The present invention relates to a fixture for tack welding of temperature stubs with
header pipe line in high pressure steam generator and method for the same. More
particularly the invention relates to a fixture and method for tack welding of
temperature stub on the header pipe line without manual intervention.
BACKGROUND OF INVENTION
In the high pressure steam generators, manufacturing of header with stub is
necessary for different uses. In order to measure the temperature of the fluid flowing
in the pipe line, probes are to be inserted to measure the temperature. The
temperature probes are to be inserted and supported by stubs which are to be
welded in the high pressure, pipe line. The tack welding of stubs in the pipe line are
normally carried out by manually holding the stub near the drilled hole of the pipe
where it is to be tack welded for subsequent full welding. This process is a time
consuming and requires support pieces to be welded first between the stub and pipe
to carry out the tack welding.
Tack welding with support pieces in the header pipe line of P91 grade may generate
the cracks attack welding area or weld affected zone.

The concentricity of the Centre line of temperature stub and the hole provided on the
header pipe line is very difficult to maintain while manual positioning of the
temperature stub with header pipe line. The positioning of the header pipe is
mandatory to maintain the horizontal axis which requires the crane availability during
the tack welding process. After the tack welding process over the support pieces are
to be removed by hammering, which will damage the header pipe line and grinding is
to be carried out for smooth surfaces. Since the header pipe line is coming under the
high pressure application nondestructive testing is to be carried out while repairing
the under cuts due to the removal of support pieces.
The number of temperature stub to be welded is about five hundred per annum in
one work Centre an alternative method is to be found out to increase the productivity
and also to maintain the good quality during the temperature stub tack welding
process.
PRIOR ART:
IN263KOL2014A describes a method for inserting stubs perpendicularly inside the pipe
hole at pre-determined position for tack welding. In this process the concentricity is to
be ensured perfectly by manual intervention. Whereas the present invention using the
guide pin which ensure the concentricity automatically and thus not have any hand
adjustment which is not required and hence the above invention it’s not relevant to
the present invention.

OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a fixture for tack welding of
temperature stubs with header pipe line in high pressure steam generator and method
for the same which is able to provide concentrically support to the stub with pipe line
for tack welding.
Another object of the invention is to propose a fixture for tack welding of temperature
stubs with header pipe line in high pressure steam generator and method for the
same which is capable of eliminating manual intervention for the tack welding.
A still another object of the invention is to propose a fixture for tack welding of
temperature stubs with header pipe line in high pressure steam generator and method
for the same which is able to reduce seventy-five percent of time required in prior art.
SUMMARY OF THE INVENTION
For supporting the temperature probes to be inserted in the pipe line, stubs are tack
welded. For that purpose, the temperature stub is positioned on the step provided on
a guide pin. A support cap is placed on the stub from the top. The support cap has a
threaded hole. One end of guide pin goes inside the support cap.
A locking screw from the top of support cap is threaded into the guide pin having the

matching threaded hole and thus holding the cap, stub and guide pin concentrically in
the same vertical line of axis. The whole assembly of cap, stub and guide pin are
placed on the header pipe line where a hole is available in the pipe for allowing the
other end of guide pin to be inserted.
A pin for root gap is inserted between the above assembly and the header pipe line
maintaining uniform root gap of 2 mm circumferentially for tack welding. Then the
tack welding is carried out in the diametrically opposite place of interval grooves
provided in the guide pin between the stub and the pipe line. After the completion of
tack welding a locking pin is inserted in the hole provided on the support cap as well
as in the guide pin to prevent rotation of the guide pin and support cap while
unlocking the locking screw from the top. Then the locking pin as well as the support
cap is taken out outside of the header pipe when the guide pin is taken out from
inside the header pipe.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - shows the place of tack welding the temperature stub with header pipe
line.
Figure 2 - shows the assembly of header pipe line and temperature stub after the
tack welding is over.

Figure 3 - shows the assembly of all the individual components in position ready
for tack welding.
Figure 4 - shows the guide pin provided with internal thread, step, internal groove,
linear groove, and hole for inserting locking pin.
Figure 5- shows the temperature stub which is to be welded on the header pipe
line.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Accordingly, referring to the fig:3. The temperature stub (02) which is to be tack
welded with the pipe line (07) is inserted in the guide pin (01). A step (08) is provided
in the guide pin (01). Now the support cap (03) is positioned on the top surface of the
temperature stub (02). The hole provided on the support cap (03) is used to insert
the locking screw (04). The external thread provided in the locking screw which match
with the internal thread on the guide pin (01) and there by tightening the locking
screw (04) which automatically position the support cap (03) concentrically. So that
the Centre line of the support cap (03), temperature stub (02) and guide pin (01) are
coincided. The whole assembly of the temperature stub (02), guide pin (01), support
cap (03) and locking screw (04) is taken near to the header pipe line (07), where a
drilled hole is available for insertions the part of the guide pin (01). The pin for root

gap (06) is inserted between the above assembly and the header pipe line (07) to
maintain the root gap of 2mm circumferentially, maintaining uniform root gap for tack
welding using conventional TIG welding process. The internal groove (09) of four
numbers provided in the guide pin (01) are made with equal space on the diameter of
the guide pin (01), So as to is the tack welding and allowing the weldment between
the step and the header pipe line (07). So by this arrangement concentrically in four
place tack welding carried out. The linear grooves (10) made in the guide pin (01) will
take care of the shrinkage during the tack welding process. Prior to tack welding, the
conventional preheating the temperature stub (02) and the header pipe line (07) is
carried out to avoid the risk of cracking due to alloying elements presents in the
temperature stub (02) and the header pipe line (07). The linear groove (10) made in
the guide pin (01) is used to take care of the shrinkage during the above conventional
preheating process also.
Now the tack welding is carried out in the diametrically opposite place of the internal
groove (09) of the guide pin (01) between the temperature stub (02) and the header
pipe line (07). Once the tack welding is completed locking pin (05) is inserted in the
hole (11) provided on the support cap (03) and as well as it passes through the hole
(12) provided on the guide pin (01). By this arrangement the rotation of the assembly
of guide pin (01) and support cap (03) is prevented while unlocking the locking screw
(04). Since the locking screw (04) is taken out, the locking pin (05) is taken out so
that the support cap (03) is taken out on the outside of the header pipe (07) and the

guide pin (01) is taken out from the inside of the header pipe (07). By this process
the time taken to tack weld one temperature stub (02) is reduced by 50% than the
process explained in the background of the invention. This process is also mainly
useful for the materialP91 grade header pipes (07) where the support pieces welding
is not permitted for temperature stub (02) welding.
Invention of this project made an efficient process, eliminating reworks, reduced
manpower, reduced cycle time and improved the safety for the Temperature stub fit-
up.
ADVANTAGES OF THE INVENTION COMPARED TO PRIOR ART
• Elimination of safety issues
• Improved productivity & quality
• Improved customer satisfaction
• Elimination of extra movement
• Reduced man power requirement
• Minimized crane usage
• Reduced the cycle time
• Minimized welding rework

WE CLAIM
1. A fixture for tack welding of temperature stubs with header pipe line in high
pressure steam generators comprising;
a guide pin (01) having a step (08) provided on it for a temperature stub (02)
to be inserted and rested on the said step (08);
a support cap (03) having a hole at the middle for insertion of a locking screw
and positioned on the top of the stub (02);
a threaded hole (13) disposed on one end (14) of the guide pin inserted in the
support cap (03);
a pin (06) inserted between the assembly and header pipe line (07) for
maintaining a uniform root gap of 2mm circumferentially for tack welding;
a pin (05) inserted in the hole (11) provided on the support cap (03) and in the
hole (12) provided on the guide pin (01) after the tack welding for preventing the
rotation of the assembly of guide pin (01) and support cap (03) while unlocking
the locking screw (04); wherein
a locking screw (04) is threaded into the matching thread (3) of the guide pin
for holding the assembly of support cap (03), temperature stub (02) and the guide
pin (01) concentrically in the same vertical line and for placing the said assembly
with a part of the guide pin being inside a hole configured on the header pipe line
(07) for carrying out the tack welding in a diametrically opposite place of a polarity

of internal grooves disposed on the guide pin (01) between the temperature stub
(02) and the header pipe line;
2. A method for tack welding of temperature stubs with header pipe line in high
pressure steam generator by the fixture claimed in claim 1 comprising the step of;
arranging a guide pin (01) with step diameter;
providing a threaded hole (13) in the smaller diameter of the said guide pin
(01);
inserting a temperature stub (02) in the guide pin (01) allowing it to sit on the
step (08) of the guide pin (01);
placing a support cap (03) having a hole at the top, on the top face of
temperature stub (02);
inserting a locking screw (04) through the top hole of the said support cap (03)
into the threaded hole (13) of the guide pin (01);
tightening the locking screw (04) to make an assembly (A) of the temperature
stub (02), support cap (03) and guide pin (01) such that centerline of all three
concentrically lie in the same vertical line;
inserting a pin (06) for root gap between the assembly (A) and header pipe line
(07) to maintain uniform root gap circumferentially;
providing a plurality of internal groove (09) equally spaced on the diameter on
the guide pin wherein

the assembly (A) of temperature stub (02) with support cap (03) and guide pin
(01) is placed on the header pipe line (07) with bigger diameter end of guide pin
(01) being inserted into the said pipe line (07) through a hole configured on the
header pipe (07) when tack welding is carried out in the diametrically opposite
place of a plurality of internal grooves (09)of the guide pin (01) between the
temperature stub (02) and header pipe line (07) wherein, after the tack welding
being completed, a locking pin (05) is inserted in the hole (11) provided on the
support cap and passes through a hole (12) provided on the guide pin (01) to
prevent rotation of the assembly while locking screw (04) is unlocked, when
locking screw (04), locking pin (05), support cap (03) and guide pin (01) are taken
out.
3. The method as claimed in claim 2, wherein uniform root gap maintained is 2mm
circumferentially.
4. The method as claimed in claim 2, wherein number of grooves provided in the
guide pin (01) are four.