NIPPON STEEL TECHNICAL REPORT No.

90 JULY 2004

UDC 621 . 791 . 753 . 9

Development of Two-electrode Electrogas Arc Welding Process

Kiyohito SASAKI*1 Kazutoshi SUDA*1
Ryu-ichi MOTOMATSU*1 Yuji HASHIBA*2
Shigeru OHKITA*2 Shiro IMAI*3

Abstract
Electrogas arc welding (EGW) is used for vertical position welding of sheer strakes
and hatch side coamings of container ships because of its higher welding efficiency.
However, in ordinary welding processes for ultra-thick steel plates, defects such as
the lack of fusion are likely to occur. In order to solve this problem and others, a
two-electrode VEGA® (Vibratory Electrogas Arc Welding) process was developed by
the authors. This paper provides an outline thereto and describes the essential char-
acteristics of this newly developed process for vertical position welding on extra-
heavy-sectioned steel plates. It was demonstrated that the VEGA® process achieves a
stabilized fusion-line profile for ultra-thick steel plates with higher welding effi-
ciency. It was then confirmed that joint performance in this study satisfies regula-
tions such as class NK KEW53 and KEW53Y40.

(sheer strakes, see Fig. 1) are ultra-thick, it was extremely difficult

1. Introduction to attain an integrity of weld joints and good properties of the welds
In recent years, there has been a growing trend for ultra-thick, using the conventional single pass EGW method. Hatch side coamings
and higher strength steel plates. This trend is a result of the continu- which also is a vertical position welding method (see Fig. 1 for the
ing race for ever larger steel structures. These have resulted in in-
creased demand for higher efficiency of forming, higher quality and
higher strengths of welding materials to handle these increased thick-
nesses of steel plates.
We have also witnessed a dramatic increase in the sizes of con-
tainer ships. The increasing sizes are evidence of shipping compa-
nies’ need for increased shipping efficiency. Larger container ships
require thicker steel plates and a higher strength. Because vertical
position welding is applied to the sheer strakes and hatch side
coamings on the container ships when they are block-assembled in
the dry dock, the most prevalent method for welding is the electrogas
arc welding (hereinafter referred to simply as EGW) which is ca-
pable of a single pass, vertical position welding that is highly effi-
cient.
However, because the steel plates that are used in a ship’s side Fig. 1 Cross-section of container vessels
1 3
* Nippon Steel Welding Products & Engineering Company Limited * Plate Sales Division
*2 Steel Research Laboratories

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NIPPON STEEL TECHNICAL REPORT No. 90 JULY 2004

edge portion of the hatch) is generally used for even thicker steel shows the general concept for the single-electrode VEGA® welding
plates. However, because of the application of a 2-pass welding proc- process.
ess, worker-hour cost need to be applied has increased. In view of The development of the single-electrode VEGA® welding pro-
the conditions described above, a two-electrode VEGA® (Vibratory cess enabled easier formation of top surface beads and back surface
Electro-gas Arc Welding) process was developed based on the VEGA® beads. Also, because it was possible to reduce the welding heat in-
process which is a simple electrogas arc welding method. The ob- put and the amount of weld metal, HAZ toughness and processing
jective of this new process is to stabilize the fusion-line profile for efficiency were dramatically increased. As can be seen in Photo 1,
ultra-thick steel plates and attain higher welding efficiency. This when the macrostructure of the weld cross-section was compared
paper describes how this two-electrode VEGA® welding process was with the conventional EGW method and the single-electrode VEGA®
developed and outlines its features. welding process, the welds by VEGA® process showed narrow weld
bead and heat affected zone, even on the same thickness of steel
2. Conventional Technologies and Related Issues plate. Also, there was no lack of fusion even for 50 mm steel plates.
Degradation of the conventional EGW method1) which was de- Thus it was demonstrated that a sound weld could be attained.
veloped in the 1960’s was a problem because of the low impact prop- Nevertheless, there is a trend for steel plate thicknesses to in-
erty of the welds. This was mainly caused because high heat input crease to 58 mm, and even to 65 mm and 70 mm thicknesses due to
was apt to apply and because the wire diameter (2.4 to 3.2 mm) was the growth in the size of container ships. Such steel thicknesses are
thick so the sectional area of groove was wide. This caused the coarse used in the shear strakes and the hatch side coamings on the con-
microstructure of the heat affected zone (HAZ). tainer ships. As can be seen in Photo 2, when the thickness of the
To overcome those demerits, a single-electrode VEGA® welding steel plate exceeds 50 mm, welding defects (such as a lack of fusion)
process was developed in the 1970’s by the Nippon Steel Welding are generated even when using the conventional single-electrode
Products & Engineering Company Limited. This new process en- VEGA® welding process. Thus, to handle these increased plate thick-
abled a welding with a narrower groove. To reduce the heat input nesses, the necessary dwelling time for an arc to fully fuse a groove
with the single-electrode VEGA® welding process, a fine diameter
wire was used to lower the welding current and to allow to use a
narrow groove. Also, to attain a sound weld bead formation near the
front and back surfaces of a joint, this welding apparatus is equipped
with a mechanism to oscillate the wire (welding torch) in the plate
thickness direction. Also, provided with a mechanism for holding of
wire extension to a constant as a result that the rising speed of the
carriage is controlled by detecting the welding current. To differen-
tiate with the two-electrode VEGA® welding process which is de-
scribed below, this single-electrode welding process will hereinafter
referred to as the single-electrode VEGA® welding process. Fig. 2

Photo 1 Comparison of cross-sections of welds by conventional EGW

process and single-electrode VEGA®

Photo 2 Example of “lack of fusion”(indicated by allow) in weld by

Fig. 2 Schematic illustration of single-electrode VEGA® single-electrode VEGA® (plate thickness: 70mm)

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 NIPPON STEEL TECHNICAL REPORT No. 90 JULY 2004

face is insufficient when only using a single-electrode, even if arc

oscillating width is increased. Therefore, welders required an ex-
tremely high level of technical skill to weld steel plates that exceeded
thicknesses of 50 mm without the welding defects that are often as-
sociated with the single-electrode VEGA® welding process.

3. Development of Two-electrode VEGA® Welding

Process
3.1 Development targets
In order to resolve the issues described above, the authors em-
barked on efforts to develop the two-electrode VEGA® welding proc-
ess with the presumption of employing a narrow groove to reduce
heat input during welding. To attain their objective, the number of
electrodes was increased to uniformly distribute welding heat input
in a stable manner in the plate thickness direction. It was supposed
that it would be effective to reduce the width of oscillation for each
of the two electrodes. The following three points were the targets
for the development of the two-electrode VEGA® welding process.
The authors also maintained a view to the need to overcome any arc
interference that could be caused by the application of a second elec-
trode, the overall simplicity of the structure of the apparatus and the
need to optimize welding conditions.
(1) Welding must be possible on steel plates having thicknesses any-
where from 50 mm to 70 mm. There must be no welding de-
fects and joints must be sound.
(2) There must be good mechanical properties of welds.
Fig. 4 Schematic illustration of two-electrode VEGA®
(3) Good welding workability must be attained and it must contrib-
ute to improved efficiency of welding work.
3.2 The two-electrode VEGA® welding process apparatus The power source for welding was a direct current. This was
In the same way as the conventional single-electrode VEGA® selected because of the stability of the arc. If both electrodes have
welding process, the apparatus which is a vertical position single- the same polarity, specifically, if they are both positive or negative,
pass welding method is arranged with a water cooled copper shoe the arc becomes highly unstable. Accordingly this produces great
that automatically rises along with the carriage on the front surface amounts of spatter. For this reason, the polarity of the two elec-
side of the groove, and a light weight ceramic backing material to trodes was made opposites. Also, normally if the electrode is posi-
touch the backside of the groove. This was configured to prevent tive, the beads are wider, and the fusing is shallow. Conversely, if
fusing slag and weld metal from flowing out. Fig. 3 shows the con- the electrode is negative the beads are narrow and fusing is deep2).
figuration of the 2-electrode VEGA® welding process apparatus; Fig. From these facts, to weld a wide single V groove, the positive elec-
4 shows a model thereof. trode was arranged on the grooved surface side because of its ability
The two-electrode VEGA® welding process is a simple structure for a wide fusing, and the negative electrode was arranged on the
that applies one more electrode to the single-electrode VEGA® weld- narrow backside of the groove.
ing process. Mounting and dismounting the welding torch of the 3.3 Improved welding workability
second electrode is simple. Furthermore it is easy to change the The amount of slag generated when welding greatly affects weld-
structure into a single or two-electrode apparatus according to the ing workability when using the EGW method. The welding work-
thickness of the steel plate targeted for welding. ability described in this report was evaluated according to the amount
of spatter generated, and the external appearance of the beads.
Initially, flux-cored wire which is dedicated to the single-elec-
trode VEGA® welding process was used in both poles for the 2-elec-
trode VEGA® welding process and for the backing material, a prod-
uct that is supported by the single-electrode VEGA® welding proc-
ess was used. It was learned that there was a great amount of spatter
generated and that long-term welding would be difficult. A great
amount of fusing slag was built up on the molten pool near the back
side of the groove. On the other hand, the backing material for the
single-electrode VEGA® welding process was provided arc shaped
grooves as shown in Fig. 5 (a) to attain the same kind of excess weld
metal as for general welding. However, this is not a shape that is
appropriate for promoting the discharge of fusing slag that is exces-
sively produced. Two types of backing material were manufactured
with depths of gap to promote discharge of slag (see Fig. 5 (b) and
Fig. 3 Two-electrode VEGA® apparatus (c)) with the objective of discharging fused slag that is retained in

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NIPPON STEEL TECHNICAL REPORT No. 90 JULY 2004

Fig. 5 Backing materials with various shapes

excess, to the backing material side. Then the welding workability

was evaluated. The welding conditions used are shown in Table 1; Fig. 6 Groove configuration
The groove face configuration is shown in Fig. 6; and the results of
the test are shown in photo 3.
The amount of spatter (spattered slag) generated was lower in was reduced. This was used in an attempt to suppress the amount of
the order of the No. 1 configuration then the No. 2 configuration (for slag spatter that is generated. Table 2 shows the welding wire used
the single-electrode VEGA® welding process) of the backing mate- in the test, the steel plate and the welding conditions. Note that the
rials (see Fig. 5 (b) and (c)). A thorough reduction in the amount of groove face configuration is the same as that depicted in Fig. 6. Table
spatter was observed in the process using the shape No. 2. However, 3 shows the results of evaluations on the welding when using they
undercuts were generated at the toe of back bead. Because this is flux-cored wire that has half the amount of flux as the wire used with
thought to be a cause of fatigue failure, the backing material having the single-electrode VEGA® welding process, and a solid wire that
the shape No. 1 was employed. conforms to JIS Z 3325 TGL1-4G (AP). Because it was learned that
It is insufficient to reduce the amount of spatter generated for the the solid wire possesses characteristics having lower slag generating
markets and the actual process simply by changing the shape of the amounts in comparison to the flux-cored wire, it can be expected to
backing material. Next, by adjusting the amount of flux of the welded affect the production of the amount of slag generated on the back
wire, the amount of slag that is generated from the welding material side of the groove where slag retention is high. The study was un-

Table 1 Welding conditions

Current Voltage Travel Heat Electrode Oscillation Shielding gas
Electrodes Welding wire (A) (V) speed input spacing width Composition Flow rate
(cm/min) (kJ/cm) (mm) (mm) ( /min)
1st Flux-cored wire*1 420 42
5.0-5.5 366-404 15 35 100% CO2 30
2nd Flux-cored wire*1 400 40
*1
: For single-electrode VEGA®
Base plate: EH40 (plate thickness: 70mm)

Photo 3 Weld test results by various backing materials

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 NIPPON STEEL TECHNICAL REPORT No. 90 JULY 2004

Table 2 Welding conditions

Travel Heat Electrode Oscillation Shielding gas
Test Electrodes Welding wire Current Voltage speed input spacing width Composition Flow rate
No.
(A) (V) (cm/min) (kJ/cm) (mm) (mm) ( /min)
1st Flux-cored wire*1 420 42
1 5.0-5.5 366-404 15 35 100% CO2 30
2nd Flux-cored wire*1 400 40
*1
1st Flux-cored wire 420 42
2 5.0-5.5 366-404 15 35 100% CO2 30
2nd Solid wire*2 400 40
*2
1st Solid wire 420 42
3 5.0-5.5 366-404 15 35 100% CO2 30
2nd Solid wire*2 400 40
*3
1st Flux-cored wire 420 42
4 5.0-5.5 366-404 15 35 100% CO2 30
2nd Solid wire*2 400 40
*1 ®
: For single-electrode VEGA
*2
: JIS Z 3325 TGL1-4G (AP)
*3
: For two-electrode VEGA® (contains one-half the flux compared with the wire for single-electrode VEGA®)
Base plate: EH40 (plate thickness: 70mm)

Table 3 Test results with various welding wires

Test results
Test
Electrodes Welding wire Amount of Bead Comprehensive evaluation
No.
spatter appearance for actual constructions
1st Flux-cored wire*1
A Very large Good Not suitable
2nd Flux-cored wire*1
*1
1st Flux-cored wire
B Large Good Not suitable
2nd Solid wire*2
*2
1st Solid wire
C Very small No good Not suitable
2nd Solid wire*2
*3
1st Flux-cored wire
D Small Good Suitable
2nd Solid wire*2
*1 ®
: For single-electrode VEGA
*2
: JIS Z 3325 TGL1-4G (AP)
*3
: For two-electrode VEGA® (contains one-half the flux compared with the wire for single-electrode VEGA®)
Base plate: EH40 (plate thickness: 70mm)

dertaken with regard to the application of this solid wire to the sec- good shape, and to form beads on the backside. This development
ond electrode which arranged on the narrow backside of the groove. means that now welders can perform their duties without much worry
Case A which employed the flux-cored wire for the single-elec- with regard to welding defects such as poor penetration or lack of
trode VEGA® welding process on both electrodes, had the greatest fusion when changing the oscillating conditions (width of oscilla-
amount of spatter generated. In the order of B, C, and D, cases C and tion and stopping time of both ends when oscillating, and position of
D showed that spatter had reduced to an acceptable amount. As a aim of the wire) or the gap. Therefore, it can be said that this newly
result, it is suggested that the amount of slag generated from the developed method of welding is highly applicable because it does
welding wire greatly affects the amount of spatter. not require welders to have high levels of technical training or skill
Thus, as described above, research was conducted into the back- to weld steel plates that exceed 50 mm in thickness. See photo 4.
ing material configuration and the composition of the welding wire. This shows sectional views of sample microstructures of welds on
Overall evaluations were also conducted on the welding workabil- steel plates having 50, 60 and 70 mm thicknesses. Furthermore, the
ity. As a result, a decision was made to use the backing material of penetration of weld metal near the front surface, backside surface of
the shape No. 1, and to apply the flux-cored wire that halves the the plate and to the groove face was stabilized allowing for good
amount of flux as the wire used with the single-electrode VEGA® quality welding without the defects often associated with welding
welding process on the first electrode and the solid wire on the sec- such as poor penetration or lack of fusion.
ond electrode. These realized superior welding workability that also 4.2 Improved welding efficiency
could withstand actual welding work. Because the 2-electrode VEGA® welding process is substantially
twice the welding speed of the single-electrode welding process,
4. Results of Application of the Two-electrode deposition rate for a single electrode when using the same groove
VEGA® Welding Process shape is approximately doubled, as shown in the Fig. 7, thereby dem-
By applying a variety of improvements to welding workability, it onstrating that this method of applying two electrodes to be highly
has become possible for a highly efficient single pass welding of efficient. Furthermore, the amount of time required for setup of the
steel plates that have thicknesses anywhere from 50 mm to 70 mm apparatus is substantially the same as that for the single-electrode
using the 2-electrode VEGA® welding process. The following out- VEGA® welding process so efficiency, considering the entire proc-
lines the effects of this method of welding. ess of welding from set up to actual welding, is substantially twice
4.1 Stabilized penetration of weld metal that of the single-electrode VEGA® welding process. Still further,
With the development of the 2-electrode VEGA® welding proc- when using the single-electrode, or the 2-electrode VEGA® welding
ess, it has become possible to easily attain front side beads that have process, almost all of the welding wire used is contained on single-

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NIPPON STEEL TECHNICAL REPORT No. 90 JULY 2004

Photo 4 Cross-sections of welds by two-electrode VEGA®

Fig. 7 Comparison of travel speed with single- and two-electrode VEGA® Fig. 8 Comparison of amount of shielding gas consumption with single-
and two-electrode VEGA®

reel, 20 kg spools, so it is necessary to replace the welding wire and (see Fig. 8).
20 kg units. Therefore, the possible welding length without inter- 4.4 Welding performance and application to ship building
ruption on the 2-electrode VEGA® welding process is approximately The Mo-Ti-B type weld metal3-7), which is an alloy designed to
two times that of the single-electrode VEGA® welding process. When attain low temperature toughness that is essential in high heat input
welding is terminated, gouging occurs in that position. It is neces- welding, was also applied to the 2-electrode VEGA® welding proc-
sary to repair that using a shielded metal arc welding or a gas-shielded ess. Table 4 shows the materials and welding conditions used in the
metal arc welding. This translates into a greatly shortened amount test; Fig. 9 shows the groove face configuration; Fig. 10 shows the
of processing time through the application of the 2-electrode VEGA® locations of the test specimen. As can be seen in Table 5, perfor-
welding process. mance was attained that met the standards of KEW53 and
4.3 Reduction in the amount of shielding gas KEW53Y40 as prescribed by the Nippon Kaiji Kyokai (Class NK).
Because the welding speed with this newly developed method is See Photo 5 for a view of the microstructure of the weld metal (cen-
substantially doubled, the amount of shielding gas consumed per tral location) on the steel plates. An extremely fine microstructure
single welding length is approximately halved that for a single elec- was attained under high heat input welding. Also, mechanical per-
trode. This again allows for a highly economical method of welding formance was attained that had thorough mechanical property of HAZ

Table 4 Welding conditions

Plate Travel Heat Electrode Oscillation Shielding gas
Current Voltage
thickness Electrodes Welding wire speed input spacing width Composition Flow rate
(A) (V)
(mm) (cm/min) (kJ/cm) (mm) (mm) ( /min)
1st Flux-cored wire*1 410 41
50 7.1 281 15 5 100% CO2 30
2nd Solid wire*2 400 40
1st Flux-cored wire*1 410 41
60 6.2 321 15 17 100% CO2 30
2nd Solid wire*2 400 40
1st Flux-cored wire*1 420 42
70 5.8 382 15 35 100% CO2 30
2nd Solid wire*2 460 42
*1
: For two-electrode VEGA® (contains one-half the flux compared with the wire for single-electrode VEGA®)
*2
: JIS Z 3325 TGL1-4G (AP)
Base plate: EH40 (plate thickness: 70mm)

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 NIPPON STEEL TECHNICAL REPORT No. 90 JULY 2004

of the applied EH40 steel.

In 2001, the 2-electrode VEGA® welding process was applied to
the welding of sheer strakes and hatch side coamings (plate thick-
ness: 58 mm) of large sized container ships at Mitsubishi Heavy In-
dustries Limited Kobe shipyard & Machinery Works (see Photo 6).
Also, in 2002, this method of welding was applied to hatch side
coamings of steel plates having thicknesses of 65 mm.
As described above, success was achieved in the development of
the 2-electrode VEGA® welding process which is a single-pass, and
highly efficient automatic welding method that attains stable pen-
etration of weld metal even when vertically welding steel plates hav- 100µm
ing thicknesses between 50 mm and 70 mm. This method was suc-
cessfully applied the building of ultra large-sized container ships. Photo 5 Microstructure of weld metal welded by two-electrode VEGA®
(center)

Fig. 9 Groove configuration

Photo 6 An example of construction site where two-electrode VEGA®
operated

5. Conclusions
According to the processes described above, success was attained
in the development of the 2-electrode VEGA® welding process as a
highly efficient automatic welding method for vertical position when
welding steel plates having thicknesses of 50 mm to 70 mm. The 2-
electrode VEGA® welding process realizes stable weld metal pen-
etration and high efficiency in single-pass, vertical position welding
of steel plates having thicknesses between 50 mm and 70 mm, and
has obtained valuable tried and tested data through its applications
in actual container ship building. The scope of application to steel
plate thicknesses will expand in the future and can be expected to
Fig. 10 Sampling locations of test specimens become more widely applied because of its superior applicability as
a welding method.

Table 5 Mechanical test results of weld metal with two-electrode VEGA®

Plate Tensile test Charpy impact test
thickness Classification 0.2% proof stress Tensile strength Elongation Absorbed energy at –20°C
(mm) (MPa) (MPa) (%) (J)
50 EH36 473 610 25 89
60 EH40 471 611 23 86
70 EH40 506 656 24 79
ClassNK KEW53 ≥375 490-660 ≥22 ≥34
ClassNK KEW53Y40 ≥400 510-690 ≥22 ≥41

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NIPPON STEEL TECHNICAL REPORT No. 90 JULY 2004

Acknowledgements References
1) Inagaki, M. et al.: Automatic Vertical Position Welding – Electroslag
The authors wish to express their deep gratitude to the Mitsubishi
Welding/Electrogas Welding. First edition. Tokyo, THE NIKKAN
Heavy Industries Limited Kobe Shipyard & Machinery Works for KOGYO SHIMBUN Limited,1966, p.151
their cooperation in the development of the 2-electrode VEGA® weld- 2) Japan Welding Sosiety: Welding and Joining Technology. First edition.
ing process. Tokyo, SANPO PUBLICATIONS Incorporated, 1993, p.388
3) Mori, N. et al.: Seitetsu Kenkyu. (307), 104(1982)
4) Mori, N. et al.: J. Jpn. Weld. Soc. 50(2), 174(1981)
Note that the VEGA® welding process is a registered trademark 5) Mori, N. et al.: J. Jpn. Weld. Soc. 50(8), 786(1981)
of Nippon Steel Welding Products & Engineering Company Lim- 6) Ohkita, S. et al.: Australian Weld. J. 29(3), 29(1984)
ited. 7) Ohkita, S. et al.: ISIJ Int. 35(10), 1170(1995)

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