Apparatus for working on a tube portion using a laser beam, and use thereof on pipe tubes on a marine pipe-laying or pipe recovery barge

The laser apparatus (L, G, T) is placed on a stand (B) which carries the support for the working head (T) of the apparatus in rotary manner, and the apparatus together with its stand are housed in a container (C) through which the tube passes, which container is fixed to the tube while work is taking place, the mass of the container together with that of its contents considerably damping the transmission of stresses from the tube to the working head.

The present invention relates to an installation for working on a zone of 
the wall of a tube by means of a laser beam directed at said zone and 
moved to scan the zone. 
By way of example, the work may comprise cutting, or welding, or surface 
treatment. 
Numerous devices have been proposed for performing such work. Essentially, 
they comprise a laser beam generator, a working head that includes both 
means for focusing the laser beam and an outlet nozzle for the focused 
beam, a waveguide for guiding the laser beam from the generator to the 
working head, and means for moving the working head so that the laser beam 
travels over the zone to be worked. 
In certain applications, the means for moving the working head comprise a 
support that carries the working head and that revolves so that the 
working head moves around the tube, e.g. to cut the tube or to butt weld 
two tubes together. 
The support which carries the working head must therefore be positioned 
accurately relative to the tube so that the axis of rotation of the 
support has a position that is defined relative to the tube, and that 
coincides therewith, at least approximately. 
Publication FR-A-2 704 166 describes an installation as defined in the 
preamble of claim 1, and in which the rotary support is mounted on a plate 
which is directly fixed on the tube, however that solution is 
inappropriate when the tube is subjected to motion and vibration while the 
work is taking place, which applies in particular to tubes making up a 
pipeline that is being laid at sea from a barge. When working with a laser 
beam, it is most harmful for vibrations of the tube to be transmitted to 
the working head and to the beam waveguide. 
To make a pipeline at sea, tubes of transportable length, generally 10 
meters (m) to 24 are welded together on the "laying ramp" of the barge. 
After a tube has been welded into place, the barge is advanced by the 
length of the tube, with a corresponding length of pipeline being laid 
behind the barge. The barge is held in place by anchor lines and it is 
moved by winches. It is naturally subjected to the motion of the sea and 
its position is not absolutely fixed during welding even though the 
position of the pipeline which rests on the sea bed is practically 
constant along its axis. Relative movement is therefore continuously 
taking place between the barge and the pipework in the axial direction of 
the pipework, and this also gives rise to vibration. 
An object of the present invention is to position the rotary support 
carrying the working head accurately relative to the tube without tube 
vibration being transmitted to the working head and to the waveguide 
connecting said head to the laser beam generator. 
According to the invention, this object is achieved by placing the 
apparatus on a stand which carries the working head support in rotary 
manner, and in housing the apparatus and its stand inside a container 
having openings through which the tube can pass and including means for 
being temporarily fixed to the tube, the container also carrying the 
control cabinet and the high frequency cabinet for the laser generator, 
whereby the rotary support is fixed to the tube only via the container 
whose mass together with that of its contents considerably damps the 
transmission of stresses from the tube to the working head and to the 
waveguide. 
The absence of direct fixing between the tube and the rotary support of the 
head also presents the advantage of making it very easy to adapt the 
system to tubes of different diameters. 
By placing the high control cabinet and the frequency cabinet for the laser 
generator as stationary items in the container where the stand carrying 
the generator is also stationary during welding, it is certain that the 
high frequency cable connecting the high frequency cabinet to the 
generator is not subjected to any mechanical stress during welding, which 
is very important. 
The invention also relates to a particular preferred embodiment of the 
working head. 
In this embodiment, the working head includes a chassis fixed firstly to 
said rotary support and secondly to the end of the waveguide, and a 
movable assembly mounted to move in translation on the chassis and 
including both the focusing means for focusing the laser beam coming from 
the waveguide and the outlet nozzle for said beam, the axis of said 
translation being that of the incident laser beam on the focusing means 
and being parallel to the axis of rotation of the rotary support, said 
chassis also carrying a motor suitable for driving said assembly in 
translation under appropriate control. 
It is sometimes necessary to cause the laser beam leaving the nozzle of the 
working head to perform small displacements as it rotates around the tube. 
This can apply, for example, when butt welding two tubes together, where 
the abutment zone of the tubes to be scanned by the laser beam is not 
perfectly circular, whereas the head travels round a circle and the 
apparatus must include means for applying small correctional displacements 
to the beam leaving the head during the circular travel of the head. 
Moving the head of the assembly constituted by the focusing means and the 
nozzle in translation along the chassis makes it possible to perform "join 
tracking" correction without such correction requiring the waveguide to be 
displaced since the chassis on which the assembly slides and to which the 
waveguide is fixed remains stationary during the corrective displacement. 
In addition, by suitably programming the control of the motor that causes 
said assembly to move in translation, it is possible to cause the laser 
beam that leaves the head to have deliberately oscillating motion which is 
appropriate when welding with a filler metal, thus making it possible to 
weld together tubes having chamfered ends of great thickness without any 
need to increase the power of the laser, and also making it possible to 
weld together tubes made of material that is not normally weldable by 
means of a laser beam.

The following description and the accompanying drawings disclose other 
characteristics of the present invention. 
The installation shown in the figures essentially comprises a container C, 
and a stand B carrying apparatus constituted by a laser generator L, a 
waveguide G, a working head T, and a rotary support S. 
The container C (FIGS. 1 and 2) which contains the stand and the apparatus 
carried by the stand is mounted on a barge represented by a guide rail 1 
enabling the container to be moved longitudinally on the barge along the 
axis of the pipeline, e.g. by being mounted on wheels 2 and being moved on 
demand by a constant tension winch 3, or by motors driving the wheels. The 
container has an entrance 4 and an exit 4' through which tubes V pass, and 
it includes fixing and damping means enabling it to be fixed with damping 
to the tubes passing through it. These means are represented 
diagrammatically at 5 and 5' and may be constituted, for example, by 
abutments or by jaws provided with damping pads and actuated by actuators 
secured to the container so as to clamp the tubes between them. 
By way of indication, in a typical example, the container is a rectangular 
box that is about 10 m long, about 5 m high, and about 3 m wide. It 
includes appropriate inspection hatches or openings, and means are 
provided to make it possible, from the outside, to control and observe the 
container and the controllable members found inside the container. 
The stand B is disposed inside the container so as to be capable of being 
adjusted in height by means of actuators 6 and of being displaced 
longitudinally to adjust its position along tubes relative to the location 
of the weld to be made. In the solution shown, the stand slides on 
slideways 7 being driven by actuators 7' having a stroke of several tens 
of millimeters. The container also contains a floor 8 on which the control 
cabinet 9 and the high frequency cabinet 10 of the laser generator L are 
placed. The container is also fitted with air conditioning means 11 for 
air conditioning the zone Z of the container which contains the cabinets 9 
and 10, and refrigerator means 12 for refrigerating the high frequency 
cabinet and the laser generator. 
Umbilical cords 13 convey such water, gas, and electricity to the container 
as are required. 
The stand is very rigid and supports the laser generator L (FIGS. 3 to 5) 
and adjustment means 14, 15, and 16 are provided to adjust at will the 
level and the trim of the generator on the stand so that the laser beam 
has the appropriate direction on leaving the generator. 
The stand B also carries a plate 17 having a vertical turntable S mounted 
thereon to rotate about a horizontal axis x, which turntable serves as a 
support for a head T connected by a waveguide G to the laser generator L. 
The plate and the turntable have a central passage for passing the tubes 
V. The turntable is rotated by a motor M and a transmission belt (FIG. 6). 
The waveguide is made up in conventional manner by a sequence of 
rectilinear lengths g.sub.0, g.sub.2, g.sub.4, g.sub.6, and g.sub.8 
connected one to another by hinges g.sub.1, g.sub.3, g.sub.5, g.sub.7, and 
g.sub.9. Each hinge is constituted by a single bend including a mirror 
that deflects the laser beam through 90.degree., or by two facing bends 
each including a deflecting mirror and connected together either directly 
or via a short rectilinear length. 
All of the hinges are at locations on the stand which are fixed, with the 
exceptions of the last hinge g.sub.9 which is secured to the head and 
which travels therewith, and of the penultimate hinge g.sub.7 which is a 
double hinge being connected to the last hinge g.sub.9 via a telescopic 
rectilinear length g.sub.8 and to the preceding hinge g.sub.5 via another 
rectilinear length g.sub.6, the rectilinear lengths g.sub.6 and g.sub.8 
acting like the legs of a compass whose vertex is constituted by the 
double hinge g.sub.7. 
The above-described waveguide is preferred in the present invention because 
it has a minimum of moving parts, however the person skilled in the art 
could choose some other type of waveguide for such and such a particular 
reason. 
The working head T (FIGS. 8 to 10) in the invention comprises a chassis 19 
carrying a slideway 20 for a moving assembly E which includes a parabolic 
focusing mirror 21 and an outlet nozzle 22 for the focussed beam. The 
chassis is designed to be fixed to the end of the waveguide G so that the 
laser beam coming from the waveguide penetrates into the chassis going 
towards the parabolic mirror along the translation axis x' of the assembly 
E, and the chassis 19 is also fixed to the rotary support S so that the 
translation axis x' is parallel to the axis of rotation x of the rotary 
support. The moving assembly E is moved in translation by a ball screw 23 
driven by a motor 24 mounted on the chassis. The motor 24 is controlled by 
means that are known per se (and not shown) on the basis of signals 
delivered by a join detector fixed to the head so as to cause the laser 
beam that leaves the nozzle to move back towards the join between the two 
tubes that are to be welded together, should that be necessary ("join 
tracking"). 
The chassis 19 is fixed to the end of the waveguide G by any appropriate 
means that allow relative pivoting between the chassis and the waveguide 
about the axis x' of the laser beam. The fixing means are represented in 
FIG. 8 by a ring P. 
The chassis 19 is fixed to the turntable S so as to capable of moving in 
translation on the turntable by means of slideways 20' extending along an 
axis z lying in the plane defined by the axes x' and x and extending 
perpendicularly thereto. This translation movement is controlled by a 
motor 25 mounted on the chassis 19 and actuating a ball screw 26. The 
motor is controlled in conventional manner on the basis of signals 
delivered by the join detector so that the distance between the point of 
focus of the laser beam and the outside surface of the join is appropriate 
for obtaining proper welding ("skin tracking"). 
It will be observed that during welding the length of the waveguide is 
substantially constant, with the only change in length being due to 
variation in the length of the telescopic arm due to movement of the head 
for skin tracking, which variation is at most of the order of 1 
centimeter. 
According to an advantageous feature of the invention, the moving assembly 
E also includes a dispenser 27 for feeding a filler metal 28 into a zone 
where welding is taking place. 
On a barge for laying a pipeline at sea, the following operations are 
performed for welding and laying the pipeline: 
the tube to be welded is presented to the end of the last tube of the 
pipeline and the two tubes are held together in an appropriate position 
for welding them together, this being done by conventional means, and 
preferably by internal clamping jaws; 
the container is moved to bring the welding head to the vicinity of the 
zone where the weld is to be made and fixing means are engaged between the 
pipeline and the container; 
the position of the stand is adjusted so that the working head is in an 
appropriate position to begin welding the join, taking the diameter of the 
tubes into account (FIGS. 1 to 7); 
the join is welded; 
the barge is advanced along the pipeline to lay in the sea the additional 
length thereof that has just been added by welding; 
a new tube is presented for welding and the end of the pipeline is locked 
thereto by moving the internal clamping jaws to the location of the new 
join that is to be made; 
the container which has remained fixed to the pipeline at the location of 
the preceding weld is released and brought up to the new welding position, 
it being specified that the container could be released before the barge 
has finished advancing so as to reduce container displacements and 
accelerate throughput; and 
the new join is welded. 
To raise a pipeline laid at sea, the same operations as above can be 
performed in reverse order, with the laser beam outlet nozzle being fed 
with an appropriate gas in order to cut the pipeline up into tubes of 
appropriate length. 
The invention is not limited to the embodiment described above.