Patent Application
20120241547
The invention is related to the field of fiber reinforced plastic tubes. Depending on the nature of the fibers applied, such tubes usually have a high strength. For instance, polyester fibers make the tubes in question suitable for the transport of high pressure liquids and gasses. Examples thereof are crude oil and natural gas, which may comprise aggressive components. Such components may be detrimental to steel pipes, for which reason it is desirable to use fiber reinforced tubes having a proper liner which can withstand the aggressive nature of such fluids.
The strength of the tube therefore depends heavily on the fiber reinforcement. As mentioned, the tubes comprise an inner liner so as to convey the fluids. Onto the liner, the fiber reinforcement layer is applied, and finally the coating layer is applied onto the fiber reinforcement layer. This fiber reinforcement layer may be carried out in various shapes. As an example, the fiber reinforcement layer may be a braided layer. Alternatively, the fibers may be embedded in a tape which is wound around the liner according to a helical shape. Also, the fibers may be wound onto the liner according to various plies and winding angles.
Due to the nature of the plastics and the fibers used, the tube has a stiff character in such a way that it maintains its circular shape, also when exposed to moderate external pressure loading. Depending on the diameter of the tube, this stiffness will resist the bending of the tube to a greater or lesser extent. Generally, it is still feasible to wind a tube of relatively small cross sectional diameter onto a reel, the diameter of which however must not be too small as otherwise the tube will buckle or kink while being wound onto the reel.
The step of winding the tubes on a reel is highly desirable having regard to the fact that it is thereby made possible to supply a great uninterrupted tube length. Tubes of a great length have the advantage that relatively few couplings need to be made to make up a complete trajectory, which is beneficial for both the reliability of such trajectory and for limiting the cost thereof. It will however be clear that the maximum dimensions of reel with a tube wound thereon are limited, having regard to the requirements which are imposed when using road transport. As a tube of relatively large cross sectional diameter has by its very nature a high resistance against bending, it is hardly feasible to wind such tube onto a reel which, in view of road transport, has moderate dimensions. This means that a tube with relatively large diameter is usually supplied in straight sections of limited length. As mentioned, this has disadvantages both in view of the cost of the trajectory obtained and the cost thereof.
The object of the invention is therefore to enable the supply of relatively great lengths of a fiber reinforced tube of moderate up to large diameters, while maintaining the possibility of transport efficiency, such as road transport. This object is obtained by a method for handling a fiber reinforced tube the tubular wall of which has a stiffness which allows the tube to maintain a nominal circular cross section of its own, said tube comprising a liner, a fiber reinforcement surrounding the liner and a coating surrounding the fiber reinforcement, comprising the steps of:
It appears that the tube, despite its stiff character, is still capable of being compressed so as to obtain a flattened shape. The tube may nevertheless maintain its integrity, despite the formation of possible longitudinal folds in the wall thereof. However, the formation of longitudinal folds, if any, depends on the amount of compression applied. After flattening, the tube has relatively little resistance against bending, which has the advantage is that the tube may be wound onto a reel, even in case the original circular tube was of a relatively large diameter. The risk of kinking or buckling is greatly diminished, having regard to the fact that a flattened tube has a relatively low bending stiffness. The flattened shape has the further advantage that it allows more windings to be accommodated onto the reel, for a given maximum outer diameter of the combination of reel and wound tube.
In this connection, a distinction should be made between the tubes in question with which the invention is concerned and so-called hoses. A hose does not have a wall which provides a stiffness which could make the hose to maintain a circular shape. Instead, a hose is of a very flexible nature and collapses as soon as an internal overpressure is relieved. Thereby, a hose can be readily wound onto a reel as it has already, by its very nature, a flattened shape.
The step of flattening the tube may be carried out in several ways, and may for instance directly be carried out after manufacturing the tube. Preference is given to the steps of:
The facing parts of the caterpillars provide a stable support for the tube, in such a way that said tube can be flattened in a stable and reliable manner. However, the tube may alternatively be flattened by the steps of:
According to a further alternative, the method may comprise the steps of;
The sliding surfaces may be provided with a low friction coating, so as to enable the tube to slide through the funnel with low resistance while being flattened.
Preferably, the rotational axes of the caterpillars or rollers are generally parallel to the axis of the reel. Preferably, the nominal diameter of the tube is larger than 75 mm. Furthermore, the ratio of the wall thickness of the tube over the outer diameter thereof may be larger than 5% and preferably smaller than 15%. The amount of flattening of the tube, expressed as the ratio of the nominal diameter of the circular tube and the maximal thickness of the flattened tube, said thickness being measured in the direction of flattening, may be at least 3. The ratio of the minimal radius of curvature of the wound tube and the diameter of the circular tube may be smaller than 15, preferably smaller than 10.
After the reel with the wound tube has been delivered at a specified location, the following steps may be carried out:
In particular, the tube may regain the circular nominal cross section thereof by increasing the internal pressure thereof in comparison to the pressure outside the tube. After the pressure is relieved, the tube with its resumed circular shape is self supporting again, and is able to maintain said circular shape against external pressure loadings, gravity and the like.
The invention is furthermore related to the combination of a reel and a flattened tube wound onto the reel by the method addressed before. The amount of windings of the flattened tube on the reel may be at least 2.
The tube may be carried out with different materials, provided that a certain level of elasticity is ensured so as to enable the flattening deformations of the tube. These deformations may be completely elastic, in such a way that the tube may regain the perfect original circular shape again. However, the invention is not limited to such fully elastic deformations. It may also be possible to deform the tube to such an extent that plastic deformations occur, that is deformations which leave a lasting trace in the tube.
Preference is given to a liner material comprising (high density) polyethylene (HDPE), polyamides like polyamide 11 or polyamide 12, polyvinylidenedifluoride (PVDF), polypropylene (PP) or other thermoplastic resin. The reinforcement layer preferably comprises a ductile or thermoplastic fiber, such as polyester fiber, nylon fiber, polyamide fiber. Alternatively, the reinforcement layer may comprise a steel reinforcement, such as steel fiber, steel cord or steel strips.
The invention will now be described further with reference to the drawings.
The tube 4 as shown in
Due to the fact that the several layers, in particular the liner and the reinforcement layer, serve completely different purposes, the materials used for these layers are different as well. As a result, the layers in question do not adhere to each other as the materials thereof are usually chemically incompatible. Thus, the liner is able to settle somewhat with respect to the reinforcement layer. In fact, the behavior of the layers under bending deformations of the tube could be regarded as being independent from each other. This phenomenon plays an important role upon bending the tube, such as occurs while winding the tube onto a reel.
The tube 4 according to the invention is therefore not to be wound directly onto a reel. In a first step, as shown in
Once flattened, the tube 4, 5 is wound onto a reel 13 as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 11159523.7 | Mar 2011 | EP | regional |
