Method and machine for forge welding of tubular articles and exothermic flux mixture and method of manufacturing an exothermic flux mixture

Abstract

A method of forge welding includes placing at least two components for welding together, adjacent each other and with an exothermic flux mixture placed between the components. The exothermic flux mixture is heated to initiate an exothermic reaction and the faying surfaces of the two components are pressed together. The components being welded may be tubular, in particular pipes. Apparatus for the method of forge welding and exothermic flux mixtures for the method of forge welding are also provided.

Claims

1. A method of forge welding comprising: placing at least two components for welding together adjacent each other with an exothermic flux mixture placed there between, each component having a faying surface; heating the exothermic flux mixture to initiate an exothermic reaction, and melting the exothermic flux mixture to produce a molten flux; and pressing the faying surfaces of the two components together to squeeze out molten flux and to forge weld the faying surfaces together.

2. The method of claim 1 wherein the components being welded are tubular and the faying surfaces are ends of the tubes, in particular wherein the tubular components are pipes.

3. The method of claim 1 further comprising applying external heating to the joint being prepared.

4. The method of claim 1 further comprising at least one of a controlled cooling procedure and a post welding heat treatment.

5. The method of claim 1 further including carrying out the procedure in a chamber filled with an inert gas or an active gas.

6. The method of claim 1 wherein the procedure is carried out in air.

7. The method of claim 2 wherein two tubular components are welded and the end of at least one of the components being welded has its wall profiled into one of: a male radial shape, a female radial shape, and a profile that slopes backwards, away from an end of the tubular component at an inside wall of the tubular component, towards an outside of the wall of the tubular component.

8. The method of claim 7 wherein both of the tubular components have ends of the tubes that have walls of a male radial shape.

9. The method of claim 7 wherein one of the tubular components has an end with a wall of a male radial shape and the other has an end with a wall of a female radial shape.

10. The method of claim 9 wherein the wall end of a female radial shape has a concave cavity that accepts a corresponding convex profiled male shape of the wall end of the male radial shape; and wherein the radius of the female curvature is larger than the radius of the corresponding male end.

11. The method of claim 2 wherein two tubular components are being welded and the thickness of the walls of the components is reduced at the ends being welded.

12. The method of claim 2 wherein two tubular components are being welded, and wherein they are welded when in a vertical orientation.

13. The method of claim 1 wherein two components are being welded and they are moved towards each other in at least two pre-forge stages before pressing the faying surfaces together, the pre-forge stages including: a), a first movement before the ignition of the exothermic mixture; and b), a second movement, faster than the first movement, after the ignition of the exothermic flux.

14. The method of claim 13 wherein the two components are either: moved simultaneously towards each other; or one component is moved towards the other.

15. The method of claim 1 wherein the exothermic flux mixture placed between the two components is in the form of a shaped solid unit.

16. The method of claim 1 wherein the exothermic flux mixture comprises: a fuel selected from the group consisting of aluminium, silicon, calcium, magnesium, titanium, mixtures of two or more of these elements, and alloys comprising two or more of these elements; one or more transition metal oxides, boron oxide, and halides.

17. The method of claim 16 wherein the exothermic flux mixture has a composition by weight of 20-50% transition metal oxides, 10-25% fuel, 10-60% boron oxide, and 0-50% of fluorides and/or chlorides.

18. The method of claim 16 wherein the transition metal oxides are selected from the group consisting of oxides of iron, manganese, nickel, copper, cobalt, titanium, molybdenum, and chromium.

19. The method of claim 16 wherein the exothermic flux mixture further comprises up to 30% by weight of oxides selected from the group consisting of: alkali metal oxides, alkaline earth metal oxides, oxides of silicon, and combinations thereof.

20. The method of claim 16 wherein the exothermic flux mixture comprises CaAl alloy as sole or one of the fuels and the alloy contains from 10-50 wt % Al.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the present invention will appear from the following detailed description of some embodiments illustrated with reference to the accompanying drawings in which:

(2) FIGS. 1a to 1f illustrate forge welding of tubes with an exothermic flux ring;

(3) FIG. 2 illustrates forge welding of oilfield drilling pipes, in situ;

(4) FIG. 3 is a flow chart showing the steps to manufacture an exothermic ring; and

(5) FIGS. 4a to 4d show profiled pipe ends being joined by forge welding using an exothermic flux ring;

(6) FIGS. 5a and 5b show joining two pipes having a male (convex) profiling on top and a female (concave) profiling on the bottom; and

(7) FIGS. 6a and 6b show joining of pipes making use of profiles that direct the molten flux to the outside.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS AND EXPERIMENTAL RESULTS

(8) The following examples illustrate the exothermic mixtures and the preparation of exothermic rings, for joining pipes, using the mixtures; however they should not be regarded as limiting.

Example 1

(9) An exothermic flux ring is prepared (as illustrated in FIG. 3, discussed below) using a mixture of (wt %) 31.9% Iron (Ill) Oxide, 6.0% Calcium, 8.1% Aluminum, 9.7% Sodium fluoride, 6.5% Aluminum fluoride, and 37.8% boron oxide.

(10) First, the exothermic mixture was prepared by weighing the constituent powders according to the ratios stated above. The powders were then mixed thoroughly by traditional powder mixing techniques such as tumbling or ball milling. About 6 grams of the intimately mixed mixture of reactant powders is then pressed in a die having two plungers with convex profiles to produce a green pre-form with about 60% of the theoretical density and having concave grooves for receiving pipe ends as described hereafter and with reference to FIG. 4, forming an exothermic flux ring having dimensions of about 50 mm outside diameter, 5 mm wall thickness and 4 mm height. The green pre-form ring was then heat treated at 460 C. for 2 minutes and then allowed to cool naturally.

(11) The heat treated pre-form with, for example a height of about 4 mm is then placed between two steel pipes with convex profiled ends. The steel pipe ends are heated by induction. Upon reaching a temperature of approximately 750 C, the pre-form ignites with the reaction generating heat (calculated adiabatic combustion temperature of 1600K without accounting for the pre-heat) and producing molten product materials containing calcium, aluminum, and boron oxides, sodium and aluminum fluorides, iron metal, and compounds thereof. The high temperature product materials provide heat to the surface of the pipe ends and rapidly dissolve surface oxides and protect from new oxidation. The pipes are then moved together a total of 8 mm (4 mm to account for the starting 4 mm gap and 4 mm of forging distance. The molten flux is squeezed out and the pipes fuse to form a weld.

Example 2

(12) An exothermic flux ring is prepared (as illustrated in FIG. 3) using a mixture of (wt %) 23.5% Iron (Ill) oxide, 9.3% Nickel oxide, 13.9% Calcium, 3.9% Aluminum, 5.4% Barium fluoride, 9.6% Calcium fluoride, 9.6% Magnesium fluoride, and 24.8% Boron oxide. In this example the fluorides were pre-melted together and the resultant fluoride mixture cooled and then powdered to form a mixed fluoride component for the flux ring mixture. The exothermic mixture was then prepared by weighing the constituent powders according to the ratios stated above. They were then mixed thoroughly by traditional powder mixing techniques such as tumbling or ball milling. About 6 grams of the intimately mixed mixture of reactant powders is then pressed in a die having two plungers with convex profiles to produce a green form with about 60% of theoretical density, with dimensions of about 50 mm outside diameter, 5 mm wall thickness and 4 mm height. The green pre-form was then heat treated at 460 C. for 4 minutes followed by natural cooling. The pre-form with a height of 4 mm is then placed between two steel pipes with convex profiled ends. The steel pipe ends are heated by induction. Upon reaching a temperature of approximately 750 C., the pre-form is ignited with the reaction generating heat (calculated adiabatic combustion temperature of 1700K without accounting for the pre-heat) and product materials containing calcium, aluminum, and boron oxides, barium, calcium, and magnesium fluorides, iron and nickel metals, and compounds thereof. The high temperature product materials provide heat to the surface of the pipe ends and rapidly dissolve surface oxides and protect from new oxidation. The pipes are then moved together a total of 8 mm (4 mm to account for the starting 4 mm gap and 4 mm of forging distance. The molten flux is squeezed out and the pipes fuse to form a weld.

(13) In Examples 1 and 2, iron (III) and nickel oxide were used as the oxygen source, and calcium and aluminum were used as the fuels for the exothermic reactions. Other transition metal oxides, such as iron (II,III) oxide, manganese oxides, copper oxides, molybdenum oxides, etc. can also be used as the oxygen source. In addition, instead of elemental calcium and aluminum other fuels such as magnesium, silicon, or other metals may also be used. Moreover, alloys of these metals may also be used as fuels.

Example 3

(14) An exothermic flux ring is prepared (as illustrated in FIG. 3, discussed below) using a mixture of (wt %) 36.2% Manganese (IV) Oxide, 14.2% Calcium-Aluminum alloy (containing 25%, by weight, of aluminum), 8.0% barium fluoride, 1.6% calcium fluoride, 1.5% magnesium fluoride, and 38.5% boron oxide.

(15) First, the exothermic mixture was prepared by weighing the constituent powders according to the ratios stated above. The powders were then mixed thoroughly by traditional powder mixing techniques such as tumbling or ball milling. About 75 grams of the intimately mixed mixture of reactant powders is then pressed in a die having two plungers with convex profiles to produce a green pre-form with about 60% of the theoretical density and having concave grooves for receiving pipe ends as described hereafter and with reference to FIG. 4, forming an exothermic flux ring having dimensions of about 248 mm outside diameter, 11 mm wall thickness and 3.5 mm height. The green pre-form ring was then heat treated at 450 C. for 30 minutes and then allowed to cool naturally.

(16) The heat treated pre-form with, for example a height of about 3.5 mm is then placed between two steel pipes with convex (male) profiled ends. The steel pipe ends are heated by induction. Upon reaching a temperature of approximately 750 C, the pre-form ignites with the reaction generating heat (calculated adiabatic combustion temperature of 1800K without accounting of pre-heat) and producing molten product materials containing calcium, aluminum, manganese and boron oxides, barium, calcium and magnesium fluorides, manganese metal. The high temperature product materials provide heat to the surface of the pipe ends and rapidly dissolve surface oxides and protect from new oxidation. The pipes are then moved together a total of 8 mm (4 mm to account for the starting 4 mm gap and 4 mm of forging distance. The molten flux is squeezed out and the pipes fuse to form a weld.

(17) A calcium-aluminum alloy containing 25 wt % aluminium is used in Example 3. However other CaAl alloys containing from 10-50 wt % Al may be used.

(18) The method of forge welding as applied to pipe sections is illustrated schematically in FIGS. 1a to 1f.

(19) In FIG. 1a two pipe sections 1 and 2 are shown in partial elevation. Both pipe sections 1, 2 have profiled ends 4, 6, (bevelled in this example). The lower pipe section 1 is held in a jig (not shown) and has an exothermic flux ring 8 (not shown in this figure but see FIG. 1b) located on top of end 4. Pipe section 2 is located above and in alignment with pipe section 1, by means of an appropriate jig.

(20) An induction heating coil (not shown, for clarity) is located around the pipe ends 4,6 and exothermic flux ring 8. Heating by use of the induction coil ignites the flux ring 8 and the upper pipe section 2 is advanced as indicated by arrow A downwards to squeeze out the molten flux formed from the flux ring 8. The molten flux cleans the pipe ends 4,6 removing oxides from their surfaces and preventing ingress of oxygen or air.

(21) The process is continued until the pipe sections contact at 12 as shown in FIG. 1 c. At this stage the molten flux has been driven out from between the contacting pipe surfaces, and the temperature is suitable for forge welding (about 800 to 1200 C. typically). Motion A is continued to provide a forging force between pipe sections 1,2 as suggested by arrow B in opposition to arrow A; and arrow C indicating the outwards direction of softened pipe material from the contact area 12. it will be appreciated that there may also be some inwards (towards the centre of the pipe) movement of material as the forge force is applied.

(22) FIG. 1d shows the finished weld between pipe sections 1 and 2, indicated by dashed lines 14. By selection of appropriate pipe end profiling, size and type of exothermic flux ring and application of forge force, a smooth joint, requiring little post welding treatment (such as removal of remaining flux and or excess metal at the joint) may be produced. If required or desired the method may also include heating and cooling treatments following the initial welding step to improve the quality of the join.

(23) FIG. 1e shows the exothermic flux ring 8 of FIG. 1b in plan view and the shape of the ring 8, to conform with the bevelled edges 4,6 is more clearly seen in cross section elevation along X-X (FIG. 1f). The cross section 10 of the ring 8 is shaped to fit about the bevelled pipe ends 4,6.

(24) In FIG. 2 a process similar to that shown in FIG. 1 is illustrated schematically. An oil well drilling platform 16 has a drilling pipe 1 (drill string) extending downwards from it in the usual fashion. The pipe 1 requires another pipe section 2 to be fitted to allow drilling to greater depth to continue. (The drill driver etc will be conventional and are not shown in this illustration). The new pipe section 2 has been hoisted into position above pipe 1 (hoist indicated by line 18). The two pipes 1,2 to be joined are held a forge welding machine, not shown in detail but indicated by dashed line 20. The machine includes a jig or jigs to hold the pipe ends in position and to drive pipe 2 towards pipe 1 as required. The machine 20 also includes heating means (such as an induction coil) to heat pipe ends 4,6 and the exothermic flux ring employed (not shown). Cooling means such as water or gas may also be provided. The machine 20 may also have an integral ultrasonic or other non-destructive testing means fitted to test completed joins. A controller indicated schematically by box 22 controls the operation of machine 20. In use machine 20 carries out a forge welding process similar to that shown in FIG. 1. By this means rapid and secure joining of new pipe sections to the drill string may be achieved in drilling operations. Typical weld times achieved in testing may be from say 5 to 12 minutes, including the time to load a new pipe section into place and, following welding to become ready for drilling operations again.

(25) FIG. 3 is a flow diagram illustrating the preparation of a solid unit of exothermic flux material, for example the flux rings discussed above in examples 1 and 2. The constituent powders are weighed 24 and then mixed intimately together 26. The intimate mixing is typically carried out by methods such as tumbling together in a suitable drum or other mixing vessel. Ball milling may also be employed. The mixture is then loaded into a suitable mould or dies 28 before being pressed 30 into the desired shape, such as a ring for use in joining pipes. The pressed solid unit, typically 50 to 80% of the theoretical density is then heat treated 32 to form the finished solid unit. The heat treatment 32 is designed to melt the boron oxide fully or partially depending on the amount of boron oxide in the mixture. This can increase the mechanical strength of the ring, allowing for easier handling.

(26) FIG. 4 show schematically an example of profiling of pipe ends suitable for the forge welding procedures of the invention. FIG. 4a shows a pipe section 1 viewed looking at an end 4, which is profiled with a radial male shape ending in a convex curve.

(27) The pipe section is shown in cross section, along line AA, in FIG. 4b with a magnified detail of the end 4 cross section surface (circled part X) shown in FIG. 4c. As can be seen in FIG. 4c the profile of pipe end 4 includes a bevelled portion 34 on outer wall 36 and a somewhat less bevelled portion 38 (of shallower angle and shorter length) on inner wall 40. The outer edge of the profile (the pipe wall viewed in cross section) of pipe end 4 is concluded by two parallel short portions 42, 44 and a convex end face 46.

(28) When joining two pipe ends having the profiling of FIG. 4c, an exothermic flux ring 8 having two concave grooves 48 as shown in partial cross section FIG. 4d may be employed. The method proceeds as discussed above with reference to FIG. 1 or 2. On heating and ignition of exothermic flux ring 8 and appropriate advancing of the pipe ends 4 and 6 towards each other the convex end faces 46 will first contact each other at the outermost points 50 on their surfaces.

(29) As the forge force (suggested by arrows A and B) is applied and the heat softened pipe ends 4,6 distort and fuse together the molten flux will be squeezed outwards from the forming joint and metal at the contact area will also tend to be forced outwards as suggested by arrows C and D, thickening the pipe walls at the forming joint. The bevelled portions 34 and 38 of the pipe ends will accommodate at least some of this thickening, mitigating or even preventing the joint from having a larger diameter than the original pipe diameter. After cooling and any heat treatment cycles applied to improve the quality of the joint are completed, the joint may be finished by cleaning or abrading as desired or required.

(30) FIGS. 5a and 5 b illustrate schematically another example of profiling of pipe ends suitable for the forge welding procedures of the invention. In this example a vertical forging operation is being carried out.

(31) FIG. 5a shows the schematic partial cross section profile of two pipe ends 4 and 6 in a similar view to that of FIG. 4d. The upper pipe end 4 has a male radial shape, including bevels 34,38 and a convex end face 46 on its wall. The lower pipe end 6 has two bevels 34,38 and a female radial shape with a concave end face 52. An exothermic flux ring 8 is not shown in any detail but suggested by dashed line. The flux ring is formed to fit the profiles of the pipe ends as discussed before.

(32) FIG. 5b the same two pipe ends 4,6 in similar partial cross section detail view to that of FIG. 5a but during a forge welding process after ignition of the exothermic flux ring and as the two ends 4,6 are being forced together by the forge force suggested by arrows A and B. Molten flux will tend to be retained in the concave end face 52 of the wall of lower pipe end 6, bathing the surfaces that are to be fused together in the molten flux, allowing more heat transfer and efficient cleaning of the metal surfaces.

(33) The radius of the concave 52 profiling on the lower end 6 is larger than that of the convex profiling 46 on the upper end 6 to make sure the molten flux can be readily squeezed out in the subsequent forging operation as suggested by arrows 54.

(34) FIG. 6a shows two pipe ends, 4,6 in similar partial cross section detail view to that of FIG. 5b. The pipe ends 4,6 are in contact as a forge force suggested by arrows A and B is being applied. In this example the upper of the two pipe ends 4 has a profile that slopes backwards, from the inside of the pipe wall 40 at its very end 55 towards the outside of the pipe wall 36, to guide the molten flux and any Impurities away from the bond line, where the join is made, to the outside of the pipe. This squeezing out of the molten flux is indicated by arrow 54. In this way the majority of the flux is directed to the outside of the pipe where removal of material adhering to the pipe after joining is easier. It will be appreciated that the profile employed in such embodiments of the invention need not be a flat bevel 56 sloping radially outwards as indicated in FIG. 6a but may have for example a convex curvature sloping backwards and away from the inside wall at the end of the pipe.

(35) In FIG. 6b a view comparable to that of FIG. 6a is shown, but in this example both pipe ends 4,6 are profiled to direct (arrow 54) molten flux towards the outside wall 36 of the pipe as the forge force is applied.

(36) It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

(37) Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.