Lined pipe wherein the liner comprises a one-way valve

A pipe for the transport of fluids, which pipe is internally provided with a liner, wherein the liner is provided with at least one non-return valve arranged in the liner wall, wherein the non-return valve has an inlet end arranged near the outer surface of the liner wall and an outlet end arranged near the inner surface of the liner wall.

PRIORITY CLAIM

The present application claims priority on European Patent Application 00311528.4 filed on 21 Dec. 2000.

1. Field of the Invention

The present invention relates to a pipe for transporting a fluid under pressure, which pipe is internally provided with a liner. More particular, the present invention relates to a liner for such a pipe, which liner is adapted such that it cannot be damaged by a pressure that is exerted by a fluid accumulated in an annulus between the liner and the pipe.

In the specification and in the claims the word pipe will be used to refer to any conduit for transporting a fluid, such as for example a pipeline.

2. Background of the Invention

In many industrial applications pipes are used to transport a fluid. Operating and environmental conditions usually require high mechanical strength of the pipe, and for this reason many pipes are made from metal such as carbon or low alloy steel. On the other hand, the pipe material is subject to corrosion and other detrimental influences than can be caused by the fluid in the interior of the pipe. Therefore, pipes are often provided with a corrosion-resistant internal liner.

The liner serves to prevent direct contact of fluid contained in the interior of the pipe with the inner surface of the pipe wall. To this end, the liner usually has the form of a hollow tube that conforms more or less to the inner surface of the pipe, and wherein the tube is made of a corrosion-resistant material, e.g. a polymer such as polyethylene or polyamide, a rubber, another synthetic material, or stainless steel. The space between the outer surface of the liner wall and the inner surface of the pipe wall in a certain region of the lined pipe will in the specification and in the claims be referred to as the intermediate space.

The size of the intermediate space, i.e. its shape and volume, is in part determined by the construction design of the lined pipe. For example, the liner may be fitted loosely or tightly into the surrounding pipe, and even with tight fitting liners it is possible that grooves or channels in the pipe wall and/or the liner wall constructively determine an intermediate space of a particular size. Further, in pipelines which are formed by attaching a plurality of lined pipes to each other, in the area of flanges between individual pipes an intermediate space may be present.

Further, the size of the intermediate space may change during operation of a lined pipe. Although commonly used synthetic liner materials are highly corrosion-resistant, they may be permeated by certain fluids or fluid components, for example hydrocarbon gas. Permeation can for example take place by molecular diffusion through the liner wall. The main driving force for diffusion is a difference of the partial pressures of fluid components that are able to permeate the liner wall material between the interior of the lined pipe and in the intermediate space. The speed of diffusion depends on the properties of the liner material, the fluid component, and other parameters such as temperature. As a result of the diffusion, or by another way of leakage, fluid may migrate to the intermediate space and accumulate therein thereby increasing the pressure in the intermediate space. Even with tight fitting liners wherein the constructively defined intermediate space is negligibly small, gaseous or liquid components of the fluid in the interior of the liner may permeate over time through the liner wall. Consequently, this can cause some detachment of the liner from the pipe thereby creating an intermediate space of a particular size.

During normal operation, when the lined pipe is filled with fluids under pressure, this leakage is not much of a concern since the pressure of the fluid in the interior of the liner (the internal pressure) equals or exceeds the pressure of the fluid in the intermediate space. However, during the operation of a lined pipe it can happen that the internal pressure drops, for example if the pipe is emptied or evacuated. Then, suddenly the pressure in the intermediate space can exceed the internal pressure sufficiently in order to cause further detachment of the liner from the pipe, deformation of the liner or even a complete collapse, rupture or other damage of the liner. This constitutes a serious practical problem for the application of lined pipes.

A known solution to this problem is to provide the pipe with a so-called annulus vent opening, through which fluid can escape from the intermediate space through the pipe wall. The annulus vent opening can directly open into the atmosphere, or when the pipeline is buried, an exhaust conduit can be connected to the vent opening which extends to the surface. The outflux of fluid can be regulated by an operator manipulatable valve, which can be arranged at the vent opening or along the exhaust conduit. Then, in order to prevent accumulation of fluids in the space between the liner and the pipe, this space has to be regularly vented, and to this end an operator has to attend each valve to allow venting of fluids from the annulus. Apart from being labour intensive, this presents potential safety risks, and if the valves are not opened quickly enough in case of a pressure drop in the pipe, the liner can still become damaged.

In order to avoid venting to the atmosphere in the known solutions, the fluid can be conducted to a fluid disposal system. However, for an extended pipeline such a fluid disposal system becomes rather complex and requires additional infrastructure to be installed.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a lined pipe, wherein venting of the intermediate space is provided for in an easy way.

It is a further object of the present invention to provide a lined pipe, wherein the intermediate space is not vented to the environment and wherein no external fluid disposal system is required.

The present invention is based on the insight, that an efficient venting of the intermediate space is achieved by arranging a non-return valve in a passage through the liner wall, such that fluid can only pass from the intermediate space to the interior of the liner through the non-return valve.

Accordingly there is provided a pipe for the transport of fluids, which pipe is internally provided with a liner, wherein the liner is provided with at least one non-return valve arranged in the liner wall, wherein the non-return valve has an inlet end arranged near the outer surface of the liner wall and an outlet end arranged near the inner surface of the liner wall.

The invention also relates to a liner for fitting into such a pipe, which liner is provided with at least one non-return valve.

International patent application with publication number WO 00/17479 herein incorporated by reference and discloses a reinforced flexible tubular pipe comprising an outer jacket and an inner liner separated by a lumen, in which one or more reinforcing layers are arranged. In the known pipe, the accumulation of fluid in the lumen is prevented by providing a flow path for conveying fluid from an inlet in the lumen, out through the outer coating where the flow path is provided with a one-way valve, and back into the pipe where the flow path debouches in an outlet in the interior of the liner.

International patent application with publication number WO 00/08368 herein incorporated by reference and discloses a pipe provided with a liner, wherein the pipe wall is provided with a non-return valve for venting of fluid accumulated in the intermediate space between liner and pipe to the outside of the pipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is made toFIG. 1. The pipe1in this example has cylindrical shape, and is internally provided with a liner2. The pipe1has a pipe wall4having an outer surface5and an inner surface6. The liner2is a hollow tube having a liner wall7and an interior8. The liner wall7has an outer surface9and an inner surface10. All surfaces5,6,9and10are smooth surfaces. The liner of this example is a tight fitting liner, such that after the initial fitting of the liner2into the pipe1the outer surface9of the liner wall7presses against the inner surface6of the pipe wall4. As shown inFIG. 1, in a certain region of the lined pipe1an intermediate space12can be present or can be formed during operation between the outer surface9and the inner surface6.

According to the invention, the liner is provided with at least one non-return valve arranged in the liner wall, wherein the non-return valve has an inlet end arranged near the outer surface of the liner wall and an outlet end arranged near the inner surface of the liner wall, and wherein the non-return valve is arranged such that during normal operation fluid flow from the outlet end to the inlet end is prevented.

To this end, in this example a passage14is arranged in the liner wall7, in the form of a bore extending from the outer surface9to the inner surface10. A non-return valve16is fitted into the passage sealingly, i.e. such that fluid cannot pass through the passage while bypassing the non-return valve16. The non-return valve has an inlet end18arranged near the outer surface9and an outlet end19arranged near the inner surface10of the liner wall7. Details of the non-return valve16will be discussed with reference toFIG. 2. The non-return valve16is arranged such that if the pressure at the inlet end18exceeds the pressure at the outlet end19by more than a critical differential pressure, the non-return valve opens, such that the inlet and outlet ends are in fluid communication. If the pressure at the inlet end does not exceed the pressure at the outlet end by the certain value, the non-return valve is closed, such that there is no fluid communication between inlet and outlet ends. The critical differential pressure is determined by the valve closing force which is a characteristic of the non-return valve. In the practice of an application the critical differential pressure will normally be predetermined on the basis of e.g. constructive, operational, or safety parameters, and the valve closing force will be selected accordingly.

During normal operation, fluid is flowing at elevated pressure through the interior8of the liner2, and therefore at the same time through the lined pipe1. The fluid, or certain components thereof, can migrate through the liner wall7and accumulate in the intermediate space12. Migration can for example take place by molecular diffusion through the liner wall, or by leakage. As a result, the pressure in the intermediate space will increase.

If the pressure in the interior8of the lined pipe drops such that the pressure of the fluid accumulated in the intermediate space12exceeds the pressure in the interior8by more than the critical differential pressure, the non-return valve16opens such the intermediate space12is in fluid communication with the interior8via the inlet end18and the outlet end19. Due to the larger pressure in the intermediate space12fluid flows out of the intermediate space, and the pressure in the intermediate space decreases. If the pressure in the intermediate space has sufficiently decreased, the non-return valve will close.

Reference is now made toFIG. 2, which shows schematically detail II ofFIG. 1on a larger scale, wherein the non-return valve16which is sealingly mounted in a passage14through the wall7of a liner2. The non-return valve16comprises a substantially circular symmetric housing30having an inlet end18and an outlet end19. The housing is formed by two separate members, an inlet member35and an outlet member40, which members are connected to each other in axial direction by means of thread43. The two members embrace a valve chamber45. The valve chamber45is connected to the inlet end18by an axial bore46through the inlet member35, wherein the opening48of the bore46into the valve chamber45forms the inlet to the valve chamber. The part of the inlet member35that surrounds the opening48is referred to as the valve seat49. In the valve chamber45a valve body50is arranged, wherein the valve body50has cylindrical symmetry and is aligned with the axis55of the housing30. The valve body50comprises a base51, a flange52and a conical tip53facing towards the valve seat49, wherein the diameter of the base54of the conical tip53is larger than the diameter of the bore46. To the base51of the valve body50one end of a helical spring56is attached, which spring is also aligned with the axis55. The other end of the helical spring rests on a shoulder58of the outlet member40. The shoulder58is formed at the transition from an inner axial bore60to an outer axial bore61, which bores connect the valve chamber45to the outlet end19, wherein the inner bore60has a larger diameter than the outer bore61. The spring56has, when fully expanded, a length greater than the distance between the valve seat49and the shoulder58. Therefore, when assembled in the valve30, the spring is compressed in axial direction, and it therefore acts as a means for forcing the valve body50against the valve seat49with a closing force. The closing force is determined by the spring constant and the compressed and fully expanded lengths of the spring56.

In order to arrange that fluid can only pass from the intermediate space12to the interior8of the liner7through the non-return valve16, the non-return valve16is sealingly fitted in the passage14through the liner wall7. To this end, the head pieces63of the inlet member35and the head piece64of the outlet member40are provided with circular bevelled edges66and67, respectively, which bevelled edges can carve tightly into the liner wall7. Further, the diameter of the passage14can be selected such that the housing30of the non-return valve fits tightly into the passage14. The size of the gap69between the housing30and the passage14has been exaggerated in the drawing for the sake of clarity. For mounting of the non-return valve16in the passage14, the circumferences70and71of head pieces63and64have hexagonal shape when viewed from the top or bottom, such that they can be turned with a spanner. Further, the thickness of the head piece63of the inlet member35in axial direction is kept to a minimum, in order to allow tight fitting of the liner2to the pipe1. The outer face73of the head piece63is curved slightly convex, and a number of channels75are arranged in the head piece63. The channels75allow fluid communication between the intermediate space12and the inlet end18of the non-return valve16, even if the outer face73presses firmly against the inner surface6of the wall4of the pipe1.

The thickness in axial direction of the head piece64of the outlet member40is also kept to a minimum, and the outer face77is curved slightly convex. In this way the flow of fluid through the interior8of the liner is not substantially disturbed. Also the inspection of the lined pipe, using for example a so-called pigging tool, is not hampered.

During normal operation of the non-return valve16, the helical spring56presses the valve body50against the valve seat49with the closing force, such that the conical tip53closes the opening48which is the inlet to the valve chamber45. The situation can occur that the pressure in the intermediate space12exceeds the pressure in the interior of the liner8by more than the critical differential pressure. Then, the axial force that acts on the valve body50in the direction from the inlet end18to the outlet end19of the non-return valve exceeds the total of axial forces that act on the valve body50in the direction from the outlet end19to the inlet end18. Therefore, the valve body lifts off the valve seat, which brings the inlet end18into fluid communication with the outlet end19.

The non-return valve can be made of any suitable material or combination of materials, for example a corrosion resistant alloy, or the liner material itself. The selection of the liner material, like other valve design parameters, can also depend on the technique used for liner installation.

In another embodiment (not shown) the non-return valve can be a flapper valve. In particular, the valve body of the flapper valve can be integral with the liner, and the flapper can for example be arranged to fit into a recess at the side of the inner wall of the liner. Further, the flapper can essentially be made of the liner material.

Although the present invention has in the examples been described with reference to a tight fitting liner it will be clear that it can also be applied in the case of a loose fitting liner.

It will be understood that in the practice of the application of the present invention the liner can be provided with a plurality of non-return valves which are sealingly fitted into a plurality of passages through the liner along and/or around the circumference of the pipe. Suitably, valves can be placed in the vicinity of any flanges of the liner and/or the pipe. It can also be advantageous to arrange pairs of valves, spaced by ca. 180 degrees around the circumference of the pipe. The circumferential position of a valve will often not have an influence on its operation, but if necessary the formation of liquid in the bottom part of the pipe can be taken into account to select the circumferential position.