Device for the assembly or mechanical reinforcement and the anti-corrosion treatment of elements of immersed structures, and assembly and treatment process relating thereto

A device and process for reinforcing underwater structures of branched joints having a main element (1) and at least one secondary element (2), one end to which is integral with the surface of element (1). The device incorporates a flange (3, 3'), a first portion (3') of which is initially fixed to the secondary element (2), and a second portion (3') of which is thereafter fixed to the first portion. The flange portions define an annular space between the flange and the elements. A liquid composition which generates an elastic polymerized material (4) is introduced into an enclosure to fill the annular space and encapsulate the flange, which enclosure defines the outer boundary of the polymerized material (4).

TECHNICAL FIELD 
The invention relates to a device for the rigid assembly or mechanical 
reinforcement of elements forming part of immersed structures, such as the 
branch joints which exist, for example, on offshore drilling platforms. 
The invention further relates to a process for the rigid assembly or 
mechanical reinforcement and the anticorrosion treatment of such 
structural elements, and to a device for carrying out the said process. 
BACKGROUND ART 
All immersed structures, for example bridge pillars, dikes, dams or 
offshore drilling platforms, are subject to the effects of corrosion in 
the longer or shorter term. Such effects tell in particular on all the 
metal parts immersed in a marine environment and, depending on the extent 
of the corrosion, they often result in mechanical weakening of the entire 
structure. The strength and lifetime of the structure are accordingly 
reduced. 
The anticorrosion treatments which have been carried out hitherto use 
quasi-manual techniques. The most widely practiced solution in fact 
consists in utilizing the services of divers, who, under several meters or 
tens of meters of water, manually coat the elements to be treated with, 
for example, paints, resins or mastics. Such techniques, practiced under 
difficult conditions, are very expensive, hazardous for the workforce and, 
most frequently, rather unsatisfactory in terms of their effectiveness. 
In addition to the adverse effects due to corrosion, immersed structures of 
this kind suffer the consequences of various mechanical stresses such as, 
for example, gravity, the repeated impact of the waves, the pressure of 
underwater currents or the traction on anchorage points. Offshore drilling 
platforms are relatively sensitive structures in this respect, by virtue 
of both their construction and their exposure to the natural elements. 
Under the effect of the swell over a prolonged period, constituent 
elements such as branch joints are continually subjected to forces of 
traction, compression or even shear or torsion. Since they generally 
contain a large number of welds, these branch joints constitute weak 
points which should be checked regularly, protected or even reinforced if 
necessary, these operations being difficult, if not dangerous, at very 
great depths. 
Although simulations on mock-ups or with the aid of theoretical models are 
possible and enable the weakest points of such structures to be identified 
beforehand if necessary, the number and variety of the effects to which 
branch joints of immersed drilling platforms may be subject are such that, 
in practice, one has to make do with taking action a posteriori, i.e. when 
the structure is already in service, after a more or less prolonged period 
of immersion. 
To carry out the rigid assembly or mechanical reinforcement and the 
anticorrosion treatment of elements forming part of immersed structures, 
such as branch joints, for example, it is essential for those skilled in 
the art to have at their disposal technical solutions which are easily 
applicable, non-hazardous and reliable. This is advantageously achieved by 
using the device and following the installation procedure set forth 
herein. 
SUMMARY OF THE INVENTION 
It has in fact been discovered that the device according to the invention 
can advantageously be used for the rigid assembly or mechanical 
reinforcement and the anticorrosion treatment of elements forming part of 
highly complex structures, such as branch joints of members--girders or 
tubes--supporting offshore drilling platforms, for example. 
It has been observed in particular that such elements assembled with the 
aid of the device according to the invention are capable of withstanding 
traction or compression forces which are considerably greater than, or in 
some cases more than twice as great as, those withstood by assemblies 
constructed using the common techniques, before they suffer deformation or 
their welds break.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the embodiment shown in the Figures mentioned above, the device 
according to the invention is designed for the rigid assembly or 
mechanical reinforcement and the anticorrosion treatment of a branch joint 
made up of a main tubular element 1 and a secondary tubular element 2, one 
of the ends of which is integral with the surface of the said element 1. 
This type of embodiment in no way implies a limitation. 
According to the invention, the device comprises a flange 3, 3' fixed to 
the secondary element 2, either to its sides (FIG. 4) or to its end (FIGS. 
1 to 3). The said flange is made up of a first portion 3 which is integral 
with the element 2 and shaped so as to surround at least part of the main 
element 1, and at least one second portion 3'--if necessary several flange 
segments 3' cooperating with one another which is shaped so that it can be 
fixed to the first portion 3 in order to form, with the latter, a flange 
3, 3' surrounding the element 1 with a certain amount of play. The 
portions 3 and 3' can be fixed to one another by any appropriate means 12 
such as, for example, bolts, rivets or spot welds. 
When the flange portion 3 is fixed to the end of the element 2 (FIG. 3), 
the fixing is effected in most cases by means of a weld. When the flange 
portion 3 is fixed to the sides of the element 2 (FIG. 4), the said 
portion can, for example, extend into a shape 13 enveloping the said 
element 2 over part of its outer surface; in such a case, the fixing can 
be effected by means of clamping collars 14. 
According to the invention, the flange 3, 3' is shaped so as to surround 
the main element 1 with a certain amount of play. This play is actually 
necessary to permit the insertion of elastic polymerized material 4, 
which, once in contact with all the metal surfaces to be treated, can thus 
fully exert its corrosion-inhibiting effect. The mass 4 should also be 
uniformly distributed on either side of the flange 3, 3' in order to 
ensure a good distribution of the mechanical stresses to which the unit is 
subject. The play created between the outer surface of the element 1 and 
the inner surface of the flange 3, 3' can vary, from case to case, from 
several millimeters to several centimeters; it will most commonly be of 
the order of the thickness of the metal plates used to construct the 
elements 1 and 2 and the flange 3, 3'. 
As indicated, the portions of the elements 1 and 2 which cooperate with the 
flange 3, 3' are set in a mass of elastic polymerized material 4 (FIG. 2). 
According to the invention, this is a homogeneous mass whose coefficient 
of elasticity can be adjusted at will in accordance with the mechanical 
stresses to be withstood. It is up to those skilled in the art to make 
such an adjustment: an attempt will be made in particular to avoid thereby 
introducing hard points into the immersed structure as a whole. 
In order to carry out the fixed assembly or mechanical reinforcement and 
the anticorrosion treatment of elements such as those described above, the 
following operations are performed under water, the situation supposedly 
being one in which the weld initially joining the element 2 to the surface 
of the element 1 has given way and the end portion of the element 2 has 
been sawn or abraded (FIG. 3): 
A first flange portion 3 is fixed to the sawn or abraded end of the element 
2, most commonly by means of a weld, the portion 3 being shaped so as to 
surround at least part of the element 1. This operation can be repeated 
several times if the branch joint has several secondary branches. 
A second flange portion 3' is then fixed to the first portion 3 using 
appropriate means 12. If necessitated by the configuration of the point to 
be treated, it is possible to assemble several flange portions 3', 
cooperating with one another, and to fix them to the first portion 3 to 
give the desired flange 3, 3'. The shape and arrangement of all the 
elements making up the flange 3, 3' are of course designed so that the 
flange surrounds the element 1 with the predefined play. 
Finally, a liquid composition generating an elastic polymerized material 4 
is poured into an enclosure 5 surrounding the unit formed by the flange 3, 
3' and the portions of the elements 1 and 2 which cooperate therewith. 
In a situation where the device according to the invention is more 
particularly intended for the mechanical reinforcement and the 
anticorrosion protection of branch joints in which the secondary element 2 
remains welded to the main element 1, it is possible, for example, to 
adopt the following procedure (see Figure 4): 
For such purposes, a first flange portion 3, or, if necessary, several 
first portions are used which extend into the shape of an envelope 13. 
This extension 13 is shaped so that it can be laid against the sides of 
the element 2, on its outer surface, in the vicinity of the end welded to 
the element 1. 
The said flange portion 3 is fixed to the element 2 by way of its extension 
13, the rigidity of this unit being provided by, for example, clamping 
collars 14. 
A second flange portion 3' is then fixed to the first portion 3, the flange 
formed being shaped so as to surround the element 1 with the desired play. 
Finally, the liquid composition generating elastic polymerized material 4 
is poured in, as indicated above. 
According to the invention, the said liquid composition has a greater 
density than the surrounding liquid medium. Using appropriate means, which 
will be described below, it is brought to the lower zone of the space 
inside the enclosure 5, the said space then being progressively filled 
from the bottom and the liquid composition driving the water upwards out 
of the said space as it enters. This procedure avoids undesired mixing of 
the liquids present, which can lead to the formation of emulsions and in 
some cases to homogeneity defects in the mass 4 once it has polymerized. 
As indicated previously, the liquid composition generating elastic 
polymerized material has a greater density than the surrounding liquid 
medium. The density is adjusted in conventional manner using commercial 
products. The said liquid composition also has the characteristic of 
polymerizing without shrinking, under the conditions of the surrounding 
medium: it is this quality which makes it possible to guarantee a good 
adhesion of the polymer to the element treated, for example metal or 
concrete, and consequently optimum anticorrosion protection and mechanical 
reinforcement. Moreover, the liquid composition is designed so as to 
generate an elastic polymerized mass and preferably a polymerized mass 
whose modulus of elasticity can be adjusted at will in accordance with the 
desired effects of mechanical reinforcement. 
Liquid compositions which can advantageously be used are two-component 
mixtures generating epoxy resins or polyurethanes, these being mixed, if 
necessary, with various additives such as, for example, ballasting 
substances, polymerization retarders or colorants. The essential 
requirement is to obtain a liquid composition which polymerizes under 
water and whose characteristics can be adapted at any time to suit the 
needs described above: those skilled in the art can easily achieve this 
using specialized commercial products. 
The enclosure 5 mentioned above also forms part of the invention: it is 
utilized as a means of carrying out the above process. The invention 
relates more precisely to a device comprising preformed sections of 
shuttering, 6, 7, 8 etc. which can be joined together, around the point to 
be treated, to form an enclosure 5 which is open at the top and, on some 
of its faces, has passages 9, 10 etc. which fit closely around the 
periphery of the elements 1 and 2 cooperating with the said faces, and 
comprising means 11 for bringing the liquid composition to the lower zone 
of the space defIned by the saId enclosure 
The detail of a particular embodiment of such a device (see FIG. 1) and its 
use according to the invention will be described below. Over at least part 
of its edges, each of the sections of shuttering 6, 7, 8 etc. has one or 
more recesses located so as to coincide with one or more corresponding 
recesses in the adjacent section of shuttering, thus forming passages 9, 
10 etc. whose axis of symmetry is most commonly represented by the edge 
shared by two assembled sections. The said passages 9, 10 etc. are shaped 
so as to fit closely around the periphery of the elements 1 and 2 of the 
immersed structure. This type of preforming does not present any 
particular problems because it can be prepared very accurately on land 
using the construction drawings of the structure to be treated. 
As the case may be, the periphery of the passages 9, 10 etc. can be 
provided with elastic gaskets, one of the purposes of which is to 
compensate for the imperfections in the construction or preforming. Such 
gaskets can also be provided on the edges along which the sections of 
shuttering have to cooperate. 
The device also comprises means which enable the assembled sections of 
shuttering 6, 7, 8 etc. to be fixed together. Any appropriate known means, 
for example a latch, a clip or a screw or bolt system, can be used for 
such purposes. The said means will be designed so as to ensure either 
temporary or permanent assembly of the sections of shuttering, as the case 
may be. 
The device also comprises means 11 which enable a polymerizable liquid 
composition to be brought to the lower zone of the space defined by the 
enclosure 5. An example of a means 11 which can be used is an injection 
pump connected to a pipe whose lower end comes out near the bottom of the 
enclosure 5, inside the latter. The simplest solution consists in using a 
flexible tube of adequate diameter, which brings the liquid composition 
from the surface. 
The device is positioned in the following manner. Firstly, rigid preformed 
sections of shuttering 6, 7, 8 etc. are brought to the level of a point on 
the structure which is to be treated, and they are then assembled, at 
least in pairs, by their edges to form an enclosure 5 around the point to 
be treated, the said enclosure being open at the top and some of its faces 
allowing elements 1 and 2 of the structure to pass through the passages 9, 
10 etc. Once the said sections have been fixed together and the unit has 
thus been rendered rigid around the point on the structure which is to be 
treated, the space defined by the enclosure 5 is filled with a liquid 
composition which polymerizes without shrinking. 
As the case may be, to enable the sections of shuttering to be removed 
easily from the polymerized mass 4, the inner face of the said sections 
can be lined beforehand with a sheet or film of polymer exhibiting weak 
adhesion towards the mass 4, for example a sheet of polyester. 
Also, as the case may be, the sections of shuttering 6, 7, 8 etc. can be 
reinforced with angles or ties arranged according to the mechanical 
stresses to be suffered. To make them easier to handle in a liquid medium, 
the said sections will preferably be made of a material whose density is 
substantially similar to that of the surrounding liquid medium: it is 
possible to use simple or composite materials such as high-density wood or 
polyester reinforced with glass fibers, for example, suitably ballasted 
with metal elements if necessary. 
As the case may be, the sections of shuttering used can also be made of 
steel, the said sections then being kept suspended with the aid of floats 
or, where possible, held up by cables or any other appropriate means at 
the surface. In cases where immersed metal structures are treated, a 
so-called sandwich (metal/ polymer/metal) is obtained which also 
contributes to the mechanical reinforcement of the unit, the sections of 
shuttering used then being left in place.