WO2003102313A1

WO2003102313A1 - Apparatus for removing sediment and functional unit for use therein

Info

Publication number: WO2003102313A1
Application number: PCT/NL2003/000359
Authority: WO
Inventors: Michiel Arthur Westermann; Frank Hoos
Original assignee: Seatools B.V.
Priority date: 2002-06-04
Filing date: 2003-05-16
Publication date: 2003-12-11
Also published as: EP1513987A1; MXPA04012244A; NL1020754C2; AU2003241212A1

Abstract

What is disclosed is an apparatus for removing sediment (14), such as sand, clay and the like, from installations present below the water surface, such as pipelines (15) or the like, comprising a functional unit (7) which can be connected to a hoisting unit (2) by means of hoisting and control cables, which functional unit is provided with a channel (11) in which a driveable propeller is disposed for creating a water flow through the channel from an inlet side to an outlet side thereof. Two independently driven propellers (12,13) are disposed substantially coaxially behind each other in said channel, the first of said propellers being designed to create a low-discharge, high-velocity water flow through the channel, and the second propeller being designed to create a high-discharge, low-velocity water flow through the channel.

Description

Apparatus for removing sediment and functional unit for use therein.

In the first place, the invention relates to an apparatus for removing sediment, such as sand, clay and the like, from installations present below the water surface, such as pipelines or the like, comprising a functional unit which can be connected to a hoisting unit by means of hoisting and control cables, which functional unit is provided with a channel in which a driveable propeller is disposed for creating a water flow through the channel from an inlet side to an outlet side thereof. Offshore installations present in or on the seabed, such as gas and oil pipes, are covered by sediment (such as sand, clay or the like) with the passage of time. Moreover, gas and oil pipes are frequently laid in a trench formed in the seabed and covered with sand or rock material (which is considered to be covered by the term "sediment" within the framework of the present application) immediately after being laid. When such installations are to be inspected, repaired or even removed, it is generally necessary to remove the sediment first. To that end, a known functional unit is low- ered by means of the hoisting unit to a position just above the layer of sediment that is to be removed. The hoisting unit may be present on the deck of a vessel, for example. Surrounding seawater is sucked in on the inlet side of the channel and forced out at an elevated velocity via the outlet side by suitably driving the propeller. In this way a water flow is created, by means of which the sediment can be washed away from the installation in question.

It is an object of the present invention to provide an apparatus of the type referred to in the introduction ex- hibiting an improved operation.

In order to accomplish that objective, the apparatus according to the invention is characterized in that two independently driven propellers are disposed substantially coaxi- ally behind each other in said channel, the first of said propellers being designed to create a low-discharge, high- velocity water flow through the channel, and the second propeller being designed to create a high-discharge, low- velocity water flow through the channel .

The characterising aspects of the present invention are based on the recognition that the properties of the sediment play an important role in the removal thereof. The most effective way of removing sediment not exhibiting any cohe- sion (sand, for example) is to use a high-discharge, low- velocity water flow. Sediment exhibiting a high degree of cohesion (clay, for example) , on the other hand, can be removed most effectively by means of a low-discharge, relatively high-velocity water flow. Disposing the aforesaid two inde- pendently driven propellers in the channel makes it possible to drive one propeller, the other propeller or even both propellers in dependence on the nature of the sediment to be removed, so that a water flow having the desired characteristics will be obtained. In order to obtain the desired properties (low/high discharge and high/low velocity, respectively) , the actual propeller design may be based on the constructional aspects that are known per se from the field of hydrodynamics. An example of such an aspect is the fact that a propeller for cre- ating a low-discharge, high-velocity water flow has a small diameter, whereas a propeller for creating a high-discharge, low-velocity water flow has a large diameter. It is also conceivable, however, to use special channel contours in order to obtain the aforesaid characteristics. Such aspects are known from the field of hydrodynamics, and consequently they need not be explained in more detail herein.

In an advantageous embodiment of the apparatus according to the invention, the first propeller is positioned nearest the outlet side of the channel . This minimises the extent to which the impetus created in order to obtain a high velocity is lost before the water flow reaches the sediment to be removed. Furthermore, the first and the second propeller preferably rotate in opposite directions. As a result, the external moments generated by the rotating propellers are of opposite sign, so that said moments can offset each other in whole or in large measure. As a result, the extent to which additional measures are required in order to stabilise the functional unit can be minimised. If the two propellers would rotate in the same direction, the external moment being generated would cause the functional unit to turn, which might constitute a risk as regards the control thereof by means of the hoisting cables and the control cables.

In an alternative embodiment of the apparatus according to the invention, the functional unit is provided with at least two channels lying side by side, each channel housing a first and a second propeller. Such channels lying side by side create different water flows, which makes it possible to further enhance the operating range and the effectiveness of the functional unit.

Referring to the above as regards the external mo- ments generated by the rotation of the propellers, it is possible in such a case to have the propellers disposed in one and the same channel both rotate in the same direction, in which case the propellers of one channel will rotate in a direction opposed to the direction of rotation of the propel- lers of the other channel, however. In this way it is also possible to reduce the overall external moment entirely or substantially entirely to zero.

When at least two channels lying side by side are used as described in the foregoing, it will furthermore be quite convenient for the angle between the two channels to be adjustable. If, for example, the channels do not extend at an angle with respect to each other (the generated water flows extend substantially parallel to each other in that case) , removal of the sediment can take place over a relatively great depth but small width. Adjusting an angle of the channels relative to each other (the water flows no longer extend parallel to each other in that case, but at an angle with respect to each other) makes it possible to reduce the depth over which the sediment is being removed and at the same time increase the width of the area being covered.

Construction-wise, such adjustability of the two channels with respect to each other can be realised e.g. by using a functional unit consisting of two functional unit halves which are pin-pivoted together, each unit half being provided with one of the aforesaid channels. Within this framework, the two functional unit halves may e.g. also be interconnected by means of a driving unit, such as a cylin- der-piston assembly, at a position some distance away from said pivot pin. Operation of the cylinder-piston assembly will cause the unit halves to pivot about the aforesaid pivot pin relative to each other, so that a desired angle between the channels can be adjusted. Also other driving units are possible, of course, for realising such adjustment of the angle between the channels .

In view of the conditions below the water surface, the propellers are preferably driven by hydraulic motors, al- though it should be understood that also other types of driving units are possible within the framework of the present invention. It would also be possible, therefore, to use electric motors, for example.

In a special variant of the apparatus according to the invention, the hoisting unit comprises a telescoping arm, whose free end carries an auxiliary arm, which is pivotable about a substantially vertical pivot, over which auxiliary arm the hoisting cables for the functional unit are carried. The use of such a pivotable auxiliary arm makes it possible to change the position of the functional unit in such a manner that pivoting about the top pivot thereof takes place. This may be convenient, for example if the hoisting unit is present on board a vessel and the vessel takes up a position in which the swell is minimised. The functional unit can be pivoted about the aforesaid top pivot independently of the position of the vessel, such that the unit will take up the operationally most advantageous position with respect to the sediment to be removed. In the second place, the invention relates to a functional unit for use in an apparatus for removing sediment according to the invention.

The invention will be explained in more detail here- inafter with reference to the drawing, which shows an embodiment of the apparatus according to the invention.

Fig. 1 is a highly schematic view of an apparatus according to the invention, which is installed on board a vessel ; Fig. 2 is a perspective view of an embodiment of a functional unit as used in an apparatus according to Fig. 1;

Fig. 3 is a longitudinal sectional view of the functional unit that is shown in Fig. 2; and

Fig. 4 it is a perspective view of an embodiment of a hoisting unit as used in the apparatus according to Fig. 1.

Fig. 1 shows a vessel 1, on board of which a hoisting unit 2 is present. As will be explained in more detail yet, the hoisting unit inter alia comprises a telescoping arm 3, whose free end carries an auxiliary arm 5, which is pivo- table about a substantially vertical pivot 4. The hoisting cables for a functional unit 7, among other elements, pass over said auxiliary arm 5. Fig. 1 does not show control cables for the functional unit 7.

In the illustrated embodiment, the functional unit 2, which is suspended from the hoisting unit 2 by means of the hoisting cables 6, comprises two functional unit halves 8 and 9, which are pivoted together at their upper sides by means of a pivot pin 10. Each functional unit half 8, 9 is provided with a channel 11, in each of which two independ- ently driven propellers 12, 13, respectively, are disposed substantially coaxially behind each other.

The sediment 14 can be removed from an installation disposed below the water surface, such as a pipeline 15, by means of the functional unit 7, in a manner to be described hereinafter.

Reference is now made to Fig. 2, which shows the functional unit 7 in perspective view. The Figure shows the two functional unit halves 8 and 9, which are pivoted to- gether by means of a pivot pin 10. A cylinder-piston assembly 16 is fixed to the functional unit halves 8 and 9 with both ends, and telescoping movement of the cylinder-piston assembly 16 will result in an adjustment of the angle between the two functional unit halves 8 and 9 (with the two unit halves pivoting relative to each other about the pivot pin 10) .

Fig. 2 furthermore shows the hoisting cables 6, by means of which the functional unit 7 is suspended from the hoisting unit 2. Each functional unit half furthermore com- prises ballast means 17, tensioning means 18 for fixing the functional unit 7 to the deck of the vessel 1 in an inoperative position thereof, whilst furthermore an arm 20 is shown, on which monitoring means (such as a camera) for monitoring the process to be carried out can be mounted. Fig. 2 shows the upper side (the inlet side) of the channels 11. The propellers 12 are shown to be present in said channels.

Reference is now made to the longitudinal sectional view of Fig. 3 for a more detailed explanation of the func- tional unit that is shown in Fig. 2. Present in each channel 11 is an upper propeller 12 and a lower propeller 13. The propeller 12 is disposed nearest the inlet side of the channel 11, whilst the propeller 13 is disposed nearest the outlet side of the channel 11. Each propeller 12 is driven by a driving source 21, and each propeller 13 is driven by a driving source 22. Said driving sources may be hydraulic motors, for example .

Each assembly 12, 21 and 13, 22, respectively, consisting of a propeller and an associated driving source is suspended inside the channel 11 via suspension means 23 and 24, respectively.

As is apparent from the view of Fig. 3, the diameter of each upper propeller 12 is larger than the diameter of each lower propeller 13. Furthermore, each lower propeller 13 is disposed in a narrowed auxiliary channel 25. Each upper propeller 12 creates a high-discharge, low-velocity water flow from the inlet side to the outlet side of the channel 11. Each propeller 13, on the other hand, creates a low- discharge, high-velocity water flow. The desired water flow for removing sediment from an installation 15 can be created at the outlet side of each channel 11 by selectively activating the driving sources 21 and 22. The selection of the type of water flow is made in dependence on the nature of the sediment to be removed.

In the embodiment of the apparatus according to the invention that is shown in Figs. 2 and 3, the propellers 12 of the functional unit halves 8 and 9 are of opposite pitch, and consequently they rotate in opposite directions. As a result, any external moments that may occur will offset each other. This also applies with regard to the propellers 13.

Reference is now briefly made to Fig. 4, which shows a hoisting unit 2 in perspective view. The hoisting unit 2 has a telescoping arm 3, which can be operated by a cylinder- piston assembly 26, for example. Present on the free end of said arm 3 is an auxiliary arm 5, which is pivotable with respect to the arm 3 about a substantially vertical pivot 3 (see Fig. 1) . Guide means 27 for the hoisting cables 6 are mounted on the auxiliary arm 5. Fig. 4 furthermore shows control cables 28, by means of which various operative parts of the functional unit 7 can be operated in a manner which is not shown. Such control cables may include hydraulic lines, for example . In the position that is shown in Fig. 4, the arm 3 takes up its fully telescoped position and the functional unit 7 is present on board the vessel that supports the hoisting unit 2. The functional unit 7 is fixed to the deck of the vessel, e.g. by means of the tensioning devices 18 (see Fig. 2) in that position.

When the functional unit 7 is to be used, the arm 3 is telescoped out (possibly after being lifted slightly with its free end, for which purpose a pivot 29 may be used, for example) until the functional unit 7 extends beyond the board of the vessel. Subsequently, the hoisting cables 6 and the control cables 28 are paid out, so that the functional unit 7 can be lowered to the desired depth, a desired distance above the sediment 14. The position of the functional unit 7 with respect to an installation present in the sediment 14 can be adjusted by pivoting the auxiliary arm 5 with respect to the arm 3 so as to obtain an optimum operation of the functional unit. Following this, the propellers 12 and 13 are operated, as a result of which a water flow is created, by means of which the sediment 14 can be removed. Also the angle between the functional unit halves 8 and 9 can be adjusted by means of the cylinder-piston assembly 16 for the purpose of controlling the water flow from the two channels 11. The invention is not limited to the embodiment as described above, which can be varied in several ways without departing from the scope of the invention as defined in the claims .

Claims

1. An apparatus for removing sediment, such as sand, clay and the like, from installations present below the water surface, such as pipelines or the like, comprising a functional unit which can be connected to a hoisting unit by means of hoisting and control cables, which functional unit is provided with a channel in which a driveable propeller is disposed for creating a water flow through the channel from an inlet side to an outlet side thereof, characterized in that two independently driven propellers are disposed substantially coaxially behind each other in said channel, the first of said propellers being designed to create a low- discharge, high-velocity water flow through the channel, and the second propeller being designed to create a high- discharge, low-velocity water flow through the channel.

2. An apparatus according to claim 1, wherein the first propeller is disposed nearest the outlet side of the channel .

3. An apparatus according to claim 1 or 2 , wherein said first and said second propeller rotate in opposite directions .

4. An apparatus according to any one of the preceding claims, wherein the functional unit is provided with at least two channels lying side by side, each channel housing a first and a second propeller.

5. An apparatus according to claim 4, wherein the propellers disposed in one and the same channel both rotate in the same direction, but wherein the propellers of one channel rotate in a direction opposed to the direction of rotation of the propellers of the other channel .

6. An apparatus according to claim 4 or 5 , wherein the angle between the two channels is adjustable.

7. An apparatus according to claim 6, wherein said functional unit consists of two functional unit halves which are pin-pivoted together, each unit half being provided with one of the aforesaid channels.

8. An apparatus according to claim 7, wherein the functional unit halves are interconnected by means of a driving unit, such as a cylinder-piston assembly, at a position some distance away from said pivot pin.

9. An apparatus according to any one of the preceding claims, wherein the propellers can be driven by hydraulic motors .

10. An apparatus according to any one of the preceding claims, wherein the hoisting unit comprises a telescoping arm, whose free end carries an auxiliary arm, which is pivotable about a substantially vertical pivot, over which auxiliary arm the hoisting cables for the functional unit are carried.

11. An apparatus according to any one of the preced- ing claims, wherein the hoisting unit is present on board a vessel .

12. A functional unit for use in an apparatus for removing sediment, such as sand, clay and the like, from installations present below the water surface, such as pipe- lines or the like, which functional unit is provided with a channel in which a driveable propeller is disposed for creating a water flow through the channel from an inlet side to an outlet side thereof, characterized in that two independently driven propellers are disposed substantially coaxially behind each other in said channel, the first of said propellers being designed to create a low-discharge, high-velocity water flow through the channel, and the second propeller being designed to create a high-discharge, low-velocity water flow through the channel .

13. A functional unit according to claim 12, wherein the first propeller is disposed nearest the outlet side of the channel .

14. A functional unit according to claim 12 or 13, wherein said first and said second propeller rotate in oppo- site directions.

15. A functional unit according to any one of the claims 12 - 14, wherein the functional unit is provided with at least two channels lying side by side, each channel housing a first and a second propeller.

16. A functional unit according to claim 15, wherein the propellers disposed in one and the same channel both ro- tate in the same direction, but wherein the propellers of one channel rotate in a direction opposed to the direction of rotation of the propellers of the other channel .

17. A functional unit according to claim 15 or 16, wherein the angle between the two channels is adjustable.

18. A functional unit according to claim 17, wherein said functional unit consists of two functional unit halves which are pin-pivoted together, each unit half being provided with one of the aforesaid channels.

19. A functional unit according to claim 18, wherein the functional unit halves are interconnected by means of a driving unit, such as a cylinder-piston assembly, at a position some distance away from said pivot pin.

20. A functional unit according to any one of the claims 12 - 19, wherein the propellers can be driven by hy- draulic motors.