CA1080813A - Method for longitudinally seam-welding pipe-blanks for welded steel pipe from the inside along a groove - Google Patents
Method for longitudinally seam-welding pipe-blanks for welded steel pipe from the inside along a grooveInfo
- Publication number
- CA1080813A CA1080813A CA274,579A CA274579A CA1080813A CA 1080813 A CA1080813 A CA 1080813A CA 274579 A CA274579 A CA 274579A CA 1080813 A CA1080813 A CA 1080813A
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- Prior art keywords
- welding
- pipe
- blank
- current
- polarity
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/06—Arrangements or circuits for starting the arc, e.g. by generating ignition voltage, or for stabilising the arc
- B23K9/073—Stabilising the arc
- B23K9/0737—Stabilising of the arc position
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Plasma & Fusion (AREA)
- Mechanical Engineering (AREA)
- Arc Welding In General (AREA)
- Butt Welding And Welding Of Specific Article (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An improvement is provided in longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove by the G.M.A. welding process. That process comprises supplying D.C. current as the welding current to at least two even number of consumable electrodes in tandem through current supply cables, the current supply cables exten-ding alongside each other longitudinally within the pipe-blank and then longitudinally seam-welding the pipe-blank for welded steel pipe from the inside along a groove by means of the respective consumable electrodes fed through a respective even number of welding torches in tandem, while moving a boom carrying the welding torches through the pipe-blank relative to the pipe-blank in the same direction as that of welding, the boom having a free end which carries the welding torches and having a length at least equal to that of the pipe-blank. The method of this invention comprises the steps of connecting one-half of the even-number of consumable electrodes to the D.C. current so as to be positive in polarity, and connecting the other half of the even number of consumable electrodes to the D.C. current so as to be negative in polarity. In this way, the direction, longitudi-nally of the pipe-blank, of the D.C. current flow to the one-half of the electrodes is opposite to the direction of the D.C. current flow to the other half of the electrodes so that the lines of magnetic force produced by the direct current for welding flowing through at least one cable intro-duced into the pipe-blank cancel each other, substantially to prevent magnetization of the pipe-blank. Consequently, this method substantially prevents magnetic arc blow of the welding arc. The weld thus provided is sound and substantially free from welding defects.
An improvement is provided in longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove by the G.M.A. welding process. That process comprises supplying D.C. current as the welding current to at least two even number of consumable electrodes in tandem through current supply cables, the current supply cables exten-ding alongside each other longitudinally within the pipe-blank and then longitudinally seam-welding the pipe-blank for welded steel pipe from the inside along a groove by means of the respective consumable electrodes fed through a respective even number of welding torches in tandem, while moving a boom carrying the welding torches through the pipe-blank relative to the pipe-blank in the same direction as that of welding, the boom having a free end which carries the welding torches and having a length at least equal to that of the pipe-blank. The method of this invention comprises the steps of connecting one-half of the even-number of consumable electrodes to the D.C. current so as to be positive in polarity, and connecting the other half of the even number of consumable electrodes to the D.C. current so as to be negative in polarity. In this way, the direction, longitudi-nally of the pipe-blank, of the D.C. current flow to the one-half of the electrodes is opposite to the direction of the D.C. current flow to the other half of the electrodes so that the lines of magnetic force produced by the direct current for welding flowing through at least one cable intro-duced into the pipe-blank cancel each other, substantially to prevent magnetization of the pipe-blank. Consequently, this method substantially prevents magnetic arc blow of the welding arc. The weld thus provided is sound and substantially free from welding defects.
Description
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The present invention relates to an improvement in the method for longitudinally seam-welding a pipe-blank for welded steel pipe, from the i~side along a groove or cleft by the metal arc welding process, involving using direct electric current supplied to a plurality of con-sumable electrodes arranged in tandem through at least one current supplying cable as the welding current.
Conventionally, in longitudinally seam-welding for manufacturing a welded steel pipe, the groove or cleft of an 0-shaped plate (hereinafter called the "pipe-blank"), which is formed into a cylindrical shape by a forming process, e.g~, the U-O process (abbreviation of the U-ing/0-ing process) or the bending roll process, takes place. It is the usual welding practice to employ an inside welding machine equipped with a welding torch attached to the free end of a boom, the boom having a length at least equal to that of the pipe-blank to be welded, the fixed end of the boom being fixPd to a carriage. The boom is inserted into the pipe-blank in advance. The pipe-blank is then longitudinally seam-welded from the inside along the groove or cleft with a consumable electrode. Such consumable electrode is fed through the welding torch while the boom is moved by the carriage, together with current supply cable serving to supply 20 welding current to the consumable electrode in the withdrawal direction from the pipe-blank, i.e., in the welding direction. An inside welding - machine may be equipped with two welding torches, one leading and the other trailing, and two consumable electrodes. However, an inside welding machine may have one welding torch and one consumable electrode, or it may be provided with more than two welding torches and more than two con-sumable electrodes.
Another conventional method of welding a pipe-blank invovles adopting a welding process which includes using direct electric current as the welding current with a consumable electrode as the anode, namely, the - 30 reverse-polarity G.M.A. welding process (G.M.A. welding process is the _ _ _ _ _ . _ _ .. . . _ . . . . . . .
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abbreviation of the gas metal arc welding process which involves carrying out welding while shielding a molten metal and a welding arc produced in the space between the base metal and the consumable electrode from open air with shielding gases, e.g. "~n inert gas and a carbon dioxide gas).
In such process, the welding arc from the consumable electrode is deflected toward the upstream side of the welding direction, i.e., in the opposite direction to that of welding, and takes the form as if it were drawn in by the molten metal. When the welding arc takes such form as if it i9 drawn in by the molten metal as mentioned above, the plasma jet stream produced at the tip of the consumable electrode is also deflected toward the molten metal and acts on the molten metal as a dynamic pressure. This pushes the molten metal away toward the upstream side of the welding direction, i.e., in the opposite direction to that of welding. As a result, the space below the consumable electrode becomes substantially dry without molten metal, thus impairing the affinity between molten droplets from the consumable electrode and the base metal, at the groove or cleft of the pipe-blank. Welding defects, e.g., undercut of bead, humping bead and lack of fusion of base metal thus tend to occur easily.
-~ In addition, frequent occurrence of boiling and spattering in the molten metal tends to result in a deteriorated appearance of the weld bead. When the welding arc is deflected as described above, furthermore, the tip of the consumable electrode is melted only on one side. Under such circum-stances, the transfer mode of molten droplets from the consumable electrode - cannot be a desirable spray transfer, but takes an undesirable mixed form of globular transfer and short-circuit transfer. As a result, coarse spatters are splashed with a crackling short-circuiting noise and are deposited on the weld bead surface, thus leading to a deteriorated appear- - ;
ance of the weld bead. i~oreover, splashed spatters are deposited on the opening at the tip of the shielding nozzle of the welding torch to disturb the gas shield and entangle the air. In this case, it may practially be -: . , , , , . . :
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impossible to carry out satisfactory welding.
The above-mentioned deflection of the welding arc toward the upstream side of the welding direction, i.e., in the opposite direction to that of welding and the resulting irregular w~ld bead and welding de-fects are not limited only in the case of the conventional G.M.A. welding process, but occur also in the case of the submerged-arc welding process using direct electric current as, the welding current. In both cases, it has been difficult to obtain a sound weld substantially free from welding defects.
An object of a broad aspect of the present invention is there-fore to provide an improvement in the method for longitudinal seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft by the G.M.A. welding process by using direct electric current as the welding current supplied to a plurality of consumable electrodes, through at least one current supply cable as the welding current, thereby to pro-vide a sound weld substantially free from welding defects.
An object of another aspect of the present invention is substan-tially to prevent the occurrence of the magnetization of the pipe-blank for welded steel pipe and the resulting magnetic arc blow of the welding arc in longitudinally seam-welding the pipe-blank from the inside along a groove or cleft by the G.M.A. welding process.
In accordance with a broad aspect of the present invention, an improvement is provided in a welding method for longitudinally seam-welding a pipe-blank from the inside thereof applying the G.M.A. welding process comprising: supplying D.C. current as the welding current to an even number of consumable electrodes in tandem through at least one current - supply cable, the current supply cable extending alongside each other ; longitudinally within the pipe-blank; and longitudinally seam-welding the pipe-blan~ for welded steel pipe from the inside along a groove or cleft 30 with respective consumable electrodes fed through a respective plurality B - 3 - ~
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1~38V~313 of welding torches in tandem, while moving a boom carrying the welding torches through the pipe-blank relative to the pipe-blank in the same direction as that of welding, the boom having a free end which carries the welding torches and having a length at least e~ual to that of the pipe-blank, the method comprising the steps of: using at least two even-numbered consumable electrodes; connecting one-half of the consumable electrodes to the D.C. current so as to be positive in polarity; connec-ting the other half of the consumable electrodes to the D.C. current so as to be negative in polarity; thereby to enable lines of magnetic force produced by the direct electric current for welding flowing through at least one current supply cable introduced into the pipe-blank to cancel each other, thereby substantially preventing magneti~ation of the pipe- ~-blank.
By one variant, the boom is inserted in advance into the pipe-blank together with the current supply cables; and the pipe-blank is longitudinally seam-welded while withdrawing the boom, together with the current supply cables, from the pipe-blank relative thereto in the same direction as that of welding.
By another variant, the pipe-blank is longitudinally seam-welded while inserting the boom, together with the current supply cables, into the pipe-blank relative thereto in the same direction as that of welding.
By a further variant, the method includes connecting one-half, leading in the welding direction, of the even number of electrodes to the D.C. current so as to be positive in polarity, and connecting the other half, trailing in the welding direction, of the even number of electrodes to the D.C. current so as to be negative in polarity.
In the accompanying drawings, Figure 1 is a schematic side view illustrating a conventional method according to the prlor art for longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft, and . ::: .: - : ~: :: .
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an apparatus for ~he implementation thereof;
Figure 2 is a partially enlarged schematic drawing illustrating a form of welding in the conventional reverse-polarity G.M.A. welding process of the prior art involvi.ng using direct electric current as the welding current with a consumable electrode as ~he anode;
Figure 3 is a partial cutaway schematic side view illustrating a form of welding in longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft by the conventional reverse-polarity G.M.A. welding process of the prior art;
Figures 4A and 4B are vector diagrams illustrating the relation between the direction of the electric current flowing through a welding arc, the magneti~ing direction at the groove or cleft of a pipe-blank for welded steel pipe, and the direction of the force acting on the welding arc at the groove or cleft in the conventional reverse-polarity G.M.A.
welding process of the prior art;
Figure 5 is a schematic side view illustrating an embodiment of the method of one aspect of the present invention;
Figure 6 is a photograph showing the state of a weld bead obtained by the conventional reverse-polarity G.M.A. welding process of the prior art; and Figure 7 is a photograph showing the state of a weld bead obtained by the method of an aspect of the present invention.
As seen in schematic form in Figure 1, in longitudinally seam-welding for manufacturing a welded steel pipe, a groove or cleft of an ;
0-shaped plate ~namely, a pipe-blank), which is formed into a cylindrical shape by a forming process, e.g., the U-0 process or the bending roll process, it is the usual practice of welding to employ an inside welding macine equipped with a welding torch 1 attached to the free end of boom 2, the boom 2 having a length at least equal to that of the pipe-blank 3 to be welded. The fixed end of the boom 2 is fixed to a carriage 4. The ,, .
~ _ 5 _ 108~3 boom 2 is inserted into the pipe-blank 3 in advance. The pipe-blank 3 is then longitudinally sea~-welded Erom the inside along the groove or cleft with a consumable electrode 5. Consumable electrode 5 i5 fed through the welding torch 1, while the boom 2 is moved by the carriage 4, together with a current supply cable 9 wh:ich serves to supply welding current to the consumable electrode 5. The current supply cable 9 is moved in the withdrawal direction from the pipe-blank 3, i.e., in the welding direction, as indicated by the arrow in the drawing. ~s shown, the inside welding machine may be equipped with two welding torches 1, 1, one leading, and the other trailing, and ~wo consumable electrodes 5, 5, one leading, and the other trailing. However, the inside welding machine may have one welding torch and one consumable electrode, or it may be provided with more than two welding torches and more than two consumable electrodes.
- Figure 2 shows, in partially enlarged schematic form, a conven~
tional method of welding a pipe-blank, when adopting a welding process involving using direct electric current as the welding current with a con-sumable electrode as the anode, namely, the reverse-polarity G.M.A. welding process. The welding 6 from the consumable electrode 5 is deflected toward the upstream side of the welding direction indicated by the arrow in the drawing, i;e., in the opposite direction to that of the welding and takes the form as if it were drawn in by the molten metal 7. When the welding arc 6 takes that form as if it is drawn in by the molten metal 7 as men-tioned above, the plasma jet stream produced at the tip of the consumable electrode 5 is also deflected toward the molten metal 7 and acts on the , molten metal 7 as a dynamic pressure. This pushes the molten metal 7 away toward the upstream side of the welding direction, i.e., in the opposite direction to that of the welding. As a result, the space below the consumable electrode 5 becomes substantially dry without any molten metal, thus impairing the affinity between molten droplets from the consumable - 30 electrode 5 and the base metal, at the groove of the pipe-blank 3. Welding .
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1~8~8~3 defects, e.g., undercut of bead, humping beand and lack of fusion of the base metal thus tend to occur easily~ In addition, frequent occurrence of boiling and spattering in the weld bead surface tends to result in a deteriorated appearance of the weld bead. When the welding arc 6 is deflected as described above, the tip of the consumable electrode 5 is melted only on one side as shown in Figure 2. Under such circumstances, the transfer mode of molten dropl~ets from the consumable electrode 5 cannot be a desirable spray transEer, but takes an undesirable mixed form of globular transfer and short circuit transfer. As a result, coarse spatters are splashed and are deposited on the weld bead surface, thus leading to a deteriorated appearance of the weld bead. Moreover, as indi-cated before, splashed spatters are deposited on the opening at the tip of the shielding nozzle (not shown) of the welding torch to disturb the gas shield and entangle the air. In this case, it may be practically impossible to carry out welding.
The irregular weld bead and wèlding defects, e.g., undercut of bead, humping bead, lack of fusion of base metal and spattering, observed in longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft by the conventional welding process as mentioned above, is believed to be attributable to the deflection of a plasma jet stream toward a molten metal caused by the deflection of a welding arc, and also that the deflection of the welding arc is brought about by a line of magnetic force produced by the direct electric current for welding flowing through a current supply cable introduced into the pipe-blank.
More specifically, for instance in longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft by the conventional reverse polarity G.M.A. welding process comprising using direct ~electric current as the welding current with a consuamble electrode as the anode, direct current for welding flows, as shown in the ~ 7 ~ , -'~ ' ~ `' ' : ' ,. - ` : ` ' `
~L~38~8~1L;3 partial cutaway schematic side view glven in Figure 3, in the opposite direction to that of welding, as indicated by an arrow in the drawing, through a current supply cable 9 introduced into the pipe-blank 3. There-fore, a line of magnetic force lO,which is clockwise as viewed from the right-hand side of the dra~ing, is produced by the direct electric current, and a strong magnetic field is formed around the current supply cable 9.
As a result, the pipe-blank 3 is strongly magnetized in the same clock-wise direction 11 as that of the line of magnetic force 10 by the magnetic field, thus causing leakage of a strong line of magnetic force from the groove of the pipe-blank 3, and a strong magnetic field is formed at the groove. When welding a groove where such a strong magnetic field is formed, the welding arc from a consumable electrode 5, which is a flow of charged corpuscle, is deflected by the strong magnetic field at the groove or cleft. This phenomenon is called the magnetic arc blow of the welding arc.
The relation between the direction of the electric current flow-ing through a welding arc, the magnetizing direction at the groove of a pipe-blank and the direction of the force acting on the welding arc at the groove is illustrated in the vector diagrams of Figures 4A and 4B. In these drawings, A is the direction of the electric current flowing in the welding arc 6 through the consumable electrode 5; B is the magnetizing direction at the groove of the pipe-blank 3; C is the welding direction;
and F is the direction of the force acting on the welding arc 6. As shown in Figures 4A and 4B, the direction F of the force acting on the welding arc 6 is the same as that of the direct electric current for welding flowing through the current supply cable 9 (refer to Figure 3) and is opposite to the welding direction C. As described hereinabove with refer-ence to Figure 2, therefore, the welding arc 6 is deflected toward the upstream side of the welding direction C, i.e., in a direction opposite to that of welding C, thus resulting in an irregular weld bead and welding : . , , : -.
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1~8()~-~3 defects, e.g., undercut of bead, humping bead, lack of fusion of base metal and spattering.
In its broad aspects, the present invention, which has been based on the aEorementioned finding, enables, in longitudinally seam-welding a pipe-blank from welded steel pipe from the inside along a groove or cleft by the conventional G.M.A. welding process which involves using direct electric current supplied to a plurality of consumable electrodes in tan-dem through at least one current supply cable as the welding current, lines of magnetic force produced by the direct electric current for welding flowing through at least one current supply cable introduced into the pipe-blank to cancel each other, by using at least two even-numbered electrodes, connecting one-half of the consumable electrodes in the reverse-polarity manner, i.e., to be positive in polarity, and connecting the other half in the straight polarity manner, i.e., to be negative in polarity, thereby substantially preventing magnetization of the pipe-blank and the resulting magnetic arc blow of the welding arc.
More specifically, in the method of an aspect of the present invention, the conventional metal arc welding process is applied, involving using direct electric current supplied to a plurality of consumable elec-trodes in tandem through current supply cables as the welding current. Asshown in the schematic side view of Figure 5, a boom 2, having a length at least equal to that of a pipe-blank to be welded 3, is equipped with a leading welding torch la and a trailing welding torch lb in tandem at the -free end thereof. The fixed end thereof is fixed to a carriage (not shown) and is inserted in advance into the pipe-blank 3 together with current supply cables 9a and 9b. ~ leading consumable electrode 5a, fed through - the leading welding torch la, is connected via current supply cable 9a in - the reverse-polarity manner, i.e., to be positive in polarity, and a trailing consumable electrode 5b, fed through the trailing welding torch lb, is connected via current supply cable 9b in the straight-polarity ':
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manner, i.e., to be negative in polarity. Pipe-blank 3 is long~tudinally seam-welded from the inside along the groove or cleft in the welding direction as indicated by an arrow 14 in the drawing, with the leading consumable electrode 5a, and the trailing consumable electrode 5b, while withdrawing the boom 2, together with the current supply cables 9a and 9b, from the pipe-blank 3 by the carriage.
In the aforementioned method of an aspect of the present inven-tion, as shown in Figure 5, the direct electric current flowing through the current supply cable 9a flows in the direction as indicated by an arrow 12 from right to left toward the consumable electrode 5a ln the drawing. A clockwise line of magnetic force 13 as viewed from the right-hand side of the drawing is therefore produced by the direct electric current. On the other hand, the direct electric current flowing through - the supply cable 9b flows in the direction as indicated by an arrow 15 from left to right from the consumable electrode 5b. A counterclockwise line of magnetic force 16, just reverse in direction to the line of magnetic force 13, as viewed from the right-hand side of the drawing, is therefore produced by the direct electric current. Consequently, because of the di~ference in polarity between the leading consumable electrode Sa and the trailing consumable electrode 5b, the direction of the line of magnetic force 13 is opposite to that of the line of magnetic force 16.
Therefore, the lines of magnetic force 13 and 16 cancel each other, and as a result, the pipe-blank 3 is hardly magnetized. It is thus possible substantially completely to prevent the occurrence of the magnetic arc blow of the welding arc and the resulting irregular weld bead and weldi~ng defects, e.g., undercut of bead, humping bead, lack of fusion of base metal and spattering.
The magnetization of a pipe-blank can be substantially preve~ed also by another embodiment of the method of an aspect of the present invention. This embodiment comprises, also with reference to Figure 5, .
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~3V8~3 connecting, contrary to the teachings of the first embodiment, the consum-able electrode 5a in the straight-polarity manner, i.e., to be negative in polarity, and the consumable electrode 5b, in the reverse-polarity manner, i.e., to be positive in polarity. The pipe-blank 3 i5 longitu-dinally seam-welded from the inside along the groove or cleft with the consumable electrodes 5a and 5b in the direction opposite to that indica~ed by arrow 14, while inserting the boom 2, together with the current supply cables 9a and 9b, into the pipe-~)lank 3 from the right-hand side of the drawing by the carriage (not shown in the drawing). In this case, it is clear that the consumable electrode 5b is the leading electrode, and the consumable electrode 5a, is the trailing electrode.
In any of the aforementioned embodiments of the method of aspects of the present invention, it is possible substantially completely to pre-vent the magnetization of a pipe-blank, and hence substantially completely to prevent the occurrence of the magnetic arc blow of the welding arc and the resulting irregular weld bead and welding defects, even by connecting ~-the leading consumable electrode in the straight-polariy manner, i.e., to be negative in polarity, and a trailing consumable electrode, in the reverse-polarity manner, i.e., to be positive in polarity. However, by connecting the leading consumable electrode in the reverse-polarity manner, -:
i.e., to be positive in polarity, and the trailing consumable electrode, in the straight-polarity manner, i.e., to be negative in polarity, better~
- results can be obtained, because of the easy availability of a deeper fusion penetration required on the leading electrode side. -The method of an aspect of the present invention is now described in more detail by way of the following example.
- EXAMPLE ~.
In longitudinally seam-welding two pipe-blanks for welded steel pipe from the inside along a groové or cleft, having a wall thickness of ;~ 30 1 inch, an outside diameter of 48.inches and a length of 12 meters by the ''.' :
. .
~~` tandem-headed G~M.A. welding process which includes using direct electric current supplied to two leadîng and trailing consumable electrodes through current supply cables as the welding current, the method of an aspect of the present invention described above with reference to Figure S was applied to a pipe-blank. That method comprises, also with reference to Figure 5, inserting the boom 2 in advance into the pipe-blank 3 together with the current supply cables 9a and 9b. The boom 2 is equipped with the leading welding torch la and the trailing welding torch lb in tandem at the free end thereof The boom 2 is fixed to a carriage (not shown) at the fixed end thereof. The leading consumable electrode 5a, fed through the leading welding torch la, is connected in thP reverse-polarity manner, i.e., to be positive in polarity via the current supply cable 9a. The trailing consumable electrode 5b, fed through the trailing welding torch lb, is connected in the straight-polarity manner, i.e., to be negative in polarity via the current supply cable 9b. The pipe-blank 3 is longitu-dinally seam-welded from the inside along the groove or cleft with the leading and trailing consumable electrodes 5a and 5b in the welding direction as indicated by the arrow 14 in the drawing, while withdrawing the boom 2,together with the current supply cables 9a and 9b from the pipe-blank by the carriage.
On the other hand, the conventional reverse-polarity G.M.A~
welding process, which is outside the scope of the present invention, was applied to the other pipe-blank for comparison purposes, such conventional method including the same steps as mentioned above, except for the step of connecting both of the above-mentioned leading consumable electrode and the trailing c~nsumable electrode reversely in the reverse-polarity manner, i.e., to be positive in polarity.
The state of the weld beads obtained as a resuLt`is shown in photographs of Figures 6 and 7.
In the weld bead obtained by the conventional reverse-polarity :
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G.~.A. welding process, as shown in the photograph of Figure 6, not only is the appearance poor, but the X-ray test also revealed such weldlng defects as lack of fusion of base metal and undercut of bead. This i9 attributable to the occurrnece of boiling of the molten metal caused by the magnetic arc blow of the welding arc towards the upstream side of the welding direction, i.e., in the opposite direction to that of welding.
The weld bead obtained by the welding method of an aspect of the present invention, in contrast, has the appearance as shown in the phorograph of Figure 7, with no significant trace of welding defects observed even by the X-ray test and by an ultrasonic flaw detection test, thus permitting ascertainment that a very sound weld can be obtained by the welding method of an aspect of the present invention.
Similarly good results have also been obtained by the welding method of another aspect of the present inveniton, (as will be described in ~xample 2), which comprises, also with reference to Figure 5, connec-ting, contrary to the foregoing, the consumable electrode 5a in the straight-polariy manner, i.e., to be negative in polarity, and the consum-able electrode 5b inthe reverse polarity manner, i.e., to be positive in ~' polarity. The pipe-blank 3 is longitudinally seam-welded from the inside along the groove or cleft with the consumable electrodes 5a and 5b in a direction opposite to that indicated by the arrow 14, while inserting the ~-boom 2, together with the current supply cables 9a and 9b, into the pipe-- blank 3 from the right-hand side of the drawing by the carraige (not shown in the drawing). In this case, the consumable electrode 5b is the leading electrode, and the consumable electrode 5a, the trailing electrode.
The above description of the method of aspects of the present invention has covered only the case where a pipe-blank is fixed while moving a boom equipped with welding torches in tandem. The essential requirement in the process of aspects of the present invention covers also cases in which the pipe-blank is moved while the boom equipped with the . ~ - 13 --{~--~
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~ welding torches is fixed. In other words, in the method of aspects of the present invention, it suffices to move the boom equipped with the welding torches through the pipe-blank in the welding direction~
According to the method of aspects of the present inveition, as described above in detail, in longitudinally seam-welding a pipe-blank for welded steel pipe Erom the inside along a groove or cleEt by the G.M.A.
welding process which includes using direct current supplied to a plurality of consumable electrodes through at least one current supply cable as the welding current, it is possible substantially completely to prevent the occurrence of the magnetization of the pipe-blank caused by direct electric . . _ . .
current flowing through at least one current supply cable introduced into the pipe-blank and the resulting magne~ic arc blow of the welding arc.
- Therefore, it is possible to obtain a sound weld bead, thus providing industrially useful effects.
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The present invention relates to an improvement in the method for longitudinally seam-welding a pipe-blank for welded steel pipe, from the i~side along a groove or cleft by the metal arc welding process, involving using direct electric current supplied to a plurality of con-sumable electrodes arranged in tandem through at least one current supplying cable as the welding current.
Conventionally, in longitudinally seam-welding for manufacturing a welded steel pipe, the groove or cleft of an 0-shaped plate (hereinafter called the "pipe-blank"), which is formed into a cylindrical shape by a forming process, e.g~, the U-O process (abbreviation of the U-ing/0-ing process) or the bending roll process, takes place. It is the usual welding practice to employ an inside welding machine equipped with a welding torch attached to the free end of a boom, the boom having a length at least equal to that of the pipe-blank to be welded, the fixed end of the boom being fixPd to a carriage. The boom is inserted into the pipe-blank in advance. The pipe-blank is then longitudinally seam-welded from the inside along the groove or cleft with a consumable electrode. Such consumable electrode is fed through the welding torch while the boom is moved by the carriage, together with current supply cable serving to supply 20 welding current to the consumable electrode in the withdrawal direction from the pipe-blank, i.e., in the welding direction. An inside welding - machine may be equipped with two welding torches, one leading and the other trailing, and two consumable electrodes. However, an inside welding machine may have one welding torch and one consumable electrode, or it may be provided with more than two welding torches and more than two con-sumable electrodes.
Another conventional method of welding a pipe-blank invovles adopting a welding process which includes using direct electric current as the welding current with a consumable electrode as the anode, namely, the - 30 reverse-polarity G.M.A. welding process (G.M.A. welding process is the _ _ _ _ _ . _ _ .. . . _ . . . . . . .
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- : : . . .. .
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1~8`~
abbreviation of the gas metal arc welding process which involves carrying out welding while shielding a molten metal and a welding arc produced in the space between the base metal and the consumable electrode from open air with shielding gases, e.g. "~n inert gas and a carbon dioxide gas).
In such process, the welding arc from the consumable electrode is deflected toward the upstream side of the welding direction, i.e., in the opposite direction to that of welding, and takes the form as if it were drawn in by the molten metal. When the welding arc takes such form as if it i9 drawn in by the molten metal as mentioned above, the plasma jet stream produced at the tip of the consumable electrode is also deflected toward the molten metal and acts on the molten metal as a dynamic pressure. This pushes the molten metal away toward the upstream side of the welding direction, i.e., in the opposite direction to that of welding. As a result, the space below the consumable electrode becomes substantially dry without molten metal, thus impairing the affinity between molten droplets from the consumable electrode and the base metal, at the groove or cleft of the pipe-blank. Welding defects, e.g., undercut of bead, humping bead and lack of fusion of base metal thus tend to occur easily.
-~ In addition, frequent occurrence of boiling and spattering in the molten metal tends to result in a deteriorated appearance of the weld bead. When the welding arc is deflected as described above, furthermore, the tip of the consumable electrode is melted only on one side. Under such circum-stances, the transfer mode of molten droplets from the consumable electrode - cannot be a desirable spray transfer, but takes an undesirable mixed form of globular transfer and short-circuit transfer. As a result, coarse spatters are splashed with a crackling short-circuiting noise and are deposited on the weld bead surface, thus leading to a deteriorated appear- - ;
ance of the weld bead. i~oreover, splashed spatters are deposited on the opening at the tip of the shielding nozzle of the welding torch to disturb the gas shield and entangle the air. In this case, it may practially be -: . , , , , . . :
:: . - . . - . . . ::. : . . :: ::: , :
impossible to carry out satisfactory welding.
The above-mentioned deflection of the welding arc toward the upstream side of the welding direction, i.e., in the opposite direction to that of welding and the resulting irregular w~ld bead and welding de-fects are not limited only in the case of the conventional G.M.A. welding process, but occur also in the case of the submerged-arc welding process using direct electric current as, the welding current. In both cases, it has been difficult to obtain a sound weld substantially free from welding defects.
An object of a broad aspect of the present invention is there-fore to provide an improvement in the method for longitudinal seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft by the G.M.A. welding process by using direct electric current as the welding current supplied to a plurality of consumable electrodes, through at least one current supply cable as the welding current, thereby to pro-vide a sound weld substantially free from welding defects.
An object of another aspect of the present invention is substan-tially to prevent the occurrence of the magnetization of the pipe-blank for welded steel pipe and the resulting magnetic arc blow of the welding arc in longitudinally seam-welding the pipe-blank from the inside along a groove or cleft by the G.M.A. welding process.
In accordance with a broad aspect of the present invention, an improvement is provided in a welding method for longitudinally seam-welding a pipe-blank from the inside thereof applying the G.M.A. welding process comprising: supplying D.C. current as the welding current to an even number of consumable electrodes in tandem through at least one current - supply cable, the current supply cable extending alongside each other ; longitudinally within the pipe-blank; and longitudinally seam-welding the pipe-blan~ for welded steel pipe from the inside along a groove or cleft 30 with respective consumable electrodes fed through a respective plurality B - 3 - ~
~ : . ' ~ , : : ................. ' , '- :
:: , , ' , . ~ .
.. . . . ~ ..
1~38V~313 of welding torches in tandem, while moving a boom carrying the welding torches through the pipe-blank relative to the pipe-blank in the same direction as that of welding, the boom having a free end which carries the welding torches and having a length at least e~ual to that of the pipe-blank, the method comprising the steps of: using at least two even-numbered consumable electrodes; connecting one-half of the consumable electrodes to the D.C. current so as to be positive in polarity; connec-ting the other half of the consumable electrodes to the D.C. current so as to be negative in polarity; thereby to enable lines of magnetic force produced by the direct electric current for welding flowing through at least one current supply cable introduced into the pipe-blank to cancel each other, thereby substantially preventing magneti~ation of the pipe- ~-blank.
By one variant, the boom is inserted in advance into the pipe-blank together with the current supply cables; and the pipe-blank is longitudinally seam-welded while withdrawing the boom, together with the current supply cables, from the pipe-blank relative thereto in the same direction as that of welding.
By another variant, the pipe-blank is longitudinally seam-welded while inserting the boom, together with the current supply cables, into the pipe-blank relative thereto in the same direction as that of welding.
By a further variant, the method includes connecting one-half, leading in the welding direction, of the even number of electrodes to the D.C. current so as to be positive in polarity, and connecting the other half, trailing in the welding direction, of the even number of electrodes to the D.C. current so as to be negative in polarity.
In the accompanying drawings, Figure 1 is a schematic side view illustrating a conventional method according to the prlor art for longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft, and . ::: .: - : ~: :: .
: -- : : :
.: . . . . . ..
~8{)B~
an apparatus for ~he implementation thereof;
Figure 2 is a partially enlarged schematic drawing illustrating a form of welding in the conventional reverse-polarity G.M.A. welding process of the prior art involvi.ng using direct electric current as the welding current with a consumable electrode as ~he anode;
Figure 3 is a partial cutaway schematic side view illustrating a form of welding in longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft by the conventional reverse-polarity G.M.A. welding process of the prior art;
Figures 4A and 4B are vector diagrams illustrating the relation between the direction of the electric current flowing through a welding arc, the magneti~ing direction at the groove or cleft of a pipe-blank for welded steel pipe, and the direction of the force acting on the welding arc at the groove or cleft in the conventional reverse-polarity G.M.A.
welding process of the prior art;
Figure 5 is a schematic side view illustrating an embodiment of the method of one aspect of the present invention;
Figure 6 is a photograph showing the state of a weld bead obtained by the conventional reverse-polarity G.M.A. welding process of the prior art; and Figure 7 is a photograph showing the state of a weld bead obtained by the method of an aspect of the present invention.
As seen in schematic form in Figure 1, in longitudinally seam-welding for manufacturing a welded steel pipe, a groove or cleft of an ;
0-shaped plate ~namely, a pipe-blank), which is formed into a cylindrical shape by a forming process, e.g., the U-0 process or the bending roll process, it is the usual practice of welding to employ an inside welding macine equipped with a welding torch 1 attached to the free end of boom 2, the boom 2 having a length at least equal to that of the pipe-blank 3 to be welded. The fixed end of the boom 2 is fixed to a carriage 4. The ,, .
~ _ 5 _ 108~3 boom 2 is inserted into the pipe-blank 3 in advance. The pipe-blank 3 is then longitudinally sea~-welded Erom the inside along the groove or cleft with a consumable electrode 5. Consumable electrode 5 i5 fed through the welding torch 1, while the boom 2 is moved by the carriage 4, together with a current supply cable 9 wh:ich serves to supply welding current to the consumable electrode 5. The current supply cable 9 is moved in the withdrawal direction from the pipe-blank 3, i.e., in the welding direction, as indicated by the arrow in the drawing. ~s shown, the inside welding machine may be equipped with two welding torches 1, 1, one leading, and the other trailing, and ~wo consumable electrodes 5, 5, one leading, and the other trailing. However, the inside welding machine may have one welding torch and one consumable electrode, or it may be provided with more than two welding torches and more than two consumable electrodes.
- Figure 2 shows, in partially enlarged schematic form, a conven~
tional method of welding a pipe-blank, when adopting a welding process involving using direct electric current as the welding current with a con-sumable electrode as the anode, namely, the reverse-polarity G.M.A. welding process. The welding 6 from the consumable electrode 5 is deflected toward the upstream side of the welding direction indicated by the arrow in the drawing, i;e., in the opposite direction to that of the welding and takes the form as if it were drawn in by the molten metal 7. When the welding arc 6 takes that form as if it is drawn in by the molten metal 7 as men-tioned above, the plasma jet stream produced at the tip of the consumable electrode 5 is also deflected toward the molten metal 7 and acts on the , molten metal 7 as a dynamic pressure. This pushes the molten metal 7 away toward the upstream side of the welding direction, i.e., in the opposite direction to that of the welding. As a result, the space below the consumable electrode 5 becomes substantially dry without any molten metal, thus impairing the affinity between molten droplets from the consumable - 30 electrode 5 and the base metal, at the groove of the pipe-blank 3. Welding .
-- . . - - : , - . ~
.:.......... ~- .- .
. ~ . : - : , ., , ,, . . ~ .
- . : :
.. . . .
1~8~8~3 defects, e.g., undercut of bead, humping beand and lack of fusion of the base metal thus tend to occur easily~ In addition, frequent occurrence of boiling and spattering in the weld bead surface tends to result in a deteriorated appearance of the weld bead. When the welding arc 6 is deflected as described above, the tip of the consumable electrode 5 is melted only on one side as shown in Figure 2. Under such circumstances, the transfer mode of molten dropl~ets from the consumable electrode 5 cannot be a desirable spray transEer, but takes an undesirable mixed form of globular transfer and short circuit transfer. As a result, coarse spatters are splashed and are deposited on the weld bead surface, thus leading to a deteriorated appearance of the weld bead. Moreover, as indi-cated before, splashed spatters are deposited on the opening at the tip of the shielding nozzle (not shown) of the welding torch to disturb the gas shield and entangle the air. In this case, it may be practically impossible to carry out welding.
The irregular weld bead and wèlding defects, e.g., undercut of bead, humping bead, lack of fusion of base metal and spattering, observed in longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft by the conventional welding process as mentioned above, is believed to be attributable to the deflection of a plasma jet stream toward a molten metal caused by the deflection of a welding arc, and also that the deflection of the welding arc is brought about by a line of magnetic force produced by the direct electric current for welding flowing through a current supply cable introduced into the pipe-blank.
More specifically, for instance in longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove or cleft by the conventional reverse polarity G.M.A. welding process comprising using direct ~electric current as the welding current with a consuamble electrode as the anode, direct current for welding flows, as shown in the ~ 7 ~ , -'~ ' ~ `' ' : ' ,. - ` : ` ' `
~L~38~8~1L;3 partial cutaway schematic side view glven in Figure 3, in the opposite direction to that of welding, as indicated by an arrow in the drawing, through a current supply cable 9 introduced into the pipe-blank 3. There-fore, a line of magnetic force lO,which is clockwise as viewed from the right-hand side of the dra~ing, is produced by the direct electric current, and a strong magnetic field is formed around the current supply cable 9.
As a result, the pipe-blank 3 is strongly magnetized in the same clock-wise direction 11 as that of the line of magnetic force 10 by the magnetic field, thus causing leakage of a strong line of magnetic force from the groove of the pipe-blank 3, and a strong magnetic field is formed at the groove. When welding a groove where such a strong magnetic field is formed, the welding arc from a consumable electrode 5, which is a flow of charged corpuscle, is deflected by the strong magnetic field at the groove or cleft. This phenomenon is called the magnetic arc blow of the welding arc.
The relation between the direction of the electric current flow-ing through a welding arc, the magnetizing direction at the groove of a pipe-blank and the direction of the force acting on the welding arc at the groove is illustrated in the vector diagrams of Figures 4A and 4B. In these drawings, A is the direction of the electric current flowing in the welding arc 6 through the consumable electrode 5; B is the magnetizing direction at the groove of the pipe-blank 3; C is the welding direction;
and F is the direction of the force acting on the welding arc 6. As shown in Figures 4A and 4B, the direction F of the force acting on the welding arc 6 is the same as that of the direct electric current for welding flowing through the current supply cable 9 (refer to Figure 3) and is opposite to the welding direction C. As described hereinabove with refer-ence to Figure 2, therefore, the welding arc 6 is deflected toward the upstream side of the welding direction C, i.e., in a direction opposite to that of welding C, thus resulting in an irregular weld bead and welding : . , , : -.
-: : . :
. .
1~8()~-~3 defects, e.g., undercut of bead, humping bead, lack of fusion of base metal and spattering.
In its broad aspects, the present invention, which has been based on the aEorementioned finding, enables, in longitudinally seam-welding a pipe-blank from welded steel pipe from the inside along a groove or cleft by the conventional G.M.A. welding process which involves using direct electric current supplied to a plurality of consumable electrodes in tan-dem through at least one current supply cable as the welding current, lines of magnetic force produced by the direct electric current for welding flowing through at least one current supply cable introduced into the pipe-blank to cancel each other, by using at least two even-numbered electrodes, connecting one-half of the consumable electrodes in the reverse-polarity manner, i.e., to be positive in polarity, and connecting the other half in the straight polarity manner, i.e., to be negative in polarity, thereby substantially preventing magnetization of the pipe-blank and the resulting magnetic arc blow of the welding arc.
More specifically, in the method of an aspect of the present invention, the conventional metal arc welding process is applied, involving using direct electric current supplied to a plurality of consumable elec-trodes in tandem through current supply cables as the welding current. Asshown in the schematic side view of Figure 5, a boom 2, having a length at least equal to that of a pipe-blank to be welded 3, is equipped with a leading welding torch la and a trailing welding torch lb in tandem at the -free end thereof. The fixed end thereof is fixed to a carriage (not shown) and is inserted in advance into the pipe-blank 3 together with current supply cables 9a and 9b. ~ leading consumable electrode 5a, fed through - the leading welding torch la, is connected via current supply cable 9a in - the reverse-polarity manner, i.e., to be positive in polarity, and a trailing consumable electrode 5b, fed through the trailing welding torch lb, is connected via current supply cable 9b in the straight-polarity ':
9 _ ' , ', 3V~
manner, i.e., to be negative in polarity. Pipe-blank 3 is long~tudinally seam-welded from the inside along the groove or cleft in the welding direction as indicated by an arrow 14 in the drawing, with the leading consumable electrode 5a, and the trailing consumable electrode 5b, while withdrawing the boom 2, together with the current supply cables 9a and 9b, from the pipe-blank 3 by the carriage.
In the aforementioned method of an aspect of the present inven-tion, as shown in Figure 5, the direct electric current flowing through the current supply cable 9a flows in the direction as indicated by an arrow 12 from right to left toward the consumable electrode 5a ln the drawing. A clockwise line of magnetic force 13 as viewed from the right-hand side of the drawing is therefore produced by the direct electric current. On the other hand, the direct electric current flowing through - the supply cable 9b flows in the direction as indicated by an arrow 15 from left to right from the consumable electrode 5b. A counterclockwise line of magnetic force 16, just reverse in direction to the line of magnetic force 13, as viewed from the right-hand side of the drawing, is therefore produced by the direct electric current. Consequently, because of the di~ference in polarity between the leading consumable electrode Sa and the trailing consumable electrode 5b, the direction of the line of magnetic force 13 is opposite to that of the line of magnetic force 16.
Therefore, the lines of magnetic force 13 and 16 cancel each other, and as a result, the pipe-blank 3 is hardly magnetized. It is thus possible substantially completely to prevent the occurrence of the magnetic arc blow of the welding arc and the resulting irregular weld bead and weldi~ng defects, e.g., undercut of bead, humping bead, lack of fusion of base metal and spattering.
The magnetization of a pipe-blank can be substantially preve~ed also by another embodiment of the method of an aspect of the present invention. This embodiment comprises, also with reference to Figure 5, .
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.. ~, .
:
. .
- ' . :
~3V8~3 connecting, contrary to the teachings of the first embodiment, the consum-able electrode 5a in the straight-polarity manner, i.e., to be negative in polarity, and the consumable electrode 5b, in the reverse-polarity manner, i.e., to be positive in polarity. The pipe-blank 3 i5 longitu-dinally seam-welded from the inside along the groove or cleft with the consumable electrodes 5a and 5b in the direction opposite to that indica~ed by arrow 14, while inserting the boom 2, together with the current supply cables 9a and 9b, into the pipe-~)lank 3 from the right-hand side of the drawing by the carriage (not shown in the drawing). In this case, it is clear that the consumable electrode 5b is the leading electrode, and the consumable electrode 5a, is the trailing electrode.
In any of the aforementioned embodiments of the method of aspects of the present invention, it is possible substantially completely to pre-vent the magnetization of a pipe-blank, and hence substantially completely to prevent the occurrence of the magnetic arc blow of the welding arc and the resulting irregular weld bead and welding defects, even by connecting ~-the leading consumable electrode in the straight-polariy manner, i.e., to be negative in polarity, and a trailing consumable electrode, in the reverse-polarity manner, i.e., to be positive in polarity. However, by connecting the leading consumable electrode in the reverse-polarity manner, -:
i.e., to be positive in polarity, and the trailing consumable electrode, in the straight-polarity manner, i.e., to be negative in polarity, better~
- results can be obtained, because of the easy availability of a deeper fusion penetration required on the leading electrode side. -The method of an aspect of the present invention is now described in more detail by way of the following example.
- EXAMPLE ~.
In longitudinally seam-welding two pipe-blanks for welded steel pipe from the inside along a groové or cleft, having a wall thickness of ;~ 30 1 inch, an outside diameter of 48.inches and a length of 12 meters by the ''.' :
. .
~~` tandem-headed G~M.A. welding process which includes using direct electric current supplied to two leadîng and trailing consumable electrodes through current supply cables as the welding current, the method of an aspect of the present invention described above with reference to Figure S was applied to a pipe-blank. That method comprises, also with reference to Figure 5, inserting the boom 2 in advance into the pipe-blank 3 together with the current supply cables 9a and 9b. The boom 2 is equipped with the leading welding torch la and the trailing welding torch lb in tandem at the free end thereof The boom 2 is fixed to a carriage (not shown) at the fixed end thereof. The leading consumable electrode 5a, fed through the leading welding torch la, is connected in thP reverse-polarity manner, i.e., to be positive in polarity via the current supply cable 9a. The trailing consumable electrode 5b, fed through the trailing welding torch lb, is connected in the straight-polarity manner, i.e., to be negative in polarity via the current supply cable 9b. The pipe-blank 3 is longitu-dinally seam-welded from the inside along the groove or cleft with the leading and trailing consumable electrodes 5a and 5b in the welding direction as indicated by the arrow 14 in the drawing, while withdrawing the boom 2,together with the current supply cables 9a and 9b from the pipe-blank by the carriage.
On the other hand, the conventional reverse-polarity G.M.A~
welding process, which is outside the scope of the present invention, was applied to the other pipe-blank for comparison purposes, such conventional method including the same steps as mentioned above, except for the step of connecting both of the above-mentioned leading consumable electrode and the trailing c~nsumable electrode reversely in the reverse-polarity manner, i.e., to be positive in polarity.
The state of the weld beads obtained as a resuLt`is shown in photographs of Figures 6 and 7.
In the weld bead obtained by the conventional reverse-polarity :
-: . . : , - . : .
.~. . . . ~ . -.
: ~ ' " ~ ~ . ' .,' .:
~'- : . ' . ' ' -- lV~
G.~.A. welding process, as shown in the photograph of Figure 6, not only is the appearance poor, but the X-ray test also revealed such weldlng defects as lack of fusion of base metal and undercut of bead. This i9 attributable to the occurrnece of boiling of the molten metal caused by the magnetic arc blow of the welding arc towards the upstream side of the welding direction, i.e., in the opposite direction to that of welding.
The weld bead obtained by the welding method of an aspect of the present invention, in contrast, has the appearance as shown in the phorograph of Figure 7, with no significant trace of welding defects observed even by the X-ray test and by an ultrasonic flaw detection test, thus permitting ascertainment that a very sound weld can be obtained by the welding method of an aspect of the present invention.
Similarly good results have also been obtained by the welding method of another aspect of the present inveniton, (as will be described in ~xample 2), which comprises, also with reference to Figure 5, connec-ting, contrary to the foregoing, the consumable electrode 5a in the straight-polariy manner, i.e., to be negative in polarity, and the consum-able electrode 5b inthe reverse polarity manner, i.e., to be positive in ~' polarity. The pipe-blank 3 is longitudinally seam-welded from the inside along the groove or cleft with the consumable electrodes 5a and 5b in a direction opposite to that indicated by the arrow 14, while inserting the ~-boom 2, together with the current supply cables 9a and 9b, into the pipe-- blank 3 from the right-hand side of the drawing by the carraige (not shown in the drawing). In this case, the consumable electrode 5b is the leading electrode, and the consumable electrode 5a, the trailing electrode.
The above description of the method of aspects of the present invention has covered only the case where a pipe-blank is fixed while moving a boom equipped with welding torches in tandem. The essential requirement in the process of aspects of the present invention covers also cases in which the pipe-blank is moved while the boom equipped with the . ~ - 13 --{~--~
. - - ., ... . - . - - - .
: :-..... -. ., .. - .. , -. - : - . . . :
.,: ..... ~ - :. :. , - .. .
- -.::: -:.
~ welding torches is fixed. In other words, in the method of aspects of the present invention, it suffices to move the boom equipped with the welding torches through the pipe-blank in the welding direction~
According to the method of aspects of the present inveition, as described above in detail, in longitudinally seam-welding a pipe-blank for welded steel pipe Erom the inside along a groove or cleEt by the G.M.A.
welding process which includes using direct current supplied to a plurality of consumable electrodes through at least one current supply cable as the welding current, it is possible substantially completely to prevent the occurrence of the magnetization of the pipe-blank caused by direct electric . . _ . .
current flowing through at least one current supply cable introduced into the pipe-blank and the resulting magne~ic arc blow of the welding arc.
- Therefore, it is possible to obtain a sound weld bead, thus providing industrially useful effects.
': ;
. ~ . .
: ', -:
Claims (4)
1. An improvement in a welding method for longitudinally seam-welding a pipe-blank from the inside therof by applying the G.M.A. welding process including: using direct electric current supplied to a plurality of consumable electrodes in tandem through at least one current supply cable as the welding current; and longitudinally seam-welding the pipe-blank for welded steel pipe from the inside along a groove or cleft with said respective consumable electrodes fed through a plurality of welding torches in tandem, while moving a boom through said pipe-blank in the same direction as that of welding, said boom being equipped with said welding torches at the free end thereof and having a length at least equal to that of said pipe-blank; said improvement comprising the steps of:
using at least two even-numbered consumable electrodes;
connecting one-half of said even number of consumable elec-trodes to said direct current so as to be positive in polarity; and connecting the remaining half of said even number of consum-able electrodes to said direct current so as to be negative in polarity;
thereby to enable lines of magnetic force produced by said direct electric current for welding flowing through said at least one current carrying cable introduced into said pipe-blank to cancel each other, thereby sub-stantially preventing magnetization of said pipe-blank.
using at least two even-numbered consumable electrodes;
connecting one-half of said even number of consumable elec-trodes to said direct current so as to be positive in polarity; and connecting the remaining half of said even number of consum-able electrodes to said direct current so as to be negative in polarity;
thereby to enable lines of magnetic force produced by said direct electric current for welding flowing through said at least one current carrying cable introduced into said pipe-blank to cancel each other, thereby sub-stantially preventing magnetization of said pipe-blank.
2. A method as claimed in claim 1, wherein said boom is inserted in advance into said pipe-blank together with said at least one current supply cable; and wherein said pipe-blank is longitudinally seam-welded while withdrawing said boom, together with said current supply cables, from said pipe-blank relative thereto in the same direction as that of welding.
3. A method as claimed in claim 1, wherein said pipe-blank is longitudinally seam-welded while inserting said boom, together with said current supply cables, into said pipe-blank relative thereto in the same direction as that of welding.
4. A method as claimed in claim 1 wherein one-half, leading in the welding direction, of said even number of electrodes is connected to said direct current so as to be positive in polarity; and wherein the other half, trailing in the welding direction, of said even number of electrodes is connected to said direct current so as to be negative in polarity.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA341,274A CA1097748A (en) | 1976-03-24 | 1979-12-05 | Welding method for longitudinally seam welding a pipe blank from the inside using the metal arc welding process |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3139376A JPS52114545A (en) | 1976-03-24 | 1976-03-24 | Welding method |
| JP7277976A JPS52156149A (en) | 1976-06-22 | 1976-06-22 | Welding process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1080813A true CA1080813A (en) | 1980-07-01 |
Family
ID=26369839
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA274,579A Expired CA1080813A (en) | 1976-03-24 | 1977-03-23 | Method for longitudinally seam-welding pipe-blanks for welded steel pipe from the inside along a groove |
Country Status (5)
| Country | Link |
|---|---|
| CA (1) | CA1080813A (en) |
| DE (1) | DE2712027C3 (en) |
| FR (1) | FR2345257A1 (en) |
| GB (1) | GB1554523A (en) |
| IT (1) | IT1104776B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5285042A (en) * | 1992-11-25 | 1994-02-08 | Fmc Corporation | Gas tungsten arc welding torch apparatus |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE104998C (en) * | ||||
| DE617229C (en) * | 1930-11-04 | 1935-08-15 | Aeg | Device for automatic arc welding using direct current |
| DE645672C (en) * | 1933-12-14 | 1937-06-01 | Daimler Benz Akt Ges | Process for producing the cutting edges of cutting tools with a soft base material by means of electric arc welding |
-
1977
- 1977-03-07 GB GB944777A patent/GB1554523A/en not_active Expired
- 1977-03-18 DE DE19772712027 patent/DE2712027C3/en not_active Expired
- 1977-03-23 IT IT2159677A patent/IT1104776B/en active
- 1977-03-23 CA CA274,579A patent/CA1080813A/en not_active Expired
- 1977-03-24 FR FR7708856A patent/FR2345257A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE2712027C3 (en) | 1983-05-19 |
| FR2345257A1 (en) | 1977-10-21 |
| DE2712027A1 (en) | 1977-10-06 |
| DE2712027B2 (en) | 1981-05-14 |
| FR2345257B1 (en) | 1982-02-05 |
| IT1104776B (en) | 1985-10-28 |
| GB1554523A (en) | 1979-10-24 |
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