Transcript NKBansal PRESENTATION ON VIBRATION

WELCOME
ERECTION / OVERHAULING
CHECKS AND VIBRATIONS
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.
(a)
(b)
(c)
(d)
(e)
ALIGNMENT OF ROTORS
COUPLING OF ROTORS
CATENARY OF THE MACHINE
SWING CHECK
TURBINE ROTORS
(f) ROLL CHECK OF VARIOUS CASINGS
(g) HORN DROP CHECKS
(h) BEARINGS
(i) TURBINE PEDESTALS
(j) TURBINE CASINGS
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.

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.

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/ 0.
04-mm. bottom opening is advisable.
(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.
(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.

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.
(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.

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.

All coupling bolts are to be tightened / elongated equally in a
sequential manner during recording of swing check. No indifferent 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.
(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.
(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.

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.
(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.

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.
(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.

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.
(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 regrouted.

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.
(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 refinning 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.

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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