Method of arc welding

In underwater arc welding in a chamber filled with gas a consumable flux cored arc welding wire is fed to a welding torch and an arc is struck between the wire and the work to be welded so as to effect transfer of weld metal from the wire to the work. The arc welding wire contains at least one strong deoxidizer selected from the group consisting of magnesium, aluminium, zirconium, titanium, barium, lithium and calcium. A shielding gas is fed to the torch and emerges therefrom as an annular curtain of gas which shields the arc. The shielding gas also helps stabilize the arc from the effects of underwater pressure. The shielding gas comprises at least one oxygen-containing gas selected from oxygen and carbon dioxide.

BACKGROUND OF THE INVENTION 
(a) Field of the Disclosure 
This invention relates to a method of arc welding in a chamber in which 
there is a gaseous environment at superatmospheric pressure. The method is 
particularly intended for operation under water. 
(B) Description of the Prior Art 
With the growth of the offshore industry it has become essential to be able 
to make welds under water to a standard that satisfies certain nationally 
and internationally recognised welding codes. 
Attempts have been made to weld under water without taking any steps to 
protect the welding arc from water. These have been unsuccessful, partly 
because water entering the arc becomes dissociated and the hydrogen thus 
formed is dissolved in the weld pool. The rapid quenching effect of the 
water on the weldments creates hard martensitic structures in the heat 
affected zone (HAZ) which are susceptible to hydrogen induced cracking, 
owing to hydrogen diffusion into the heat affected zone, particularly in 
joints subject to restraint. 
It has been proposed to prevent water entering the arc by using a welding 
torch with a nozzle which is adapted to form a protective annular curtain 
of water spaced apart from the welding arc. With this piece of equipment 
it has been proposed to use a semi-automatic welding method with a 
consumable welding wire and a shielding gas including a large proportion 
of argon or carbon dioxide. This method is described inter alia in the 
Journal of the Japan Welding Society, 1974, pp 23 to 30, and pp 141 to 
146. 
However, when it is required to vary the angle of the welding torch in 
relation to the work, (i.e. in "out-of-position" welding) as in manually 
operated GMA welding, the water curtain shielding cannot be fully 
maintained to prevent relatively large quantities of water from entering 
the arc, and the resultant turbulence seriously impairs the welder's 
visibility. Even when a constant angle is maintained so as to preserve the 
water curtain (e.g. in automatic straight line welding) fume emitted by 
the consumable welding wire will tend to be confined to the region of the 
arc by the water curtain thereby also seriously impairing the welder's 
visibility of the arc. Alternatively, it has been proposed to use `in the 
wet` a flux cored wire or a solid wire with a shielding gas under water, 
without any water curtain. The use of solid wire with a shielding gas is 
the conventional so-called GMA welding process. Such proposals have been 
made in a number of papers, for example, by M. L. Levin in Marine 
Technology, Vol. 4, No 3, June 1973, pp 73 to 77, and by I. M. Savitch in 
the proceedings, International Conference, Welding in Offshore 
Constructions, 26 to 28 February 1974, paper No. 20, pp 217 to 220. In the 
latter case no western Investigator has been able to repeat the claimed 
results. 
Satisfactory welds may be achieved under water using semi-automatic GMAW by 
forming under water a fixed chamber, displacing water from the chamber by 
passing gas into it, and then welding by means of the conventional GMA 
process in the short-circuiting mode which employs a solid wire. Such a 
process is described in U.S. Pat. No. 3,876,852 (Topham). M. L. Levin in 
`Welding in the Sea`, Marine Technology, Vol 4 No. 3, June 1973 pp 73-77 
also refers to using a semi-automatic MIG welding process in a gas filled 
chamber under water in order to make `top quality` welds. He specifically 
states that the welding electrode would not have any flux. P. L. J. Leder 
and F. W. Lunau in a paper entitled `High duty Welding` published in the 
Australian Welding Journal 18, No 5 pp. 149-159, September-October 1974 
also refers to GMA welding under water, this time in a small hand-held 
gas-filled chamber having transparent walls. 
We have surprisingly found that despite the aforementioned publications to 
use underwater a semi-automatic GMA (i.e. solid wire) arc welding process 
in a chamber containing gas this process often fails to produce sound 
welds, there often being lack of fusion between the weld metal and the 
parent metals i.e. the weld metal solidifies before adequate fusion with 
the parent metal has taken place. 
With the objects of providing a method welding under water or at 
superatmospheric pressure (or both) which makes possible the deposition of 
weld metal having sound mechanical and metallurgical properties from a 
consumable welding wire and which also makes possible the attainment of 
adequate fusion between the weld metal and the parent metal copending 
application Ser. No. 758,867, Pinfold, filed Jan. 12, 1977 (Pinfold 
assignor to BOC Limited) provides a method of arc welding in a chamber 
containing a gaseous environment, including the steps of forming the 
gaseous environment in the chamber by passing into the chamber at least 
one inert gas selected from the group consisting of argon, krypton, xenon 
and helium and at least one oxygen-containing gas selected from the group 
consisting of oxygen and carbon dioxide, and depositing weld metal from a 
consumable, flux-cored, arc-welding wire containing at least one strong 
deoxidiser selected from the group consisting of magnesium, aluminium, 
zirconium, titanium, barium, lithium and calcium, the proportion of oxygen 
(if any) in the gaseous environment having a partial pressure less than 
the partial pressure of oxygen in air and constituting less than 14% by 
volume of the gaseous environment. 
Although this method provides an improvement over the prior art it suffers 
from two disadvantages. First, it will generally require relatively large 
containers of gas to be shipped to the site where the weld is to be made. 
For under water welding, this means ensuring that the supply ship from 
which the under water welders operate needs to be provided with adequate 
supplies of the necessary gas before it leaves the shore. Second, and more 
importantly when welding under water the atmosphere or gaseous environment 
in the welding chamber will inevitably be saturated with moisture unless 
an elaborate chamber, in which the gaseous environment is created, is 
sealed from the surrounding water and provided with dehumidification 
apparatus. Such moisture may tend to affect the mechanical properties of 
the weld adversely and may also give rise to hydrogen embrittlement of the 
weld metal, particularly at large superatmospheric pressures. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide a method of welding under water 
which makes possible the deposition from a consumable welding wire of weld 
metal having sound mechanical and metallurgical properties. 
It is a further object of the invention to provide a method of welding 
under water which makes possible the attainment of adequate fusion between 
the weld metal and the parent metal. 
It is a yet further object of the invention to provide a method of 
underwater welding which employs a consumable welding electrode in a 
chamber holding a gaseous atmosphere so as to limit any deleterious effect 
moisture in the gaseous atmosphere may have on the mechanical properties 
of the weld. 
DESCRIPTION OF THE INVENTION 
According to the present invention there is provided a method of arc 
welding under water, including the steps of: 
(a) establishing a chamber containing a gaseous atmosphere about the work 
to be welded; 
(b) feeding a consumable flux-cored arc-welding wire to a welding torch and 
striking an arc between the wire and the work to be welded so as to effect 
transfer of molten weld metal from the wire to the work, the arc welding 
wire containing at least one strong deoxidiser selected from the group 
consisting of magnesium, aluminium, zirconium, titanium, barium, lithium, 
and calcium, and 
(c) shielding the arc and molten weld metal by feeding to the torch a 
shielding gas comprising at least one inert gas selected from argon, 
krypton, xenon, and helium and at least one oxygen-containing gas selected 
from oxygen and carbon-dioxide, the shielding gas issuing from the welding 
torch as an annular curtain of gas around the welding wire. 
The term "strong deoxidiser" is used herein to indicate a metal whose 
reaction with oxygen is considerably more exothermic than that between 
iron oxygen. For the avoidance of doubt, manganese and silicon although 
used extensively in welding electrodes as deoxidisers are not classified 
herein as "strong-deoxidisers". The following metals are classified herein 
as strong deoxidisers: magnesium, aluminium, zirconium, titanium, barium 
and lithium. 
Metals such as calcium are, theoretically speaking, suitable for use as 
"strong deoxidisers" but tend to react so readily and so violently with 
oxygen or moisture that the difficulties in storing them, handling them, 
and manufacturing an electrode incorporating them, renders their use as 
"strong deoxidisers" either hazardous or inconvenient or both. For some 
metals, for example calcium, it has been alleged that some of the 
difficulties mentioned in the preceding sentence may be reduced by forming 
an alloy of the metal with, typically, iron. 
Preferred strong deoxidisers are aluminium and magnesium. 
Flux-cored welding wires containing strong deoxidisers are commercially 
available and may be used in the method according to the present 
invention. It is notable that such welding wires containing strong 
deoxidisers are we believe, examples of the class of welding electrodes 
termed "self-shielding or "in-air" welding electrodes. Although it has 
been proposed to use "strong deoxidisers" in flux-cored welding wires we 
believe that no such welding wire has hitherto been used with an 
externally supplied shielding gas. It may thus be said that the method 
according to the present invention makes use of welding wires of the 
`self-shielding` or `in-air` type with an externally-supplied shielding 
gas. 
Preferred electrodes for use in conjunction with the method according to 
the present invention are sold-under the registered trade mark 
"Innershield". Innershield 203 M and Innershield 203 Ni electrodes are 
particularly suitable for use in the method according to the present 
invention. "Self-shielding" electrodes sold under the mark "Fabshield" are 
also suitable. It is, however, entirely within the scope of the present 
invention to make up a flux-cored electrode especially for use in the 
method of the present invention. Such an electrode could be unsuitable for 
arc welding without an external shielding gas at atmospheric pressure. 
By the term "inert gas" as used herein is meant a gas which does not react 
chemically with any constituent of the welding wire and does not adversely 
affect the metallurgical properties of the weld metal. The preferred inert 
gas is argon. Helium, may, however, be used as an inert gas in addition 
to, or instead of, argon. Also, one or more `noble` gases such as krypton 
and xenon may if desired be used instead of or in addition to argon or 
helium. 
If the gaseous environment acts as the shielding gas mixture it may contain 
just one inert gas, for example, argon or helium. Alternatively, it may 
include both argon and helium. Almost inevitably, unless a welding gun 
having its own built-in fume extractor is used, a relatively large 
quantity of fume will be emitted by the welding wire. It is desirable to 
remove this fume from the chamber so as to prevent the fume obscuring the 
view of the welder. 
The shielding gas mixture may be fed to the arc with the welding wire as an 
annular stream surrounding the welding wire as it emerges from the welding 
gun. This practice is advantageous if the weld is to be made under sea in 
a chamber which is large enough to accommodate a welder. This is because 
it avoids the need to transport out to sea a large volume of relatively 
expensive inert gas so as to create the gaseous environment in the 
chamber. Instead, a pump may be used to extract air from the atmosphere 
and supply it under water to the chamber. Although a volume of inert gas 
will be required for the shielding gas mixture, this volume will generally 
be relatively small compared with the volume of air required to provide 
the gaseous environment in the chamber. It is possible, however, to use 
inert gas such as argon or helium, or a mixture thereof, as the gaseous 
environment. 
The method according to the present invention may be used when it is 
desired to weld under water. In the interior of the chamber there may be 
controls for adjusting the supply of gas thereto and for regulating the 
supply of electrical power to electrically-operated apparatus, such as 
lighting systems, therein. In such a chamber people may work without their 
own independent breathing apparatus. Typically, such a chamber will have 
removable base or removable side wall (or portion thereof) to permit 
access to be gained to its interior and to permit water to be displaced 
therefrom. The wall of such a chamber will typically be made of relatively 
thick steel which is well capable of withstanding the super-atmospheric 
pressures to which it is likely to be subjected in use. Such chambers 
suffer from the disadvantage of requiring complicated support equipment on 
the surface of the water. 
It is preferred to use a form of chamber in which the welder relies on his 
own breathing equipment and supply of oxygen. Such a chamber is adapted to 
be fitted around the workpieces to be welded together, and preferably has 
an open base. Gas (typically air or argon) is then supplied to the chamber 
to displace water from, and to create a gaseous environment in, its 
interior. The chamber may be large enough for a welder-driver to work with 
his head and shoulders (or substantially his whole body) in the gaseous 
environment. On the other hand the chamber may merely be sufficiently 
large to enable a welder-diver to insert the welding gun into the gaseous 
environment. If the chamber is not sufficiently large for a welder-diver 
to work with his head within the gaseous environment the chamber may have 
one or more walls of transparent material through which he can see what he 
is doing when he is welding. 
An alternative (but one which is not preferred) is to use a portable 
chamber comprising a small cylinder in which a welding torch terminates. 
The cylinder is closed at one end, preferably by a transparent plate, and 
is open at the other. The open end preferably has attached to it a 
contoured flexible seal which is adapted to be pressed against the 
workpieces to be welded. The welding torch preferably enters the cylinder 
through a flexible gland at one side. When gas is passed into the cylinder 
water is displaced through the open end and gaseous environment is created 
within the cylinder. A welder-diver is able to manipulate the welding 
torch with one hand while holding the cylinder against the workpieces with 
the other, and to observe a weld being deposited through the transparent 
plate. 
The method according to the present invention is also suitable for welding 
in a hyperbaric chamber on dry land or on the surface of the water. 
The flux of the electrode preferably contains substances capable of giving 
a viscous slag. Typically the electrode may contain calcium flouride and a 
compound of strontium or barium. It is believed that these compounds, 
together with magnesium oxide and aluminium oxide which are formed under 
the conditions of the arc if the electrode contains magnesium and 
aluminium as strong deoxidisers, are capable of giving a viscous slag. By 
forming a viscous slag it is possible to weld out-of-position (e.g. in the 
horizontal vertical, vertical or overhead positions) with a substantially 
greater heat input than with a solid wire GMA welding process. 
It is also preferred that the core of the electrode contain a compound, 
such as lithium fluoride, or a lithium oxide which under the conditions of 
the arc releases a metal vapour. It is believed that such metal vapour 
tends to shield the arc and to reduce diffusion of gas from the gaseous 
environment into the weld metal being deposited. 
It is believed that the Innershield 203 M and Ni electrodes include in 
their core magnesium, aluminium, barium fluoride and a compound of 
lithium. 
The core of the electrode may also contain if desired, metal oxides such as 
iron oxide. These react exothermically with strong deoxidisers such as 
aluminium and magnesium supplying extra heat to the weld pool. This 
results in fusion characteristics superior to those associated with those 
conventional welding processes in which a solid or flux-cored wire is used 
with an externally supplied shielding gas. 
In addition, the core of the electrode may also contain alloying metal 
powder such as nickel. 
If the welding wire has been formulated for use at atmospheric pressure 
without a shielding gas, the proportion of strong deoxidants will have 
been selected with the aim of avoiding two causes of weakness in the weld 
metal deposited by the wire. One cause of such weakness is insufficient 
strong deoxidant. When the level of strong deoxidant is insufficient 
oxygen and nitrogen will enter and become chemically combined with the 
weld metal. The other cause of such weakness is excessive strong 
deoxidant. When the level of strong deoxidant is excessive not all of it 
will be consumed in reacting with oxygen and nitrogen to form slag. Some 
will thus enter the weld metal. It has been found that the presence of 
excessive strong deoxidant or excessive oxygen in the weld metal can be 
deleterious. Formulators of `self shielding` electrodes for use at 
atmospheric pressure thus try to select the proportion of strong deoxidant 
such that when welding it is substantially all consumed without excessive 
quantities of oxygen or nitrogen entering the weld metal. 
What we believe is that if a welding wire which has been formulated for use 
in air at atmospheric pressure without a shielding gas is used in air at 
above atmospheric pressure there is a decline in the strength of weld 
metal deposited. This effect becomes increasingly pronounced as the 
pressure grows. There are a number of possible reasons why this should be 
so. One of these is that as the pressure increases more molecules of 
oxygen and nitrogen will tend to diffuse into the arc and may possibly 
cause excess contaminant gases to enter the weld metal giving rise to 
embrittlement. However, it would be surprising if this were the sole 
reason for the reduction in metallurgical properties at super-atmospheric 
pressure. For example, if the electrode employs a self-generated metal 
vapour shield this may tend to break down as the pressure increases. 
Moreover, increasing pressure also tends to affect the stability of the 
arc, and this too will lead to a poor weld. 
We have found that the adverse effects of super-atmospheric pressure on the 
mechanical properties of the weld may be reduced by using the welding wire 
with a shielding gas mixture containing a selected proportion of oxygen, 
the proportion having been selected to complement the composition of the 
welding wire at the prevailing pressure. The proportion of oxygen that is 
preferably included would appear not to have any strict relationship with 
partial pressure of oxygen in air at atmospheric pressure. Conceivably, it 
might be expected that for the weld metal to have tolerable mechanical 
properties, the percentage by volume of the oxygen in the shielding gas 
multiplied by the pressure in the chamber should be approximately equal to 
the partial pressure of oxygen in air at atmospheric pressure. In this 
way, the number of molecules of oxygen entering the arc per unit time 
might be kept the same as at ambient pressure. However, this factor does 
not appear to be at all critical and it is found that there is quite a 
wide tolerance on the proportion of oxygen that may be included in the 
shielding gas. 
For example, at 3 bars (absolute) the gas mixture may typically contain 
from 2 to 7% by volume of oxygen, and at 5 bars (absolute) from 1 to 4.2% 
by volume of oxygen. We have further found that at about 9 bars (absolute) 
a gas mixture containing 98% by volume of inert gas and 2% by volume of 
oxygen may, for example, be used. At about 15 bars (absolute) a gas 
mixture containing 99% by volume of inert gas and 1% by volume of oxygen 
may be used. 
Indeed, we have found it convenient to use an annular stream of shielding 
gas mixture consisting of 98% by volume of argon and 2% by volume of 
oxygen at pressures in the order of 3 bars (absolute), as well as at about 
9 bars (absolute). This gas mixture is available commercially and thus 
there is no need to mix the gases on site. Similarly a mixture of 99% by 
volume of argon and 1% by volume of oxygen is commercially available and 
may be used at about 15 bars. 
It may seem surprising that the same gas mixture can be used to provide a 
moving shielding gas stream over a wide range of pressures. We believe 
that this is made possible by a tendency at higher pressures for the 
welding electrode to emit increasing volumes of hydrogen. Thus, there 
tends to be a requirement for more oxygen at higher pressures to oxidise 
the hydrogen, which requirement tends to counteract the tendency for a 
smaller proportion of oxygen to be needed in the gas mixture to react with 
the strong deoxidisers. Another significant factor is that the design of 
the nozzle of the welding torch will influence the rate at which gas from 
the chamber atmosphere is entrained in the shielding gas mixture. If the 
chamber atmosphere is air such entrainment will enhance the oxygen content 
of the shielding gas mixture, whereas if the chamber atmosphere is argon 
such entrainment will further dilute the oxygen in the shielding gas 
mixture. We have found it preferable to use a nozzle which keeps such 
entrainment to a minimum. Such a nozzle is made by the Tweco Company. It 
has a standard 5/8 of inch tapered nozzle and is designated by Type No. 
24A-62SS. At pressures up to about 9 bars the nozzle may be arranged such 
that the contact tip terminates in the same plane as the shroud of the 
nozzle. At pressures above about 9 bars the contact tip is preferably set 
back a small distance relative to the shroud. Thus by appropriately 
selecting the chamber atmosphere and the welding torch a 
commercially-available shielding gas mixture may be used over a wide range 
of pressures. However, we have found it possible to use gas mixtures 
containing 2% of oxygen and 92% of argon (percentages are by volume) at 
pressures as high as 20 bars. It is also possible to use such shielding 
gas mixtures containing a greater proportion by volume of oxygen for 
example, a shielding gas mixture containing up to 6% by volume of oxygen 
the balance being inert gas such as argon may be used at pressures up to 
20 bars. 
By using the method according to the present invention we have been able to 
weld in an atmosphere fully saturated with water vapour at pressures up to 
at least 131/2 bars (equivalent to a depth of water of about 400 feet). 
Welding under the same conditions at greater depths of water is also 
possible. 
Since strong deoxidisers will react exothermically with oxygen-containing 
gas we postulate that it is possible, though not preferred, to use an 
oxygen-containing gas instead of some or all of the oxygen in the 
shielding gas mixture. 
The optimum proportion to be used at any pressure, may course, be 
determined by simple experiment. 
If desired, nitrogen may be included in the shielding gas mixture in an 
attempt to simulate more closely conditions which prevail when the welding 
wire is used in air at atmospheric pressure. However, we have found it 
unnecessary to do this. Moreover, if nitrogen is included in the shielding 
gas mixture care should be taken to prevent it from entering the weld 
metal. Thus we believe that if included at all it should be present in 
relatively small quantities and that its percentage by volume in the 
shielding gas multiplied by the pressure in the welding chamber should not 
exceed the partial pressure of nitrogen in air. 
The preceding discussion of how much oxygen or oxygen-containing gas to 
include in the shielding gas mixture has been based on the assumption that 
the shielding gas mixture will be used with a commercially available 
welding wire. It is of course possible to formulate a welding electrode 
especially for use in the method according to the present invention, 
though this is likely to be economically disadvantageous as the potential 
market for the wire would be limited. Nonetheless, it might be 
advantageous from the point of view of obtaining good welds under water to 
include in the wire unusually large quantities of iron oxide and a strong 
deoxidiser, such as aluminium. Iron oxide and aluminium react together 
very exothermically to form iron and aluminium oxide. The heat generated 
by this reaction would facilitate fusion of the weld metal and the work 
and helps to counteract the tendency of thick workpieces to act as heat 
sinks making adequate fusion more difficult to achieve. The process is 
thus superior in this respect to conventional solid wire GMA welding 
processes. It may also be advantageous to include in the welding wire 
rather more arc stabiliser than is conventional so as to combat the 
tendency of the welding arc to become unstable at elevated pressure. Salts 
of alkali metals and rare earths are generally suitable as arc 
stabilisers. 
If oxygen and oxygen-containing gas is omitted from the gas mixture at 
pressures above atmospheric the weld does not wet the workpieces to be 
welded together as well as it does when oxygen is included in the gas 
mixture. The improved wetting given by including oxygen in the gas mixture 
is of particular importance when welding under water as it reduces 
difficulties in removing slag from the edges of the weld between weld 
runs. 
The invention includes within its scope pipelines and other offshore 
installation when welded using the method according to the present 
invention. 
The method according to the present invention will now be described by way 
of example with reference to the accompanying drawing which is a schematic 
view of one form of apparatus suitable for performing the methods 
according to the present invention.

Referring to the drawing, a DC power source 2 located above water is 
connected in electrical circuit with the contact tip of a welding torch 24 
via a lead 14 which passes under water through an umbilical tube 16. The 
welding circuit is completed by a lead 17 which is connected between the 
power source 2 and a workpiece 32 to be welded. A conventional submersible 
wire feed unit 6 shown schematically in FIG. 1, contains a drive motor 4, 
a traction element 8 and a wire spool 10. These components together with 
the motor are located in a water-tight casing 12. The motor 4 is connected 
to the power source 2 by means of lead 15 which is received by the 
umbilical tube 16 via suitable control circuits 13. For convenience, the 
electrical connections between the lead 15 and the motor 4 are not 
illustrated. However, suitable wiring arrangements are well known in the 
art. Alternatively the drive motor 4 may have its own independent power 
supply. The umbilical tube 16 also receives a flexible gas conduit 18 
connected at one end to a gas mixer 20 which is located above water, a 
flexible gas conduit 70 which is connected to an above-water source 72 of 
compressed gas (e.g. argon), and a flexible gas conduit 74 which is 
connected to an above-water source 76 of compressed gas (e.g. argon). The 
umbilical tube 16 protects the leads and conduits therein as these leads 
and conduits pass into the submersible wire feed unit. The conduit 74 
terminates in the casing 12 and thereby provides in the casing 12 a gas 
pressure just greater than the surrounding hydrostatic pressure, venting 
of gas being effected through a suitable demand valve (not shown) which is 
set so as to prevent the pressure in the casing 12 becoming excessive. 
From the wire feed unit 6 a continuation 25 of the umbilical tube 16 
protects welding wire from the spool 10, a continuation of lead 14 and the 
shielding gas conduit 18 as they pass to the welding torch 24 which a 
welder-diver is able to insert into a welding chamber 40. The conduit 18 
terminates short of the torch 24, the gas being supplied to the nozzle of 
the torch, the arrangement being that shielding gas therefrom issues from 
the nozzle of the torch, in an annular stream around the consumable 
welding wire. 
The welding chamber 40 has a wall 42 which is of transparent material. The 
upper wall 44 of the chamber has a contoured flexible seal 30 attached to 
it, while the bottom of the chamber is open to the sea. The flexible 
conduit 70 continues from the casing 12 and enters the chamber 40 through 
the upper wall 44 thereof so as to conduct into the chamber gas from the 
conduit 70. 
The gas mixer 20 has two conduits 84 and 86 which are both joined to the 
shielding gas conduit 18. The other ends of the conduits 84 and 86 
terminate in a source 22 of oxygen gas and a source 23 of argon gas 
respectively. The sources 22 and 23 are conventiently cylinders of 
compressed gas. Associated with the gas sources 22 and 23 are pressure 
regulators 50 and 52 respectively. In the conduits 84 and 86, downstream 
of the pressure regulators 50 and 52, are control valves 54 and 56 
respectively. Associated with the control valves 54 and 56 are flowmeters 
58 and 60 respectively. By observing the flow rate of gas through the flow 
meters 58 and 60 the valves 54 and 56 may be preset to give any desired 
mixture of oxygen and argon. 
Alternatively a cylinder containing a mixture of argon and oxygen in chosen 
proportions may be used instead of the gas mixer. 
In operation, the chamber 40 is held against the workpiece 32 by its shape, 
e.g. annular, or by holding devices such as clamps, and the workpiece is 
connected directly to the power source 2. The wire feed unit 6 is 
positioned under water as close as possible to the region where the weld 
metal is to be deposited. The power source 2 itself, together with the 
sources of gas and the mixer 20 and also the control unit 13 for 
controlling welding parameters, is located above the surface of the water. 
The power supply 2 and the wire feed unit 12 are energised and the supply 
of gases from sources 22 and 23 and argon from the sources 72 and 76 is 
commenced when the welder-diver is ready. The argon passing into the 
chamber 40 displaces sea water from within the chamber through the bottom 
thereof. The welder-diver inserts his torch 24 into the localised `dry` or 
gaseous environment thus provided. The gas mixture from the mixer 20 
provides for the welding wire (preferably "Innershield" welding wire) 
(Innershield is a Registered Trade Mark) a shielding gas containing a 
controllable proportion of oxygen. 
An arc is struck between the tip of the consumable welding wire and the 
workpiece, and molten metal is transferred from the electrode to the 
workpiece in the globular mode. 
The chamber 40 preferably has a conduit 46 extending from within the 
chamber 40 through the wall 42 and terminating above the wall 42. In the 
region outside the chamber 40 the conduit 40 has a manually-operable 
control valve 48 which may be set to give a steady flow of gas out of the 
chamber 40. The gas may be supplied to the chamber 40 at a corresponding 
rate throughout a welding operation. This provides for a continuous flow 
of gas through the chamber to expel the fume evolved when welding. 
It is desirable that the gaseous environment in the chamber should contain 
less oxygen than would create a fire or explosion hazard at the prevailing 
pressure. In general, the maximum concentration of oxygen tolerable in the 
gaseous environment is 14% by volume of oxygen, but as relatively high 
pressures this concentration will be reduced. By supplying a shielding gas 
mixture containing 98% by volume of argon and 2% by volume of oxygen at 
all depths down to 600 feet when welding in a chamber having an argon 
`atmosphere`, the results shown in Tables 1 and 2 have been obtained with 
a Lincoln Innershield 203M flux-cored welding wire. 
The tests were made in accordance with the procedure specified in BS 639. 
It should be noted that the weld metal was not heat treated for hydrogen 
removal as may be performed within BS 639. 
TABLE 1 
__________________________________________________________________________ 
Reduction 
Weld Metal 
Depth of Water 
Yield Stress 
Ultimate Tensile Strength 
Elongation 
of area 
Hardness 
Feet 
Meters 
Tn/ln.sup.2 
N/mm.sup.2 
Tn/ln.sup.2 
N/mm.sup.2 
% % VPN (LONG Load) 
__________________________________________________________________________ 
0 0 33.7 
520 38.0 586 29 72 
##STR1## 
66 20.1 
32.3 
506 38.9 600 27 66 
##STR2## 
120 36.6 
32.8 
506 38.6 595 25 45 
##STR3## 
230 76.3 
37.2 
574 41.9 647 21.4 58.3 
##STR4## 
450 137 35 540 39.5 610 22 61 
##STR5## 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Charpy Impact Strength 
Depth of Water 
60.degree. C. 
30.degree. C. 
0.degree. C. 
30.degree. C. 
-00.degree. C. 
Feet 
Meters 
Ft-lbs 
J Ft-lbs 
J Ft-lbs 
J Ft-lbs 
J Ft-lbs 
J 
__________________________________________________________________________ 
0 0 132 180 
121 165 
96 130 
66 90 
37 50 
06 20.1 
155 210 
151 205 
121 165 
97 132 
52 71 
120 36.6 
162 219 
149 202 
129 175 
85 116 
50 68 
250 76.3 
140 190 
111 151 
74 101 
55 75 
30 41 
450 137 144 195 
133 180 
108 145 
72 100 
43 60 
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