Positioning of an additional tubular element on a tubular structure

In the positioning of an additional tubular element, e.g. a pipe section, on a tubular structure, e.g. a pipe-line in the course of immersion, where the end surfaces to be brought into contact are not in radial planes, the additional element is brought in alignment with the structure and at a short distance from the latter. The end surfaces of the element and structure are then brought into contact, the contacting ends are centered, and a compressive force is applied to them in such a way that the element can pivot about the point of contact between the element and the structure until its end surface is brought into complete contact with the end surface of the structure.

BACKGROUND OF THE INVENTION 
The present invention relates to the positioning of an additional tubular 
element on a tubular structure which may be subject to a random movement 
and where the planes of the end surfaces of the structure and of the 
additional element to be brought into contact have slight angular 
deviations with reference to each other and with reference to the 
corresponding theoretical planes orthogonal to the respective longitudinal 
axes of the structure and the additional element. 
Since the aim is to make the two confronting end surfaces coincide, there 
are two difficulties due to the particular conditions involved. 
With regard to the angular deviations mentioned, it will be understood that 
they may constitute the major obstacle to correct positioning, i.e. to 
realising simultaneously the coincidence of the end surfaces and the 
alignment of the axis of the additional element with that of the original 
structure. 
The problems produced by angular deviations in the end surfaces can, in 
certain cases, be overcome, where the ends of the element and of the 
structure are to be welded together, after positioning. If the welding 
process adopted is welding by high-frequency electric current and if the 
additional element is applied to the structure with a high compressive 
force, this has the effect of causing upsetting of the material, as occurs 
during forging, so as to bring the two end surfaces into coincidence, 
respecting as far as possible the coaxiality of the additional element 
relative to the structure. Such a method may also be applied even in cases 
where strict coaxiality of the element and the structure is not essential. 
It will be appreciated that whatever the welding process adopted, and more 
particularly where electron beam welding is involved, the primordial 
condition for good assembly remains the realisation of perfect coincidence 
between the end surfaces in contact. This is also so in the case of 
assembly by screwing. 
With the regard to the movements to which the original structure may be 
subject, they are likewise such as to compromise the success of the 
assembly operation, without considering the damage which might result to 
the components involved. From this point of view, it is necessary to 
ensure good retention of the element relative to the structure to enable 
risks associated with relative random movement to be avoided. 
SUMMARY OF THE INVENTION 
According to one aspect of the present invention there is provided a method 
of positioning an additional tubular element on a tubular structure 
subject to random movement, the planes of the confronting end surfaces of 
the ends of said structure and of said additional element having slight 
angular deviations with reference to each other and to the corresponding 
theoretical planes orthogonal to the respective longitudinal axes of said 
structure and of said additional element, said method comprising bringing 
said additional element to a position in which it is substantially coaxial 
relative to said end of said structure and in which said end surface 
thereof is in contact with said end surface of said structure, contact 
there between occurring at the closest points of said end surfaces, 
exerting a compressive force across said contacting end surfaces adjacent 
said end surfaces, and simultaneously centering said end surfaces relative 
one to another and laterally guiding said additional element, such that 
said additional element inclines relative to said structure to completely 
apply said end surface thereof against said surface of said structure. 
Said structure may, by way of example only, have, at least in its region 
adjacent its said end surface, which is uppermost, a nearly vertical 
position, said additional element being initially positioned with its 
lower end adjacent said upper end of the structure and substantially 
contiguous therewith. Said structure may for example be a pipeline in the 
process of being laid on the sea bed from a floating structure, and said 
additional element may be an additional pipeline section to be assembled 
there with. 
Said additional element is then brought into general alignment with said 
structure with which it is to be assembled, said upper end of said 
structure and said lower end of said element then being a certain distance 
from one another and substantially coaxial. 
The additional element may be suspended in this position by any suitable 
known means while, as will be described, guide means may be arranged in a 
region near the upper end of said element for guiding said element 
laterally whilst permitting axial movement thereof. The element is then 
moved towards said structure until contact is established between said end 
surfaces of said structure and said element. It is at this stage that the 
compressive force is applied and in such a way as to permit the additional 
element to incline relative to said structure. The upper end of said 
additional element is guided by means such that the upper end can incline 
relative to the lower end, and the lower end of said additional element is 
maintained centered on the upper end of said structure. The compressive 
force is applied at at least three angularly spaced points. 
The above arrangement results firstly in a rocking movement of said 
additional element about an axis passing through said point of contact of 
said two end surfaces producing complete coincidence of said surfaces with 
each other. It may also result in a vigorous locking of said element to 
said structure, which will enable the unwelcome consequences, which 
movements to which the structure may be subject could have upon the 
sequence to operations, to be avoided. 
Correct centering of said additional element with reference to said 
structure is perferably ensured from the interior of both said structure 
and said element and said centering may be maintained until completion of 
any assembly operations which may be performed after the positioning 
process is complete. 
The compressive forces are advantageously applied in regions near the ends 
of said structure and said element. 
Preferably during the rocking of said element, the guide means follow the 
corresponding movements of the upper part of the said element and, when 
the two end surfaces of said element and said structure have been brought 
into coincidence, said guide means are locked in position, while still 
leaving said element free to move axially. This having been done, said 
compressive forces exerted on the end surfaces may be relieved. 
This is particularly indicated in cases where, after positioning, it is 
proposed to assemble said element with said structure by high-frequency 
welding. It is, in fact, advantageous in this case to try to increase the 
skin effect due to the high-frequency current, this current appearing at 
the surfaces of the ends of said structure and said element; to this end, 
whilst continuing the high-frequency heating, said additional element may 
be raised by a certain distance parallel to itself, and such movement not 
modifying the balance of the forces present. Then, after having maintained 
said additional element in this raised position for a sufficient time, 
said element is lowered again and a powerful compression is again applied 
at the level of the contacting end surfaces, to cause the upsetting of the 
material already mentioned, this upsetting being akin to that obtained 
during a forging operation. 
However, in comparatively favourable cases high-frequency welding may be 
undertaken directly, without previous raising of said element, but by 
exerting, as before, a more vigorous compression after welding, with the 
same result as described above. 
According to another aspect of the invention there is provided apparatus 
for use in carrying out the above described method, the apparatus 
comprising guide means for laterally guiding said additional element while 
permitting inclination thereof, said guide means being arranged in the 
region of the upper end of the said additional element remote from said 
structure, means for exerting compressive force on said additional element 
and said structure and tending to bring said element and said structure 
together, and centering means for centering said additional element 
relative to said structure, adapted to be arranged in the region of said 
end surfaces thereof, and permitting inclination of said element relative 
to said structure. 
No description will be given hereinbelow of the means, which are known per 
se, by which said additional element is brought into alignment with said 
structure. In this position, said additional element is generally located 
a certain distance from said structure. 
As already explained, lateral guiding means, e.g. hydraulic stops, are 
provided in the region near the upper end of said additional element for 
maintaining said additional element in position in spite of the possible 
random movements, and also for supporting the component, perpendicular to 
the axis of said element, of the weight of said element, which necessarily 
deviates from the vertical. The stops are, however, arranged to permit 
movement of said element along its axis. They also permit a certain 
lateral movement of the upper part of said element during the rocking 
movement of said element. They may however be locked after said additional 
element has assumed its final position, while still allowing said 
additional element to move in the direction of its axis. 
The means for exerting a compressive force on said additional element and 
said structure may comprise two beams adapted to be fixed respectively to 
said structure and said additional element adjacent the ends thereof to be 
brought into contact, said beams being interconnected by a plurality of 
jacks regularly arranged around the circumferences of said beams and 
mounted on said beams so as to permit inclination of said additional 
element relative to said structure. Preferably the jacks are articulated 
at their ends to the respective beams. 
In operation, said cross-beams are fixed to the respective ends of said 
additional element and said structure and said additional element is then 
moved towards said structure until contact is made between the closest 
points of the two confronting end surfaces. The two beams are then joined 
together by said jacks. The jacks are then activated and the simultaneous 
action of all of them produces rocking of said additional element on said 
structure until said two end surfaces are brought into full contact, and 
then, if desired, compression of said additional element against said 
structure, as has already been described. 
Said guide means may comprise, in respect of each stop, means for 
contacting said additional element, e.g. an idler roller, rotatable about 
an axis which is substantially orthogonal to that of said element, so that 
axial movement of said element can occur substantially without friction. 
An embodiment of the apparatus according to the present invention will now 
be described, by way of example only, with reference to the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 there is shown, very schematically, the upper end of a tubular 
structure 1 which is, in this embodiment, a pipe in the course of 
immersion from a floating platform 5. The end of the structure 1 is 
supported in a frame 2 made integral with the platform 5. The water level 
is shown at 6. 
An additional pipe element 3 is to be positioned on, and eventually 
assembled with, the end of the structure 1. The element 3 is illustrated 
in a position close to alignment, with two beams 7 and 8, and a centering 
device 9 being in place. The beams 7 and 8 are fixed to the element and 
the structure respectively adjacent the ends to be assembled, and are 
interconnected by at least 3 jacks 10 regularly spaced apart around the 
beams and articulated to the beams at points 11. The jacks 10 are supplied 
with a common fluid under pressure which causes the surface of the lower 
end of the element 3 to come into contact with the surface of the upper 
end of the structure 1 and then to pivot about its point of contact to 
bring the end surface of the element 3 into coincidence with the end 
surface of the structure 1. The apparatus also comprises retaining and 
guide means 4 adjacent the upper end of element 3. An embodiment of these 
means is shown in FIG. 2 and comprises idler rollers 13 each of which is 
associated with a stop 15 which bears against an element of the frame 2. 
As shown, the rollers 13 are arranged symmetrically with reference to the 
element 3 and bear upon four points, arranged in a cross, of the external 
surface of the element 3. The stops 15 may for example be jacks which may 
be supplied with a common fluid under pressure or may be short-circuited 
together in opposite pairs and having opposite effects, for following the 
movements of inclination of the element 3. 
A mutually opposed pair of rollers and their associated stops may serve as 
weight-compensating means, whilst the other pair may serve as anti-rolling 
stops where a submerged pipe is involved. 
It is, however, self-evident that the number and arrangement of the rollers 
and stops may be varied according to requirements. 
An embodiment of the centering device 9 is shown in FIG. 3 and comprises a 
body 16, for example of steel, the lower part 17 of which, located beneath 
the joint plane 18, is cylindrical with a slightly smaller diameter than 
that of the end of the structure 1. The part 19 of the body 16 arranged 
above the joint plane 18 has a reduced section and is slightly conical at 
least at its junction with part 17 so as to permit the inclination of the 
additional element 3 on the end of the structure 1. Alternatively an 
exterior centering device may be used, the device being flared in its 
upper part surrounding the element 3. 
The centering device is equipped with sectorial contact shoes 20, with 
toroidal seal elements 21, which may for example be of the inflatable 
type, and rolling wheels 22. The shoes, seals and wheels are moveable 
between operative positions and inoperative positions in which they are 
retracted into their respective housings in the body 16. 
The centering device is suspended by means of a cable 23, with which the 
pipelines for the supply and remote control of the shoes, seals and wheels 
described above may be associated. 
If it is desired to effect a connection by screwing or friction welding, 
additional means for rotating the additional element may be provided. In 
the case of assembly by screwing, compression is removed during rotation 
whereas in the case of friction welding, compression is maintained during 
rotation. 
The additional rotatable means may be a rotatable gripping device which 
engages and rotates the additional element. The gripping device could, for 
example, be mounted in part 25 of beam 7. Such a rotatable gripping device 
is known in drilling and will differ according to the diameter of the pipe 
to be inserted. The gripping device could additionally serve to conduct 
electric welding current. 
Friction welding requires interior and exterior scraping devices for 
removing bulges formed during welding. The interior scraping device may be 
mounted on the centering device 16 and the exterior scraping device may be 
activated by a jack bearing on the beam 8. 
It is self-evident that the present invention is not intended to be limited 
to the embodiment which has just been described; modifications of detail 
may be made to it without thereby departing from the scope of the 
invention. 
It will also be appreciated that while the invention has been described in 
terms of a structure having a vertical upper end and substantially 
vertical additional element, the orientation of the structure and element 
may vary.