Swing Check of Steam Turbine
Steam Turbine Swing Check Measure During Turbine Overhauling. Fundamentals & Basics Aspects of Steam Turbine Maintenance.
1.) Swing Check:-
- Swing check is a measurement which shows the mating accuracy of the coupling faces of the two rotors coupled together.
- It is the measurement of the radial throw at the free end due to coupling face geometric form of the two rotors coupled together.
- It is carried out by removing the Real bearing and putting a false bearing/Lifting tackle on which the rotor is supported. This false bearing has larger side oil clearances. Dial is put at the horizontal level and then rotors are rotated . Readings are taken at many positions, The max throw is the Swing of the rotor.
- Readings are to be recorded after elongation of all coupling bolts of HP-IP and IP-LP coupling.
- The value of the swing depends upon the facial run outs of the coupling , diameter of the coupling and Length of the Rotor shaft.
- The final dial gauge reading at start position should be same as the Initial set Dial gauge reading at start position.
- This check measures how much a shaft will swing in the horizontal plane when the actual bearing is removed and supported on the dummy bearing which is floating.
- This check is carried out when the final coupling has been done and bolts has been extended .
- Here the Real front bearing is removed and rotor is supported on a false bearing which is further supported by a Sling with the help of EOT Crane by keeping the same seal bore reading at bottom as with the Real rotor
- Dial gauges are fixed with their pointers at left-horizontal and right-Horizontal and at top of the journal
- After above the Rotor is rotated by suitable means
- The maximum throw at sides gives the value of the SWING.
If the swing value is on the Higher side then it can be corrected by following means.
— By interchanging the coupling position
If this is done then all the balancing weights on the Rotor other than installed during the refurbishment at OEM Works should be removed.
— Improving facial run out of the couplings
For this one of the rotor may required to lifted for doing necessary corrections.
— Honing and reaming & fixing with new coupling bolts
By reaming and honing of coupling holes and putting new coupling bolts of finer tolerances .
However decision to implement any one of the decision depends upon the criticality of the situation at Site.
4.) Check List:-
Readings are to be recorded after elongation of all coupling bolts of HP-IP and IP-LP coupling.
Allowable run out is the value calculated by assuming 0-02 mm facial runout at coupling when measured at a distance where bearing is positions.
The final dial gauge reading at position no 1 should be same as the Initial set Dial gauge reading at position no 1
Swing Check_1 : with HP & IP coupled and front bearing removed, Journal supported on lifting device , The coupled assembly Rotated, the ‘swing’ value, as run out on the HP Front Journal is measured: typically to be restricted to be 0.1 mm.
‘Swing check value’ reflects the degree of throw caused by the rotor axis misalignment.
Swing Check_2: The same thing is repeated after aligning LP and the norm to be achieved is 0.18mm /0.20mm
In case the CRO coupled run outs exceed by +/-0.01mm of the free Run Out
The swing check value exceeds 0.18 mm
The face is found convex
Correction on the face is carried out under the shop supervision or in some cases if the facial run out is only marginally higher a second face fit may advised by shop.