.
Observed that the LP casing roll check values in vertical direction are increasing and in horizontal direction are reducing due to distortion in LP inner casing. The distortion in casing is caused due to high exhaust hood temperature during operation of the machine etc.

16. (g) HORN DROP CHECKS
Check/Record horn drop value of HP casing during COH after dismantling of all pipelines and if required make necessary correction in palm packer to improve the values. Afterward check the horn drop values after connection of the various pipelines. In case of major variation in horn drop values the correction has to be made in pipelines by making a free joint with the casing.
Check/Record horn drop value of IP casing along with the connected pipelines. In case of major variation in loading of the palm from earlier values a correction can be decided suitably.
Ensure healthiness of the piping supports for HP/IP casing up to strainers before checking of horn drop values.
Major correction in piping joints for any piping pull is recommended in case of very poor loading in any of the palm of the casing.

17. During initial checking of horn drop the casing should be free in its movement and the centralizing keys are to be removed however one set of final value is recorded with all the keys in position.
Based on the horn drop value with all centralizing keys in position if any correction is recommended then the reading is to be re-checked without assembly of centralizing keys of the casing.
The major correction in piping has been done in HP exhaust lines in 210 mw machine in few places due to variation in horn drop value.

18. (h) BEARINGS
Check/Ensure contact between torus/ spherical and its support. Scrapping / lapping may be done in case of spherical bearings but no hand cutting is permitted on bearing with torus arrangement and need machining only for correction of the line contact.
Replace complete set of bearing along with its support if required. Do not replace only torus or its support.
Check/Ensure side oil and top oil clearances of the bearings. No askew in clearances should be permitted.
Replacement of bearings may be done by centring with piano wire arrangement for better performance of the bearing. Always re- dowel the support of the bearing during any replacement except for the thrust bearing.

19. Check/Ensure thrust pad contact during any replacement of pads or adjustment of axial keys of the thrust bearing.
Ensure that the adjustment in left/right/ height of torus is not more then ± 0.30 mm as cumulative since machining / assembly of bearings. In case of requirement, the total cylindrical/spherical support of the bearing may be shifted radially.
Adjustment/Replacement of yoke keys are to be done during alignment of rotors
Sometimes pitting is observed in the axial keys of thrust bearing resulting in looseness of the bearing and higher axial shift value. The pitting is caused due to higher shaft vibration on HP rear end of the shaft. The pitted portion of the key/ bearing needs machining and re- fitting of keys by adjusting shims etc.

20. (i) TURBINE PEDESTALS
Check centring of pedestal with piano wire arrangement in each COH of the machine and carryout necessary correction in front / centre pedestal after considering HP/IP/LP rotor alignment values in sliding pedestal machine.
Check level of the individual pedestal and catenary on pedestal parting plane with water level jars. Carryout necessary correction in pedestal nos.1 & 2 for its level and catenary if required in sliding pedestal machine.
Check / Ensure colour contact of the packers between pedestal and its sole plate in sliding pedestal machine.
Variation in catenary of pedestal number 3 & 4 is to be adjusted in the bearings as these pedestals are grouted and no adjustment in height is possible unless pedestals are re-grouted.

21. Check centring of pedestal with piano wire arrangement in each COH for the reference in case of fixed pedestal machine.
Check / Ensure the tightening of foundation bolts for all the pedestals during COH. If the elongation values of the foundation bolts are reducing in subsequent check then check / ensure the contact of the anchor plates also.

22. (j) TURBINE CASINGS
Check condition of the casing blades for any damage, rubbing, looseness etc. in each COH and suitable corrective action.
Measurement of ovality in HP/IP/LP casing in each COH.
Check condition of the casing seal fins in glands, inter-stages and balancing piston area for rubbing, dislodging etc. The re-finning can be done at BHEL works only.
The parting plane gap to be checked with normal design value of elongation of bolts in HP/IP casing. Further 50% additional elongation is permitted to achieve feeler tight joint.
Repair for none of the above works can be done at site and module is required to be sent to BHEL, works only. In such cases a spare module can be installed at site and repair of existing module can be planned.

23. Centring of HP/IP inner casing during shop assembly is done with the alignment shaft but during COH this practice is not followed. It is essential to check the centring with alignment shaft during COH of the module too. The alignment shafts are required to be procured for site work.

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