NO142316B - PROCEDURE FOR THE CONSTRUCTION OF UNDERWATER PIPES AND APPARATUS FOR USE IN THE IMPLEMENTATION OF THE PROCEDURE - Google Patents

Description

The invention relates to a method for laying

of underwater pipelines on the seabed, comprising forming a fibre-reinforced pipe from a thermosetting resin and weight coating the formed pipe. The invention also relates to a device for use when carrying out the method.

Conventional subsea oil pipelines are made from lengths of weight-coated steel pipe that are welded together on a laying barge and lowered into the sea. The greater the depth of the seabed, the greater the tension that must be maintained on the pipeline during laying, with the result that laying pipelines on

depth greater than approx. 30 meters has entailed significant technical difficulties and has necessitated the use of relatively thick steel pipes to withstand the stresses this entails. The difficulty of laying steel pipelines is significantly increased due to the harsh conditions at sea, and when the wave height becomes greater than a given size, with any laying technique the laying must be interrupted. This means that for many months during the year, the laying of pipes is very difficult, if not impossible, in certain maritime areas, e.g. The North Sea.

One purpose of the present invention is to provide a method for laying underwater pipelines intended for the flow of crude oil, which method can be carried out essentially independently of the sea conditions. A further purpose is to provide a device which is intended for laying underwater pipelines.

According to the invention, a method has been provided for laying underwater pipelines intended for bringing crude oil ashore, which method is characterized by what appears in the claims.

From Norwegian generally available patent application no. 3496/72 as well as U.S. patents no. 2718684 and 3532132, methods and equipment for continuous production and laying of pipes on land are widely known. The pipe is produced in vehicles which then lay it out. The vehicle thereby has a speed that corresponds to that with which the pipe is laid. Although there are certain points of similarity here, the technique known from the above-mentioned documents cannot be directly transferred to the laying of pipes on the seabed. The technical problems that must be overcome when laying pipelines at sea are completely different from the problems you have on dry land. The equipment shown in the piping counters will clearly only work in a normal air atmosphere. - Should one use the technique known from the above-mentioned documents, this would have to be done in such a way that the equipment was placed in a surface vessel/ from which the pipeline is lowered.

The actual shaping of tubes from thermosetting resins is well known and can easily be adapted for operation in an underwater vessel. Such a technique is described e.g. in chapter II (Tube and Rod Production) of the book "Glass Reinforced Plastics", 2nd edition, by Philip Morgan. Such a technique may include extruding filament windings.

Many different types of reinforcing fibers can be used, e.g. the fibers can be inorganic or organic. Examples of inorganic fibers are glass fibers and metal fibers, e.g. steel wire. Examples of organic fibers of many polymeric fibers which are not attacked by the thermosetting resin used, e.g. if unsaturated polyester resin systems, nylon, terylene and carbon fibers are used. Mixtures of different fibers can produce pipes with desired properties. The preferred thermosetting resins are unsaturated lead esters and polyepoxy resins.

The shaped pipe must be coated with a weight load to ensure stability on the seabed. The preferred weight load consists of an aggregate which is bonded together to form a solid coating with a suitable thermosetting resin. The use of a bonded aggregate has the advantage that the binder that gives the finished coating good impact strength is easily available and that the aggregate has the necessary pressure resistance to be able to withstand the pressures that arise when laying and using pipelines at great depths. Preferably, the resin used to connect the aggregate is the same as that used in the manufacture of the pipe. This ensures a good connection between the pipe and the weight-bearing coating.

A preferred weight bearing coating consists of an unsaturated lead ester resin/aggregate mixture containing a graded aggregate> so that the spaces between the aggregate particles are as small as possible and that therefore the need for unsaturated polyester resin is reduced. Preferably, the ratio between aggregate and resin is between 1-7 and 1-15 calculated from weight. Ordinary vibrating equipment can be used to unify the weight coating around the pipe before curing.

The outer surface of the weight coating is preferably made as soft as possible to minimize the problem of sealing walls, or partitions in underwater vessels where the pipe must be passed through and where there is a difference in pressure. This can be achieved by surrounding the shaped pipe with a mold that defines a cavity into which the aggregate and binder can be introduced. If the inner surface of the mold is smooth, the finished surface of the weight coating will also be smooth and easy to pass through suitable sealing rings. Appropriately, in continuous production, the mold is movable with the tube and at the same speed, and the thermosetting resin is arranged so that it hardens to a sufficient extent by the time the mold has passed the work area or the station where the weight coating is formed. Where a step-by-step pipe forming technique is used, it may be unnecessary to move the mold because the curing of the weight coating can be arranged to be sufficiently advanced to allow the pipe to be extruded by the time a standard length of pipe is formed.

The shaped fiber-reinforced tube can advantageously be provided with an outer collar in the weight coating area, which collar has a larger inner diameter than the outer diameter of the tube and is designed to surround the tube to define a cavity for the tube and cover into which a weight material can be poured and allowed to harden. The collar can be left in position on the pipe and form its outer surface.

Any plastic material can be used to shape the collar. It is preferred to use a plastic material that has a good impact strength, i.e. a plastic material with an "Ozod" impact strength greater than 2, and suitably between 3 and 5. By impact strength is meant a strength factor as measured according to British standard test no. 3126, appendix A. High density polyethylene and copolymers of ethylene with minor amounts of other monomers such as propylene, butene and hexene are particularly preferred. If desired, the requirements can be made from foamed plastic materials.

The collars may be of any internal shape provided they can be placed over the pipe to define a cavity between themselves and the pipe of sufficient volume so that when filled with weighting material the final combination has sufficient weight and ensures that the pipes fall down and remain on the seabed. Under certain circumstances, it may be desirable to use collars which, when placed on the pipe, form a cover with one or more flat surfaces that facilitate the placement of the underwater line on the seabed. However, it is usually most appropriate to arrange collars with the same shape as the pipe on which they are to be used. In most cases, the collar is therefore round to fit the round pipe that is usually used.

The collars can be arranged close to each other, but are arranged or designed in such a way that the weight material in one collar is somewhat separated from the weight material in the next collar or only has contact over part of its thickness near the pipe.

In this way, a final product is obtained which can bend more easily than a pipe which is completely covered with a uniform thickness of hardened weight material. The collars can be designed so that the plastic material is arranged between the separate weight materials in adjacent collars. By choosing a plastic material with good yielding properties, the total space between adjacent weight materials can be filled without affecting the flexibility of the pipe. This can reduce the possibility of the pipe being damaged, e.g. of trawl wires, or -that -cables are infiltrated between adjacent weight materials fmews-?de "mistakes that the pipe body can be bent while it is laid on the seabed.

The requirements on a pipe can be of different lengths along the pipe although it is preferred that they are all identical.

Each plastic collar is preferably produced in two or more parts which can be joined together to form a complete collar around the fibre-reinforced pipe. Conveniently, it is made of two halves which are shaped so that it is easy to fasten them around the pipe. Once attached around the pipe, the individual halves or sections can be held together while the weight material is added or joined together by means of adhesive, plastic welding or by other suitable methods.

The requirements must have a certain distance from the pipe to determine a forming cavity into which the weight material can be introduced. Preferably, if their relative shape permits, the covering is arranged symmetrically around the tube, so that in the final product the hardened weight material has the same, or at least symmetrical thickness around the tube. The distance for covering can be achieved by means of spacer rings or similar spacers between the fibre-reinforced pipes and the plastic collar. For example the plastic collar may be formed with internal ribs or internal extensions which serve to position the cover on the pipe and also, especially in the case of ribs, to strengthen the plastic cover. If internal ribs are used, it is important to ensure passage between them, so that the weight material can easily fill the entire space between the pipes and the plastic collar. Ribs or spacer rings are preferably attached at each end of the plastic collar to define the ends of the forming cavity formed between collar and tube. These end ribs or rings can form the yielding material that separates the weight material in adjacent collars.

The edges of adjacent collars can be designed so that they overlap each other and thus form a protective cover over the separation that may be desired between adjacent weight material sections or recesses in continuous lengths of weight material. The collars are preferably designed with internal ribs that are undercut or are held so that when a flowable, hardenable weight material is used, the collars will be effectively locked to the pipe during curing. Furthermore, the reinforcement materials for the weight material can be attached either between the ribs or in the circumferential direction, both for stiffening the collar and the weight material and to assist the locking of the collar to the weight material.

Each collar may be designed with a hatch located at such a location that it is the top when the collar is placed on the pipe. This hatch allows the introduction of the hardenable weight material. It is advantageous that these hatches can be equipped with hatch covers which themselves have smaller hatches. In this way, the amount of hardenable weight material can be introduced through the large hatch opening, after which the hatch cover is placed and the filling is carried out through the small hatch opening, the small hatch opening being either covered with a cover when the filling is completed or alternatively the weight material can be shaped to

provide a smooth surface at the hatch.

Weight coating of the shaped pipe can be achieved by rolling an outer cover around the pipe, while at the same time or afterwards weight material is introduced between the pipe and the cover. The outer covering can be applied as a simple cylindrical part, but is preferably wound on the pipe in a helical manner which facilitates continuous operation. Many different materials from thin metal sheets to flexible plastic sheet materials can be used to form the cover. A particularly useful material is high density polyethylene which can be easily produced as a continuous strip with a cross-section which allows each successive turn for the cover to fit with the preceding turn to form a smooth outer surface. The cross-section of the strip can be shaped, if desired, so that the finished weight-coated pipe has grooves or other notches or depressions in its outer surface which provide the desired degree of flexibility to allow it to conform to the seabed where it is laid. The cover strip can be formed with a rib which projects into the pipe and helps to keep the cover at the desired distance from the pipe - to allow the introduction of sufficient weight material. It can also be designed to assist with the retention of the weight material before it is finally cured in place and if desired to ensure that the covering remains connected to the weight material in the finished pipeline. The presence of the rib in the weight material can, by suitable design of the rib, increase the flexibility of the finished pipeline.

An advantage of high density polyethylene for the cover is that it can be designed to form part of the finished pipe. However, other covering materials can be used which break down over a period of time on the seabed, provided that the weight load material has suitable resistance to the water environment.

As mentioned above, a preferred thermosetting resin for use both for the formation of the pipe and as a binder for the aggregate which is to form the weight coating is an unsaturated polyester resin. Such resins are generally or can easily be designed to be resistant to crude oil or other natural materials that may be carried through an underwater pipeline.

The term "unsaturated polyester" is used in the most common sense as polycondensation products of dicarboxylic acids or anhydrides with dihydroxy alcohols if one of the reactants present during the polycondensation reaction contains a polymerizable double bond. Unsaturated polyesters can be modified by the presence in the polycondensation reaction mixture of monocarboxylic acids, monohydroxyl alcohols and small amounts of polycarboxylic acids or polyhydroxyl alcohols. Particularly suitable unsaturated polyesters are obtained by esterification of saturated dihydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, trimethylene glycol, α-propylene glycol, 1:3-butylene glycol and bisphenol A adductors with ethylene oxide and propylene oxide with α-unsaturated, α,γ-dicarboxyl acids, such as maleic, fumaric, itaconic and citraconic acids. This type of unsaturated polyester can be modified by replacing some of the unsaturated dibasic acids with an equivalent amount of a saturated dicarboxylic acid, e.g. succinic, adipic, sebacic, phthalic, isophthalic, azelaic, tetrahydrophthalic, endomethylenetetrahydrophthalic or hexachloroendemethylenetetrahydrophthalic acids. Unsaturated polyesters are generally in the presence of an unsaturated monomer which can effect a copolymerization with the unsaturated polyester. Examples of such monomers are styrene, which is the most commonly used, vinyltoluene, α-methylstyrene, methyl methacrylate, ethylene glycol dimethacrylate, ethyl acrylate, acrylonitrile, vinyl acetate, diallyl phthalate, diallyl maleate and triallyl cyanurate.

The rate of curing of unsaturated polyesters and their blends with copolymerizable monomers is usually increased by the presence of polymerization catalysts that include organic peroxides, such as benzoyl peroxide, lauryl peroxide, isopropylbenzene hydroperoxide, methyl ethyl ketone peroxide, and 1-hydroxycyclohexyl hydroperoxide-1. The curing rate of polyester resin can also be modified by the addition of suitable inhibitors, such as hydroquinone, α-naphthol, tertiary butyl, catechol, benzaldehyde or tetrachloroquinone, and foreign substances, such as certain amines such as dimethylaniline, diethylaniline, di-n-propylaniline, dimethyl-para-coluidine, diethyl-a-naphthylamine, para-dimethyl-amino-azobenzene and dimethyl meta-aminophenol and metallic salts, such as vanadium, cobalt and manganese naphthonate. The use of such curing catalysts and curing promoters enables the curing of polyester resin to be carried out under ambient conditions and in a period of time which is within the speed of movement of the pipe through the underwater vessel when using continuous operation.

The weight coated pipe can be led from the underwater vessel directly from the weight coating station, provided that the appropriate seal between the coated pipe and the wall of the underwater vessel is present. However, it is preferred to pass the coated pipe through a series of compression chambers in the underwater vessel, as each chamber can be kept at an increasing pressure, so that the pressure difference between each time two chambers and between the last chamber and the seawater outside of the underwater vessel will not pose too great sealing problems . Also, a series of chambers may allow some seawater to pass through the last seal or seals and be easily pumped back to sea. Appropriately, the weight-coated pipe is led directly from the submerged underwater vessel to the seabed when the underwater vessel moves forward.

The invention also relates to a device for implementing the method, i.e. an underwater vessel for laying underwater pipelines, which vessel can perform a controlled movement on or near the seabed and is characterized by what appears in the device requirements.

The underwater vessel should be able to carry out a controlled movement on or near the seabed. Thus, the vessel must either be equipped with wheels or belts that can make the vessel move along the seabed, or nozzles, propellers and the like that can cause it to move through the water provided that it is in a sufficient state of buoyancy. Adjustment of the buoyancy can be achieved by ordinary devices using floating tanks and the like. A controlled movement of the running gear can also be achieved by a combination of mechanical and hydraulic devices. Thus, a combination of a guiding device in contact with the seabed to stabilize the vehicle and hydraulic devices to move it can provide a steady traction on the extruded pipe and ensure that it is not destroyed during laying.

The pipe forming and weight coating can be carried out in

the same or in separate stations. These can be built up in the underwater vessel in a similar way as in normal factories on land, as particular consideration must be given to the control of any exhaust gases that may be emitted from the thermosets used.

they resins. It is preferred to use separate stations and provide devices for guiding the shaped tube to the coating station.

The device for guiding the coated pipe to sea-

the bottom has been described above as preferably comprising a series of compression chambers. The device for guiding the weight-loaded pipe from the vehicle should be adjustable at sea-

end, so that the extruded tube can be straightened up to the surface. Thus, risers etc. can be formed by attaching buoyancy devices

more or floats to the extruded tube.

The underwater vessel must contain all necessary items

to keep a crew on or near the seabed for a sufficient

equally long period of time which enables the laying of pipes. The use of nuclear power is particularly appropriate in this connection. Preferably, therefore, the underwater vessel will be equipped with an electric

ler several docking ports, on which supply pipes or the supply submersible can be placed. Through such ports, the underwater vessel can be supplied with raw materials that are necessary for form-

ing of weight-laden pipelines and food, fuel and other essentials for the crew.

In one design, a sealed pipe is formed in the underwater vessel, weighted and brought to the seabed, the pipe is further formed at the speed with which the pipe is laid on the seabed when the underwater vessel moves away from the starting point. When end-

point is reached, the pipe in the vessel can be sealed and fed to the seabed where it can be connected to land or the oil platform using normal techniques.

Normal submarine safety conditions must be observed

in the design of the underwater vessel. The danger of flooding in the vessel due to collapse or softness of the laid pipe can be reduced by providing a mandrel in the pipe, which mandrel can be expanded to seal the inside of the pipe in the underwater vessel in response to an increase in pressure in the pipe caused by the pipe -

failure outside the vessel.

In the following, the invention will be described in more detail by means of a schematic drawing showing the underwater vessel according to the invention. In the drawing, the underwater vessel 1 has rollers 2 with the help of which it can be moved on the seabed. At a first station 3, polyester resin is fed from the tank 4 together with glass reinforcement from the store 5 to the pipe forming machine 6. This machine of standard design produces a pipe which is taken to a second station 7 where aggregate is fed from the storage container 8 and unsaturated polyester resin from the storage container 9 to a form 10 for forming a weight load around the pipes. The polyester resin systems used at the two stations are set so that the formed pipe is sufficiently cured by the time it is fed to the second station to withstand the weight of the aggregate/resin mixture, and the weight coating is sufficiently cured to allow it to form an effective seal -ning between the second station and the first compression chamber 11. The coated pipe is then passed through further compression chambers 12 and leaves the underwater vessel through the seal 13 and is laid on the seabed when the underwater vessel is moved in the opposite direction at the same speed as the coated pipe is pushed out.

Vehicles have hatches 14, 15, 16 and 17 which lead to various storage containers, through which fresh supplies can be delivered via a second underwater supply vessel which is equipped with suitable outlet openings which can be attached to the pipe-laying vessel or via pipes from a surface vessel. The underwater vessel is also equipped with other hatches through which the crew can leave the vessel while it is underwater when a supply vessel is locked to the hatch. The underwater vessel also has other supply systems and the like which are of a conventional nature and not shown in the schematic drawing.

Claims (3)

1. Procedure for laying an underwater pipeline on the seabed, comprising the formation of a fiber-reinforced tube of a thermosetting resin and weight coating of the formed tube, characterized in that the weight-loaded tube is shaped in a submerged underwater vessel (1) and led out from this down onto the seabed through one or more seals, as the vessel is moved over the seabed as the pipe is brought out, and that the pipe is shaped into a continuous length which is at least longer than the length of the vessel (1). 2. Method according to claim 1, characterized in that the coated pipe is passed through a series of compression chambers (11, 12) between the seals in the underwater vessel (1), which chambers are supplied with increasing pressure from the inside outwards in order to reduce the pressure difference between two chambers and between the last chamber and the seawater side of the underwater vessel (1). 3. Device for use when laying an underwater pipeline in accordance with the method according to claim 1 or 2, including devices (4-6; 8-10} for forming a fiber-reinforced plastic pipe and weight coating of this, characterized in that the device is designed as a submersible underwater vessel (1) which is equipped with one or more seals that are adapted to the dimensions of the weight coating for sealed passage of the weight-coated pipe, and that the vessel (1) is movable at a speed that corresponds to the speed at which the pipe is laid on the seabed 4. 'Device according to claim 1', characterized in that a mandrel is arranged in the pipe, which mandrel can be expanded to seal the pipeline.