FIELD OF THE INVENTION
The invention generally relates to mechanized Hot Wire GTAW technique for
dissimilar weld joints of SS 304H and T91 to produce boiler components. More
particularly, the invention relates to an improved HW-GTAW process for
producing dissimilar material tube butt joints of Super 304 H Austenitic Stainless
Steel (SS 304H) and 9%Cr and ½ % Mo Ferritic-Martensitic steel (T91).
BACKGROUND OF THE INVENTION
HW-GTAW process for producing dissimilar weld joints are not known in the art,
in particular dissimilar butt welding of SS 304H and T91 tube using fully
mechanized HW-GTAW procedure. However, technology related to HW-GTAW
process disclosed in the art may include:
Patent No. EP 0194045 B1, Filing Date: February 10, 1986, Publication date
January 31, 1990.
This invention relates to TIG (Tungsten Inert Gas) welding equipment, and more
particularly to welding equipment suitable for performing semi-automatic hot
wire TIG arc welding. In this investigation the applicant (Babcock - Hitachi
Kabushiki Kaisha) claims that a semi-automatic hot wire TIG (Tungsten Inert
Gas) welding equipment comprising: a portable TIG arc torch; a portable filler
wire feed torch; a hot wire switching power source for energizing said TIG arc

torch, said filler wire feed torch and a base metal; a filler wire feeding device for
feeding the wire to said wire feed torch at a desired rate; a welding condition
control device for controlling the welding conditions, the welding conditions
being determined by parameters including an arc current, a wire feed rate and a
power coefficient; and a voice identification-control device for identifying an
aural signal from a welder to set the welding conditions and transmitting same to
said welding control device.
Patent No. EP 0139249 B1, Filing date: September 26, 1984. Publication date
May 2, 1990.
This invention relates to a ho-wire TIG welding (i.e. hot-wire inert-gas tungsten
arc welding) apparatus. In this investigation the applicant (Babcock - Hitachi
Kabushiki Kaisha) claims a hot-wire TIG welding apparatus comprising an electric
power source for providing a TIG arc, another electric power source for feeding a
wire-heating electric current to a wire by effecting alternatingly both the feed
and pause of electric power so as to heat the wire, a TIG arc torch for feeding
wire, characterized by control means having: means (22 and 23; 43; 58) for
providing an electric signal proportional to a feed speed of wire; detecting means
(25; 35; 36 and 43; 35, 36 and 58) for detecting wire electric current and wire
voltage to detect wire-heating instantaneous electric power, said detecting
means providing an electric signal corresponding to the detected instantaneous
wire-heating power; and comparing-and-controlling means (27, 43, 55 and 58)
and a switching element (31, 42 and 54) provided in a circuit of wire-heating

electric power feetl, said comparing-and-controlling means comparing the electric
signal of the wire-heating instantaneous electric power with the electric signal
proportional to the feed speed of the wire so as to control the time duration of
electric power fed through the switching element on the basis of the result of the
comparing so that the wire-heating electric power corresponds to the feed speed
of the wire, the feed of wire heating current is paused when the arc current
reaches a peak level, the wire heating current being fed when the arc current
becomes a base level, the time duration of feed of the wire heating current being
not longer than t he time duration of the arc base current.
In the line of above, some more patents are also available and given in Table - 1


OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a fully mechanized HW-
GTAW process for producing dissimilar tube butt joints of SS304H and T91.
Another object of the invention is to propose a fully mechanized HW-GTAW
process for producing dissimilar tube butt joints of SS304H and T91, which
improves 200% productivity.
A still another object of the invention to propose a fully mechanized HW-GTAW
process for producing dissimilar tube butt joints of SS304H and T91, which
eliminates the requirement of skilled welder.
A further object of the invention is to propose a fully mechanized HW-GTAW
process for producing dissimilar tube butt joints of SS304H and T91, which
improves the quality of the weld joint in reference to soundness, mechanical and
metallurgical properties as well as reduction in defects.
SUMMARY OF THE INVENTION
The present invention is fully mechanized HW-GTAW technique for dissimilar
joining the tube to tube butt joint.
The welding is carried out by multi-pass deposition from one side at conventional
V groove butt joint having included an angle of 75° without root face and root
gap.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows schematic diagram of weld groove. The schematic diagram of weld
groove is shown in Figure 1.
DETAIL DESCRIPTION OF THE INVENTION
WELDING CONDITION OF THE INVENTION IS AS UNDER:
Filler Material : YT 304H (Dia. 1mm)
Shielding composition Gas and Flow Rate : 99.98 and 15 litres/min
Purging Gas Flow Rate : 4 - 4.5 litres/min
Preheating Temperature : Nil
Inter-Pass Temperature : Less than 100°C
Welding Position : IG
Tungsten Electrode Extension : 3.15 mm (2% thoriated)

WE CLAIM:
1. An improved HW-GTAW process for producing dissimilar material tube
butt joints of Super 304 H Austenitic Stainless Steel (SS 304H) and 9% Cr
and ½ % Mo Ferritic-Martensitic steel (T91), the improvement is
characterized in that the welding is carried out at 1G position by multipass
deposition without preheating from one side at conventional V-groove but
joint having included an angle of 75° without root face and root gap.
2. The process as claimed in claim 1, wherein the purging gas flow rate and
shielding gas flow rate are 4-4.5 L/minute and 15L/minute respectively
wherein inter-pass temperature is less than 100°C, and wherein the
tungsten electrode extension is 3-15 mm.
3. The process as claimed in claim 1, wherein the hot wire feed rate, hot
wire stick out, hot wire current, welding arc current, arc voltage, and
travel speed in the first weld pass are 1.8 m/min, 30 mm, 45 amp, 125-
135 amp, 1-.5-12.1V, and 11 cm/min respectively.
4. The process as claimed in claim 1 or 3, wherein the hot wire feed rate,
hot wire stick-out, hot wire current, welding arc current, arc voltage, and
travel speed in the second weld pass are 2.0 m/min, 30 mm, 45 amp,
120-130 amp, 11.9-12.9 V, and 12 respectively.

5. The process as claimed in claim 1, wherein the shielding gas has
composition of 99.98% Argon.

ABSTRACT

The invention relates to mechanized Hot Wire GTAW technique for dissimilar
weld joints of SS 304H and T91 tube. More particularly the invention relates to
an improved HW-GTAW process for dissimilar material tube butt joints of Super
304 H Austenitic Stainless Steel (SS 304H) and 9% Cr and ½ % Mo Ferritic-
Martensitic steel (T91). The process can be applied for welding of the boiler
components.