DEVICE FOR USE IN JOINING PIPES IN A BUTT-WELDED JOINT

Abstract: In a device for shutting off one (25) of two pipes (25, 26) to be joined by welding (at 27) and supplying purge gas, the main novel features are that the purge gas is distributed through evenly distributed radial nozzles (14) into a gap (28) of limited radial depth, so that the purge gas flows laminarly or quasi-laminarly past the welding line (27), and that the composition of the purge gas (especially its oxygen content) is sensed at the free end of the gas sampler or sensor (6), i.e. well downstream of the welding site (27).

Description: DEVICE FOR USE IN JOINING PIPES IN A BUTT-WELDED JOINT TECHNICAL FIELD The present invention relates to a device of the kind set forth in the preamble of claim 1. BACKGROUND ART Similar equipment is disclosed in an article "Gas purging for pipe welding" from "Welding & Metal Fabrication", January/February 1989. As will be seen especially from Figure 2 in the article, a space of a substantial volume exists between the right- hand (upstream) barrier, through which the purge gas is supplied, and the left-hand (downstream) barrier, through which the purge gas flows out and at this location is possibly examined for its oxygen content, the lengths of said space having to be at least 2 x 150 mm in order to avoid the heat of welding damaging the barrier members. A space of such a size will necessarily require a cor¬ respondingly large quantity of purge gas to be supplied, and since the stream of purge gas occupies the entire space within the pipes, it must necessarily - if it is also to have a certain cooling effect on the upstream barrier member - have a rather high flow velocity and hence require a correspondingly large quantity of gas per unit time to be supplied. Further, the equipment described in said article is cumbersome in use, since it comprises two barrier members, viz. one for each of the two pipes to be welded together. DISCLOSURE OF THE INVENTION It is on this background the object of the present in¬ vention to provide a device of the kind referred to ini¬ tially, with which it is possible to avoid the waste of time and gas referred to, and this object is achieved according to the present invention by means of the fea¬ tures set forth in the characterizing clause of claim 1. The effect achieved by the feature set forth in item c of claim 1 is that the purge gas will flow laminarly or quasi-laminarly past the welding site, so that the latter is "rinsed" in such a manner that adsorbed gasses, espe¬ cially oxygen, are removed from the inside walls of the pipes. A further effect is that the formation of eddies, that could carry unwanted gases into the region of the welding site, is avoided. The effect of the feature set forth in item d of claim 1 is that the oxygen content at the position referred to will during use always be higher than at the welding site. This means that as soon as it has been ascertained that the oxygen content at said position is equal to or lower than the permissible limiting value, one can be certain that the oxygen content at the welding site does not exceed the limiting value. The effect of the embodiment set forth in claim 2 is that the barrier member can easily be centered axially in the pipe in question, so that the position, at which the gas sampling or gas sensing device samples gas or senses its content, will be situated centrally in the other pipe and thus facilitate a reliable sampling or sensing of the oxygen content of the gas. BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the present descrip¬ tion, the invention will be explained in more detail with reference to the exemplary embodiment of a rear-gas device according to the invention shown in the drawing, in which Figure 1 shows the device itself in longitudinal section and the accessory equipment diagrammatically, and Figure 2 shows the device of Figure 1 placed close to the mutually adjacent ends of two pipes to be welded together, of which the ends are shown in longitudinal section. DESCRIPTION OF THE PREFERRED EMBODIMENT The equipment consists of a main part, "the plug", an adaptor and three flexible gas tubes for connection to the requisite supporting equipment. The plug consists of an aluminium body 1, an expansible tube 2, two conical clamping rings 3 and 4, a union nut 5 and a probe 6. The adaptor 7 consists of a solid cylinder, one end of which carries three tube connectors 8a, 8b and 8c, and the other end of which comprises three tubular prongs 9a, 9b and 9c in fluid-tight engagement with corresponding soc¬ kets 10a, 10b and 10c in the body 1. Three axially extending ducts 11a, lib and lie are bored through the body 1, the adaptor 7 and the prongs 9a-c. The duct 11a serves for supplying gas to the expansible tube 2, while the duct lib serves for supplying rear gas or backing gas to the welding site, and the duct lie is connected to the probe 6 with a view to measuring the oxygen content. In the forward end - i.e. the end facing towards the left in Figures 1 and 2 - the body 1 is provided with a rounded head 12, the size of which is attuned to the internal diameter of the pipes to be welded, i.e. roughly to the external diameter of the clamping rings 3 and 4, in such a manner that an annular gap 28 of a certain limited radial width is formed between the head 12 and the inside wall of the surrounding pipe. The probe 6 extends coaxially to the head 12 and is screwed into a threaded hole in the latter. The head 12 is connected to the body 1 through a neck 13 provided with a large number of radially debouching holes 14, all connected to the rear-gas duct lib. In the middle of the body 1, the duct 11a continues in a radial hole 15 debouching on the inside of the expansible tube 2, the ends of which are clamped between internal conical surfaces on the clamping rings 3 and 4 and exter¬ nal conical surfaces 16 with circumferential grooves 16a on the body 1. The clamping rings 3 and 4 are screwed onto the body 1 by means of screw threads 17, so that they can clamp the ends of the expansible tube 2 against the conical surfaces 16 on the outside of the body l with their internal conical surfaces 3a and 4a, all coni¬ cal surfaces preferably having the same conicity. In the relaxed state, the internal diameter of the ex¬ pansible tube 2 corresponds to the smallest diameter of the conical surfaces 16, so that the inherent elasticity of the tube will cause it to lie in abutment with or close to said surfaces. Through the adaptor 7, by a union nut 5 being secured to the body 1, the three ducts 11a, lib and lie are connected to three flexible gas tubes 18a, 18b and 18c, respective¬ ly. The gas tube 18a is connected to a three-way valve 21, so that it may optionally be connected to atmosphere or to the outlet side of a reducing valve 20, the inlet side of which is connected to a gas cylinder 19 containing gas of the kind intended for use as rear gas or backing gas in each particular case. Likewise, the gas tube 18b is connected to the outlet side of the reducing valve 20 through a regulating valve 23 with associated flow sensor 22. The gas tube 18c is connected to an oxygen-measuring device 24 being adapted such as by means of a pump (not shown) to aspirate gas from the probe 6 to the duct lie and thus measure the oxygen content in the region im¬ mediately surrounding the tip of the probe. When, c.f. Figure 2, two pipes 25 and 26 are to be welded together at a welding line 27, the rear-gas equipment is inserted into one pipe 25 to such an extent that the tip of the probe 6 will be situated on the opposite side of the welding line 27. When the rear-gas equipment is inserted in the pipe 25, it is solely the clamping rings 3 and 4 and the expan¬ sible tube 2 that will come into contact with the internal surface of the pipe. Since it is contemplated that these parts are to be made of relatively soft materials, such as e.g. PTFE and silieone rubber, respectively, even electro-polished pipes having extremely sensitive internal surfaces will not be scored, and at the same time the equipment may be held securely in the pipe, as will be explained below. When the equipment has been placed in the manner referred to in the pipe 25, the three-way valve 21 is set to con- nect the gas tube 18a to the outlet of the reducing valve 20. The pressurized gas from the cylinder 19 will then cause the tube 2 to expand, so that it will clamp the equipment securely and centered in the pipe, the latter at the same time being closed in a completely fluid-tight manner. Now, the regulating valve 23 is opened, and the gas flow is adjusted by means of the flow sensor 22. This causes gas to flow through the tube 18b, the duct lib and the radially directed holes 14 out into the space around the neck 13, from where it flows in a laminar or at least quasi-laminar flow through the annular gap 28 towards the welding line 27. Since the gas flow is laminar or quasi- laminar, a large proportion of the oxygen having been adsorbed on the internal surface of the pipes will be removed. The laminar or quasi-laminar stream of gas continues past the welding line 27 and covers it completely, so that it will not be necessary to establish a counter- pressure from the opposite end of the pipe 26. For this reason, the pipe 26 may remain open and hence at atmos¬ pheric pressure. Since the two pipes 25 and 26 are only to be filled with gas in the space between the neck 13 and the tip of the probe 6, the filling may be carried out very rapidly using a very small amount of gas. If, at this moment, it has not yet been done, the pump associated with the oxygen measuring device 24 is started, so that gas from the tip of the probe 6 is aspirated through the duct lie and the tube 18c. In this manner, the oxygen content in the pipe 26 on the far side of the welding line 27 is measured, and since the rear gas coming out from the holes 14 and the annular gap 28 flows along the sides of the pipes, the gas in the immediate vicinity of the welding line 27 will always have a lower oxygen content than the gas being aspirated through the probe 6 and measured in the oxygen-measuring device 24. This means that when the oxygen content in the pipe 26 as measured is equal to or less than the limiting value permitted for welding, one can be certain that the oxygen content in the immediate vicinity of the welding line 27 does not exceed the permissible value, and the welding operation may now begin. When the welding operation is completed, the pipes 25 and 26 having been joined by welding are cooled. Since as described above, the stream of gas flows closely past the walls of the pipes, the welding line and its sur¬ roundings will be cooled more rapidly than with conven¬ tional rear-gas filling, cf. also the equipment known from the initially mentioned article, in which the stream occupies the whole space within the pipes. After cooling, the three-way valve 20 is opened to atmosphere, and the expansible tube 2 is emptied, so that the equipment may be withdrawn and made ready for the next task. If the next task is to be carried out in pipes of a different dimension, the union nut 5 is unscrewed, after which the adaptor 7 may be secured to a different body 1 having suitable dimensions. LIST OF PARTS 1 (aluminium) body 2 expansible tube 3 clamping ring 4 clamping ring 5 union nut 6 probe 7 adaptor 8a-C tube connector 9a-c (tubular) prong lOa-c socket lla-c duct 12 head 13 neck 14 holes 15 hole 16 conical (sealing) surface 16a groove 17 screw thread 18a-c (flexible) gas tube 19 gas cylinder 20 reducing valve 21 three-way valve 22 flow sensor 23 regulating valve 24 oxygen-measuring device 25 pipe 26 pipe 27 welding line/site 28 annular gap

Claims: C L A I M S; 1. Device for use in joining two pipes in a butt- weld and of the kind comprising a) a barrier member (1,2) adapted to shut off a part of the internal space of a pipe from another part of same in a substantially fluidum-tight manner, b) gas supply means (12,13,14) debouching on the side of said barrier member (1,2) intended to face a welding site (27) and being connected or adapted to be connected to a gas supply device (19), c h a r a c t e r i z e d in c) that said gas supply means (12,13,14) comprise a projection (12) placed on said barrier member (1,2) and having a somewhat smaller diameter than the latter, whereas a plurality of nozzles (14) are angularly evenly distributed about the part of said projection situated closest to the barrier member, said nozzles (14) being connected or adapt¬ ed to be connected to the gas supply device (19) , and by d) a gas sampling or gas sensing member (6) secured to said barrier member and extending to a position at a greater distance from the barrier member (1,2) than said gas supply means (12,13,14) and adapted to sample gas from said position and transfer the sample to a testing apparatus (24) and/or to sense at said position a parameter of importance for the composition of the gas. 2. Device according to claim 1, c h a r a c t e r¬ i z e d in a) that the assembly consisting of said barrier member (1,2) and the gas sampling or gas sensing device (6) is substantially rotationally symmetrical, and that said barrier member (1,2) comprises an in¬ flatable wall (2) capable in the inflated state to be pressed in fluid-tight manner against the inner wall of a pipe, said barrier member com¬ prising a body (1) and an inflatable tubular wall (2) of rubber or rubber-like material, in both the non-inflated and the inflated state surrounding the body (1) , said wall (2) at each end being secured in a fluid-tight manner to the body (1) by means of a connection comprising two circum¬ ferential conical sealing surfaces (16) on the outside of the body (1) as well as two clamping rings (3,4) adapted to embrace the end parts of the wall (2) and press said end parts against said sealing surfaces (16) in a fluid-tight en¬ gagement, each clamping ring (3,4) having an in¬ ternal circumferential conical surface (3a,4a) with substantially the same conicity as said seal¬ ing surfaces (16) , each ring being adapted to be moved relative to the body (1) in such a direction that the space between said sealing surfaces (16) and said internal conical surfaces (3a,4a) de- creases, e.g. by said clamping ring (3,4) being connected to the body (1) through a screw connec¬ tion (17).

Inventors: PEDERSEN HANS-JOERGEN, PEDERSEN, HANS-JOERGEN
Applicants: METALEX AS, PEDERSEN HANS JOERGEN, METALEX A/S, PEDERSEN, HANS-JOERGEN
Application year: 1995
Main classification: B23K9
IPC codes: B23K9