3.Trombay-Run Out Device

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SUGGESTIONS FOR BESTPRACTICES IN RUN-OUT

DEVICES

By:

G.Sridhar

Sr.Manager/TG

BHEL Site Office, TATA Trombay


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INTRODUCTION

During the course of erection and commissioning ofHigher Rating Steam Turbines, the need to improveupon certain existing methods of erection was felt.

Among the many that need improvement are thestandard, time consuming, laborious and not soperfect methods of:

Setting the pedestal seal bore by piano wire before

grouting the pedestals Measurement of face run-out of the IP & LP Rotors by

rotating the rotors on saddle supports


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1. MEASUREMENT OF FACE RUN-

OUT OF IP & LP ROTORS BEST

PRACTICE


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Normal Practice

The normal practice of measurement of face run-

outs of IP & LP Turbine Rotors is to place them on

saddle supports and rotate them. Lifting action of

the crane hook causes rotation of the rotor. To aid inrotation of the rotor, copper sheets are placed in

between the saddle and the rotor and, grease is

smeared to reduce friction during rotation. It has

been noticed that this method has a few problems

associated with it:-


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It is not possible to restrict the axial movement of therotor in order to avoid overshooting the range of thedial gauge.

The area of contact being very small, it requiresextreme care and control while operating the EOT, lest itshould cause an irreparable accident and lead to loss ofboth men and material.

It has often been noticed that there is quite an errorbetween the measurement made at shop and thosemade at site leading to avoidable loss of time incorrespondence, summoning experts from MUs, etc.

It gives the feeling of using a very primitive and un-

reliable method of measurement. Overall, it is never like measuring the run-outs by

anchoring the rotor on a lathe to take the measurementsand thats exactly the cause of the error.


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Suggested New Method

To tide over the above problems, a very simple device was made atsite. To make the device, the following material was made use of:

Shaft of 40mm x 1000mm long 1 no.

Ball Bearings with Plummer block for above shaft 2 nos. Supports to anchor the Plummer blocks 2 nos.

Cross arm 1 no.

Dial Gauges for mounting to X-arm 2 nos.

The sketch of the fixture is as in the adjoining slide.


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Brg with

Plummer Block

Cross Arm

Shaft Support provided by Unit

External Support

for anchoring the

Plummer Block

Dial

Pointers

Dia 40

Shaft


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Advantages:

This method is very user friendly and costs only Rs.5000/- to make.

Does not require too much of a precision in machining the shaft.

Does away with repeated rotation of the rotor for every reading.

Reduces the risk of the rotor toppling during rotation by EOT crane.

Compares well with the values attained at works on a lathe.

Overall, an improvement in the positive direction.


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2. CENTERING OF TURBINE

BEARING PEDESTALS

BEST PRACTICES


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Normal Practice

The usual practice is to draw a piano wire

coinciding with the centre-line of the TG Axis and

centre the pedestals at the seal bore by measuring

the distance between the seal bore and the pianowire by an Inside Micrometer. Though the method

has been used successfully in the past, there have

been elements of doubts cast over its correctness.

These are enumerated in adjoining slide:


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There is no scientific method to determine the amount oftension to be given to the piano wire

During windy seasons, the piano wire oscillates so muchthat no two readings are consistent, there by introducingthe element of human error.

The effect of ambient temperature on thesemeasurements has always been noticed and over theyears it has been assumed that the best period torecord the measurements is the early hours of the day

i.e.; between 0600 & 0700 hrs.

This method can be used to align the pedestal in oneaxis only. It cannot be used to set the elevation of thepedestal.


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Recommended Method

LASER ALIGNMENT is a method being used by manyan OEM to good and accurate effect. This device as isunderstood from reliable sources takes into account thevariations of temperature and also is not affected by

wind. It can be used to center the pedestal as well as setthe elevation simultaneously. This vastly reduces the timetaken for each reading and the overall time taken foralignment of the pedestals as a whole. Also, it eliminatesthe human error that is likely to occur.

The method can be extended to alignment of CondenserTube Support Plates as well.


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3. COUPLING OF TURBINE

ROTORS


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Normal Practice

The normal practice of coupling of Turbine Rotors is

to Ream & Hone the coupling, machine the bolts to

the required diameter, balance the coupling bolts,

insert and stretch them to the required values. Theentire job of Reaming, Honing, Machining of

Coupling Bolts and Balancing of the rotors is a time

consuming and costly one.

There are certain pitfalls associated with this

arrangement:


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The process is long and arduous.

It depends too much on the skill of the person carrying out

the job.

The requirements are very stringent and many a times inremote areas, facilities for high-accuracy machining is notavailable.

The process is irreversible; meaning, one mistake in themachining of the bolts and the bolt cannot be used.


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Recommendation

Since the basic idea is to develop contact pressure

and thus transmit torque, the use of coupling bolts

and nuts similar to the ones being used in BFPs can

be thought of. Once alignment is completed,coupling is a very easy and quick job in a BFP. This

concept can be extended to the Turbine as well.


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Advantages:

No time lost between alignments and coupling.

Reaming, Honing, Bolt Machining and Balancing can

be done away with. A significant reduction in cycletime considering that it takes at least a week foreach coupling.

Due to the above, the element of human error is

totally done away with. Easy on the contractor as well; the cost of Reaming,

Honing and Bolt Machining is saved.


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Documents

3.Trombay-Run Out Device