HOT AIR SHUT OFF GATE:
MECHANICAL:
1. In one of hot air gate, Blade was having bow at middle and the
blade is seating over the retainer plate of bonnet side in open
condition towards up stream side.
2. Misalignment between of power cylinder & gate, which promote
sticking with sides.
3. The blade protection cover prohibits inspection of the piston gate
connection and limit switch lever adjustment. Some times the
removal of cover is very expensive & tedious job as about 150
nos of nut & bolts connection are to be handled. It is to be
reviewed for elimination of the cover and if the cover is
necessary, provision of inspection opening cover with swing
arrangement shall be thought off.
Page 64 of 175
4. The side transition box connection for seal air to the seal
chamber done at works invariably leaks and after connecting the
seal air pipe, attending the leak difficult requires extensive re
work and only temporary measures like application of M-SEAL is
solution, which is not acceptable and becomes permanent
pending point.
5. The bore of gaskets used for fixing the flanged butterfly valve in
all the assembly was found less and hence prevent valve
opening. Site has to remove the valve assembly and correct
which consumes time and effort.
6. The out side seal box cover fixing with the seal box frame, the
bolting system at present, makes removal of bolts difficult as the
whole bolt rotates as the head tack welding with frame gives
way and rotates.
POWER CYLINDER OF HOT AIR GATES:
1. The rubber seals of power cylinders in 7 out of 10 in unit#3 and
3 out 10 in unit#4 were to be replaced after erection due to
piston seal passing. The piston seal should be good viton quality
having high temp withstand characteristics and reliable lip
reversal. To open the power cylinder weighing more than 250 kg
at 45 mtr elevation, specially where no platform / beam is
available above power cylinder, and bring down at ground level
is a very risky & tedious job. We have to call the supplier’s
technicians for the replacement of seals.
2. The requirement of lubricator shall be eliminated.
3. The Air filter regulator shall be of metallic than plastic which is
prone for damage.
ELECTRICAL
1. The junction boxes location is the top of the frame and hence
approach is difficult for any checking and maintenance. The
location of JB was changed at site.
2. The limit switches assembly is provided in the up stream side of
the gate makes it difficult for attending any defect due to heat
while boiler is in service. At site, modification was carried out to
suit the O&M requirements.
PNEUMATIC CONNECTIONS
1. The copper tubing is prone for theft and it is to be reviewed for
switch over to flexible hoses/ SS tubing with hoses at ends.
2. The requirement of lubricator shall be eliminated with usage of
seals which operate on dry air.
3. The Air filter regulator body shall be of metallic and not plastic
one as presently supplied which is prone for damage and it
happens during erection and no spares are supplied. We have to
procure 5 nos from the party.
CONTROLLED CIRCULATION PUMP (CC PUMP):
M/s KSB Germany make.
In one of three CC pumps installed in Boiler#4, 4 nos studs were
struck up in the casing at the time of removing the dummy after the
hydro test of boiler. These were removed forcibly by heating and
hammering causing the damages of all the four studs/ nuts and thread
damage of the casing.
The new studs (4 nos), nuts (7 nos) & jointing ring (1 no) were
procured from M/s KSB Germany and the threads of the casing were
rectified at site with the help of M75X2 tap sets.
This last pump was commissioned without the help of vendor’s
representative.
It is recommended to follow strictly the Erection and O&M manual
while heat tightening the studs with the casing, using lubricants &
torque wrench supplied with equipments.
FEED WATER SYSTEM – INPUT SHAFT OF GEAR BOX
TDBFP-3B commissioned on 05.06.2005 was in continuous in operation
for the last 5 months. On 23.11.2005, it was noticed that the drive
turbine rear bearing vibration increased from 22 micron to 40 micron.
The gear box vibration (located between drive turbine & booster
pump) also increased alarmingly.
The gear box was decoupled from drive turbine to check the
alignment between turbine & gear box. During this process, it was
noticed that input drive shaft of the gear box is damaged ie shaft
material is chipped off in triangular shape along the length of the input
shaft for a length of 40mm near the coupling hub & keys are
dislocated from their position.
The gear box was removed from its position. The defective input shaft
got sheared off while removing it from gear box by puller. The input
shaft already got cracked along the cross section of the shaft.
Page 78 of 175
It was suspected that the parent material of the input shaft was
defective.
The supplier’s representative was called to supervise the assembly of
the new shaft & investigation of the failure. The machine was made
ready in the second week of January 2006.
BOILER HOISTS – CABLE TROLLEYS:
The cable trolleys units associated with mill handling system DSL are
breaking down quite frequently which were supplied by M/s Consolidated
Hoists. The fabrication of these trolleys is under sized, perhaps suitable for
short length tracks where cable pulling load is less.
The observations on these cable trolley problems as below:
a) The two side cover plate thickness is about 2.5mm,
b) The two long distance screw size is about dia 6mm.
c) Welding of stud bolt with the power cable holding clamp is inadequate.
The total distance of the mill service crane DSL track beam is about 110 m
(Rihand is having rear mill combination) and the entire cable-pulling load
acts on the nearest trolley to the service crane. Due to less thickness, the
cover plates of trolley as well as the distance screws easily get bent, the
alignment of the trolley thus get disturbed, open up and disengage from the
track beam.
As the first one fails, subsequently the supply cable-pulling load comes on
the next trolley and one by one they fall down along with the power cable.
Since proper reinforcement is not provided on the cable clamp with the stud,
the joint fails and the power cable along with cable clamps get detached from
the trolley.
The commissioning of whole mill handling system could not be done and
during initial trials itself a lot of break downs occurred with the DSL trolleys.
For ESP transformers handling system (PGMA 78-773), much heavier trolleys
were supplied by M/s Power build hoist maker. This is made of channel with
5mm thick plates. Here the track length is almost half (50m long) and that
too for pulling much lesser cable size compared to Mill service crane DSL
cable.
The similar problem may be faced in ECO coil handling system also, long
track with same trolleys. At a high elevation (+72m level), repair & frequent
maintenance of trolleys in the mid air is very difficult and simply
unimaginable. The DSL lengths of ID Fan, APH elements handling system are
also more and these are also not at lower elevations for easy maintenance.
The matter has been referred to Trichy engineering for review of design with
the supplier M/s Consolidated Hoists and replacement of all such trolleys and
track beams with improved design. The trolleys for ESP & TG side are more
rigid & steady, supplied by M/s Herculous & M/s Power Build.
The photos of trolleys (both assembly and in knocked down condition) of mill,
ESP handling system and other typical system as below:
No comments:
Post a Comment