FIELD OF THE INVENTION:
The present invention relates to a method of drilling in larger diameter pipes.
More particularly, the present invention relates to a method of making the drilling holes
in circular pipes without marking on the pipes for drilling on both ends of the pipes.
BACKGROUND OF THE INVENTION:
Circular pipes having outside diameter around 711 mm with thickness 12 mm are used
in high pressure steam generators for the transportation of pulverized fuel (coal) from
pulverizes (mills) to the furnace on the high capacity utility boilers. There are more than
6 mills and each mill will have 4 outlets for cater this in one elevation and then for 6
elevations per boiler, there will be 24 pipe lines routed from mill outlet to furnace inlet.
The approximate distance between the mills to furnace is 100 m and the route will have
different bends. The pipes are connected by metallic couplings and the coupling is
connected by studs circumferentially on the pipes from both top and bottom end. The
drill hole diameter is 48 mm and 16 holes on equal space are to be drilled in both top
and bottom of the pipes for interconnection. The maximum length of the pipe in 10 m
and there will be 10 couplings for one routing and there are about 24 routings and the
holes on the pipes are to the drilled in the conventional radial drilling machine. The
marking on the pipes for drilling is a time consuming process since the activity is carried
out by rolling the pipe and marking at regular intervals on each marking line a punch is
to be made at a predetermined distance (200 mm) from the end of the pipe on both

ends. Maintaining the accuracy of the marking is difficult and hence there is a need to
find out a novel method of marking which takes less time and at the same time
maintaining the accuracy thereby increasing the productivity.
OBJECTS OF THE INVENTION:
One of the object of the invention is to develop a method of indirect marking of larger
diameter of circular pipes used for fuel pipe lines in the high pressure boilers that
ensures marking the drilling holes on the periphery of circular pipes easily, accurately
and with lesser time.
SUMMARY OF THE INVENTION:
Accordingly there is provided a rectangular Compressed Asbestos Fiber (CAF) sheet
having a thickness 2mm and the length of the sheet being equal to the perimeter of the
pipe wherein an overlapping length of 25mm is provided at either side of the asbestos
fiber for locking purpose. The marking method comprises calculating the pitch of the 16
holes by dividing the circumferential dimension of the pipes by the number of holes to
be marked on the pipes.
According to the pitch distance, vertical lines are drawn. Depending on the distance
from the end of pipe, one horizontal line is drawn on the sheet. Points of intersection
are punched for drilling of 3 mm diameter hole.

The above process of marking is repeated for a further distance of 200 mm reference
distance. This marking is used only for checking at (filed) site, while assembling the
pipe lines.
Now fastening the band strap of width 25 mm is stitched on either end of the sheet.
The sheet is rounded on the surface of the pipe and both ends are fastened by strap.
The punch marks are made on the pipe line by dot punch.
Then the sheet is dismantled by just a releasing from the strap and fixed on the other
end of the pipe for punching to make drilling hole as well as reference marking. Now,
the strap CAF sheet is removed and the pipe is ready for drilling at both ends.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig.l : shows the isometric view of pipe with drilled holes on both ends.
Fig.2 : shows the isometric view of Compressed Asbestos Fiber (CAF)
sheet with strap band on either side.
Fig.3 : shows the Compressor Asbestos Fiber sheet with hook and loop stitched on
each end respectively.
DETAILED DESCRIPTION OF THE PREFERED EMBODIMENT OF THE
INVENTION:
Accordingly, the compressed asbestos fiber sheet (01) is cut to length of equal to
perimeter of the fuel pipe (04) and width is equal to 300 mm the X-Y coordinate
marking is carried out, first by marking vertical line along the length 65 mm from the
one edge. Another vertical line along with length for 250 mm from the same edge.

There are 16 holes of 48 mm diameter are to be drilled on the circumference of the
pipe. The pitch distance is calculated between the center of the holes. According to the
pitch distance, vertical lines are drawn. Depending on the distance from the end of
pipe, one horizontal line is drawn on the sheet. Points of intersection are punched for
drilling of 3 mm diameter hole. Now 25 mm width and 300 mm length hook (03) and
loop (02) tape are cut and stitched on either side of the compressed aspects of fibber
sheet (01). The marked compressed aspects fibber sheet (01) is taken to conventional
drilling machine to drill 3 mm diameter holes on all the point of intersection as the
punch marks.
The assembly of compressed aspects fibber sheet along width hook (03) and loop (02)
is placed on the circumference on the fuel pipe (04) by coinciding the one end of the
pipe (04) and one end of the marked compressed aspects fibber sheet (01). Locking is
carried out by hook (03) and loop (02). Now the punching is transferred to fuel pipe
line (04) by means of hammering with dot punch tool through 3 mm diameter drilled
hole on the CAF sheet (01). After punching the assembly of the compression aspects
fibber sheet removed from the fuel pipe line (04) by just unwrapping the hook (03) and
loop (04). The process is repeated for the other end of the fuel pipe line for marking on
the other end. Now the punched fuel pipe (04) is moved to drilling work center for
drilling.

We claim
A method of indirect marking on large diameter of pipes in high pressure boilers,
comprising the steps of:
- cutting to length the compressed asbestos fiber sheet (01) according to the perimeter
of fuel pipe (04) and with a width 300 mm approximately;
- marking a first vertical line at a distance of 65 mm from one longitudinal side;
- marking a 2nd vertical line at a distance of 250 mm from the same side and parallel
to the first vertical line;
- drawing horizontal lines at pitch distance for finding out the point of intersection
with the vertical lines that denotes the center of 16 holes for a particular row;
- dot punching the points of intersection;
- stitching the hook tape (03) of size 25mm x 300m in one end of the compressed
asbestos (01) and loop tape (02) on the other end of compressed asbestos (01);
- drilling the 3mm dia holes in the punch marked locations thus obtaining the
compressed asbestos assembly (05);
- placing the asbestos assembly (05) over the fuel pipe (04) matching the side end of
asbestos assembly (05) with one end of fuel pipe (04) and locking in that position by
hook (03) and loop (02);
- punching on the periphery of fuel pipe with the help of dot punch tool and hammer
by locating through the 3mm diameter already drilled hole of the compressed
asbestos assembly (05);

- unlocking the asbestos assembly (05) and removing the assembly from the pipe
(04);
- performing the drilling operations on the punch marked locations of the pipe (04) on
conventional radial drilling machine.