Note: Descriptions are shown in the official language in which they were submitted.
20187~
ME~OD FOR ON~-SID8 ROOT PASS WELDING
OF A PIP~ JOINT
Field of the Invention
The present invention relates to a method for one-side ` --
root pass welding of a pipe joint in a pipe-laying work.~ p
Brief Description of the Drawings
Fig. 1 (A) is an enlarged sectional view of the prior art
groove shape;
Fig. 1 ~B) is a schematic illustration showing a state of
a build-up weld of the prior art groove; `i~
Fig. 2 i8 a schematic illustration of an automatic
welding machine used for a welding method of the present
invention;
Fig. 3 (A) and (B) are enlarged sectional views of groove
shapes of the present invention;
Fig. 3 (C) is a schematic illustration showing a state of
a build-up weld in case of the groove of the present
invention;
Fig. 4 (A) and (B) are schematic illustrations showing a `
~itate of a root gap and a d$slocation between both pipe ~.
plates;
Fig. 5 iB a diagram of pulse waveforms of welding current
of the present invention; ,i`'~
Fig. 6 (A) to (F) are diagrams showing the relationship
between a position of pulse and a-position of rotation of arc; ;l,
Fig. 7 is a circuit diagram of a pulse synchronizing `i ~"
control used for a controlling method of the present ; ~i
invention; and ~ ~ ~"`
Fig. 8 is a timing chart showing movements of controlled
waveforms of Fig. 7.
Description of the Prior Art ~'/;'`',.~'~r;`.'~
A groove shape in a circumferential butt weld of a pipe
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joint is generally formed a8 shown in Fig. 1 (A). The pipe
joint is welded as shown in Fig. 1 (B). That is, root pass
welding (I), hot pass welding (H), filler pass welding (F~ and
cap pass welding (C) oi the pipe joint are carried out in this
order. Firstly, the root pass welding (I) is carried out by
the use of an internal welding machine. A welding speed of
the root pass welding (I) i~ about 75 cm/min and weaving of a
torch is not carried out. Then, after the root pass welding
(I) has been carried out, the hot pass welding (H), filler
pass welding (F) and cap pass welding (C) are carried out in
this order from an outer surface of pipes with the use of an
external welding machine. The welding speed of the hot pass
welding (H) is about 100 cm/min and the weaving of the torch
i8 not carried out. The welding speed of the filler pass
welding (F) and the cap pa8~ welding (C) i8 about 30 to
40cm/min and the pipe joint is welded while the weaving of 6
to 7 mm corresponding to a width oi the groove is being
carried out.
Since any weaving of a torch is not carried out during
welding of the pipe joint by the root pass welding and the hot
pass welding in the above-described prior art, a seam tracking
control o$ welding cannot be carried out with the use of arc
sensors. Accordingly, time and labour are required to adapt
a welding torch of a welder to the center of a groove of the
pipe joint. Moreover, defects are liable to occur in a bead
of the root and hot pass due to such factors as a propensity
o~ wire to bend and errors of the torch in pointing at
positions.
Welding current is limited to about 200 A in the prior
art root pass welding. Because a shape of a bead becomes
convexed particularly in a position of the torch pointing
upward at the time of using electric current higher than 200
A since any weaving of a welding torch cannot be applied.
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2~187~1 ;
Accordingly, welding of the pipe joint has been regarded as ~;~
impossible at a higher speed. -
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An automatic seam tracking control by the use of the arc
sensors is carried out as follows~
(a) Make the welding torch weave in the groove in the
direction of the groove width.
(b) Detect the deviation of the welding torch by ;-~
detecting the waveforms of welding current and arc
voltage. -~'~
(c) Track the welding seam automatically by correcting `~
the torch position on the basis of the information
of (b). `~ `
Since a vibrating weaving method is adopted in the prior
art arc sensors, it is difficult for the weavin~ frequency to
exceed 10 ~z because of mechanical limits such as vibration, ~-
backlash or the like. Due to the limitation of the weaving -
frequency, a welding speed applicable from a viewpoint of
responsivenes~ of the arc sensors and shapes of beads is ~ Ci~
limited. The automatic seam tracking control cannot be
applied at a welding speed of 75 cm/min in the prior art root
pass welding.
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Summary of the Invention ; ;~
It 1~ an ob;ect of the present invention to increase a
welding speed of a root pass welding and to secure a stability
of weld quality during a circumferential butt welding of a
pipe ~oint.
The above ob~ect and other objects and advantages of the
present invention will become apparent from the detailed
description which follows, taken in conjunction with the
appended drawings.
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2~187Gl `~
Description of the Preferred Embodiment
Preferred Embodiment
In this method, since a rotating weaving of arc is
carried out at a high rate of 10 to 150 Hz/sec, an automatic
seam tracking with the use of arc sensors can be applied in a -~
high speed welding at 75 to 300 cm/min. Since the automatic
seam trac~ing is carried out, positions of a weld torch are
roughly determined in a short time. Defects in a weld are not
produced by the deviation of the torch position. - ~
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Moreover, since pressure and heat input of arc are
dispersed by a high-speed rotation of the arc, a surface shape -~ `
of bead i8 made uniform. In consequence, a good shape of bead `
can be obtained even at the high welding speed of 75 to 300 ~;;
cm/min. - ~
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That is, in the circumferential butt welding of a pipe -
joint, the rotation frequency of the arc can be easily ~
increased and the arc can be let to track a V-shaped ring 'ugroove automatically in a bottom portion which is formed at
end faces of the pipes. Accordingly, when the pipe joint is
welded under the work of the high-speed rotation arc sensor
with the rotating frequency of the arc of 10 to 150 Hz and
with the rotating diameter of the arc of 1 to 4 mm while
running an automatic welding machine along a circumferential
guide rail mounted by a tack weld on the outer surface of ~
the pipes, a circumferential root pass welding of the pipe ~ ~-
joint can be carried out in all positions thereof.
Moreover, a normal back bead is formed in the root pass
welding of the pipe joint by the use of backing material
with high welding current of 200 to 500 A and a high welding
speed of 75 to 300 cm/min can be realized. Further, the
pipe ioint can be welded continuously, being followed by the
successive filler pass and cap pass weldings, with the root
pass welding as a basis.
The rôtation frequency of said arc is desired to be 30 ~ ~
to 150 Hz. When the ratation frequency is 30 Hz or more, ``
the effect of a high frequency roatation of the arc appears
remarkably. The welding current is desired to be 250 to
500 A. The welding speed is desired to be 150 to 300
cm/min. ~
Fig.2 is a schematic illustration of an automatic .
welding machine used for a method of the present invention.
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Welding machine 1 runs along circumferential guide rail
12 mounted by a tack weld on an outer surface of pipe 10.
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Welding torch 2 fixed to the welding machine 1 is made to ~ :
rotate by motor 3 by means of gear ~echanism 4. The weld
torch 2 is supported by means of x-axis slide block 5
movable in the direction of a width of groove 14 ( x-axis )
and y-axis slide block 6 movable in the direction of torch -~ ~
height ( y-axis ). Rotation frequency N of the torch 2 is -- -
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I the rotation frequency of the arc, and a rotating sPeed and
a rotation position of the arc are detected bY a rotation
frequency detector ( not shown ). A resistance welding tip `~
is fixed to the torch 2. Welding wire 7 is automatically -
fed. In this way, the rotating arc welding is carried out
at a high speed. Reference numeral 16 denotes a backing ' ~'~ A'''~''''~
material such as copper plate or the like which is attached ;~
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to a bottom portion of a weld from the reverse side of the
weld. The welding wire of 0.8 to 1.6 mm in diameter is
used.
Fig.3 (A) and (B) are enlarged sectional views of
groove shapes used for executing the method of the present
invention. Groove shape 14 is formed so that bottom
portion 14a of a groove can be V-shaped and side portion 14b
of the groove can be straight. Inclination ~ of the bottom
portion 14a is 30 to 60 . Dimension "a" is 1 to 2 mm.
Width of groove "b" is 10 mm or less for a pipe with wall
thickness "t" of 8 to 25 mm. Small groove 14c as shown in
Fig.3 (B) can be made on the inner side of a pipe having
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20~8701 ``
groove 14.
The following are realized by the welding torch 2 shown
in Fig.2 under the work of the rotating arc sensor by
forming a V-shaped bottom portion of the groove 14.
Firstly, the welding torch can be made to accuratelY track
the center of the bottom portion 14a with a definite length
of the arc. Secondly, an outer hot pass welding H following
root pass welding 17 can be carried out circumferentially in
all positions. Thirdly, back bead 18 can be normally made
simultaneously with the root pass welding 17.
The above-mentioned example will be described
specifically. The root pass welding 17 was carried out
under the following conditions by the use of solid wire of
0.9 mm in diameter and a smooth shape of a bead could be
obtained
Rotation frequency N of arc : 50 Hz
Rotation diameter D of arc : 2 to 3 mm
Welding current Ia : 300 A
Welding speed v : 2.0 m/min
Shieling gas : 100% C02
Subsequently, in case filler pass welding F and cap
pass welding C are carried out on the root pass 17 in
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buiId-up sequence, when the pipe joint is welded under the ` -
work of the rotating arc sensors on the basis of the root
pass 17, the circumferential butt welding of the pipe joint
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can be carried out at a high speed. Accordingly, according
to the method of the present invention, a period of a
pipe-laying work can be reduced to about 1/4 to 1/2 compared
with that in the prior art method and equiPment and the
number of laborers can be greatly decreased.
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Preferred Embodiment-2
As shown in Fig.4 (A) and (B), in a circumferential
butt joint of a pipe, occurrence of root gap (G) and
dislocation between both pipe plates (J) cannot be avoided
in welding at a site. There are required welding
procedures which generally allow a root gap of 1.0 mm at its
maximum and a dislocation between both pipe plates of 1.6
mm at its maximum. However, welding current and welding
speed are limited due to such root gap and dislocation
between both pipe plates.
In Preferred Embodiment-2, there is used a control
method wherein a peak position of a pulse welding current
waveform ls synchronized with an optimal position of arc.
A pulse and a synchronized position of rotation of the arc
are controlled. The synchronized position of the arc is
determined by controlling conditions of the pulses such as
peak welding current and pulse welding current waveforms.
In a pulse arc welding having a pulse welding current
waveform as shown in Fig.5, it is necessary to generate arc
symmetrically relative to rotation of arc to exactly carry
out a seam tracking control ~ y the use of rotating arc
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20~87~1
sensors. Methods of determining pulse cycles of peak
current lp comprise methods of one dividing, two dividings
and four dividings. Fig.6 (A) an (B) show a method of one
dividing. Fig.6 (C) and (D) show a method of two dividings.
Fig.6 (E) and (F) show a method of four dividings. Position
(Tp) of the pulse can be set at any position of the rotation
of arc. In the case of the one dividing, for example, the
pulse can be generated at a forward position Ct or a rear
position Cr in the welding direction WD. In the case of
the two dividings, the pulse can be generated at positions
C~ and Cr or at positions L and R. In the case of the four
dividings, the pulse can be gènerated at positions C,, Cr,
Land R or at intermediate ~ositions among those positions.
Values of average welding current I., peak welding
current Ip, base welding current IB and cycle of pulse tB as
shown in Fig.5 are freely changed dependent on welding
conditions. In case a position of pulse is set at position
C, corresponding to one dividing, for example, peak current
Ip is elevated by lowering base current IB. A degree of
elevating the peak current lp, for exa-ple, is deter~ined by
detecting arc voltage at position C,. The shapes of back
bead are exactly controlled by controlling the pulse in such
a manner. A bead shape of a root pass becomes smooth under
the effect of the high-speed rotating arc sensors and the
high-speed welding with the use of high welding current can
be realized. Moreover, since a pipe joint can be
continuously welded by successively carrying out a filler
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pass welding and a cap`pass welding on the basis of the root
pass welded in this way. Therefore, time for welding can be
reduced.
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An automatic welding and a groove shape used for
Preferred Embodiment-2 are the same as those of Figs. 2 and 3
shown in preferred Embodiment-l.
Fig. 7 shows a circuit diagram of a pulse control used in
the present invention. Fig. 8 is a timing chart designating
a working principle of a control waveform in a pulse control
circuit.
In Figs. 7 and 8, pulse welding current 51 of the pulse
welding power source 1 is, for example, made to be two
dividings by divider 22 in accordance with a dividing signal
which is predetermined by setting device 21. A divided
waveform 52 is inputted into a pulse-synchronizing control
circuit 23. A rotating position signal 53 and a rotation
frequency signal Cf of welding torch 2 are inputted into
phase-adjusting device 26 by means of rotating position signal
generator 24 and encoder 25. Arc rotating position signal 54
is inputted from the phase-adjusting device 26 into pulse-
synchronizing control circuit 23. Welding current pulse 51 is
not synchronlzed with arc rotating pulse 54. To synchronize
the welding current pulse with the arc rotating position
slgnal in accordance with a signal given by setting device 27,
the pulse welding current is converted to waveforms 53' and
54' obtained by adjusting the phase and the rotation
frequency. 8ubsequently, a position of peak current pulse is
made to coinclde wlth position C~ by causing control ...
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waveform 53" to shift by means of a delay circuit.
Rotating driver 28 is controlled by signal 53n ~-synchronized in this way. Subsequently, rotating motor 3
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is driven by a signal from rotating driver 28 and the ~ ~
rotation frequency of the welding torch is controlled. -- ;
Referential numeral 29 denotes a rotating detector of the
motor and the signal of the rotating detector is transferred
back to the rotating driver 28. -
A specific example will be described below. Solid
wire of 0.9 mm in diameter was used. When root pass ~-
welding 17 was carried out under the following conditions, `
back bead 18 of a good shape was obtained. A smooth bead of
the root path, of course, was obtained.
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Rotation frequency N of arc : 50 Hz
Rotating diameter D of arc : 2 to 3 mm ;
Average welding current la : 300 A ;~
Peak current Ip : 420 A
Base current IB : 180 A :
Pulse cycle : 10 ms ~ ,
Welding speed v : 2.0 m/-in (2 dividings)
Shieling gas : 100 X C02 gas
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Since filler pass weilding F and cap pass welding C can ~ ~-
be continuously carried out in buid-up sequence on the basis ~ ;
, of the root pass 17, a circumferential butt welding of
a pipe joint can be carried out at a high speed of 300 Z~
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cm/min.
As described above, according to Preferred ~ `
Embodiment-2, a hot pass welding can be carried out only
from an outer surface of pipes by the use of a rotating arc ~ -
sensor method. Moreover, since the back bead can be ~;
normally made simultaneously with the hot pass welding, the
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circumferential butt welding of a pipe joint can be easily
and rapidly carried out in a pipeline-laying work.
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