FIELD OF INVENTION
The present invention relates to a method for in situ repair of burnt out tile
holders inside flame tube of combustion chamber of a gas turbine. More
particularly, the present invention relates to a method of repairing the burnt out
tile holders without dismantling the combustion chamber.
BACKGROUND OF THE INVENTION
Combustion chamber is an important part of gas turbine power generating
system. The air from the compressor is heated to the turbine inlet temperature
by burning with fuel gas, fuel oil or both simultaneously, in the combustion
chambers and is taken to inlet to turbine for further action. Maximum
temperature attained by burning of fuel air mixture inside the combustion
chamber is in the range of 1200-1300 degree centigrade. The combustion
chamber is designed to handle such high temperature for its efficient working.
The combustion chamber consists of following major parts as shown in Fig-1:
1. Outer casing
2. Dome
3. Flame Tube
4. Mixing Chamber
5. Manhole

1. Outer casing:
It is a silo type fabricated structure which houses flame tube and mixing
chamber inside. This is flanged with the centre casing of turbine. Its
outside is insulated for thermal barrier.
2. Dome:
This is a top hemispherical type of construction which is placed on top of
outer casing. It houses burners and associated pipings for fuel admission
to flame tube.
3. Flame Tube:
This is a cylindrical construction with its inside lined with ceramic tilings.
The actual combustion takes place in this zone only and the ceramic tiles
are provided so that the inside high temperature as a result of fuel
combustion is not transmitted outside.
4. Mixing Chamber:
This is a knee shaped annular fabricated structure, the top of which is
connected with flame tube and bottom with inner casing of turbine. It acts
as a passage for hot gases to main turbine.
5. Manhole:
This is an entrance provided for periodic inspection of combustion
chamber hot gas components and minor maintenance activities.

As mentioned above the inside of flame tube is provided with ceramic tiles which
are a must to handle the high temperature hot gases which goes to main
turbine.
These tiles are fixed to the flame tube inside surface with special arrangements
for its firmness because any dislodging of the tile or tile broken parts will enter to
the main turbine and will severely damage the turbine blades leading to
catastrophic failure and forced shutdown of the turbine.
The maintenance recommendation foresees periodic inspections of inside of
flame tube to access the healthiness of tile fixing so that any mishappening
during operation can be avoided.
As shown in fig.l below the flame tube is having 10+2 rows of ceramic tiles. The
top two rows (A) is subjected directly to the flame coming out of the burner and
has got special arrangement for the tile fixing which can be attended from inside
of the flame tube for replacement as per need during the periodic inspection.
The remaining ten rows (B) of tiles are fixed with the help of tile holders which
are welded with the flame tube body from outside. This area is subjected to high
temperature flowing gases and not subjected to the flame directly. In these rows
during the minor inspections tiles need replacement because of their crackings
but the tile holders are designed to have a life to sustain this heat continuously
for the period when the machine will be taken for Hot Gas Path Inspection after
33,000 equivalent operating hours (EOH) in which combustion chamber is totally
dismantled and tile holders are replaced.
As shown in Fig-2 a Flame Tube and in Fig-3 the fixing arrangements for top two
rows tiles with tile holders (Section A-A) and of the remaining ten rows of tiles
with tile holders (Section B-B).

Recommendation For Maintenance & Inspection Schedule:
Gas turbine operation is characterized by the use of atmospheric air as the
working fluid and the direct injection of fuel into the compressed air. Pollutants
and dust contained in either can cause corrosion. Gas turbines are further
characterized by high operating temperatures, which cause thermal stresses and
material fatigue, as well as oxidation of hot gas path items.
As with any other machine, gas turbines are subject to wear during use.
Maintenance is performed to detect and control wear, as well as to repair or
replace wear parts as needed to restore wear reserves. With proper
maintenance, gas turbines can be operated with high reliability and availability
despite the aforementioned disadvantageous characteristics.
Wear is the price paid for operation of a machine or plant. Without restoration of
wear reserves, a gas turbine cannot be reliably operated. Inspections are
performed to determine the condition of the machine and the requisite condition-
based corrective actions or repairs. Inspections thus protect the operator from
unscheduled outages and the associated loss of hardware and power generation
income.
Three types of inspection are referred to in the following that differ in terms of
their scope and interval, as shown in Fig.5 where arrows indicate points of
access to the gas turbine:
Minor inspection, referred to the following simply as inspection, comprises
entry into the accessible regions of the machine and a largely visual inspection
thereof (Fig- 4A & 4B).
Hot gas path inspection (HGPI) essentially includes a major inspection
restricted to the hot gas path items, i.e. the compressor region is generally not
opened. In practice, however, the extended-scope of hot gas path inspection is
proven and established itself.

Major inspection includes extensive disassembly of the machine, detailed visual
inspections and non-destructive examinations as well as scheduled and
condition-based repair measures. This generally does not include unstacking of
the rotor. If inspections reveal that rotor unstacking is necessary, such work
must be agreed upon with the customer.


Maintenance of Flame Tube:
During the recommended minor inspections generally following works are done:
- Cleaning for any deposits on hot gas components as the deposits
leads to heat concentration and subsequent erosions
- Cleaning of all the cooling holes for proper cooling of components
during operation
- Inspection of all ceramic tiles for any cracks and if required they
are replaced
- Replacement of burnt out tile holders in top two rows, tightening of
tile holders for ensuring proper fixing of top two rows tiles
- In the remaining ten rows of tiles, if any tile appears to be loose
then the tile is removed and the fixing pair of tile holders are
checked. If they are burnt or eroded then the problem becomes
unattainable. Normally these tile holders and its fixing is designed
for the life of 33,000 Equivalent Operating Hours and in the above
stated case the unit needs forced shutdown for hot path inspection
and repair.
But in a very unusual situation of premature failure, when the machine breaks
down after running very few hours compared to its normal schedule, for example
8000 EOH instead of 33,000 EOH, and is found that tiles are loose and on the
verge of falling down as the tile holders are eroded or burnt, the only solution is
to repair the holder after dismantling the combustion chamber. It means
shutdown of the machine for a period of 2-31/2 weeks which is a huge loss of
time and money.
Accordingly, there exists a need to eliminate the disadvantages of prior art. It
necessitates to explore a method to repair the tile holders in a in situ position
avoiding dismantling of the combustion chamber.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method for in situ repair of
burnt out tile holders inside flame tube of combustion chamber of a gas turbine
which eliminates the disadvantages of prior art during an unusual breakdown
condition.
Another object of the invention is to propose a method for in situ repair of burnt
out tile holders inside flame tube of combustion chamber of a gas turbine which
undertakes repairing work without dismantling the combustion chamber during
an unusual breakdown condition.
A still another object of the invention is to propose a method for in situ repair of
burnt out tile holders inside flame tube of combustion chamber of a gas turbine
which results a huge cost saving directly and indirectly.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - shows the details of Combustion Chamber
Fig.2 - shows the Flame tube
Fig.3 - shows the fixing arrangement for tile holders in the flame tube
Fig.4A & 4B - Maintenance scope of the minor inspection
Fig.5 - shows maintenance and inspection interval
Fig.6 - shows a photograph of eroded and burnt tile holder
Fig.7 - shows a weld repaired tile holder

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The present invention involves a method to repair the tile holder (1) at the time
of a premature failure in an in situ position without dismantling the combustion
chamber (4). The combustion chamber consists of a mixing chamber (5), outer
casing (6) and a manhole (7).
As shown in fig.3, for such repair, tag welding of damaged tile holders (1) with
filler wire is the best option superseding manual arc welding and brazing.
Matching filler wire is selected. Because of erosion, the tile holders (1) are having
less thickness and hence welding even with minimum possible current, the tile
holders (1) are bound to melt. Therefore a back support is provided to the
damaged tile holder (1) for carrying out the welding. A piece of about 15 mm,
for example, is cut along the length of a fresh tile holder. This piece has an
approximate matching profile (9) with the burnt tile holder. This piece is held
from inside. Then it is intermittently tag welded along the length from left and
right hand side. A full welding run is then given from both ends. Weld deposit is
done on the tile holder (1) profile with intermittent welding and is then allowed
to cool. After complete weld deposit, the profile of the tile holder (1) does not
remain in usable condition and this is ground with a manual grinder to retain the
profile shape. The surface contact is then ensured for fitting of tile. Springing
action of the tile holder (1) is then checked by increasing and decreasing the gap
between two faces. The tile is assembled and its firmness for fitment is checked.
Manhole (7) is closed and the machine is put to operation.
As shown in fig.l, as in prior art repairing and assembling of tile holders and tiles
require dismantling of combustion chamber (4), hood assembly, burners and
associated pipings, opening of dome (8) and removal of flame tube (2) and
damaged tiles 93) cutting of damaged tile holders (1) and cleaning of holes,
assembly of new tile holders and welding from outside, reassembling of tiles (3),
reassembling of all items in reverse order. This total work takes approximately

whereas with the present invention of in situ repair method, it will take only 2-4
days in the allotted minor inspection period.
The total cost of above mentioned activities for taking out the flame tube and
doing the repair as per existing practice would have direct cost impact of
approximately Rs 10 lacs. With the present invention of in situ repair method,
the indirect cost saving is approximately Rs 14 crores as the time taken for actual
tile holder (1) repair is only 2-4 days. This is a direct gain of power generation of
approximately 15-18 days for example for a 150 MW set which is approximately
Rs 14 crores.

WE CLAIM
1. A method for in situ repair of burnt out tile holders inside flame tube of
combustion chamber of a gas turbine comprising:
matching filler wire selected to tag weld the damaged tile holders (1);
cutting a piece of at least 15 mm length of a fresh tile holder almost
matching the profile with damaged tile holders (1) to provide a back
support to the holder (1);
holding the cut piece from inside;
carrying out tag welding intermittently along the length from left and right
hand side;
carrying out a full welding run from both ends;
allowing the weld to cool;
grinding the weld deposit to retain the profile shape of the holder (1);
ensuring the surface contact for fitting of tile (3);
checking of springing action of the tile holder (1);
characterised in that the tag welding of the damaged tile holder (1) is
done in in situ position without dismantling the combustion chamber.

A method for in situ repair of burnt out tile holders inside flame tube (2) of
combustion chamber of a gas turbine consists of selecting a matching filler wire
to tag weld the damaged tile holders (1) when a piece is cut from a fresh tile
holder almost matching the profile of the damaged tile holders (1) to provide a
back support to the holder (1). The cut piece is held from inside. Tag welding is
then carried out intermittently along the length from left and right hand side and
full welding run is made from both ends. The weld is allowed to cool. The weld
deposit is then ground to retain the profile shape (9) of the holder (1) ensuring
the surface contact for fitting the tile (3). The springing action of the tile holder
(1) is then checked. The whole welding operation of the damaged tile holder is
carried out in in situ position without dismantling the combustion chamber (4).