WO1990006205A1

WO1990006205A1 - Method and tool for the welding of pipes

Info

Publication number: WO1990006205A1
Application number: PCT/DK1989/000284
Authority: WO
Inventors: Henning Bredahl
Original assignee: Tjæreborg Industri A/S
Priority date: 1988-11-30
Filing date: 1989-11-30
Publication date: 1990-06-14
Also published as: AU4662589A; DK669888D0

Abstract

In order to ensure the necessary gas coverage when welding stainless steel such as pipes (1, 2) without the consumption of gas becoming unacceptably high, and while at the same time reducing the cooling time and therewith the working time as much as possible, according to the invention there is used a method and apparatus which comprises a rear gas apparatus (5) provided with copper jaws (15) which are provided with outlet openings (36) for the gas and coolant pipes (38, 39) which cool the welding zone and the gas. In a corresponding manner, the welding apparatus (4) can be provided with gas coverage in the form of a casing (7) which is supplied with gas (11), and which is also provided with a coolant pipe (10) for the cooling of the welding zone and the gas. In this manner, it is possible to ensure that the purging gas does not contain more than approx. 25 p.p.m.O2, and that the temperature of the welding zone is reduced to below approx. 250°C and is thus below that limit at which damage as a result of corrosion can occur.

Description

METHOD AND TOOL FOR THE WELDING OF PIPES

The invention relates to a method for the welding together of metal pipes and similar items by arc welding with purging gas, where the pipes are fixed by means of an internal pipe holder, and where the welding takes place from the outside by means of welding apparatus with a welding gun, and where purging gas is supplied from the outside and pos¬ sibly also to the inside of the pipes, and a pipe holder and welding apparatus for the execution of the method.

A method and apparatus of this kind is used espec¬ ially for the welding together of items of stain¬ less steel, such as pipe systems for utility water and sea water.

It has proved, however, that attacks by corrosion often arise and, as a consequence, serious corrod¬ ing through of the pipes. These attacks are often concentrated in a zone around the welding seam, and are due especially to insufficient gas purging of the internal side of the welding seam during the welding. This results in a strong oxidation of the weld metal and of a zone in the basic material ar¬ ound the welded seam, which gives rise to a consid¬ erable deterioration in the characteristics of the steel and, as a consequence hereof, risk of attack by corrosion.

The demands on the corrosion characteristics of a welded joint are that the joint has the greatest possible resistance to the corrosion environments which can arise, in that the resistance must cor¬ respond to or be better than the selected basic mat¬ erials.

This would appear to be achieved when the material zone which is influenced by the welding is free from oxidized oxidation products when the items are taken into use. This presupposes that the welding is carried out with a sufficiently effective gas density which prevents reaction between the surface of the metal and the oxygen.

To relieve the damage of a possible tempering for reasons of this oxidation, the material effected must be removed, for example by grinding away mech¬ anically or by a chemical treatment with nitric acid -hydrofluoric^' acid pickling. However, this work can be very difficult to carry out for reasons of the construction, and the chemical treatment can be haz¬ ardous for both the personnel and the environment.

Therefore, the development has moved towards the best possible gas coverage, which in practice is achieved when the purging gas contains no more than 10-20 p.p.m. 0₂, and the gas must be introduced in such a manner that at a temperature above approx. 300 C the atmosphere around the surface of the metal must contain less than approx. 25 p.p.m. 0„. A visible oxidation and herewith tempering is here¬ by avoided.

However, experience has shown that the hitherto -known methods and apparatus do not provide a suf- ficiently satisfactory gas protection because of the high costs of the purging gas. Therefore, the costs of implementation of the known methods in¬ volve unacceptably high gas costs, which is why the above-mentioned demands with regard to gas cov¬ erage are seldom honoured. For instance, experiments have shown that a gas flow of between 10 and 15 1/m is required at a pressure which prevents the air from penetrating the weld zone. Moreover, a laminar flow is required out of regard for the purging abil¬ ity of the gas. Therefore, in practice the gas con¬ sumption will lie between 2.5 and 3.5 times the purged volume, to which must be added the consump¬ tion of gas during the time taken for tack-welding and welding operations, and the subsequent cooling of the weld seam to approx. 250 C. Below this temp¬ erature, the oxidation is minimal and thus without significance for the corrosion resistance.

It is the object of the invention to reduce this consumption of gas without the resistance to cor¬ rosion being reduced during the welding, and this is achieved by a method whereby coolant is intro¬ duced through coolant pipes during the welding, said coolant pipes extending along the rear side and possibly along the upper side of the welding zone.

The improvements achieved hereby are considerable, first and foremost for reasons of the speed at which the welding zone is cooled down, which means a great reduction in the consumption of gas, and which at the same time reduces that time in which oxidation can give rise to damage to the heat-af- fected material. To this can be added the reduc¬ tion of the work time for reasons of the shorter cooling time.

Finally, the risk of damage by corrosion is re¬ duced, in that the gas coverage can be made optim¬ ally effective without the consumption of gas being increased, for reasons of the reduced purging time.

By using a pipe holder with cooled clamping jaws, as disclosed in claim 2, one is able to effectively reduce the weld zone's material temperature after the welding, and hereby completely avoid oxidation on the inside of the pipe. This is of great impor- tance, in that the difficult mechanical or chemical treatment of the inside wall of the pipe is hereby completely avoided since the material does not oxi¬ dize.

As disclosed in claim 3, by allowing the coolant pipe to be comprised of a tube which winds around along the outside of the jaws, an efficient and uniform cooling of the jaws and herewith the pipe wall is achieved.

As disclosed in claim 4, by allowing the coolant pipe to extend a suitable distance on both sides of the jaws, these can be configured in segments, here¬ by enabling their diameter to be increased and re- duced to suit requirements.

As disclosed in claim 5, by providing the jaws with openings for the leading-out of the purging gas, there is also achieved an expedient cooling of the gas ,

As disclosed in claim 6, by configuring the pipe holder's jaw segments in such a manner that they can be swung in and out towards the inner side of the pipes, it is possible to achieve an adjustment to the one pipe and thereafter to the adjacent pipe, whereby it can be ensured that the pipes become cen¬ tred and are secured in one and the same cycle of operations.

As disclosed in claim 7, by providing the conical part of the pipe holder with a dog, it becomes easy to swing the jaw segments inwards to a smaller dia- meter by a displacement of the cone, whereby damage to the jaws is avoided during extraction of the holder.

As disclosed in claim 8, by using welding apparatus with coolant pipes through the gas-coverage casing, the temperature behind the welding zone is effect¬ ively reduced on the outer side of the pipe, which contributes towards shortening the cooling time and therewith reduces the consumption of gas.

Finally, as disclosed in claim 9, it is expedient to lead purging gas through an opening between the coolant pipe, in that the gas thus led out is cool¬ ed.

The invention will now be described in closer de¬ tail with reference to the drawing, where

fig. 1 shows a slotted pipe with pipe holder inserted and an external welding ap¬ paratus,

fig. 2 shows a sectional view of the pipe holder seen in the direction 11-11 in fig. 1,

fig. 3 shows an end view of the pipe holder seen in the direction III-III in fig. 2,

fig. 4 shows a sectional view of a second embodiment of the pipe holder before tightening up.

fig. 5 shows a sectional view of the same pipe holder after alignment and tight¬ ening up,

fig. 6 shows the welding apparatus seen from above, and

fig. 7 shows the welding apparatus seen from the side.

In figs. 1-3 is seen an example and in figs. 4 and 5 a second example of preferred embodiments of a combined pipe holder and rear gas apparatus 5.

The apparatus is inserted into a pipe 2 which is to be welded together with an adjacent pipe 1. The ends of the pipes can be provided with a chamfer which forms a notch 3 for the weld seam.

The construction of the apparatus with regard to the holding function will hereafter be described with reference to the embodiment shown in figs. 1-3.

In the centre there is mounted a cone 18 with an inclined slide face 17 against a holding element 14 which, as will be seen in fig. 3, consists of a number of wedge-shaped elements. Thus, when the cone 18 is moved into the apparatus, i.e. to the right in the drawing, the elements 14 will be pres- sed outwards towards the wall of the pipe.

In order to control this movement, the cone 18 is connected to a shaft 19 which via a threaded stud 20 is screwed together with a manoeuvring rod 21, the end of which is provided with a handwheel 30, as shown in fig. 1. Instead of a mechanical axial move¬ ment, this can also be achieved by means of, for ex¬ ample, a hydraulically operated cylinder.

Around the shaft 19 there are lying thrust elements 22 which extend from the holding elements 14, said thrust elements 22 being held pressed in against the shaft 19 by means of a series of compression springs 23, each of which rests against a screw 24 in an outer tube 25. The springs 23 will constantly press the elements 14 and 22 inwards, and the spring pres¬ sure is able to be adjusted by screwing the screws 24 out or in.

The end portion 27 of the tube part 25 is provided with a surrounding pipe section 28 which projects outside of the pipe 2, as shown in fig. 1. On the manoeuvring rod 21 there is also screwed a nut 29 on a thread on the manoeuvring rod, said nut 29 lying up against the end surface of the pipe section 28. By turning the handwheel 30, the cone 18 can thus be moved in an axial direction, whereby the ele¬ ments 14 can be moved outwards and inwards in rela- tion to the pipes 1, 2.

On the outside of the holding elements 14 there are secured jaws 15 which, as shown in fig. 3, form part of a circle and, as shown in fig. 2, have a convex cross-sectional profile.

The jaws 15 are preferably made of copper and are screwed firmly in the holding elements 14 by means of screws 16, see figs. 2 and 3.

As shown in fig. 1 , an open channel is formed in the middle of the jaws. In the middle of this chan¬ nel in each element 15 there is a discharge opening 36 for the rear gas.

Each of these openings 36 is connected to a pipe or a bore which is connected to a gas supply pipe 35 which ends in a manifold 32 mounted on the centre- most part 26 of the tube.

The gas is led to this manifold by a pipe 34 which, via a tube 33, leads the purging gas into the annu¬ lar manifold 32 , from where the gas is led out through the openings 36 and via the channel out to the rear side of the weld notch 3.

Moreover, a cooling system is mounted for the cool¬ ing of the jaws 15 and the gas supply 35. Coolant is led through a tube 37 to a coolant pipe 38 which extends along the apparatus 5 and in thro¬ ugh one of the jaws 15. From here, via a bend 39, the pipe is again fed through this jaw 15, so that a gas discharge opening 36 is located between the pipes.

All of the jaw elements 15 are thus provided with two coolant pipes. At the end of the looped coolant pipe 38 there is connected a discharge tube 40. When coolant is led through this coolant pipe, the jaws 15 will be cooled and herewith also the welding zone which lies at the pipe externally to the jaws.

In the mounting of this holding apparatus 5, the jaw elements 15 are set for clamping outwards against the pipe wall, so that the pipes are secur¬ ed during the welding. This also ensures the good heat-transferring characteristics between the heat- ed welding zone and the cooled jaws.

Upon conclusion of the welding, the cone 18 is screwed outwards, whereby the jaw elements assume a smaller diameter, after which the apparatus 5 can be extracted from below the underside of the weld seam. The long bends of the coolant pipe 38, see especially fig. 1, are so suitably yielding that this movement of the jaw elements can take place without any risk of breakage of the pipe 38.

The following is a description of the embodiments shown in figs. 4 and 5.

At the transition to the manoeuvring rod 21, the cone 18 is provided with a dog 41.

Furthermore, the end of the fixed pipe section 28 is formed as a ring 42 with a recess which forms a support for a rocker element 44 which at the head bears the one end of the jaw segment 14. The other end of the element is supported, as shown in the drawing, by the element 14 resting against the slide face 17 of the cone 18.

In order to hold the segment 14 against both the rocker element 44 and the cone 18, a tension spring 43 is mounted between the ring 42 and the underside of the segment, and in such a way that both the rocker element 44 and the tension spring 43 extend outwards in an inclined manner towards the end of the holder.

The tension spring can be adjusted by means of an adjusting screw 24 in the segment 14.

When the cone is moved outwards, towards the left in the drawing, the dog 41 will drive the holding ele¬ ment 14 to the starting position as shown by the fully drawn lines in fig. 4. In this position, the jaws 15 assume their smallest .diameter and the hold¬ er can be introduced into the one pipe 2.

Hereafter, by the movement of the cone 18 in the direction of the arrow, the holder can be tightened so much that the jaws tip outwards towards and are secured against the pipe 2. The rocker piece 44 will thus turn towards the inner side of the pipe, as indicated by the stippled line in the drawing, and the inside half of the jaw will be moved outwards towards the pipe.

The pipe 2 with the holder 5 can now be placed op¬ posite the adjacent pipe 1 , and the holder can be tightened further by drawing the cone 18 in the direction of the arrow, whereby the jaws 15 will be moved outwards to abut against the inner side of the pipe 1, as indicated by the stippled line in fig. 5.

At the same time that this tightening is carried out, the pipe 1 will be centred in relation to the pipe 2 for reasons of the uniform outward pressure from the jaws.

It should be noted that this also provides the pos¬ sibility of holding pipes together when their inside diameters deviate from each other, since the jaws will be able to hold them together even in a rela- tively inclined position, and such that it will al¬ ways be pipe 2 that the jaws clamp out towards and secure first, before they are fully swung out against the other pipe 1.

Consequently, what is involved is a combined align¬ ment tool and holding apparatus for the welding to¬ gether of pipes.

Hereafter, the actual welding apparatus 4 will be described with reference to figs. 6 and 7.

As indicated, the welding gun 6 is mounted at the end of the apparatus at the side of a control wheel 12 which is secured to the housing 7 by means of a suspension bracket 13.

The housing is curved, corresponding to the outer curvature of the pipe 1 , 2, so that it can serve as gas coverage for the welding.

On the underside of the housing 7, there is formed a downwardly-open chamber 8 into which purging gas is introduced through an opening 11 via a gas out- let pipe 9.

This housing 7 is also provided with a cooling sys¬ tem comprising a coolant pipe 10 which passes thro¬ ugh the housing and back again, with the gas outlet opening 11 lying between it. When coolant is led through this coolant pipe 10, the welding zone is quickly cooled, and the gas has a lower supply temperature, the result being that the welding is carried out with effective gas coverage and cooling.

Claims

C L A I M S

1. Method for the welding together of metal pipes and similar items by arc welding in the presence of purging gas, where the pipes are fixed by means of an internal pipe holder, and where the welding is carried out from the outside by means of welding apparatus having a welding gun, and whereby purging gas is introduced from the outside and possibly also internally in the pipes, c h a r a c t e r i z e d in that during the welding, coolant is supplied through coolant pipes (10, 38, 39), said coolant pipes extending along the rear and possibly along the upper side of the welding zone.

2. Pipe holder for the execution of the method ac¬ cording to claim 1 , and comprising an annular jaw arrangement made up of segments, said jaw arrange¬ ment being capable of distension and contraction in relation to the inside wall of the pipe, c h a r ¬ a c t e r i z e d in that in the vicinity of the outer side of the jaws (15), coolant pipes (38, 39) extend through the jaws from the one side to the other, said coolant pipes (38, 39) comprising one or more pipe bends which are supplied with coolant for passage through the coolant pipes (38, 39).

3. Pipe holder according to claim 2, c h a r a c ¬ t e r i z e d in that the coolant pipe (38, 39) is made up of a single pipe section which is connected to an inlet tube and an outlet tube (37, 40) for coolant.

4. Pipe holder according to claim 2 and 3, c a r- a c t e r i z e d in that the pipe bends (38, 39) ex¬ tend for a distance beyond the side edge of the jaws (15) in order to absorb the mutual movement of the jaw segments (15).

5. Pipe holder according to claims 2-4, c h a r ¬ a c t e r i z e d in that the purging gas is sup¬ plied to the jaws (15) through pipe (35) which has its egress (36) along the outer side of the jaws (15).

6. Pipe holder according to claims 2-5, c h a r ¬ a c t e r i z e d in that each jaw segment (14, 15) is supported partly at its one end by an element (44) , said element (44) abutting against a fixed underlay (42) on the holder in such a manner that the jaw segment (14, 15) can be turned outwards and inwards in relation to the holder, and partly at its other end by an element (14) forned on the inside of the segment and resting in a sliding manner against the pipe holder's conical surface (18), and furthermore in that a tension spring (43) is secured to the inner side of the jaw segment (14, 15) , the other end of said tension spring (43) being secured to the underlay (42) .

7. Pipe holder according to claim 6, c h a r ¬ a c t e r i z e d in that at the smallest diameter of the conical surface (18) there is provided a dog (41) against which the lower side edge of the ele¬ ment (14) can abut in that position in which the diameter of the jaws is at its smallest.

8. Welding apparatus for the execution of the method according to claim 1 , and comprising a hol¬ der for the welding gun and a housing behind the welding gun which extends around the outside of the pipe, said housing forming a chamber against the pipes and being supplied with gas, c h a r a c t ¬ e r i z e d in that in the vicinity of the under¬ side of the housing (7) , coolant pipes (10) extend through the housing (7) from the one side to the other, said coolant pipes (10) being comprised of one or more pipe bends which are supplied with coolant for passage through the pipes (10).

9. Welding apparatus according to claim 8, c h a r a c t e r i z e d in that the purging gas is supplied to the chamber (7) through an opening

(11) which is placed between the coolant pipes (10) and the housing (7) .