CA2047638A1 - Miab welding machine - Google Patents
Miab welding machineInfo
- Publication number
- CA2047638A1 CA2047638A1 CA 2047638 CA2047638A CA2047638A1 CA 2047638 A1 CA2047638 A1 CA 2047638A1 CA 2047638 CA2047638 CA 2047638 CA 2047638 A CA2047638 A CA 2047638A CA 2047638 A1 CA2047638 A1 CA 2047638A1
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- CA
- Canada
- Prior art keywords
- pipe
- pipes
- clamping means
- welding
- housing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Abstract
MIAB WELDING MACHINE
ABSTRACT OF THE DISCLOSURE
An apparatus for magnetically impelled arc butt welding (MIAB), particularly for welding pipes, is described. The welding head of the apparatus is disposed outside the pipe being welded. The apparatus has a pair of clamps which are operable so as to receive the pipes from above (i.e., the clamps open in an upward direction, so the pipes may be lowered into the apparatus).
A MIAB welding method for welding pipes is also described. The method requires that the pipe movement be monitored during the forging step of the welding. By monitoring the pipe movement, the amount of pipe which is lost as "upset" during the welding operation may be calculated.
ABSTRACT OF THE DISCLOSURE
An apparatus for magnetically impelled arc butt welding (MIAB), particularly for welding pipes, is described. The welding head of the apparatus is disposed outside the pipe being welded. The apparatus has a pair of clamps which are operable so as to receive the pipes from above (i.e., the clamps open in an upward direction, so the pipes may be lowered into the apparatus).
A MIAB welding method for welding pipes is also described. The method requires that the pipe movement be monitored during the forging step of the welding. By monitoring the pipe movement, the amount of pipe which is lost as "upset" during the welding operation may be calculated.
Description
2~763~
FIELD OF THE INVENTION
This invention relates to Magnetically Impelled Arc Butt welding (or "MIAB" welding") for joining pipes. This invention is particularly suitable for joining large diameter pipes (having a diameter greater than 150mm).
BACRGROUND OF THE INVENTION
MIAB is well established for joining thin wall tubular sections of thickness less than 1 mm and diameter less than 30 mm in mild steel, such as for low pressure pipe connections. Also this process has been used for thicker wall hollow sections up to 4 mm thickness for pipes and tubes of some 50 mm diameter. The MIAB technique has been extended to thicker wall pipes by orbiting one end with respect to the other in order to enable the arc to seep across the entire cross-section of the faying surfaces.
This technique has been used for welding thick walled pipes of up to 8 mm wall thickness and 150 mm diameter. Such cross-sections, however, can only be welded successfully by the orbiting technique and not by the conventional process, where the opposing ends are held co-axial with each other.
Examples of MIAB welding machines are disclosed in U.S.
patent 3,882,299 (Sciaky); 3,937,916 (Sciaky); 3,980,857 (Sciaky); 4,136,980 (Pache et al); 4,319,123 (Pache et al);
4,443,686 Pache et al); 4,273,986 (Edson et al); 4,219,722 (Rudd et al); and 4,246,464 (Altsetter et al).
Prior MIAB welding machines have been proposed for both shop work (i.e. a fixed-in-place machine~ and field work (i.e. a portable machine. In general, the portable machines of the prior art are designed to be lowered onto the pipes being welded and hence have clamping systems which open and close at a position below the pipes being welded together.
Thus, when a weld is completed, the clamps are disengaged and the MIAB welding machine is lifted off of the pipes.
Such machines have an inherent safety disadvantage when used with large diameter pipe, namely that it is necessary to observe the underside of the pipe in order to determine whether the clamping means are properly engaged (thus exposing the observer to the risk of injury if the pipe falls out of the machine or if the machine slips from its support).
Accordingly, it is an object of this invention to provide a portable MIAB machine in which the clamping means are operable so that the pipe may be lowered into the machine (i.e. as opposed to having the machine lowered onto the pipe).
MIAB welding typically produces a characteristic weld "upset" along the weld line (i.e. the "upset" is a ridge of metal, resulting from the application of forging pressure to the abutting ends of the pipes during the welding procedure). As this upset represents lost pipe material (and as this loss may be significant during the construction 20~76~8 of a long pipeline), it is desirable to minimize it.
Accordingly, it is another object of this invention to provide a MIAB welding process in which this weld upset is monitored.
~UMMARY OF THB INVENTION
In one embodiment of the invention, there is provided: a portable magnetically impelled arc butt welding apparatus for welding a joint between the adjacent ends of two pipes, said apparatus having a housing, a magnetically impelled electric arc welding head disposed outside of said pipes, first pipe clamping means and second pipe clamping means which are movably attached to said housing, wherein said first pipe clamping means and said second pipe clamping means are operable so as to receive said pipes from above said housing.
In another embodiment of the invention, there is provided: a method for magnetically impelled arc butt welding apparatus for welding a joint between the adjacent ends of two pipes, said method consisting of (a) clamping a first pipe with first clamping means, (b) establishing a zero datum condition by clamping a second pipe with second clamping means and positioning said second pipe in close proximity to said first pipe so as to establish a small gap between said pipes; (c~ generating a first signal corresponding said zero datum conditions and transmitting said first signal to a programmable controller; (d) 20~7638 establishing a magnetic field within said gap; (e) striking a welding arc between said pipes; (f) actuating a hydraulically driven forge so as to apply a forging pressure along the axial lengthwise direction of said pipes such that said pipes are forged together; (g) monitoring the movement of said pipes during the application of said forging pressure; and (h) generating a second signal corresponding to the movement of said pipes and transmitting said second signal to said programmable controller.
Embodiments of the invention will now be described in detail by way of example with reference to the non-limiting drawings, in which:
Figure 1 is an isometric view of an apparatus according to the invention.
Figures 2, 3 and 4 are views of electromagnetic systems which may be employed in this invention.
Figure 5 is a view of a permanent magnet system which may be employed in this invention.
Figure 6 is a sectional view of a pipe clamp having a castellated profile.
Figure 7 is an end view showing the clamps of a four clamping component pipe clamping system.
Figure 8 is an end view of a pipe clamping system having a positive engagement point located above the pipes.
Figure 9 is an end view of an alternative pipe clamping 20~7~38 system having a positive engagement point located above the pipes.
The MIAB process relies on the principle of establishing a magnetic field or a component thereof, at right angles to the path of the current in the arc, so that motion is obtained in the third axis. This motion is applied to the current carrying conductor, in this case an electrical arc. With a suitably arranged radial field, the arc can be made to travel in a circular direction, as shown.
Thus, in the case of circularly symmetrical components, such as pipes or tubes, and with the components separated a short distance and supporting an electric arc between them, then the application of a radial field (i.e. with respect to the circular components) will cause the arc to rotate around the abutting or adjacent faces of such tubes.
As commonly practised, the MIAB equipment as used for joining pipes of relatively thin wall and small diameter is equipped with electro-magnetic coils which generate longitudinal magnetic flux in the pipes such that the opposing faces are of the same magnetic polarity giving rise to a divergent and particularly a radial field in the vicinity of the gap between the opposing pipe ends. Then with an arc struck between the two components and with a sufficient field strength and arc current, the arc is forced to move in the circum~erential direction and rotate around the pipe axis between the abutting ends. However, in the 20~7638 intended application to pipelines and the like, it is inconvenient to use solenoid type magnetic coils, which have to be wound around the pipe. Thus, the magnet system is arranged such that a pipe component, particularly of extensive length, can be withdrawn laterally from the apparatus. In particular, for use as in pipeline laying, it is convenient to have a self-contained apparatus, which provides not only for lateral access and removal from the pipe system, but also for aligning a further pipe section to an existing pipeline, without relying on reference to ground levels and the like.
One example of an apparatus, according to the invention, is shown in Figure 1, where the overall machine (10) comprises clamping means for attachment to the circular pipe (20), together with means for aligning a further pipe section (21), to be butted against the existing pipe. Thus, according to the invention, a housing (11) i5 provided, for example with tie bars (12, 13) on which are mounted both clamping means (16, 17 together with 18, 19) for holding the existing pipe (20) and the additional pipe (21) in alignment one with the other.
As will be apparent from Figure 1, the clamping means (16, 17, 18 and 19) open in an upwards direction so as to receive the new piece of pipe to be joined from above. That is, the clamping means are open towards the sky. This configuration is different from conventional portable MIAB
machines which are lowered onto the pipes (and hence these machines open in a downwards direction welding, so as to receive the pipes from below). The present MIAB welding apparatus provides a safety feature in that it is possible to readily establish by visual observation from above whether the clamping means are properly engaged. In contrast, the conventional configuration of portable MIAB
welding machines typically request a worker to crawl underneath the machine to determine whether the clamping means are engaged.
For aligning the existing pipe (20~ with respect to the machine housing (11), a pipe positioning bar (14) is positioned as shown in Figure 1, and the end of pipe (20) is butted against the positioning bar (14) prior to closing the clamps (18, 19). The pipe positioning bar (14) is pivotally attached to the housing (11) via tie bar (12). The pivotal attachment joint (14a) is fixed with respect to the lengthwise axis of the housing (11) (i.e. the pivotal attachment joint does not move along the length of the tie bar (12)). Pipe component (21) is brought into close proximity to existing pipe (20), so that the adjacent ends of the two pipes form a small gap. Thus, the position of this gap is fixed with respect to the lengthwise axis of the housing (11) by the pipe positioning bar (14).
As shown in Figure 1, the magnet system (15) is pivotally attached to the housing (11) via the tie bar (13), but the pivot point position of the magnet system (15) is fixed with respect to the lengthwise axis of the housing (ll) (i.e. the magnet system (15) does not move long the length of the tie bar (13)). (A more detailed description of the clamping system is given with respect to Figures 8 and 9 below).
Having clamped the machine with respect to the first pipe (20) the pipe positioning bar (14) is removed and the additional pipe (21) brought up to butt pipe (20) and held in position by clamps (16, 17). In operation, the pipe component (21) is separated from the pipe (20) a short distance during the arcing stage and then is subsequently butted firmly against pipe (20) to complete the forge weld.
For convenience of presentation the actuating rams for the clamps (16, 17, 18, and 19) are not shown, nor the means for the longitudinal movement, where at least one pair of clamps are moved with respect to the other axially, along of the tie bars (12, 13). In addition, means are not shown for removing the pipe positioning bar (14) out of the system, nor for inserting the magnet system (15) into proximity with the circular pipe in order to obtain the required arc rotation about the pipe end. It should be noted that by means of the housing (11) and associated tie bars (12, 13) the apparatus is aligned with respect to one pipe component and allows for a second pipe component to be aligned with the first. The housing (11) preferably contains all the required actuators and connectors providin~ hydraulic control of the actuating rams.
For large diameter pipes, it is especially preferred to employ a hydraulic fluid accumulator (not shown) in the hydraulic system used to actuate the opening and closing of the clamps. In the absence of such an accumulator, the apparatus may be prone to excessive vibrations during transient conditions (As used herein, the term "hydraulic fluid accumulator" is meant to refer to its conventional meaning, namely a device which is used for surge control in high volume flow hydraulic systems. Such accumulators normally consist of a shell having a generally cylindrical shape, and a pressurized bladder contained within the shell.
The bladder is fabricated from a flexible material (e.g.
nitrile rubber) and is precharged with a compressible gas (i.e. nitrogen) to a pressure suitable for the system. When the hydraulic pump in the system forces hydraulic fluid into the accumulator, the gas in the bladder is compressed, and the pressure in the bladder this increases. The deformation/compression of the bladder ceases when the pressure of the hydraulic fluid balances the pressure of the gas within the bladder. When there is a subsequent demand for the hydraulic fluid, the pressure in the system is reduced and the hydraulic fluid flows into the system under the pressure exerted by the compressed gas in the bladder.
such "accumulators" are well known and are commercially 2~47~38 available from sources including tOil Air Hydraulics Inc. of Houston, Texas).
As previously noted, at least one pair of clamps is movable with respect to the other axially, along the tie bars. This axial movement provides the foregoing force requirement to complete the weld. It is preferred that only one pair of the clamps move in the axial direction, so as to minimize the number of operations which must be controlled.
Furthermore, it is highly preferred that the hydraulic system used to actuating the above described forging force also contains a hydraulic fluid accumulator.
As will be appreciated, the complete welding apparatus is self-contained and can be readily manipulated or slung from, for example, a crane into the desired position with respect to the pipe or pipeline. It is also noted that the butting force for forging the pipe component (21) onto the existing pipe (20) is obtained via the clamping system and does not rely on an end stop or end longitudinal actuator attached to the extremity of the pipe.
MIAB welding requires both of a magnet system and an electric arc system. Accordingly, the term "welding head"
used herein is mean to include the combination of the magnet system and the electric arc system. Details regarding the electric arc system and magnet system are given below.
It is preferred to provide an electric arc by simply passing a current through the clamps (16, 17, 18, and 19).
This can be readily accomplished by fabricating the clamps from an electrically conducting material (such as a ferritic material) and wiring each of them to an electrical source (not shown). It is especially preferred that the wires used for this purpose arc have substantially the same electrical resistance and are connected in parallel to a common electrical power supply, so that an essentially equivalent current is applied to each clamp.
The clamps (16, 17, 18 and 19) are provided with circular faces (22), such that the internal clamping surfaces are curved so as to substantially match the curvature of the outer surface of the circular components and which when closed provide substantially continuous contact with the exterior of the pipe with only small gaps (23) between the faces of the jaws (22) as shown in Figure 7.
Preferably the magnetic field is applied in the form of a doughnut shape surrounding the pipe, as generated by a series of permanent magnets or electro-magnets polarised to present a face with a single polarity surrounding the pipe concerned. Preferably the permanent magnets or electro-magnets are associated with the clamping means such as via the tie bars (12, 13) so as to surround the pipe at a nominally constant distance from the pipe surface.
Conveniently, with four clamps surrounding the pipe the corresponding magnet systems provide substantially a continuous magnetie pole surrounding the pipe. The return magnetic circuit via the pipe eomponents and the surrounding apparatus of ferritic material may be supplemented by ferritic material embraeing the magnet or electro-magnet on one or all sides apart from the side facing the pipe exterior. It will be apparent from Figure 1 that the welding head (i.e. the magnet system and the electrie are system, eolleetively) are disposed outside of the pipes.
As illustrated in Figure 2 for use with large pipe seetions in exeess of 150 mm diameter, especially those of 200 or even some 300 mm diameter, the magnet system (30) preferably comprises a plurality of similar magnet blocks (31) presenting a virtually eontinuous profile in terms of field strength about the circumference of the section to be butt welded. In partieular, the overall magnet system (30) preferably, comprises 4 groups of eleetro-magnets with preferably more than one eleetro-magnet (32) per quadrant.
Conveniently 2 or 3 electro-magnetic coils (32) exciting corresponding eores (33) whieh are connected together via a eommon pole piece (34) are eonneeted to a suitable energising souree (not shown). The source may be of a eommon potential and all the eleetro-magnet eoils paralleled as they are of substantially the same resistance.
Alternatively, the groups of 2 or 3 coils may be eonneeted in series and each set eonnected in parallel to a common voltage souree. Again, alternatively, corresponding coils from each quadrant may be connected in series and each set of four such coils connected to a common voltage source.
These connections are a + b + c (or al + a2 + a3 + a4 and so forth).
Conveniently, the magnetic pole facing the pipe exterior may be covered with protective layer such as stainless steel or copper sheet to avoid direct impingement of spatter from the weld zone. Equally the magnet, particularly in the case of a permanent magnet, may be protected by a non-thermally conducting layer for thermal insulation to avoid excessive temperature rise from the heated pipe ends and the rotating arc. Moreover, suitable heat sinks can be provided adjacent to the magnet to assist in avoiding excessive temperature rise. A suitable magnetic material for the permanent magnets is a polymer bonded rare earth magnet metal. The term rare earth metal is meant to convey its conventional meaning, namely the elements of the Periodic Table which are also referred to Lanthanides (especially Nd and Ce). These magnets are preferably glued or bonded into the system with a polymeric adhesive. For example, as shown in cross-section in Figure 3, the electro-magnet (33, 34) is positioned at a short distance away from the exterior of the component (20, 21) and arranged such that the flux from the pole-piece is returned via the wall of the component to the surrounding ferro-magnetic case (35, 36) of the electro-magnet. The internal face of the magnet 20~7638 system is covered with a suitable protective layer (38) to prevent spatter adhering to the magnet or potentially damaging the coils (32). The magnet system is carried on a suitable arm (37) in association with the clamping mechanism (not shown).
Preferably the aspect ratios of the magnet system should be such that the face of the magnet is substantially greater than the gap between the components to be joined and preferably of dimension at least 3 times the gap width.
Furthermore, a substantial air gap is provided between the magnet face and the exterior of the pipe being joined, such as in excess of 5 mm and preferably in excess of 8 mm such as lo mm. These dimensions define the two aspect ratios of magnet width to gap width and magnet separation to wall thickness of the pipe being joined. For example, the dimensions given are suitable for pipe wall thicknesses of 3 mm to 5 mm, and gap widths up to 3 mm. Thus as shown in Figure 4, the width (41) of the pole-piece in the axial direction transverse to the abutting face (40) should exceed at least 3 mm on either side of the gap. Preferably the width (41) of the pole-piece should be of the order of 5 mm on either side of the gap (40). Alternatively, the width should be at least one wall thickness T on either side of the gap and preferably of the order of l l/2 T on either side.
Equally, the width of the magnetic circuit (42, 43) on 20~7638 either side of the centre pole-piece (41) should be about half the width of the centre pole-piece to present a substantially symmetrical magnetic circuit and avoid magnetic saturation in the ferro-magnetic material.
Equally the separation (44) of the surface of the pole-pieces from the surface of the components to be joined should be of the same order as the width (41) of the pole-piece but preferably less, such as between 50% and 80~ of the width. Alternatively, the separation (44) should exceed the wall thickness T of the components (20, 21) to be joined preferably is in the range of 2T to 3T. In all cases the dimension (44) should preferably not exceed the dimension (41).
For permanent magnets as shown in Figure 5, the principal dimensions in the vicinity of the gap (40) are similar to those for the electro-magnet but in general a return circuit such as provided by the cheeks (35) of the electro-magnet are not required. Preferably, the permanent magnet (50) is mounted on a support (51) which is carried on a suitable arm (52). These latter are of ferro-magnetic material and can be proportioned to adjust the strength of the field in the region of the position of the gap (40) which is spaced at the distance (44) from the surface of the permanent magnet material.
In the case of polymer bonded rare earth magnets, the magnet material is preferably surrounded on either side and on the face nearest the component to be joined with thermally insulating material (53) to avoid the effects of radiated and convected heat from the magnetically impelled arc. Also the thermal insulation on the front face is particularly required to reduce the effects of radiation from the heated welded component. In addition to the thermal insulation (53), preferably a further layer (54) of material is used to limit or prevent the adherence of spatter from the arcing process. The material (54) may be a high thermal conductivity, such as copper or a temperature resisting material such as stainless steel.
For electro-magnets in place of the permanent magnets, preferably more than one excitation coil is provided on a suitable core to provide a sufficiently uniform excitation of the pole face. For example, with four magnet units embracing nominally 90 of the periphery, each unit can comprise two or more cores with exciting coils on each core.
For example, each individual electro-magnet coil may be rated at some 2,500 ampere turns (2.5A with 1,000 turns) and with 1 mm insulated copper wire the total voltage drop is of the order of 10 V giving 25 watts per coil at 100% duty cycle. For shorter duty cycles such as 1 in 10 or 1 in 20, the power dissipated per coil can be significantly increased without causing excessive temperature rise. The field strength in the region of the position of the components to be welded is preferably of the order of between 1,000 and 20~7638 2,000 gauss. For example, the field for a pipe of nominally 150 mm diameter is in the region of 1,400-1,600 gauss. The field for a larger diameter component, such as in excess of 250 mm diameter, is preferably of the order of 1,600-1,800 gauss. In general it is convenient to increase the field strength of the magnet system for larger diameters of components in order to maintain an adequate rate of rotation of the magnetically impelled arc at the preferred welding current. Moreover, fields in excess of gauss have been found suitable for welding pipe components of nominally 300 mm diameter.
Furthermore with both the permanent magnet and electro-magnet pole design, gas ports can be provided to enable suitable gas shields to be provided for the rotating arc to prevent excessive oxidation of the heated surfaces of the components being joined. Gaseous nitrogen is particularly suitable for this purpose.
The segmented magnet system not only allows, in its retracted position, for the pipe including the weld zone, to be threaded through, but also for the pipe to be completely detached from the welding head laterally out of the machine.
Accordingly, although the clamps open in an upwards direction for safety reasons (and thus the welding head can't be simply lifted off the pipes because a substantial portion of the apparatus is below the new weld in the pipes), the apparatus can be readily moved laterally along 20~7638 the pipeline to position it for the next weld.
The clamping system comprises a set of separate segments preferably at least 4, with facing surfaces of curvature matched to the pipe, within the limits of variation of the pipe as produced. Furthermore, to obtain an adequate grip, the internal surfaces of the clamps are preferably serrated or provided with a castellated profile, as illustrated, Figure 6. It is noted that the gripping reacts a longitudinally applied thrust and that each part of the serration is capable of elastically taking up a part of the total thrust. The surface (22) of the clamp is of relatively strong material, preferably with a yield strength in excess of 30kg/mm2 so that it resists deformation and has a sufficiently high elastic limit to allow thrusts of the order of 200 kg per millimetre of periphery of the pipe.
Apart from the castellated profile, the internal surface of the clamps is smooth and of a curvature substantially matching that of the exterior of the pipe to avoid significant surface indentation or distortion.
The clamps are arranged around the periphery of the pipe such that the gap between the segmented clamps is, on average, not more than about 3 mm and preferably at no stage exceeds 1% of the total circumference. Thus, overall the clamps surround the pipe to more than 95% of the circumference. Figure 7 indicates the definition of the overall degree of circumferential clamp. Thus with a clamping system comprising four segments (22) for surrounding the circular component (20, 21), the clamps are brought together such that there is a finite gap (23) between one clamp and the next. Preferably, the gap (23) is of the order 1 mm for smallest diameter of component to be gripped and does not exceed some 3 mm for the largest size of circular component. Equally, preferably any one gap (23) should not be zero or exceed some 5 mm. Where desirable, means can be provided between the segments (22) to allow for a more even distribution of the gap (23), such that the clamping is substantially symmetrical and hence distortion of a circular component is minimized.
The set of clamps can be relaxed sufficiently to allow the pipe components to be threaded through, including the weld zone. Furthermore, the clamping system opens in an upwards direction so as to receive the pipe from above. In other words, the welded pipe can be withdrawn laterally from the clamp, and the new pipe can be inserted laterally or from above.
In one arrangement with four operating and self-aligning clamps with one degree of freedom, one pair are arranged to interlock one with the other and the other pair arranged to press the pipe into the arc formed by the co-operatin~ pair, such that the pipe is substantially completely surrounded. One example of a suitable clamping arrangement is shown in Figure 8, in which the clamping 2~7638 mechanism (70) comprises two upper arms (71, 72) with pivots (73, 74) fixed to the support plate (79) and two further arms (75, 76) with pivots (77, 78) carried on actuators, not shown, with a direction of movement at nominally 45 to the vertical axis. To grip the pipe (20, 21) seen in end elevation, the upper arm (72) is first closed in the direction of the arrow (80), Figure 8a. Thereafter the co-operating upper arm (71) is closed to interlock with the arm (72~ such that the pin (82) on arm (72) falls within the hoo~ (81) of arm (71), as illustrated in Figure 8b.
Thus, the pin (82) and hook (71) form a positive engagement point that is located above the pipes. This is a safety feature, as the operator of the apparatus is readily able to visually determine that the clamps are engaged. (In contrast, prior MIAB welding machines which are lowered onto the pipes have a configuration which requires the clamps to engage at a location below the pipe).
To complete the locking arm (72) is preferably moved in the direction shown by the arrow (90) in order to present a nominally hemispherical surface for the circular components to be gripped via the faces (83, 84) on arms (71, 72) respectively. Thereafter the arms (75, 76) are moved in the direction shown in Figure 8c, at nominally 45 to the vertical, as given by arrows (87, 88) such that the clamping faces (85, 86) of arms (75, 76) locate the pipe and cause it to be centred as shown with respect to the support plate 20~7638 (79). It is noted that arms (71, 72) effectively locate the circular component in the transverse direction left or righ~
while the arms (75, 76) locate the circulate component in the upward direction, in co-operation with arms (71, 72).
It is also noted that the clamping faces (83, 84, 85 and 86) virtually surround the circular component completely with only small gaps between each nominal quadrant section.
These gaps are necessary to enable the circular component to be rightly gripped when it is smaller in diameter than the nominal size. To obtain a reasonable balance in the forces applied by the actuators to the arms (77, 78) the actuators are preferably hydraulically operated from a common pressurised supply. As previously noted, the hydraulic system used to operate the clamping system preferably includes a hydraulic fluid accumulator, particularly when the apparatus is used with large diameter pipes. In a further alternative the upward pressing clamps may be provided with more than one degree of freedom to allow for self-alignment, as shown in Figure 9. Here a pair of pivots are mounted on a common bridge, which in turn is pivoted.
Thus, as shown in Figure 9, the lower arms (75, 76) are pivoted respectively at (77, 78) on bell cranks (91, 92).
These in turn, are pivoted at (93, 94) on a oommon swivel (95) which is itself pivoted (96). Actuators as shown operating on pivots (97, 98) move the bell cranks (91, 92) in an upward direction so closing the arms (75, 76) around the circular pipe (20, 21). The swivel (95) allows for a degree of take-up between the two clamps (75, 76). Thus, although the actuators operating on pivots (97, 98) may be hydraulic rams, the further degree of freedom provided by the swivel (95) allows direct mechanical actuators such as screw jacks or cams, to operate on the ends of the bell cranks (91, 92).
Also in Figure 9 is shown an alternative arrangement for a positive engagement point of the upper clamp arms (71, 72). Here the clamp (71) is first closed in co-operation with the arm (72) such that the hook (81) passes under the pin (82). Again with outward movement of the arms (71 and/or 72) the pin (82) rests within the hook (81) and so defines the location of the circular component in an upward direction. Thereafter, the actuators on the bell cranks (91, 92) bring the lower arms (75, 76) into position encircling the pipe or circular component, as previously, and locating it with respect to the support plate (79).
These and other arrangements providing for opening of the clamping system and permitting complete withdrawal of the component in a lateral direction are within the scope of the invention as described.
For speed of operation hydraulically actuated clamps are preferred, but other convenient means can be provided, such as screw jacks or cam mechanisms.
Although, in principle, the MIAB process can be 2~47638 operated manually with butting and separating of the components to be welded to initially form the arc and thereafter with a suitable arc rotation and current level to butt the components together, it is preferable for the sequence of operations to be automatic to avoid error or any undue variation in time intervals. Furthermore it is preferable to monitor the sequence of operations and the operating levels of current, gap between components, time and (for electro-magnets) excitation current. This serves as an internal quality control and quality assurance.
Although the complete operation of the machine can be mechanised and supplemented with timers and the like, preferably the control system utilizes both hardware and software as appropriate, together with a suitable process computer. Preferably facilities are provided for two or more levels of arc current toqether with two or more levels of operating gap between the components to be joined and in the case of electro-magnets two or more levels of excitation current. For example, suitable operating conditions for nominally 12 in diameter pipe of 4.8 mm wall thickness are, current 1600 amperes, excitation 30 amperes, gap 2 mm, thrust (forge) 300 KNewtons and overall time 15 seconds.
In principle, the required applied load can be registered using load cells and the like but preferably the requisite loads are represented by pressure in the appropriate hydraulic system. However, in some cases pressure measuring devices need to be zeroed to overcome effects of drift over long periods of time. Therefore, preferably means are provided for registering zero operating conditions, such as at retraction or before the forge load is applied in hydraulic systems where the minimum pressure is not necessarily zero itself.
Such means may be hardware or software orientated but in principle detect the condition of non-operation and give an appropriate zero register to the controller.
Further details concerning a novel method to monitor/control a MIAB welding process are provided below.
As previously noted, it is desirable to establish zero datum conditions corresponding to the position of the clamped pipes, and the initial load on the hydraulic system, prior to the welding/forging operations (i.e. there may be a small load on the hydraulic system prior to the welding/forging operations). It is highly preferred to generate an electric signal corresponding to these zero datum conditions, and to forward the signal to a programmable logic controller ("PLC").
The welding/forging operations are then completed in the manner previously described. However, the movement of the pipes during the forging operation is also monitored.
In particular, it is desirable to monitor (a) the distance travelled by the pipes, and (b) the time elapsed during the forging operation, 20~763~
and to generate electric signals corresponding to (a) and (b) above. By transmitting these signals to a properly programmed PLC which PLC also contains data concerning the zero datum conditions), it is possible to calculate (a) weld upset (based on zero datum conditions combined with data defining the distance of pipe movement), and (b) forge velocity (based on zero datum conditions, combined with data concerning the distance of pipe movement, and the time required for same).
As previously noted, it is desirable to monitor weld upset so as to record the amount of pipe material which is lost during the welding operation.
Furthermore, it is highly desirable to monitor forge velocity because this parameter can often be correlated with weld quality.
Additional discussion of the forging operation is provided below.
The applied thrust for forging is arranged to avoid excess or sudden high axial loads, which could cause slip of the clamping system in an axial direction. Such control of the hydraulic system, including appropriate control of pressure build-up and collapse, are within the scope of the invention as applied to welding components with large enclosed areas and large butting cross-section as defined.
The use of a hydraulic fluid accumulator in a hydraulically 2047~38 driven forge system is particularly preferred for an apparatus used to join large diameter pipes.
For some applications the electro-magnetic system can be replaced with appropriate permanent magnets. The use of permanent magnets simplifies the operating sequence by removing one control variable. Thus only the gap between the components and the operating current need to be controlled when welding, and only the maximum forging pressure needs to be ~ontrolled after the arcing period.
Although applied to the automatic circumferential welding of line pipe, the technique can be appropriately adapted to tubes of limited length where either or both components can be brought together axially and for the tube profiles other than circular, such as elliptic or rectangular. For non-circular profiles the magnet system is adapted, particularly where there is a major change in curvature such as at the extremities of an ellipsoid shape or at the corners of a rectangular shape, so as to produce the necessary fields to maintain a sufficiently smooth arc movement around these zones. For these purposes, permanent magnets may be used for the major part of the periphery and local electro-magnets used which can be adjusted to the appropriate level for the desired arc movement.
Although the apparatus, according to the invention, is capable of being detached from a continuous pipe in a lateral direction it may also be passed along the pipe axially. (If this is desired, suitable rolls or wheels are provided to carry the apparatus about the pipe and which may be sprung or otherwise supported to allow the weld zone to pass through. Alternatively, the rolls may be set at a sufficient distance apart to provide adequate clearance for the welds.) The present apparatus is sufficiently portable to enable its use in the construction of pipelines used to transport natural gas, oil and the like. Thus, the overall dimensions of the apparatus are preferably such that pipe bends and natural flexing can be accommodated in passing the machine along the pipe length. These and other aspects of the overall lay out of the equipment are well known to those skilled in the art and do not constitute further invention.
Furthermore, the equipment can be designed for smaller pipe sizes by appropriate selection of jaw inserts to the clamping mechanism, together with appropriate position of the magnet system. Preferably, for efficiency of operation, the machine caters for a range of pipe sizes down to nominally half the maximum diameter.
FIELD OF THE INVENTION
This invention relates to Magnetically Impelled Arc Butt welding (or "MIAB" welding") for joining pipes. This invention is particularly suitable for joining large diameter pipes (having a diameter greater than 150mm).
BACRGROUND OF THE INVENTION
MIAB is well established for joining thin wall tubular sections of thickness less than 1 mm and diameter less than 30 mm in mild steel, such as for low pressure pipe connections. Also this process has been used for thicker wall hollow sections up to 4 mm thickness for pipes and tubes of some 50 mm diameter. The MIAB technique has been extended to thicker wall pipes by orbiting one end with respect to the other in order to enable the arc to seep across the entire cross-section of the faying surfaces.
This technique has been used for welding thick walled pipes of up to 8 mm wall thickness and 150 mm diameter. Such cross-sections, however, can only be welded successfully by the orbiting technique and not by the conventional process, where the opposing ends are held co-axial with each other.
Examples of MIAB welding machines are disclosed in U.S.
patent 3,882,299 (Sciaky); 3,937,916 (Sciaky); 3,980,857 (Sciaky); 4,136,980 (Pache et al); 4,319,123 (Pache et al);
4,443,686 Pache et al); 4,273,986 (Edson et al); 4,219,722 (Rudd et al); and 4,246,464 (Altsetter et al).
Prior MIAB welding machines have been proposed for both shop work (i.e. a fixed-in-place machine~ and field work (i.e. a portable machine. In general, the portable machines of the prior art are designed to be lowered onto the pipes being welded and hence have clamping systems which open and close at a position below the pipes being welded together.
Thus, when a weld is completed, the clamps are disengaged and the MIAB welding machine is lifted off of the pipes.
Such machines have an inherent safety disadvantage when used with large diameter pipe, namely that it is necessary to observe the underside of the pipe in order to determine whether the clamping means are properly engaged (thus exposing the observer to the risk of injury if the pipe falls out of the machine or if the machine slips from its support).
Accordingly, it is an object of this invention to provide a portable MIAB machine in which the clamping means are operable so that the pipe may be lowered into the machine (i.e. as opposed to having the machine lowered onto the pipe).
MIAB welding typically produces a characteristic weld "upset" along the weld line (i.e. the "upset" is a ridge of metal, resulting from the application of forging pressure to the abutting ends of the pipes during the welding procedure). As this upset represents lost pipe material (and as this loss may be significant during the construction 20~76~8 of a long pipeline), it is desirable to minimize it.
Accordingly, it is another object of this invention to provide a MIAB welding process in which this weld upset is monitored.
~UMMARY OF THB INVENTION
In one embodiment of the invention, there is provided: a portable magnetically impelled arc butt welding apparatus for welding a joint between the adjacent ends of two pipes, said apparatus having a housing, a magnetically impelled electric arc welding head disposed outside of said pipes, first pipe clamping means and second pipe clamping means which are movably attached to said housing, wherein said first pipe clamping means and said second pipe clamping means are operable so as to receive said pipes from above said housing.
In another embodiment of the invention, there is provided: a method for magnetically impelled arc butt welding apparatus for welding a joint between the adjacent ends of two pipes, said method consisting of (a) clamping a first pipe with first clamping means, (b) establishing a zero datum condition by clamping a second pipe with second clamping means and positioning said second pipe in close proximity to said first pipe so as to establish a small gap between said pipes; (c~ generating a first signal corresponding said zero datum conditions and transmitting said first signal to a programmable controller; (d) 20~7638 establishing a magnetic field within said gap; (e) striking a welding arc between said pipes; (f) actuating a hydraulically driven forge so as to apply a forging pressure along the axial lengthwise direction of said pipes such that said pipes are forged together; (g) monitoring the movement of said pipes during the application of said forging pressure; and (h) generating a second signal corresponding to the movement of said pipes and transmitting said second signal to said programmable controller.
Embodiments of the invention will now be described in detail by way of example with reference to the non-limiting drawings, in which:
Figure 1 is an isometric view of an apparatus according to the invention.
Figures 2, 3 and 4 are views of electromagnetic systems which may be employed in this invention.
Figure 5 is a view of a permanent magnet system which may be employed in this invention.
Figure 6 is a sectional view of a pipe clamp having a castellated profile.
Figure 7 is an end view showing the clamps of a four clamping component pipe clamping system.
Figure 8 is an end view of a pipe clamping system having a positive engagement point located above the pipes.
Figure 9 is an end view of an alternative pipe clamping 20~7~38 system having a positive engagement point located above the pipes.
The MIAB process relies on the principle of establishing a magnetic field or a component thereof, at right angles to the path of the current in the arc, so that motion is obtained in the third axis. This motion is applied to the current carrying conductor, in this case an electrical arc. With a suitably arranged radial field, the arc can be made to travel in a circular direction, as shown.
Thus, in the case of circularly symmetrical components, such as pipes or tubes, and with the components separated a short distance and supporting an electric arc between them, then the application of a radial field (i.e. with respect to the circular components) will cause the arc to rotate around the abutting or adjacent faces of such tubes.
As commonly practised, the MIAB equipment as used for joining pipes of relatively thin wall and small diameter is equipped with electro-magnetic coils which generate longitudinal magnetic flux in the pipes such that the opposing faces are of the same magnetic polarity giving rise to a divergent and particularly a radial field in the vicinity of the gap between the opposing pipe ends. Then with an arc struck between the two components and with a sufficient field strength and arc current, the arc is forced to move in the circum~erential direction and rotate around the pipe axis between the abutting ends. However, in the 20~7638 intended application to pipelines and the like, it is inconvenient to use solenoid type magnetic coils, which have to be wound around the pipe. Thus, the magnet system is arranged such that a pipe component, particularly of extensive length, can be withdrawn laterally from the apparatus. In particular, for use as in pipeline laying, it is convenient to have a self-contained apparatus, which provides not only for lateral access and removal from the pipe system, but also for aligning a further pipe section to an existing pipeline, without relying on reference to ground levels and the like.
One example of an apparatus, according to the invention, is shown in Figure 1, where the overall machine (10) comprises clamping means for attachment to the circular pipe (20), together with means for aligning a further pipe section (21), to be butted against the existing pipe. Thus, according to the invention, a housing (11) i5 provided, for example with tie bars (12, 13) on which are mounted both clamping means (16, 17 together with 18, 19) for holding the existing pipe (20) and the additional pipe (21) in alignment one with the other.
As will be apparent from Figure 1, the clamping means (16, 17, 18 and 19) open in an upwards direction so as to receive the new piece of pipe to be joined from above. That is, the clamping means are open towards the sky. This configuration is different from conventional portable MIAB
machines which are lowered onto the pipes (and hence these machines open in a downwards direction welding, so as to receive the pipes from below). The present MIAB welding apparatus provides a safety feature in that it is possible to readily establish by visual observation from above whether the clamping means are properly engaged. In contrast, the conventional configuration of portable MIAB
welding machines typically request a worker to crawl underneath the machine to determine whether the clamping means are engaged.
For aligning the existing pipe (20~ with respect to the machine housing (11), a pipe positioning bar (14) is positioned as shown in Figure 1, and the end of pipe (20) is butted against the positioning bar (14) prior to closing the clamps (18, 19). The pipe positioning bar (14) is pivotally attached to the housing (11) via tie bar (12). The pivotal attachment joint (14a) is fixed with respect to the lengthwise axis of the housing (11) (i.e. the pivotal attachment joint does not move along the length of the tie bar (12)). Pipe component (21) is brought into close proximity to existing pipe (20), so that the adjacent ends of the two pipes form a small gap. Thus, the position of this gap is fixed with respect to the lengthwise axis of the housing (11) by the pipe positioning bar (14).
As shown in Figure 1, the magnet system (15) is pivotally attached to the housing (11) via the tie bar (13), but the pivot point position of the magnet system (15) is fixed with respect to the lengthwise axis of the housing (ll) (i.e. the magnet system (15) does not move long the length of the tie bar (13)). (A more detailed description of the clamping system is given with respect to Figures 8 and 9 below).
Having clamped the machine with respect to the first pipe (20) the pipe positioning bar (14) is removed and the additional pipe (21) brought up to butt pipe (20) and held in position by clamps (16, 17). In operation, the pipe component (21) is separated from the pipe (20) a short distance during the arcing stage and then is subsequently butted firmly against pipe (20) to complete the forge weld.
For convenience of presentation the actuating rams for the clamps (16, 17, 18, and 19) are not shown, nor the means for the longitudinal movement, where at least one pair of clamps are moved with respect to the other axially, along of the tie bars (12, 13). In addition, means are not shown for removing the pipe positioning bar (14) out of the system, nor for inserting the magnet system (15) into proximity with the circular pipe in order to obtain the required arc rotation about the pipe end. It should be noted that by means of the housing (11) and associated tie bars (12, 13) the apparatus is aligned with respect to one pipe component and allows for a second pipe component to be aligned with the first. The housing (11) preferably contains all the required actuators and connectors providin~ hydraulic control of the actuating rams.
For large diameter pipes, it is especially preferred to employ a hydraulic fluid accumulator (not shown) in the hydraulic system used to actuate the opening and closing of the clamps. In the absence of such an accumulator, the apparatus may be prone to excessive vibrations during transient conditions (As used herein, the term "hydraulic fluid accumulator" is meant to refer to its conventional meaning, namely a device which is used for surge control in high volume flow hydraulic systems. Such accumulators normally consist of a shell having a generally cylindrical shape, and a pressurized bladder contained within the shell.
The bladder is fabricated from a flexible material (e.g.
nitrile rubber) and is precharged with a compressible gas (i.e. nitrogen) to a pressure suitable for the system. When the hydraulic pump in the system forces hydraulic fluid into the accumulator, the gas in the bladder is compressed, and the pressure in the bladder this increases. The deformation/compression of the bladder ceases when the pressure of the hydraulic fluid balances the pressure of the gas within the bladder. When there is a subsequent demand for the hydraulic fluid, the pressure in the system is reduced and the hydraulic fluid flows into the system under the pressure exerted by the compressed gas in the bladder.
such "accumulators" are well known and are commercially 2~47~38 available from sources including tOil Air Hydraulics Inc. of Houston, Texas).
As previously noted, at least one pair of clamps is movable with respect to the other axially, along the tie bars. This axial movement provides the foregoing force requirement to complete the weld. It is preferred that only one pair of the clamps move in the axial direction, so as to minimize the number of operations which must be controlled.
Furthermore, it is highly preferred that the hydraulic system used to actuating the above described forging force also contains a hydraulic fluid accumulator.
As will be appreciated, the complete welding apparatus is self-contained and can be readily manipulated or slung from, for example, a crane into the desired position with respect to the pipe or pipeline. It is also noted that the butting force for forging the pipe component (21) onto the existing pipe (20) is obtained via the clamping system and does not rely on an end stop or end longitudinal actuator attached to the extremity of the pipe.
MIAB welding requires both of a magnet system and an electric arc system. Accordingly, the term "welding head"
used herein is mean to include the combination of the magnet system and the electric arc system. Details regarding the electric arc system and magnet system are given below.
It is preferred to provide an electric arc by simply passing a current through the clamps (16, 17, 18, and 19).
This can be readily accomplished by fabricating the clamps from an electrically conducting material (such as a ferritic material) and wiring each of them to an electrical source (not shown). It is especially preferred that the wires used for this purpose arc have substantially the same electrical resistance and are connected in parallel to a common electrical power supply, so that an essentially equivalent current is applied to each clamp.
The clamps (16, 17, 18 and 19) are provided with circular faces (22), such that the internal clamping surfaces are curved so as to substantially match the curvature of the outer surface of the circular components and which when closed provide substantially continuous contact with the exterior of the pipe with only small gaps (23) between the faces of the jaws (22) as shown in Figure 7.
Preferably the magnetic field is applied in the form of a doughnut shape surrounding the pipe, as generated by a series of permanent magnets or electro-magnets polarised to present a face with a single polarity surrounding the pipe concerned. Preferably the permanent magnets or electro-magnets are associated with the clamping means such as via the tie bars (12, 13) so as to surround the pipe at a nominally constant distance from the pipe surface.
Conveniently, with four clamps surrounding the pipe the corresponding magnet systems provide substantially a continuous magnetie pole surrounding the pipe. The return magnetic circuit via the pipe eomponents and the surrounding apparatus of ferritic material may be supplemented by ferritic material embraeing the magnet or electro-magnet on one or all sides apart from the side facing the pipe exterior. It will be apparent from Figure 1 that the welding head (i.e. the magnet system and the electrie are system, eolleetively) are disposed outside of the pipes.
As illustrated in Figure 2 for use with large pipe seetions in exeess of 150 mm diameter, especially those of 200 or even some 300 mm diameter, the magnet system (30) preferably comprises a plurality of similar magnet blocks (31) presenting a virtually eontinuous profile in terms of field strength about the circumference of the section to be butt welded. In partieular, the overall magnet system (30) preferably, comprises 4 groups of eleetro-magnets with preferably more than one eleetro-magnet (32) per quadrant.
Conveniently 2 or 3 electro-magnetic coils (32) exciting corresponding eores (33) whieh are connected together via a eommon pole piece (34) are eonneeted to a suitable energising souree (not shown). The source may be of a eommon potential and all the eleetro-magnet eoils paralleled as they are of substantially the same resistance.
Alternatively, the groups of 2 or 3 coils may be eonneeted in series and each set eonnected in parallel to a common voltage souree. Again, alternatively, corresponding coils from each quadrant may be connected in series and each set of four such coils connected to a common voltage source.
These connections are a + b + c (or al + a2 + a3 + a4 and so forth).
Conveniently, the magnetic pole facing the pipe exterior may be covered with protective layer such as stainless steel or copper sheet to avoid direct impingement of spatter from the weld zone. Equally the magnet, particularly in the case of a permanent magnet, may be protected by a non-thermally conducting layer for thermal insulation to avoid excessive temperature rise from the heated pipe ends and the rotating arc. Moreover, suitable heat sinks can be provided adjacent to the magnet to assist in avoiding excessive temperature rise. A suitable magnetic material for the permanent magnets is a polymer bonded rare earth magnet metal. The term rare earth metal is meant to convey its conventional meaning, namely the elements of the Periodic Table which are also referred to Lanthanides (especially Nd and Ce). These magnets are preferably glued or bonded into the system with a polymeric adhesive. For example, as shown in cross-section in Figure 3, the electro-magnet (33, 34) is positioned at a short distance away from the exterior of the component (20, 21) and arranged such that the flux from the pole-piece is returned via the wall of the component to the surrounding ferro-magnetic case (35, 36) of the electro-magnet. The internal face of the magnet 20~7638 system is covered with a suitable protective layer (38) to prevent spatter adhering to the magnet or potentially damaging the coils (32). The magnet system is carried on a suitable arm (37) in association with the clamping mechanism (not shown).
Preferably the aspect ratios of the magnet system should be such that the face of the magnet is substantially greater than the gap between the components to be joined and preferably of dimension at least 3 times the gap width.
Furthermore, a substantial air gap is provided between the magnet face and the exterior of the pipe being joined, such as in excess of 5 mm and preferably in excess of 8 mm such as lo mm. These dimensions define the two aspect ratios of magnet width to gap width and magnet separation to wall thickness of the pipe being joined. For example, the dimensions given are suitable for pipe wall thicknesses of 3 mm to 5 mm, and gap widths up to 3 mm. Thus as shown in Figure 4, the width (41) of the pole-piece in the axial direction transverse to the abutting face (40) should exceed at least 3 mm on either side of the gap. Preferably the width (41) of the pole-piece should be of the order of 5 mm on either side of the gap (40). Alternatively, the width should be at least one wall thickness T on either side of the gap and preferably of the order of l l/2 T on either side.
Equally, the width of the magnetic circuit (42, 43) on 20~7638 either side of the centre pole-piece (41) should be about half the width of the centre pole-piece to present a substantially symmetrical magnetic circuit and avoid magnetic saturation in the ferro-magnetic material.
Equally the separation (44) of the surface of the pole-pieces from the surface of the components to be joined should be of the same order as the width (41) of the pole-piece but preferably less, such as between 50% and 80~ of the width. Alternatively, the separation (44) should exceed the wall thickness T of the components (20, 21) to be joined preferably is in the range of 2T to 3T. In all cases the dimension (44) should preferably not exceed the dimension (41).
For permanent magnets as shown in Figure 5, the principal dimensions in the vicinity of the gap (40) are similar to those for the electro-magnet but in general a return circuit such as provided by the cheeks (35) of the electro-magnet are not required. Preferably, the permanent magnet (50) is mounted on a support (51) which is carried on a suitable arm (52). These latter are of ferro-magnetic material and can be proportioned to adjust the strength of the field in the region of the position of the gap (40) which is spaced at the distance (44) from the surface of the permanent magnet material.
In the case of polymer bonded rare earth magnets, the magnet material is preferably surrounded on either side and on the face nearest the component to be joined with thermally insulating material (53) to avoid the effects of radiated and convected heat from the magnetically impelled arc. Also the thermal insulation on the front face is particularly required to reduce the effects of radiation from the heated welded component. In addition to the thermal insulation (53), preferably a further layer (54) of material is used to limit or prevent the adherence of spatter from the arcing process. The material (54) may be a high thermal conductivity, such as copper or a temperature resisting material such as stainless steel.
For electro-magnets in place of the permanent magnets, preferably more than one excitation coil is provided on a suitable core to provide a sufficiently uniform excitation of the pole face. For example, with four magnet units embracing nominally 90 of the periphery, each unit can comprise two or more cores with exciting coils on each core.
For example, each individual electro-magnet coil may be rated at some 2,500 ampere turns (2.5A with 1,000 turns) and with 1 mm insulated copper wire the total voltage drop is of the order of 10 V giving 25 watts per coil at 100% duty cycle. For shorter duty cycles such as 1 in 10 or 1 in 20, the power dissipated per coil can be significantly increased without causing excessive temperature rise. The field strength in the region of the position of the components to be welded is preferably of the order of between 1,000 and 20~7638 2,000 gauss. For example, the field for a pipe of nominally 150 mm diameter is in the region of 1,400-1,600 gauss. The field for a larger diameter component, such as in excess of 250 mm diameter, is preferably of the order of 1,600-1,800 gauss. In general it is convenient to increase the field strength of the magnet system for larger diameters of components in order to maintain an adequate rate of rotation of the magnetically impelled arc at the preferred welding current. Moreover, fields in excess of gauss have been found suitable for welding pipe components of nominally 300 mm diameter.
Furthermore with both the permanent magnet and electro-magnet pole design, gas ports can be provided to enable suitable gas shields to be provided for the rotating arc to prevent excessive oxidation of the heated surfaces of the components being joined. Gaseous nitrogen is particularly suitable for this purpose.
The segmented magnet system not only allows, in its retracted position, for the pipe including the weld zone, to be threaded through, but also for the pipe to be completely detached from the welding head laterally out of the machine.
Accordingly, although the clamps open in an upwards direction for safety reasons (and thus the welding head can't be simply lifted off the pipes because a substantial portion of the apparatus is below the new weld in the pipes), the apparatus can be readily moved laterally along 20~7638 the pipeline to position it for the next weld.
The clamping system comprises a set of separate segments preferably at least 4, with facing surfaces of curvature matched to the pipe, within the limits of variation of the pipe as produced. Furthermore, to obtain an adequate grip, the internal surfaces of the clamps are preferably serrated or provided with a castellated profile, as illustrated, Figure 6. It is noted that the gripping reacts a longitudinally applied thrust and that each part of the serration is capable of elastically taking up a part of the total thrust. The surface (22) of the clamp is of relatively strong material, preferably with a yield strength in excess of 30kg/mm2 so that it resists deformation and has a sufficiently high elastic limit to allow thrusts of the order of 200 kg per millimetre of periphery of the pipe.
Apart from the castellated profile, the internal surface of the clamps is smooth and of a curvature substantially matching that of the exterior of the pipe to avoid significant surface indentation or distortion.
The clamps are arranged around the periphery of the pipe such that the gap between the segmented clamps is, on average, not more than about 3 mm and preferably at no stage exceeds 1% of the total circumference. Thus, overall the clamps surround the pipe to more than 95% of the circumference. Figure 7 indicates the definition of the overall degree of circumferential clamp. Thus with a clamping system comprising four segments (22) for surrounding the circular component (20, 21), the clamps are brought together such that there is a finite gap (23) between one clamp and the next. Preferably, the gap (23) is of the order 1 mm for smallest diameter of component to be gripped and does not exceed some 3 mm for the largest size of circular component. Equally, preferably any one gap (23) should not be zero or exceed some 5 mm. Where desirable, means can be provided between the segments (22) to allow for a more even distribution of the gap (23), such that the clamping is substantially symmetrical and hence distortion of a circular component is minimized.
The set of clamps can be relaxed sufficiently to allow the pipe components to be threaded through, including the weld zone. Furthermore, the clamping system opens in an upwards direction so as to receive the pipe from above. In other words, the welded pipe can be withdrawn laterally from the clamp, and the new pipe can be inserted laterally or from above.
In one arrangement with four operating and self-aligning clamps with one degree of freedom, one pair are arranged to interlock one with the other and the other pair arranged to press the pipe into the arc formed by the co-operatin~ pair, such that the pipe is substantially completely surrounded. One example of a suitable clamping arrangement is shown in Figure 8, in which the clamping 2~7638 mechanism (70) comprises two upper arms (71, 72) with pivots (73, 74) fixed to the support plate (79) and two further arms (75, 76) with pivots (77, 78) carried on actuators, not shown, with a direction of movement at nominally 45 to the vertical axis. To grip the pipe (20, 21) seen in end elevation, the upper arm (72) is first closed in the direction of the arrow (80), Figure 8a. Thereafter the co-operating upper arm (71) is closed to interlock with the arm (72~ such that the pin (82) on arm (72) falls within the hoo~ (81) of arm (71), as illustrated in Figure 8b.
Thus, the pin (82) and hook (71) form a positive engagement point that is located above the pipes. This is a safety feature, as the operator of the apparatus is readily able to visually determine that the clamps are engaged. (In contrast, prior MIAB welding machines which are lowered onto the pipes have a configuration which requires the clamps to engage at a location below the pipe).
To complete the locking arm (72) is preferably moved in the direction shown by the arrow (90) in order to present a nominally hemispherical surface for the circular components to be gripped via the faces (83, 84) on arms (71, 72) respectively. Thereafter the arms (75, 76) are moved in the direction shown in Figure 8c, at nominally 45 to the vertical, as given by arrows (87, 88) such that the clamping faces (85, 86) of arms (75, 76) locate the pipe and cause it to be centred as shown with respect to the support plate 20~7638 (79). It is noted that arms (71, 72) effectively locate the circular component in the transverse direction left or righ~
while the arms (75, 76) locate the circulate component in the upward direction, in co-operation with arms (71, 72).
It is also noted that the clamping faces (83, 84, 85 and 86) virtually surround the circular component completely with only small gaps between each nominal quadrant section.
These gaps are necessary to enable the circular component to be rightly gripped when it is smaller in diameter than the nominal size. To obtain a reasonable balance in the forces applied by the actuators to the arms (77, 78) the actuators are preferably hydraulically operated from a common pressurised supply. As previously noted, the hydraulic system used to operate the clamping system preferably includes a hydraulic fluid accumulator, particularly when the apparatus is used with large diameter pipes. In a further alternative the upward pressing clamps may be provided with more than one degree of freedom to allow for self-alignment, as shown in Figure 9. Here a pair of pivots are mounted on a common bridge, which in turn is pivoted.
Thus, as shown in Figure 9, the lower arms (75, 76) are pivoted respectively at (77, 78) on bell cranks (91, 92).
These in turn, are pivoted at (93, 94) on a oommon swivel (95) which is itself pivoted (96). Actuators as shown operating on pivots (97, 98) move the bell cranks (91, 92) in an upward direction so closing the arms (75, 76) around the circular pipe (20, 21). The swivel (95) allows for a degree of take-up between the two clamps (75, 76). Thus, although the actuators operating on pivots (97, 98) may be hydraulic rams, the further degree of freedom provided by the swivel (95) allows direct mechanical actuators such as screw jacks or cams, to operate on the ends of the bell cranks (91, 92).
Also in Figure 9 is shown an alternative arrangement for a positive engagement point of the upper clamp arms (71, 72). Here the clamp (71) is first closed in co-operation with the arm (72) such that the hook (81) passes under the pin (82). Again with outward movement of the arms (71 and/or 72) the pin (82) rests within the hook (81) and so defines the location of the circular component in an upward direction. Thereafter, the actuators on the bell cranks (91, 92) bring the lower arms (75, 76) into position encircling the pipe or circular component, as previously, and locating it with respect to the support plate (79).
These and other arrangements providing for opening of the clamping system and permitting complete withdrawal of the component in a lateral direction are within the scope of the invention as described.
For speed of operation hydraulically actuated clamps are preferred, but other convenient means can be provided, such as screw jacks or cam mechanisms.
Although, in principle, the MIAB process can be 2~47638 operated manually with butting and separating of the components to be welded to initially form the arc and thereafter with a suitable arc rotation and current level to butt the components together, it is preferable for the sequence of operations to be automatic to avoid error or any undue variation in time intervals. Furthermore it is preferable to monitor the sequence of operations and the operating levels of current, gap between components, time and (for electro-magnets) excitation current. This serves as an internal quality control and quality assurance.
Although the complete operation of the machine can be mechanised and supplemented with timers and the like, preferably the control system utilizes both hardware and software as appropriate, together with a suitable process computer. Preferably facilities are provided for two or more levels of arc current toqether with two or more levels of operating gap between the components to be joined and in the case of electro-magnets two or more levels of excitation current. For example, suitable operating conditions for nominally 12 in diameter pipe of 4.8 mm wall thickness are, current 1600 amperes, excitation 30 amperes, gap 2 mm, thrust (forge) 300 KNewtons and overall time 15 seconds.
In principle, the required applied load can be registered using load cells and the like but preferably the requisite loads are represented by pressure in the appropriate hydraulic system. However, in some cases pressure measuring devices need to be zeroed to overcome effects of drift over long periods of time. Therefore, preferably means are provided for registering zero operating conditions, such as at retraction or before the forge load is applied in hydraulic systems where the minimum pressure is not necessarily zero itself.
Such means may be hardware or software orientated but in principle detect the condition of non-operation and give an appropriate zero register to the controller.
Further details concerning a novel method to monitor/control a MIAB welding process are provided below.
As previously noted, it is desirable to establish zero datum conditions corresponding to the position of the clamped pipes, and the initial load on the hydraulic system, prior to the welding/forging operations (i.e. there may be a small load on the hydraulic system prior to the welding/forging operations). It is highly preferred to generate an electric signal corresponding to these zero datum conditions, and to forward the signal to a programmable logic controller ("PLC").
The welding/forging operations are then completed in the manner previously described. However, the movement of the pipes during the forging operation is also monitored.
In particular, it is desirable to monitor (a) the distance travelled by the pipes, and (b) the time elapsed during the forging operation, 20~763~
and to generate electric signals corresponding to (a) and (b) above. By transmitting these signals to a properly programmed PLC which PLC also contains data concerning the zero datum conditions), it is possible to calculate (a) weld upset (based on zero datum conditions combined with data defining the distance of pipe movement), and (b) forge velocity (based on zero datum conditions, combined with data concerning the distance of pipe movement, and the time required for same).
As previously noted, it is desirable to monitor weld upset so as to record the amount of pipe material which is lost during the welding operation.
Furthermore, it is highly desirable to monitor forge velocity because this parameter can often be correlated with weld quality.
Additional discussion of the forging operation is provided below.
The applied thrust for forging is arranged to avoid excess or sudden high axial loads, which could cause slip of the clamping system in an axial direction. Such control of the hydraulic system, including appropriate control of pressure build-up and collapse, are within the scope of the invention as applied to welding components with large enclosed areas and large butting cross-section as defined.
The use of a hydraulic fluid accumulator in a hydraulically 2047~38 driven forge system is particularly preferred for an apparatus used to join large diameter pipes.
For some applications the electro-magnetic system can be replaced with appropriate permanent magnets. The use of permanent magnets simplifies the operating sequence by removing one control variable. Thus only the gap between the components and the operating current need to be controlled when welding, and only the maximum forging pressure needs to be ~ontrolled after the arcing period.
Although applied to the automatic circumferential welding of line pipe, the technique can be appropriately adapted to tubes of limited length where either or both components can be brought together axially and for the tube profiles other than circular, such as elliptic or rectangular. For non-circular profiles the magnet system is adapted, particularly where there is a major change in curvature such as at the extremities of an ellipsoid shape or at the corners of a rectangular shape, so as to produce the necessary fields to maintain a sufficiently smooth arc movement around these zones. For these purposes, permanent magnets may be used for the major part of the periphery and local electro-magnets used which can be adjusted to the appropriate level for the desired arc movement.
Although the apparatus, according to the invention, is capable of being detached from a continuous pipe in a lateral direction it may also be passed along the pipe axially. (If this is desired, suitable rolls or wheels are provided to carry the apparatus about the pipe and which may be sprung or otherwise supported to allow the weld zone to pass through. Alternatively, the rolls may be set at a sufficient distance apart to provide adequate clearance for the welds.) The present apparatus is sufficiently portable to enable its use in the construction of pipelines used to transport natural gas, oil and the like. Thus, the overall dimensions of the apparatus are preferably such that pipe bends and natural flexing can be accommodated in passing the machine along the pipe length. These and other aspects of the overall lay out of the equipment are well known to those skilled in the art and do not constitute further invention.
Furthermore, the equipment can be designed for smaller pipe sizes by appropriate selection of jaw inserts to the clamping mechanism, together with appropriate position of the magnet system. Preferably, for efficiency of operation, the machine caters for a range of pipe sizes down to nominally half the maximum diameter.
Claims (28)
1. A portable magnetically impelled arc butt welding apparatus for welding a joint between the adjacent ends of two pipes, said apparatus having a housing, a magnetically impelled electric arc welding head disposed outside of said pipes, first pipe clamping means and second pipe clamping means which are movably attached to said housing, wherein said first pipe clamping means and said second pipe clamping means are operable so as to receive said pipes from above said housing.
2. The apparatus of claim 1 wherein the diameter of said pipes is in excess of 100 mm.
3. The apparatus of claim 1 which further contains a pipe positioning bar that is pivotally attached to said housing in a position which is fixed with respect to the lengthwise axis of said housing.
4. The apparatus of claim 1 wherein each of said pipe clamping means contains (a) at least one upper clamping component that is pivotally attached to a tie bar; and (b) at least one lower clamping component, wherein said tie bar is attached to said housing in a direction which is parallel to the lengthwise axial direction of said housing.
5. The apparatus of claim 4 wherein said first pipe clamping means are movable in the lengthwise axial direction of said housing whilst said clamping means are engaged about said pipes.
6. The apparatus of claim 5 which further contains a first positive engagement point for said first pipe clamping means and a second positive engagement point for said second pipe clamping means, wherein both of said first positive engagement point and said second positive engagement point are located above said pipes.
7. The apparatus of claim 4 wherein each of said clamping component is fabricated from an electrically conducting material.
8. The apparatus of claim 7 wherein said electric arc welding head includes an electrical power supply and separate current carrying wires connected from said power supply to each of said clamping component, such that said wires are connected in parallel and have substantially the same electrical resistance.
9. The apparatus of claim 1 which is further characterized by having a hydraulically operated forge system which can provide a thrust in the lengthwise axial direction of said pipes that is at least five times the magnitude of the weight of said apparatus.
10. The apparatus of claim 9 wherein said hydraulically driven forge system includes a first hydraulic fluid accumulator.
11. The apparatus of claim 1 wherein each of said pipe clamping means is operated by a hydraulically driven clamping system.
12. The apparatus of claim 11 wherein said hydraulically driven clamping system includes a second hydraulic fluid accumulator.
13. The apparatus of claim 11 wherein each of said pipe clamping means has an internal clamping surface which is curved so as to substantially match the curvature of said pipes.
14. The apparatus of claim 13 wherein the internal surface of each of said pipe clamping means has a castellated profile.
15. The apparatus of claim 13 wherein each of said pipe clamping means surrounds at least 90% of the circumference of a cross section profile of said pipes.
16. The apparatus of claim 1 wherein said welding head contains permanent magnets.
17. The apparatus of claim 16 wherein said permanent magnets are fabricated from a rare earth metal.
18. The apparatus of claim 16 wherein said permanent magnets are arranged so as to provide a arrived internal surface which substantially matches the curvature of said pipes.
19. The apparatus of claim 18 wherein said magnets are pivotally attached to said housing.
20. The apparatus of claim 18 wherein said curved internal surface of said magnets is coated with a thermally insulating material.
21. The apparatus of claim 1 wherein said welding head contains ports for the provision of a substantially non-oxidizing gas.
22. The apparatus of claim 21 wherein said gas is nitrogen.
23. The apparatus of claim 22 wherein said pipe positioning bar also positions said welding head.
24. A method for magnetically impelled arc butt welding apparatus for welding a joint between the adjacent ends of two pipes, said method consisting of (a) clamping a first pipe with first clamping means, (b) establishing a zero datum condition by clamping a second pipe with second clamping means and positioning said second pipe in close proximity to said first pipe so as to establish a small gap between said pipes; (c) generating a first signal corresponding said zero datum conditions and transmitting said first signal to a programmable controller; (d) establishing a magnetic field within said gap; (e) striking a welding arc between said pipes; (f) actuating a hydraulically driven forge so as to apply a forging pressure along the axial lengthwise direction of said pipes such that said pipes are forged together; (g) monitoring the movement of said pipes during the application of said forging pressure; and (h) generating a second signal corresponding to the movement of said pipes and transmitting said second signal to said programmable controller.
25. The method of claim 24 wherein said programmable controller calculates the amount of pipe material which is lost as weld upset, using said first signal and said second signal.
26. The method of claim 25 which further consists of measuring the time of application of said forging pressure, and generating a third signal corresponding to said time of application of said forging pressure, and transmitting said third signal to said programmable controller.
27. The method of claim 26 wherein said controller calculates forge velocity using said first signal, said second signal and said third signal.
28. The method of claim 24 wherein said controller adjusts said forging pressure according to the value of said first signal.
SC/SP-CAN.013
SC/SP-CAN.013
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2047638 CA2047638A1 (en) | 1991-07-23 | 1991-07-23 | Miab welding machine |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2047638 CA2047638A1 (en) | 1991-07-23 | 1991-07-23 | Miab welding machine |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2047638A1 true CA2047638A1 (en) | 1993-01-24 |
Family
ID=4148058
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2047638 Abandoned CA2047638A1 (en) | 1991-07-23 | 1991-07-23 | Miab welding machine |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2047638A1 (en) |
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102107343A (en) * | 2011-01-14 | 2011-06-29 | 中国建筑第八工程局有限公司 | Fixing bracket for overweight butting rod piece of welding ball net rack |
| CN103949843A (en) * | 2014-05-06 | 2014-07-30 | 禹伟 | Multi-purpose pipe fitting fixing device for automatic pipe welding machine |
| CN108465999A (en) * | 2018-06-09 | 2018-08-31 | 芜湖德恒汽车装备有限公司 | A kind of assembly type has the automobile frame welding fixture of cushioning effect |
| CN109175880A (en) * | 2018-11-17 | 2019-01-11 | 中国二十二冶集团有限公司 | Large-diameter pipeline contra-aperture device |
| CN112453714A (en) * | 2020-12-07 | 2021-03-09 | 重庆康斯顿激光科技股份有限公司 | Laser marking machine convenient to operation |
| CN113210867A (en) * | 2021-04-26 | 2021-08-06 | 哈尔滨电气动力装备有限公司 | Welding device for large weak-rigidity thin-wall component of nuclear reactor coolant pump |
| CN113443424A (en) * | 2021-06-25 | 2021-09-28 | 东风柳州汽车有限公司 | Limiting device and hoisting and conveying mechanism |
| CN113732612A (en) * | 2021-08-31 | 2021-12-03 | 河南省中州环境节能科技有限公司 | Processing device of elbow for dry desulphurization |
| CN114346376A (en) * | 2022-02-22 | 2022-04-15 | 舟山惠生海洋工程有限公司 | Pipeline welding device and method |
| CN116373329A (en) * | 2023-03-31 | 2023-07-04 | 南通森萱药业有限公司 | Butt joint equipment for installing chemical infusion pipeline |
-
1991
- 1991-07-23 CA CA 2047638 patent/CA2047638A1/en not_active Abandoned
Cited By (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102107343A (en) * | 2011-01-14 | 2011-06-29 | 中国建筑第八工程局有限公司 | Fixing bracket for overweight butting rod piece of welding ball net rack |
| CN103949843A (en) * | 2014-05-06 | 2014-07-30 | 禹伟 | Multi-purpose pipe fitting fixing device for automatic pipe welding machine |
| CN108465999A (en) * | 2018-06-09 | 2018-08-31 | 芜湖德恒汽车装备有限公司 | A kind of assembly type has the automobile frame welding fixture of cushioning effect |
| CN109175880A (en) * | 2018-11-17 | 2019-01-11 | 中国二十二冶集团有限公司 | Large-diameter pipeline contra-aperture device |
| CN109175880B (en) * | 2018-11-17 | 2024-02-23 | 中国二十二冶集团有限公司 | Large-diameter pipeline aligning device |
| CN112453714B (en) * | 2020-12-07 | 2022-11-25 | 重庆康斯顿激光科技股份有限公司 | Laser marking machine convenient to operation |
| CN112453714A (en) * | 2020-12-07 | 2021-03-09 | 重庆康斯顿激光科技股份有限公司 | Laser marking machine convenient to operation |
| CN113210867A (en) * | 2021-04-26 | 2021-08-06 | 哈尔滨电气动力装备有限公司 | Welding device for large weak-rigidity thin-wall component of nuclear reactor coolant pump |
| CN113443424A (en) * | 2021-06-25 | 2021-09-28 | 东风柳州汽车有限公司 | Limiting device and hoisting and conveying mechanism |
| CN113443424B (en) * | 2021-06-25 | 2023-06-30 | 东风柳州汽车有限公司 | Limiting device and hoisting conveying mechanism |
| CN113732612A (en) * | 2021-08-31 | 2021-12-03 | 河南省中州环境节能科技有限公司 | Processing device of elbow for dry desulphurization |
| CN113732612B (en) * | 2021-08-31 | 2023-02-17 | 河南省中州环境节能科技有限公司 | Processing device of elbow for dry desulphurization |
| CN114346376A (en) * | 2022-02-22 | 2022-04-15 | 舟山惠生海洋工程有限公司 | Pipeline welding device and method |
| CN116373329A (en) * | 2023-03-31 | 2023-07-04 | 南通森萱药业有限公司 | Butt joint equipment for installing chemical infusion pipeline |
| CN116373329B (en) * | 2023-03-31 | 2023-09-19 | 南通森萱药业有限公司 | Butt joint equipment for installing chemical infusion pipeline |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20020423 |