The present invention concerns an elongated conduit comprising a tubular outer pipe, an elastic inner pipe and an annulus between the outer pipe and the inner pipe, the conduit being provided with a fluid supply device for introducing the fluid in the annulus between the outer pipe and the inner pipe. The invention further concerns a method to remove blockages in such an elongated conduit, and a method for transporting a liquid, semi-liquid, paste-like or solid material through the inner pipe of such an elongated conduit.

Pipelines are widely used for the transport of oil, gas, water etc. Pipelines may be used onshore as well as offshore. Usually these pipelines are single layer pipes made from metal, e.g. steel, copper, lead etc. For the transport of oil and gas usually steel pipelines are used. In the case of flexible pipelines, often a multilayered pipeline is used, comprising a flexible polymer pipe surrounded by several layers of helically wound metal structures. Blockages in pipelines, especially in subsea pipelines and pipelines in cold climate area's, may cause substantial damage in the form of production downtime. The blockages are typically caused by wax and/or hydrate formation, possibly resulting in gel formation in the oil. This happens especially when the flow in the pipeline is interrupted, followed by cooling of the oil. Quite often it is difficult or even impossible to remove these blockages by conventional methods, particularly when the blockage is located at a substantial distance from an accessible end of the pipeline. Increasing the pressure would often require pressures above the pipeline specification, which is clearly undesired.

In US 3,780,751, a method is described for restoring the flow in a blocked pipeline by injection fluid at several points in the pipeline.

In US 6,122,791, a retrievable pig is described for the cleaning of pipelines and the removal of blockages.

In WO 99/25495, a pipe cleaning pig provided with a tow cable. In US 6,939,082, a vehicle is described that moves along a subsea pipeline, the vehicle providing hot seawater for circulating over the outer surface of the pipeline in order to melt hydrates and/or paraffin deposits . A primary object of the invention is to provide a pipeline with specific provisions to make it possible to simply remove blockages. The assembly comprises an outer tubular wall provided with an elastic inner pipe, suitably a snug fit elastic inner pipe. By pulsing a fluid in the annulus between the outer and inner pipe some movement is created of the blockading structure, which results in deblocking the pipeline. A further object is a method to remove blockages in pipelines by using the above described pipeline. The pipeline as described above makes it possible to remove blockages in pipelines, even when the blockage is located far away from one of the two ends of the pipeline. Yet another object is to provide a method for transporting a liquid, semi-liquid, paste-like or solid material through the above described pipeline.

Thus, the present invention concerns an elongated conduit comprising a tubular outer pipe, an elastic inner pipe and an annulus between the outer pipe and inner pipe, the conduit being provided with a fluid supply device, the outer pipe being provided with inlet means for introducing the fluid in the annulus between the outer pipe and the inner pipe, which inlet means communicates with the fluid supply device.

Using the conduit of the present invention it is possible to remove blockages, especially jelly like blockages, in pipelines. The method can be applied fairly quickly, much faster than cleaning pigs or subsea vehicles.

Double layered pipelines as such are already known in the art. However, these double layered pipelines are quite different from the one described above.

Double layered pipelines are occasionally used in the industry, e.g. in the case of transport of hazardous chemicals. For instance, in US 4,915,121 a coaxial piping system is described comprising an outer conduit, an inner conduit, a space between the two conduits and a spacer system. In the case of leakage of the inner tube, the leaked chemicals will be trapped by the outer conduit. The leaked chemicals may be removed by means of a purge gas .

In WO 00/77587, a host tubular is described comprising a liner system and a fluid-circulation annulus between the two. Any undesired fluids in the annulus may be removed by circulating a removal fluid through the annulus .

In EP 465252, a conduit for compressed gas and/or cryogenic gas is described comprising a gas impermeable synthetic polymer surrounded by a structural component to provide structural integrity.

In the present invention a relatively inflexible outer pipeline is used. The fast introduction of the fluid results in a pulse flowing through the annulus between the outer and the inner pipe. The movement of the fluidum between the two pipes may be described as a wave motion. As such it is also possible to deliver a number of pulses quickly after each other in order to remove the blockage .

Preferably, the elongated conduit according to the present invention is provided with a plurality of inlet means for introducing the fluid in the annulus between the inner pipe and the outer pipe, in which the inlet means communicate with one or more common fluid supply devices or each inlet means communicates with an individual fluid supply device.

Suitably, each inlet means communicates with an individual fluid supply device.

When a plurity of inlet means is used the inlet means are suitably regularly space from each other in the length-wise direction of the elongated conduit.

Suitably, the fluid supply device or fluid supply devices are provided with a mechanism to pulse the fluid in the annulus between the outer pipe and the inner pipe.

In the annulus between the outer pipe and the inner pipe fluid can already be present, e.g. in the form of a fluid reservoir. In accordance with the present invention suitably a relatively inflexible outer pipeline can be used. Preferably, the outer pipe is a metal pipe, especially a steel pipe.

Preferably, the elastic inner pipe is made of an elastic organic polymer, preferably PE, PVC, PP, or PU.

Suitably, the inner diameter of the outer pipe is between 15 cm and 120 cm, preferably between 25 and 65 cm. The elongated conduit according to the present invention can suitably have a length between 100 m and 200 km, especially between 1 and 20 km.

Suitably, the elongated conduit is at or near its starting point provided with a pneumatic device for pulsing a pressure in the annulus between the outer pipe and inner pipe in the length-wise direction of the elongated conduit.

In another embodiment of the present invention the elongated conduit is provided with a mechanism for decreasing the pressure in the inner pipe.

Preferably, the inner wall of the outer pipe of the elongated conduit according to the present invention is provided with a number of annual projections that are regularly spaced from each other in the length-wise direction of the inner wall of the outer pipe.

Preferably, the inner pipe of the present elongated conduit is profiled in the length-wise direction.

The outer pipe and the inner pipe can form together a flange. Such an embodiment is shown in Figure 2. In that case the inlet means for introducing the fluid in the annulus can be part of the upwardly directed part of the inner pipe which together with the upwardly directed part of the outer pipe forms the flange. Alternatively, the inlet means communicates with a passage that has been established in the upwardly directed part of the inner pipe, which passage debouches in the annulus. In another embodiment, the inlet means can be part of the upwardly directed part of the outer pipe which together with the upwardly directed part of the inner pipe forms the flange. Alternatively, the inlet means communicates with a passage which has been established in the upwardly directed part of the outer part, which passage debouches in the annulus . Preferably, the inlet means communicates with a passage that has been established in the upwardly directed part of the inner pipe, whereby the passage debouches in the annulus between the outer pipe and the inner pipe.

The present invention also provides a method to remove a blockage in the inner pipe of an elongated conduit according to the present invention, in which method a fluid is introduced in the annulus between the outer pipe and the inner pipe by means of the inlet means and the fluid is transported in the annulus between the outer and inner pipe in the length-wise direction of the elongated conduit.

The present invention further provides a method for transporting a liquid, semi-liquid, paste-like or solid material through the inner pipe of an elongated conduit according to the present invention, in which method a fluid is introduced in the annulus between the outer pipe and the inner pipe by means of the inlet means and the fluid is transported in the annulus between the outer and inner pipe in the length-wise direction of the elongated conduit, enabling the material which is present in the inner pipe to be transported through the inner pipe in the length-wise direction of the elongated conduit. The fluid to be used in accordance with the present invention can suitably be selected from the group consisting of nitrogen, air, carbon dioxide, an oil, an alcohol, water or a hydraulic fluid.

Preferably, the fluid is introduced in the annulus between the outer pipe and the inner pipe at a pressure which is higher than the pressure applied within the inner pipe. Preferably, the pressure at which the fluid is introduced in the annulus between the outer pipe and the inner pipe is between 1-6 bara higher than the pressure applied within the inner pipe. The pressure applied within the inner pipe can suitably be in the range of 5-500 bara.

Preferably, the fluid is introduced in the annulus between the outer pipe and the inner pipe in pulsed manner . The period of time between each pulse may vary considerably. Suitably, the period of time between each pulse is between 1-600 seconds, but also periods of time of more than 600 seconds or less than 1 second are possible . Preferably, at or near the starting point of the conduit a pressure is pulsed in the annulus between the outer pipe and the inner pipe in the length-wise direction by means of a pneumatic device. In that case, the period of time between each pressure pulse can suitably be between 1-600 seconds.

Suitably, the difference in the pressure in the annulus between the outer pipe and the inner pipe and the pressure in the inner pipe is established by decreasing the pressure applied within the inner pipe. As mentioned before in the annulus between the outer and inner pipe fluid can already be present, e.g. in the form of a fluid reservoir, before any of the present methods is being carried out.

The liquid, semi-liquid, paste-like or solid material which in accordance with the present invention can be transported through the present elongated conduit suitably comprises a biofuel, a multiphase gas/liquid mixture, a slurry, an emulsion or a deposited solid such as a hydrate, wax, asphaltene, scale, naphthenate or sand.

In Figures 1A-1D a method for removing a blockage in the inner of an elongated conduit in accordance with the present invention is schematically shown. A fluid (1) comprising a gas and a liquid is transported through an elongated conduit (2). The elongated conduit (2) comprises an outer pipe (3) and an inner pipe (4) which is snug fit to the outer pipe (4) . In the inner pipe (4) a blockage (5) interrupts the transport of the fluid (1) . The elongated conduit (2) is provided with an inlet means (6) which communicates with a fluid supply device (7) . Via inlet means (6) a fluid (9) is passed from the fluid supply device (7) into the annulus (not shown) between the outer pipe (3) and inner pipe (4) . As a result the inner pipe (4) collapses circumferentially . As can be seen in Figures 1A-1D this collapsed part (8) of the inner pipe (4) and fluid (9) of the inner pipe (4) move due to flow of fluid (1) towards the blockage (5) until it has reached blockage (5), after which the blockage (5) is removed from the inner pipe (4) in the direction of the flow of fluid (1) .

In another embodiment of the present invention, as shown in Figure 2, the upwardly directed part of the outer pipe (3) and the upwardly directed part of the inner pipe (4) form a flange (10) . The inlet means (6) communicates with a passage (11) that is drilled through the upwardly directed part of the inner pipe (4), whereby the passage (11) debouches in annulus (12) which is located between the outer pipe (3) and inner pipe (4) . In this way, a fluid can be introduced in the annulus (12) in accordance with the present invention.