FR2514291A1 - WHITE LIGHT COLORED OR METALLIC PROTECTIVE COATINGS TO IMPROVE AND COMPLETE THERMOPLASTIC ANTI-CORROSION COATINGS EXTRUDED DIRECTLY ON THE ANTERIOR SURFACE OF CYLINDRICAL PIPES OR BODIES - Google Patents

Abstract

The coating according to the invention is distinguished by a white or other lightly coloured thermoplastic or reflecting coating (4) having been applied in a firmly adhering manner by extrusion to the black or dark anti-UV corrosion-protection coating (3) at the same time as the latter or directly to the outer surface of pipes or cylindrical objects (2).

Description

 The object of this invention is the extrusion and direct application of a thermoplastic coating which can be white or light or metallic in color, simultaneously and on the surface of a current black or other dark color anti-corrosion thermoplastic coating. extruded directly onto the exterior surfaces of pipes or hollow bodies.

 Numerous products are known which can be applied according to different processes to protect against corrosion steel pipes or prestressed concrete or cylindrical bodies. Among the most recent types of applied protective coatings, the best known are polyethylene coatings.

The difficulties Piton must overcome in providing a truly safe and long-lasting coating are manifold. The main difficulties that can between mentioned are the following
A) The materials forming the protective coating for steel or prestressed concrete pipes and hollow bodies must have the following characteristics
a) resistance to atmospheric agents and to the destructive action of the sun's ultraviolet rays,
b) resistance to corrosive actions of any kind, including biological attacks,
c) waterproof,
d) dielectric,
e) they must be intimately bonded to each other so as to form a single uniform layer, perfectly adherent to the surface to be protected.

 B) The coating must be able to not be damaged during the handling, transport and laying of pipes or cylindrical bodies and must also be able to be maintained without damage for long periods of time. To neutralize the action of accelerated aging dd to the ultraviolet rays of the sun, special additions are used such as white carbon which, however, gives the thermoplastic product a black or very dark coloring.

 The above pigments oppose the negative action of ultraviolet rays but their black color produces, when the pipe is exposed to the sun, an excessive rise in the temperature of the coating whatever the type of thermoplastic material, including polyethylene .

 It is well known that pipes or cylindrical bodies of steel or prestressed concrete are stored outside for many months and even one or two years, for technical or logistical reasons so that finally finally laid in the ground.

 Storage inside pipes or cylindrical bodies coated with their anti-corrosion thermoplastic coating including the coating of patyethylene can occur both at the coating plant and on set path docks, ports, or the like. temporary places.

 Successively the coated pipes are laid in their trenches where they are welded to each other to form a pipe for transporting water, oil, gas or other products.

The excessive rise in temperature due to exposure to the sun's rays, particularly in the regions of the Mediterranean basin or the deserts of the
Sahara and Arabian produces a softening of the materials forming the thermoplastic protective layer. In addition, the softening of the adhesive material placed between the surface to be protected and the thermoplastic protective coating considerably reduces the adhesion of the latter to the pipe or to the cylindrical body.

 Such a reduction in adhesion can cause serious drawbacks with regard to the integrity of the thermoplastic protective coating.

Among these drawbacks, mention may be made of the partial separation of the coating and / or its sliding over the protected pipe. More or less serious tears can occur and are difficult and costly to locate and repair and degrade the coating.

 The goal of. the present invention is to significantly reduce the effect of temperature on black or dark thermoplastic coatings during their exposure to the sun, without altering the beneficial action of carbon black.

 This invention consists in applying to the outside of the black or dark anticorrosion thermoplastic coating a white or very clear or metallized strip capable of reflecting the sun (the white color being preferably used).

 The application of a strip of thermoplastic of white or very clear or metallized color, which will be called thereafter "anti-solar" to simplify, adheres intimately and solidly to the thermoplastic layer of black or dark protection.

 The application of the sunscreen strip can be carried out in different ways. Two of these methods considered to be the most suitable will be described, which together with the others constitute an integral part of the invention.

 In the first example, the "sunscreen" material must flow, with polyethylene or another anti-corrosion material added with carbon black in the same extrusion head.

 In the second example, the “sunscreen” material and the polyethylene (or other thermoplastic material) are transported by two separate extrusion heads. In the second example, the thickness of the solar protection strip is completely independent of the thickness of the protective strip added with carbon black.

 Usually the anti-corrosion protective polyethylene layer or coating, or the coating of another suitable thermoplastic material consists of a strip wrapped once or more around a cylindrical body, until the desired thickness is reached. The thickness of the strip must be one submultiple of the total thickness of the protective layer and at the same time the strip is offset by the same submultiple.

EXAMPLE 1
To obtain the outer anti-solar protective layer on top of the anticorrosion layer, as indicated, two associated extruders are used: one for the black or dark thermoplastic material of the protective cover, and the other for the layer "anti-solar" which extrudes a single strip through a single extrusion strip.

 For example: application of a protective layer consisting of three overlapping offset bands.

The total thickness must be established for the protective layer, including the "anti-solar" strip.

 The pipe or cylindrical body to be reviewed advances by turning around its own axis and passes under the device for extruding the protective thermoplastic material, immediately after receiving the adhesive substance which ensures complete adhesion of the protective coating to the surfaces. to protect.

 It should be noted that the white or light colored "anti-solar" strip is in itself also protective and corrosion-proof, like the underlying black or dark stripes: it is mainly distinguished by the absence of ultra-violet anti-ray material based on carbon black.

FIGURE 1
A) pipe to be coated;
B) extruder or container containing the adhesive;
C) extrusion head or other device for applying the adhesive;
D) adhesive layer to adhere the polyethylene to the pipe;
B) extruder (s) for polyethylene containing carbon black;
F) extrusion head for both types of polyethylene;
G) part of the extruder plate for polyethylene containing carbon black;
H) extruder (s) for white, clear or reflective polyethylene;
I) part of the extrusion head for polyethylene, white, clear or reflective;
L) single strip of polyethylene extruded directly onto the pipe and offset by a third of its width, made up for two thirds of its thickness of the protective coating with carbon black and for a third of the white or very clear or reflective exterior coating ;
M) pressure roller to improve the adhesion of the protective coating on the pipe;
N) part of the pipe coated with a white or very clear or reflective coating and provided with an underlying anti-corrosion coating.

 The coating layer of the pipe or cylindrical body consists for one third of its thickness of the white or clear or reflecting substance and for the underlying two thirds of the black or dark layers of ultraviolet rays.

FIG 2
Cross section of coated pipe or cylindrical body
1) internal part of the pipe or cylinder
2) thickness of pipe or cylinder;
3) thickness of the adhesive layer;
4) thickness of the anticorrosion coating layer.

FIGURE 3:
Longitudinal section of the coated pipe or cylinder:
1) internal part of the pipe or cylinder;
2) thickness of the pipe or cylinder;
3) thickness of the adhesive layer;
4) thickness of the anti-corrosion thermoplastic layer
- a) thickness of the internal layer containing carbon black of the thermoplastic coating;
b) thickness of the intermediate strip with carbon black added to the thermoplastic coating;
- c) thickness of the "anti-solar" outer strip of the thermoplastic coating.

EXAMPLE 2
To obtain the external protection of the underlying sublayer against corrosion by the described "anti-solar" layer, two other separate extruders must be used, each having an extrusion plate; one for the thermoplastic material with carbon black added, the other for the "anti-solar" layer.

 This arrangement makes it possible to have different thicknesses for the two materials.

 In practice, a white or clear thermoplastic strip is extruded immediately after extrusion of the black or dark layer.

 The width of the "sunscreen" strip must be a sub-multiple of the width of the strip of black or dark thermoplastic material equal to the number of offset strips which form the total thickness of the black protective layer. If the black layer results, for example from three overlapping bands offset by a third of their width, the width of the anti-solar band must be one third of the black or dark band.

 In the present case, which represents one of the numerous embodiments of the present invention, the anti-corrosion protective layer is formed by four overlapping bands: three black or dark interior bands with carbon black added and the white band " anti-sun "superficial.

 This last strip may be of a thickness different from that of the three strips containing carbon fiber.

FIGURE 4:
A) part of the pipe to be coated;
B) extruder or container for the adhesive;
C) extrusion head or other adhesive application device;
D) layer of adhesive to adhere the polyethylene to the pipe;
E) extruder (s) for polyethylene containing carbon black;
F) extrusion head for polyethylene added with carbon black;
G) polyethylene strip containing carbon black extruded directly onto the pipe and wound with an offset of one third of its width in order to obtain the desired thickness;
H) polyethylene extruder for the white or clear substance "anti-solar";
I) extrusion head for white or clear "anti-solar"polyethylene;
L) white or clear "anti-solar" bandwidth equal to one third of the band G) formed of polyethylene containing carbon black and which will completely envelop the layer of polyethylene containing carbon black underlying;
M) pressure roller to adhere the protective coating to the pipe;
N) part of the pipe coated with a white or clear or reflective layer.

 To facilitate perfect adhesion of the "anti-solar" strip on the black or dark layer, it is recommended to apply the "anti-solar" strip on the underlying black or dark thermoplastic coating when the latter is still hot and A the pasty state.

Before cooling the coating, it is recommended to apply a roller on the protected external surface to make the coating perfectly regular and to facilitate the adhesion of the various layers which form the anticorrosion protective coating.

 The foregoing description clearly shows the importance of the invention which makes it possible, in a single operation, to solve several problems, in particular to continue using polyethylene and other suitable thermoplastic materials added with carbon black or other pigments suitable for protecting pipes or cylinders from ultraviolet rays and for considerably reducing the effects of solar heating thus contributing to substantially improving the mechanical resistance of the protective coating.

 The present invention has been described in the form of one of its preferred embodiments, but it goes without saying that variantsesssont possible without departing from the scope of the invention.

 One of these variants would consist in using a "knitting system" instead of the "strip" system described above for producing the anticorrosion coating.

Claims (4)

 1 A method of coating the external surface of pipes or cylindrical bodies, characterized in that a layer of white or light colored thermoplastic or reflective material is extruded to adhere it intimately to a sub-layer of black anti-corrosion material or dark forming screen vis-à-vis ultraviolet radiation, the two materials can be applied or extruded directly on said outer surface.  2. Application of the method according to claim 1 to the execution of a metallized "anti-solar" coating as well as a thermoplastic anti-corrosion coating, with a view to eliminating the drawbacks resulting from the black or dark color of the coatings anti-corrosion thermoplastics commonly used for the protection of pipes and cylindrical bodies.  3. Application according to claim 2, # charac- terized in that the material of the undercoat is polyethylene loaded with carbon black or other black or dark pigments such as to neutralize the action of ultraviolet radiation.  4. Application according to claim 2 or 5 characterized in that one can leave exposed to the sun for long periods the pipe or other coated cylindrical body, the latter being protected from heat despite the presence of an under- black or dark layer,