AU2008202719B2 - A welding purge apparatus - Google Patents

Abstract

The present invention aims to protect the inside of a pipe from oxidation during a keyhole welding process by use of a welding purge apparatus (10) that will fit to a 5 pipe (13, 15) and maintain a purge dam on the inner surface. The apparatus (10) comprises a forward hub (16) and a rear hub (18). An inlet valve (34) in the front hub (16) is provided for inlet of purge gases and an outlet (41) in the rear hub (18) is provided for outlet of purge gas. The purge gas flows around a heat sink (12) located adjacent the side of a weld. The purge gas cools plasma gas from the weld whilst the 10 heat sink (12) suppresses both positive and negative pressure surges. C> Ln C'14 CN Li rn t4 C7'- 04 Lr) Lr) C, -t CN OC) Lr) U') LL- co m CC) OD-- rn C7, Loi C14 C, m m rn

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (Original) APPLICATION NO: LODGED: COMPLETE SPECIFICATION LODGED: ACCEPTED: PUBLISHED: RELATED ART: NAME OF APPLICANT: Score Practical Welding Solutions Pty Ltd ACTUAL INVENTORS: Lauris JARVIS Joseph BANDIERA Gary LANTZKE ADDRESS FOR SERVICE: LORD AND COMPANY, Patent and Trade Mark Attorneys, of 4 Douro Place, West Perth, Western Australia, 6005, AUSTRALIA. INVENTION TITLE: "A WELDING PURGE APPARATUS" DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO'S: Australian Provisional Patent Application Number 2007903304 filed on 20 June 2007 The following Statement is a full description of this invention including the best method of performing it known to me/us: 1 TITLE "A WELDING PURGE APPARATUS" FIELD OF INVENTION 5 The present invention relates to a welding purge apparatus. BACKGROUND TO THE INVENTION The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an 10 acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application. It is known to use keyhole are welding for pipe-to-pipe and pipe-to-fitting joints. Keyhole arc processes can produce full penetration welds through significant metal thicknesses. It is known to associate keyhole arc welding with the plasma are process or another variant, keyhole gas 15 tungsten arc welding. Both the gas tungsten and the plasma arc processes have the constraints of welding position restrictions and keyhole initiation and close-out. It is known that during the keyhole are welding process there is a need to protect both the outside and inside surfaces of the pipe/plate from oxidation. In conventional welding the inside surface is sealed with a purge dam that keeps the inside pressure higher than the outside 20 pressure. Large variations in pressure are inconsequential as long as the positive pressure difference is maintained. A negative value would allow air to enter the chamber and contaminate the weld. Significant negative pressure exists when the keyhole closes. Purging systems designed for the conventional welding process do not have the ability to control the back-purge pressure and are not appropriate for keyhole welding processes. 2 The present invention attempts to overcome at least in part the aforementioned disadvantages of previous purging systems. SUMMARY OF THE INVENTION 5 In accordance with one aspect of the present invention there is provided a welding purge apparatus comprising a heat sink to suppress both positive and negative pressure surges during keyhole welding. Preferably the welding purge apparatus of the present invention comprises a forward 10 hub and a rear hub disposed on opposite sides of the heat sink, the hubs being spaced apart and being arranged to be sealed to a pipe or other fitting to form a purge chamber. More preferably the rear hub comprises a pair of spaced apart discs, an inner flow 15 compartment disc and a rear sealing face, the flow compartment disc having an aperture to allow flow of plasma gases into the rear hub, and the rear sealing face containing an aperture provided with a one-way valve to allow escape of purged gases. 20 Further, the forward hub may have a front face containing a purge gas inlet valve. Still further, each hub may be provided with at least one inflatable member, each inflatable member being arranged to be inflated so as to engage with the fitting such that in use the region between the forward and rear hubs is sealed. 3 Each inflatable member may be connected to a source of gas of elevated pressure. Also, each inflatable member may be provided with a sponge which, in use, is urged 5 against an interior of a fitting containing the apparatus. Preferably, each hub is provided with ring members opening towards outer extremities of the apparatus and containing respective inflatable members. 10 The heat sink may be formed of material having high thermal conductivity and be attached to the front and the rear hub. Preferably, in use of the apparatus of the present invention purged gas passes from the forward hub to the rear hub around the heat sink. 15 Furthermore, the heat sink is preferably arranged to be positioned, in use, in the fitting at a point in line with a joint to welded. DESCRIPTION OF THE DRAWINGS 20 The present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a cross-section of a welding purge apparatus including an adjacent flow compartment; and 4 Figure 2 is a cross-section of an alternative embodiment of welding purge apparatus according to the present invention. 5 DETAILED DESCRIPTION OF THE INVENTION Referring to the Figure 1, there is shown a welding purge apparatus 10 comprising a heat sink 12, a forward hub 16 and a rear hub 18. Figure 1 shows pipes/fittings 13 and 15 of a similar size. The welding purge apparatus 10 is sized such that it can fit inside the pipes 13 and 15 which are to be welded together using a welding torch 11. 10 The forward hub 16 and the rear hub 18 are substantially circular rings each provided with a channel 19 opening towards the outer extremities of the welding purge apparatus 10. The rear hub 18 is sealed, via a suitable attachment means, with two substantially circular discs of essentially the same diameter, an inner flow 15 compartment disc 14 and a rear sealing face 24. The inner flow compartment disc 14 contains a substantially circular aperture 40 to allow the flow of plasma gases into the rear hub 18. The rear sealing face 24 contains an aperture 41 that is sealed with a one way flow valve 42. The one way flow valve 42 is secured by a threaded fastener 43 which also allows for pressure adjustment. 20 The forward hub 16 is sealed, via suitable attachment means, with a front face 22 which is a substantially circular disc made of a material to allow for minimal visual obstruction, such as but not limited to Perspex. The front face 22 contains an inflation 5 inlet valve 26 and a purge gas inlet valve 34. A gas diffuser 36 is connected to the end of the purge gas inlet valve 34 on the inside of the welding purge apparatus 10. The diameter of the front face 22 is larger than the heat sink 12 and smaller than the 5 pipes 13 and 15 that the welding purge apparatus 10 is to fit into. The diameter of the rear face 24 and the adjacent flow compartment disc 14 is not greater than the heat sink 12. A respective spring loaded bearing 32 is attached to each of the front face 22 and the 10 rear face 24 to assist in the stabilisation of the welding purge apparatus 10 inside the pipes 13 and 15. The spring loaded bearings 32 could be sliding contacts such as fins, or roller bearings such as wheels. A respective inflatable tube 28 is placed into the channel 19 of both the forward hub 15 16 and the rear hub 18. The inflatable tubes 28 of the forward hub 16 and the rear hub 18 are connected to a gas inflation pipe 30. The gas inflation pipe 30 is connected to the inlet inflation valve 26. The gas inlet inflation valve 26 is in use, connected to a source of gas (not shown) at elevated pressure. 20 A sponge 20, made from silicon or other suitable material, is positioned above the respective inflatable tube 28 within the respective channel 19 on both the forward hub 16 and the rear hub 18. The sponges 20 are used to seal the welding purge apparatus 10 within the pipes 13 and 15. A purge chamber 38 is the space formed on the inside 6 of the welding purge apparatus 10, once the welding purge apparatus 10 is in place and the sponges 20 form seals with the pipes 13 and 15. The heat sink 12 is a closed cylinder constructed from a metal containing good 5 thermal conductivity and durability such as, but not limited to aluminium. The heat sink 12 is attached to the front hub 16 via connector rods 44, and attached to the adjacent flow compartment disc 14 with bolts (not shown) and spacers 45. The spacers 45 are sized to allow gas to flow between the heat sink 12 and the adjacent flow compartment disc 14 through to the aperture 40. 10 An alternative embodiment of this invention allows for the provision of additional cooling of the heat sink from an external source, such as water. In use, the welding purge apparatus 10 is slid into pipes 13 and 15 and positioned 15 such that the forward portion of the heat sink 12 is in line with the joint to be welded to intercept and cool the plasma plume from the welding torch 11. The inflatable tubes 28 are then inflated via the inflation inlet valve 26 which forces the sponge seals 20 against the pipe walls 13 and 15, locking the purge apparatus 10 in place and forming a gas-tight seal. Purge gas is admitted through the gas inlet valve 34 in the 20 front face 22 into the purge chamber 38 via a gas diffuser 36. The gas diffuser 36 assists in turbulence avoidance and unnecessary mixing with any air trapped within the chamber. The purge gas flows through the purge chamber 38, over and around the heat sink 12 before leaving the purge unit 10 through the one way flow valve 42 in the rear face 24. 7 The plasma plume from the welding torch 11 impacts directly onto the heat sink 12. The plasma gases from the plume continue over the heat sink 12 and down between the heat sink 12 and the adjacent flow containment disc 14 before passing through 5 aperture 40. This pathway, as it mixes with the purge gases, provides an effective cooling of the plasma gases, allowing a major reduction in the thermal energy available to raise the pressure of the total gas volume within the welding purge apparatus 10 ensuring a more effectual weld. 10 When the weld is complete and has cooled enough for the welding purge apparatus 10 to be removed, the purge gas is switched off. The pressurised gas inflating the inflatable tubes 28 is also released and the welding purge apparatus 10 is removed by pulling forward. 15 A further alternative embodiment of the present invention is shown in Figure 2 of the accompanying drawings. Like reference numerals for like parts found in Figure 1 are used in Figure 2. In Figure 2 there is shown an apparatus 50 which is mounted to distal ends of pipes 20 13, 15 which are to be welded together at a central joint using a welding torch 11. As shown, a heat sink 12 is mounted between a forward hub 16 and a rear hub 18. The heat sink 12 is attached to the forward hub 16 and the rear hub 18 by means of connector rods 44. 8 Further, it can be seen that the hubs 16 and 18 are of larger size than the interior of the pipes 13 and 15. The hubs 16 and 18 are engaged with respective distal ends of the pipes 13 and 15 by means of fasteners 52 securely mounted on respective connector rods 44 by means not shown. 5 The hub 16 contains a purge gas inlet 34 and a gas diffuser 36. The hub 18 contains a purge gas outlet 41. In use, the hubs 16 and 18 are mounted to distal ends of the pipes 13 and 15 with the heat sink 10 12 mounted there between on the connector rods 44. The heat sink 12 is positioned adjacent the joint between the pipes 13 and IS which is to be welded. In other respects the apparatus of Figure 2 operates in similar manner to the apparatus of Figure 1. 15 Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. Throughout the description and claims of this specification the word "comprise" and 20 variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps. 25 9

Claims (12)

1. A welding purge apparatus comprising a heat sink to suppress both positive and negative pressure surges during keyhole welding. 5

2. A welding purge apparatus according to claim 1, wherein the apparatus comprises a forward hub and a rear hub disposed on opposite sides of the heat sink, the hubs being spaced apart and being arranged to be sealed to a pipe or other fitting to form a purge chamber. 10

3. A welding purge apparatus according to claim 2, wherein the rear hub comprises a pair of spaced apart discs, an inner flow compartment disc and a rear sealing face, the flow compartment disc having an aperture to allow flow of plasma gases into the rear hub, and the rear sealing face containing an aperture provided with a one way valve to allow 15 escape of purge gases.

4. A welding purge apparatus according to claims 2 or 3, wherein the forward hub has a front face containing a purge gas inlet valve. 20

5. A welding purge apparatus according to any one of claims 2 to 4, wherein each hub is provided with at least one inflatable member, each inflatable member being arranged to be inflated so as to engage with the fitting such that, in use, the region between the forward and rear hubs is sealed. 10

6. A welding purge apparatus according to claim 5, wherein each inflatable member is connected to a source of gas at elevated pressure.

7. A welding purge apparatus according to claim 6 or 7, wherein each inflatable member is 5 provided with a sponge which, in use, is urged against an interior of a fitting containing the apparatus.

8. An apparatus according to any one of claims 5 to 7, wherein each hub is provided with ring members opening towards outer extremities of the apparatus and containing 10 respective inflatable members.

9. An apparatus according to any one of claims 2 to 8, wherein the heat sink is formed of material having high thermal conductivity and is attached to the front hub and the rear hub. 15

10. An apparatus according to any one of claims 2 to 9, wherein, in use purge gas passes from the forward hub to the rear hub around the heat sink.

11. An apparatus according to any one of claims 2 to 10, wherein the heat sink is arranged to 20 be positioned, in use, in the fitting at a point in line with a joint to be welded.

12. A welding purge apparatus substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings. 11