WO2004067219A1

WO2004067219A1 - Welding method

Info

Publication number: WO2004067219A1
Application number: PCT/GB2004/000363
Authority: WO
Inventors: David John Keats
Original assignee: David John Keats
Priority date: 2003-01-30
Filing date: 2004-01-30
Publication date: 2004-08-12

Abstract

The invention provides a method of underwater welding and an apparatus for use in such a method. A method of welding a first metal component to a second metal component underwater employs a metal arc welding assembly having a consumable electrode comprising weld material for forming a weld deposit, and the method comprises: locating the first and second metal components adjacent one another; positioning the electrode against a surface of the first metal component and supplying the electrode with a first current for a first time interval to cause the electrode to be partially consumed and to cause weld material to pierce through said first metal component and to cross the interface of the first metal component with the second metal component to penetrate into the second metal component; supplying the electrode with a second current, having a lower value than the first, for a second time interval to cause the electrode to be further consumed and deposit weld material across the interface between the first and second metal components to form a join therebetween.

Description

Welding Method

The present invention relates to a welding method and an apparatus for use in a welding method, particularly, though not exclusively, to a method of underwater manual metal arc ( MA) wet spot welding.

It is known within the marine industry to employ underwater manual metal arc (MMA) wet welding process for the manufacture of structures. However, known processes require a fully trained and experienced welder-diver to make welds, as a high degree of skill is required to ensure the production of quality welds. Owing to the constraints of the underwater environment there may be situations where it is very difficult, or impossible, to create an adequate weld by employing known techniques. For example, the underwater visibility conditions must allow the diver to see the welding arc and joint area to ensure acceptable weld quality. With known underwater MMA welding processes which employ a fillet welding technique the weld must be confined within a joint. This requires preparation of the components to be joined to ensure certain tolerances and for the joint area to be cleaned prior to the commencement of, and during, welding. If the preparation and cleaning techniques are not adequate then a number of weld defects may occur. In addition, since known underwater MMA welding processes employ a fillet welding technique they produce a weld that is substantially on the surface of the joined components. Consequently, the weld may be open to erosion, corrosion, premature decay or mechanical damage . The present invention aims to address at least one disadvantage associated with known underwater welding processes whether discussed herein or otherwise.

5 According to a first aspect of the present invention there is provided a method of welding a first metal component to a second metal component underwater, said method employing a metal arc welding assembly having a consumable electrode comprising weld material for forming a weld deposit, and

10 the method comprising: locating the first and second metal components adjacent one another; positioning the electrode against a surface of the first metal component and supplying the electrode with a first

15 current for a first time interval to cause the electrode to be partially consumed and to cause weld material to pierce through said first metal component and to cross the interface of the first metal component with the second metal component to penetrate into the second metal

20 component; supplying the electrode with a second current , having a lower value than the first, for a second time interval to cause the electrode to be further consumed and deposit weld material across the interface between the first and

25 second metal components to form a join therebetween.

Suitably, the first current is supplied for the first time interval such that it causes weld material from the electrode to pierce through the first metal component 30. forming an aperture therein and penetrate into the second metal component such that it creates a cavity in the second metal component . Suitably, the first and second currents are supplied for time intervals such that weld material from the electrode does not pierce through the second metal component .

Suitably, the first current is supplied for the first time interval such that weld material from the electrode creates a cavity which extends into the second metal component for at least 25% of the thickness of the second metal component. Preferably, the cavity extends for at least 50% of the thickness of the second metal component, more preferably at least 75%, for example, at least 90%.

Suitably, the first current is supplied for the first time interval such that weld material from the electrode creates a cavity which extends into the second metal component for a depth equal to at least 25% of the thickness of the first metal component. Preferably, the cavity extends for a depth equal to at least 50% of the thickness of the first metal component, more preferably at least 75%, for example, at least 90%.

Suitably, the second current is supplied for the second time interval such that weld material from the electrode is deposited such that it substantially fills the cavity created in the second metal component and extends across the interface between the first and second metal components and at least partially fills the aperture created in the first metal component. Preferably, the second current is supplied for the second time interval such that weld material from the electrode is deposited such that it substantially fills the aperture created in the first metal component as well as the cavity created in the second metal component . Suitably, the weld joining the first and second metal components comprises a spot (or plug) weld which may be produced by employing a manual metal arc (MMA) wet welding assembly.

Preferably, the first and second metal components are positioned such that a first face of the first metal component is orientated towards the second metal component and the electrode is initially positioned against a second face of the first metal component substantially opposed to the first face thereof. Preferably, the second metal component is arranged such that a first face thereof lies in contact with the first face of the first metal component .

The first metal component may comprise a substantially planar sheet portion. The first metal component may comprise a substantially planar sheet portion comprising said first and second faces which lie substantially parallel to one another. The second metal component may comprise a substantially planar sheet portion. The second metal component may be arranged such that a first face of the sheet portion thereof lies in contact with a first face of the sheet portion of the first metal component. Suitably, the first faces of the first and second metal component comprise the major faces of the sheet portions thereof .

Alternatively, the first and second metal components may each comprise any structure that will permit a face of the first metal component to lay in contact with a face of the second metal component such that the components can be welded together. For example, the first and/or second metal component may comprise a pipe, plate, sheet or RSJ. Preferably, if the first metal component comprises a pipe the second metal component also comprises a pipe and the pipes are dimensioned such that one allows the other to fit over it and allow face to face contact.

Suitably, the first current is supplied for the first time interval such that weld material from the electrode penetrates through the first metal component from the second side to the first side thereof.

Suitably, the second current is supplied for the second time interval such that the electrode deposits weld material across the interface of the first face of the first metal component with the first face of the second metal component.

Suitably, a weld formed according to the method of the present invention is substantially accommodated between the first and second metal components. Thus, the weld may be substantially protected from one or more of erosion, corrosion and mechanical damage.

Suitably, the first and/or second metal components can be employed without the faces to be joined being cleaned prior to use. Alternatively, a minimal amount of cleaning of the faces to be joined may be performed. Suitably, additional operations to ensure that tolerances are kept at a joint between the first and second members may not be necessary. Suitably, the method can be performed in poor visibility conditions. For example, the method may be performed in conditions where 'the visibility is 0.5 metres or less. The method may be performed in conditions of zero visibility with little or no decrease in the quality of the weld.

The method may be performed by an operator having no conventional welding training. Alternatively, the method may be performed by a trained welder-diver or it may be performed by an underwater robot .

Suitably, the first metal component comprises steel, most preferably a plain carbon or low alloy structural steel or stainless steel. Suitably, the second metal component comprises steel, more preferably a plain carbon or low alloy structural steel or stainless steel. The first and second metal components may comprise the same metal. Alternatively, the first and second metal components may comprise different metals, for example the first metal component may comprise stainless steel and the second metal component may comprise carbon steel .

Suitably, the portion of the first metal component to be joined to the second metal component has a thickness of between 3 and 20 millimetres, more preferably of between 6 and 16 millimetres. Suitably, the portion of the second metal component to be joined to the first metal component has a^' thickness of between 3 and 20 millimetres, more preferably of between 6 and 16 millimetres.

Suitably, the electrode comprises a flux coated electrode. Suitably, the electrode is arranged to deposit a steel weld deposit, more preferably a stainless steel weld deposit. Suitably, the electrode comprises a stainless steel weld material which contains chromium, nickel and molybdenum. Suitably, the flux contains fluoride. A suitable electrode may be of the type available under the mark HAMMERHEAD from Speciality Welds of West Yorkshire, UK.

Passing an appropriate current through the electrode suitably causes the weld material to melt. The melted weld material may, if the current is of a suitable value, cause significant melting and penetration of metal components that it contacts. If the current is of a lower value there may be only minimal melting of metal components that the weld material contacts.

Suitably, the electrode has a diameter of between 3 and 5 millimetres, more preferably of between 3.1 and 4.1 millimetres, for example, the electrode may have a diameter of 3.2 or 4.0 millimetres.

Suitably, during the welding process the electrode is arranged to lie at an angle of at least 70° to the plane of the interface between the first and second metal components, more preferably at an angle of at least 80°, for example at an angle of 90° (i.e. perpendicular to the plane of the interface) .

Suitably, light pressure is applied to press the electrode towards the interface between the first and second metal components whilst current is supplied to the electrode. Suitably, the first current has a value of between 100 and 350 Amps, more preferably of between 120 and 300 Amps, for example between 150 and 250 Amps.

Suitably, the first time interval has a duration of between 2 and 60 seconds, more preferably between 5 and 40 seconds, for example between 10 and 30 seconds. Preferably, the first time interval comprises a single, uninterrupted, time interval.

Preferably, the second current has a value of between 50 and 300 Amps, more preferably between 100 and 250 Amps, for example between 130 and 210 Amps.

Suitably, the second current value is between 60% and 90% of the first current value, more preferably between 70% and 80% of the first current value.

Suitably, the second time interval has a duration of between 2 and 60 seconds, more preferably between 5 and 40 seconds, for example between 10 and 30 seconds. The duration of the second time interval may be determined by the time it takes for the electrode to be consumed once the second time interval is commenced. Thus, an operator may not need to determine or pre-set the second time interval .

Suitably, the first time interval is arranged to allow the electrode to be partially consumed and pierce through the first metal component. Suitably, the second current is maintained until the consumable weld material of the electrode is finished and/or the weld is completed. Suitably, the weld is completed as a "one-shot" process with one consumable electrode being used to complete one weld. If a weld is not fully completed after an electrode has been employed according to the method of the invention then a new electrode may be employed and may be supplied with a current having a value substantially the same as that of the second current to continue to fill up the weld until the surface of the first metal component is reached and/or the required surface finish is produced.

The method may be repeated at a plurality of discrete points along the interface between first and second metal components.

If the method is employed at a plurality of welding points between two metal components the weld may be formed at one or more of said points by piercing through the second metal component to reach and cross the interface between the first and second metal components. The method and requirements in that case may be substantially as discussed above for forming a weld by piercing through the first metal component .

According to a second aspect of the present invention, there is provided a welding apparatus for welding a first metal component to a second, adjacent, metal component underwater, said apparatus comprising: a power source arranged to supply electrical current to a consumable electrode comprising weld material for forming a weld deposit; an electrode holder arranged to hold said electrode; and a control unit arranged to (i) cause the power source to supply said electrode with a first current for a first time interval to cause the electrode to be partially consumed and weld material to pierce through said first metal component and to cross the interface of the first metal component with the second metal component to penetrate into the second metal component and (ii) cause the power source to supply said electrode with a second current, having a lower value than the first, for a second time interval to cause the electrode to be further consumed and deposit weld material across the interface between the first and second metal components to form a join therebetween.

Suitably, the control unit comprises a safety switch arranged to be actuated by an operator to commence the supply of current to the electrode and start the welding process. The safety switch may allow an operator to interrupt and stop the welding process at any stage by cutting the current supply to the electrode.

Suitably, the control unit comprises a timing controller arranged to determine the first time interval . The timing controller may be arranged to determine the second time interval. Alternatively, the second current may be supplied until the electrode is exhausted and the duration of the second time interval may thus be automatically determined. Suitably, the time interval or intervals are selected by an operator prior to commencement of the welding process .

Suitably, the control unit comprises a current controller arranged to determine the first and second current values. Suitably, the current values are selected by an operator prior to commencement of the welding process . Suitably, the control unit is arranged to decrease the current and start the second time interval immediately upon the end of the first time interval.

Suitably, the control unit comprises an Ammeter. Suitably, the control unit comprises a Voltmeter.

The power source and control unit may form an integral unit. Alternatively, the power source and control unit may comprise individual units.

Suitably, the power source and control unit are located above water and are arranged to be connected to the electrode holder housing a consumable electrode underwater by a waterproof cable.

Suitably, the power source comprises a 3 phase DC machine and may be a transformer-rectifier, inverter or diesel/petrol generator. A suitable power source may have an output of 400 Amps at 60% duty cycle.

Suitably, the power source comprises a welding machine which is able to produce an electrical current output of varying values to supply to a consumable electrode. Suitably, the welding machine is arranged to increase or decrease the electrical current supplied thereby in response to signals from the control unit. Suitably, the control unit is connected to the welding machine by current carrying cables, which carry the current to be supplied via the control unit to the consumable electrode, and by a signal cable which carries electrical signals between the welding machine and control unit for controlling the current output of the welding machine. Alternatively, the control unit may be connected to the welding machine only by a signal cable which carries electrical signals between the welding machine and control unit for controlling the current output of the welding machine. Current carrying cables may, in this case, connect the welding machine to the consumable electrode via the electrode holder without supplying the current via the control unit .

Suitably, the welding apparatus is such that it can be employed in a method according to the first aspect.

According to a third aspect there is provided a structure comprising metal components joined by welds produced by a method according to the first aspect of the present invention and/or by employing an apparatus according to the second aspect of the present invention.

A specific embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of the components of a welding apparatus;

Figure 2 is a cross-sectional view of two metal components and a welding electrode at an intermediate welding stage;

Figure 3 is a cross-sectional view of two metal components welded together; and Figure 4 is a schematic view of the components of a further embodiment of a welding apparatus .

As illustrated by Figure 1 the welding apparatus comprises an electrode holder 18 for holding a consumable electrode

10, a welding cable 12, a welding control unit 14 and a power source 16.

The welding electrode 10 comprises a flux covered metal arc electrode. The electrode is arranged to deposit- a stainless steel weld deposit which contains chromium, nickel and molybdenum. The flux contains fluoride. Depending upon the application an electrode having a diameter of either 3.2 or 4.0 millimetres can be employed. Suitable electrodes are available under the mark HAMMERHEAD from Speciality Welds of West Yorkshire, UK.

The electrode holder 18 is arranged to receive the welding electrode 10 and to be connected via a welding cable 12 to a control unit 14 which is in turn connected to the welding power source 16 such that a current can be passed through the welding electrode 10. A second welding cable 12 is arranged to connect the metal components 20, 22 to the control unit 14 and power source 16 such that an electrical circuit is completed when the welding electrode is brought into contact with the components 20, 22 such that current can flow therethrough. The control unit 14 comprises a timing controller 26 and a current controller 28. The control unit 14 further comprises an Ammeter 30 and a Voltmeter 32 as well as a safety switch 34.

In the embodiment shown in Figure 4, the control unit 14 is in electrical communication with a power source 16, which comprises a welding machine 16a via power cables 13. The supply of electrical current from the power cables 13 via the control unit 14 to the welding cables 12 is determined by the operation of the safety switch 34. The level of current supplied by the welding machine 16a is determined by the control unit 14 which instructs the welding machine 16a with the required current level to be produced thereby via the signal cable 15.

In operation, the welding electrode 10 and electrode holder 18 as well as the metal components to be joined 20, 22 are located below water whilst the control unit 14 and power source 16 connected thereto by the welding cables 12 are located above water.

The timing controller and current controller are preset so that upon commencement of welding a first current is supplied to the welding electrode for a first time interval and then a second current is supplied for a second time interval. The first current and first time interval being arranged such that weld material 23 . from the welding electrode is caused to pierce through the first metal component 20 and penetrate into the second metal component 22, and the second current and time interval being arranged such that a welding deposit 24 is caused to be formed across the interface between the first and second metal components 20, 22 and the second metal component 22 is not pierced all the way through. An operator (not shown) above the water can initiate the process by actuating the safety switch 34 and the control unit 14 then determines the supply of current to the electrode 10 which is held in position by a diver (not shown) . In a welding method, ^■ which may employ a welding apparatus having a control unit 14 as described above, or which may alternatively employ a more basic control unit with time intervals and current values being manually controlled by an operator above the water surface, two metal components 20, 22 are joined by a welding deposit 24 according to the following process.

A welding current having a first current value of between 130 and 250 Amps is supplied to the welding electrode positioned against a first metal component 20 for a first time interval of between 10 and 30 seconds. The exact current and time being dependent upon the characteristics, and in particular the sheet thickness of the metal components 20, 22 to be joined. Gentle pressure is applied to the welding electrode 10 whilst the first current is supplied thereto such that weld material 23 is caused to pierce through the first metal component 20 to pass from a second side 20b thereof to a first side 20a

(lying adjacent to the second metal component 22) and penetrate into the second metal component 22 (illustrated by Figure 2) . The first current value and time interval are determined such that once the weld material 23 from the electrode crosses the interface between the first and second metal components 20, 22 and penetrates into the second metal component 22 the current is dropped down by approximately 20% to 30%. This provides a second current value which is supplied to the welding electrode 10 for a second time interval of between 10 and 30 seconds such that it causes a welding deposit 24 to be produced across the interface between the first and second metal components 20, 22. The second time interval is arranged such that the second current value is maintained until the consumable weld material of the electrode 10 is finished and/or a suitable weld is produced (illustrated by Figure 3) . At the first current value the weld material 23 from the electrode 10 is produced at such a rate and temperature that it causes significant melting of metal components 20, 22 it contacts. Thus, weld' material 23 and molten metal from the metal components 20, 22 are spat out from the area to be welded and there is little depositing of weld material 23. Accordingly, an aperture is created in the first metal component 20 and a cavity in the second metal component 22. When the current is reduced to the second current value, weld material 23 is produced at such a rate and temperature that it causes minimal melting of the metal components 20, 22 it contacts. Thus, the weld material 23 forms a weld deposit 24 in the cavity and aperture which joins the first and second metal components 20, 22 together.

The method is designed for a weld to be completed as a "one-shot" process with one consumable electrode 10 being used to complete one weld. However, if the weld is not fully completed a second electrode can be used and supplied with a current at the second current value for a time period sufficient to continue to fill up the weld until the surface of the material of the first metal component 20 is reached by the weld deposit 24 or the required surface finish is produced.

The method is such that during the welding operation only a moderate pressure need be applied to the electrode 10 against the surface of the first metal component 20 in order to ensure that the component is sufficiently pierced. The setting of currents and time intervals is controlled on the surface by means of a control unit, either of the type described above or by simpler control units requiring greater user input.

The range of material thicknesses that can be welded is dependent upon the size of the electrode employed as well as the current values and time intervals employed. These may be predetermined in a controlled test environment so that subsequent welding "in the field" can be carried out with great efficiency by persons having little or no welding skills. Suitably, in order for the method of the present invention to be effective the first metal component will have a thickness in the range of 6 to 16 millimetres through which the welding electrode must pierce to reach the interface with the second metal component .

The welding method and apparatus of the present invention may allow for simpler and more efficient welding of metal components in an underwater environment and may reduce the reliance upon welder-diver's skills to produce quality welds .

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method of welding a first metal component to a second metal component underwater, said method employing a metal arc welding assembly having a consumable electrode comprising weld material for forming a weld deposit, and the method comprising: locating the first and second metal components adjacent one another; positioning the electrode against a surface of the first metal component and supplying the electrode with a first current for a first time interval to cause the electrode to be partially consumed and to cause weld material to pierce through said first metal component and to cross the interface of the first metal component with the second metal component to penetrate into the second metal component; supplying the electrode with a second current, having a lower value than the first, for a second time interval to cause the electrode to be further consumed and deposit weld material across the interface between the first and second metal components to form a join therebetween.

2. A method according to claim 1, wherein the first and second currents . are supplied for time intervals such that weld material from the electrode does not pierce through the second metal component .

3. A method according to claim 1 or 2, wherein the first and second metal components are positioned such that a first face of the first metal component is orientated towards the second ^' metal component and the electrode is initially positioned against a second face of the first metal component substantially opposed to the first face thereof .

4. A method according to claim 3, wherein the first metal component comprises a substantially planar sheet portion comprising said first and second faces which lie substantially parallel to one another.

5. A method according to claim 4, wherein the second metal component comprises a substantially planar sheet portion and is arranged such that a first face of the sheet portion thereof lies in contact with a first face of the sheet portion of the first metal component.

6. A method according to any preceding claim, wherein the weld formed is substantially accommodated between the first and second metal components .

7. A method according to any preceding claim, wherein the first and/or second metal components can be employed without the faces to be joined being cleaned prior to use.

8. A method according to any preceding claim, wherein the method can be performed in conditions where the visibility is 0.5 metres or less.

9. A method according to any preceding claim, wherein the method can be performed by an operator having no conventional welding training.

10. A welding method substantially as herein described with reference to the accompanying drawings .

11. A welding apparatus for welding a first metal component . to a second, adjacent, metal component underwater, said apparatus comprising: a power source arranged to supply electrical current to a consumable electrode comprising weld material for forming a weld deposit; an electrode holder arranged to hold said electrode; and a control unit arranged to (i) cause the power source to supply said electrode with a first current for a first time interval to cause the electrode to be partially consumed and weld material to pierce through said first metal component and to cross the interface of the first metal component with the second metal component to penetrate into the second metal component and (ii) cause the power source to supply said electrode with a second current, having a lower value than the first, for a second time interval to cause the electrode to be further consumed and deposit weld material across the interface between the first and second metal components to form a join therebetween.

12. An apparatus according to claim 11, whereάn ^"the control unit comprises a timing controller arranged to determine the first and optionally second time intervals.

13. An apparatus according to claim 11 or 12, wherein the control unit comprises a current controller arranged to determine the first and second current values.

14. An apparatus according to any of claims 11 to 13, wherein the control unit is arranged to decrease the current and start the second time interval immediately upon the end of the first time interval.

15. A welding apparatus substantially as herein described with reference to Figure 1.

16. A structure comprising metal components joined by welds produced by a method according to any of claims 1 to 10 and/or by employing an apparatus according to any of claims 11 to 15.