MXPA99010451A - Method for propelling a pig along a pipeline - Google Patents

Abstract

A method is described for propelling a pig (9) along an air-filled underwater pipeline (1) comprising the steps of opening a pipeline inlet (3) to permit entry of water to the pipeline means at a pressure corresponding generally to the ambient water pressure at a proximal end (8) of the pipeline, and coupling a pipeline outlet (5) at a distal end (6) of the pipeline to a fluid venting system (10, 11, 17) in which air is maintained at a pressure sufficiently below the ambient water pressure at the proximal end of the pipeline to create a pressure differential across the pig sufficiently large to cause the air in the pipeline to be vented from the distal end thereof, whereby the pig is propelled along the pipeline. A method is also described for propelling the pig along pipeline (1) when it is filled with water, in which the pipeline outlet (5) is connected to a fluid venting system in which fluid is maintained at a pressure sufficiently below the ambient water pressure at the distal end (6) of the pipeline to cause water in front of the pig to be vented from the outlet at the distal end of the pipeline into the fluid venting system.

Description

METHOD FOR PUSHING A SCRAPER ALONG A PIPE The present invention relates, in general, to the subsea pipeline construction industry and, more specifically, the invention relates to methods for pushing a scraper along pipes under water. In particular, but not exclusively, the invention relates to methods for pushing a scraper along underwater pipes filled with gas or air, and pipes under water filled with liquid. A scraper is a device that forms a seal within the pipeline so that the scraper can be driven into the pipe creating a differential pressure through the scraper. Scrapers are used for many purposes including, among others, ensuring that a newly installed pipe, when flooded, has an "airless" content, and verifying that any waste associated with the construction of the pipe is removed from the interior of the pipe. A scraper is often used to carry out many inspection procedures within a pipeline. Currently there are two commonly known methods used to scrape an underwater pipeline. The first is to pump water, or another convenient liquid or gas, from a container or platform on the surface of the sea, to the pipe to increase the pressure behind the scraper and thus create a differential pressure through the scraper that pushes the scraper to length of the pipe. This method can be used when the scraper is to be pushed along a newly installed pipe, filled with air or gas, and also when a scraper is to be pushed along a pipe filled with liquid. The latter case may be applicable when, for example, an older pipe filled with liquid (for example water) is going to be inspected for wear, damage and / or blockages, or in the case when the water enters the pipe during installation in the seabed. The main disadvantages of this method are the need for a pumping system, and the fact that significant support vessel time is needed on the surface of the sea when pumping is taking place. Supporting vessel time is expensive and an objective of any underwater construction process is to minimize the amount of support vessel time needed. The second method is specifically to push a scraper along a pipe filled with air (or gas) and use the external pressure of the water outside the pipe to push the scraper partially along the length of the pipe, starting of the near end of it. The tubing has inlet and outlet valves at the proximal and distal ends thereof that control the flow of fluid in and out of the tubing. Both valves are closed when the pipeline is installed in the seabed, the pipeline having thus installed air trapped therein. The second method mentioned above involves holding the valve at the distal end of the closed pipe while the valve at the other end of the pipe is open: the water will enter the pipe through the open valve and push the scraper along of the pipe as the water compresses the air (which is at atmospheric pressure). The scraper continues to travel along the pipeline until the air in front of it reaches a pressure equal to the water pressure behind the scraper, which in the case of a generally horizontal pipe would be the external or "environmental" water pressure. at the proximal end of the pipe. At this stage, to further push the scraper so that it reaches the distal end of the pipe, a surface or sub-surface pumping system is employed to increase the pressure behind the scraper to create the necessary pressure differential across the scraper ( with the valve at the distal end open) to drive it forward. Usually this is not a simple procedure and again involves additional time of support vessel on the surface of the sea and / or one or more divers or robots operated remotely. These requirements introduce large additional costs to pipe construction and scraping processes. Another disadvantage is that this method only provides results of economic benefits when the pipe is sufficiently deep below the surface that a substantial portion of the pipeline is flooded by the action of the external hydrostatic head of the water. It is an object of the present invention to avoid or minimize one or more of the above disadvantages. In accordance with the above, the present invention provides a method for pushing a scraper along an underwater pipeline element having input elements at a proximal end thereof and output elements at the distal end thereof, and a scraper disposed at the at least some distance away from the distal end, the method comprising the steps of opening the entry element to allow water to enter the tubing element at a pressure generally corresponding to the ambient water pressure at the proximal end of the tubing element. pipe, and coupling the outlet element of the pipe element to a fluid ventilation system wherein the fluid is maintained at a sufficiently low pressure to create a pressure differential across the scraper large enough to cause the fluid to be vented from the distal end of the pipe element, whereby the scraper is pushed along the pipe element towards the distal end of it. It will be appreciated that the pressure in the ventilation system as well as in the "outlet" side of the scraper inside the pipe element may be non-uniform. This is particularly the case when the ventilation system and the pipe element (at least on the outlet side of the scraper) contain water further to where that same water creates a pressure head creating the same pressure gradients. Accordingly, the pressure required to stay inside the fluid ventilation system to create the required pressure differential across the scraper may be different in different portions of the fluid ventilation system, and may depend on the arrangement, example, any upward or downward inclination of the pipe, as will become more clearly apparent from the description of the various embodiments hereinafter. An advantage of the present invention is that the scraper can be continuously pushed along the pipe element using the hydrostatic pressure of the seawater hydrostatic head at the proximal (ie inlet) end of the pipe element, this being achieved by ensuring that there is always a sufficient pressure differential across the scraper, at least until the scraper reaches the desired extreme position. When the pipe element is a pipe that is filled with air or gas, pumping is not required to create the necessary pressure differential through the scraper. According to another aspect, the invention provides a method for pushing a scraper along underground pipe elements substantially filled with air having input elements at a proximal end thereof and an outlet element at a distal end thereof. , and a scraper disposed therein, at least some distance away from the distal end, the method comprises the steps of opening the entry element to allow water to enter the pipe element at a pressure that corresponds in general to the ambient pressure of water at the proximal end of the pipe element, and coupling the outlet element of the pipe element to a fluid ventilation system where the air is maintained at a pressure sufficiently below the ambient water pressure at the end proximal of the pipe element to create a pressure differential along the scraper large enough to cause substantial All the air in the pipe element, in front of the scraper, is vented from the distal end thereof, whereby the scraper is pushed along the pipe element towards the distal end thereof. According to yet another aspect, the present invention provides a method for pushing a scraper along an underwater pipeline element substantially filled with water and having input elements at a proximal end thereof and output elements at a distal end of the same, and a scraper disposed therein at least a distance away from the distal end, the method comprising the steps of opening the entry element to allow water to enter the pipe element at a pressure generally corresponding to the ambient water pressure. at the proximal end of the pipe element, and coupling the outlet element of the pipe element to a fluid ventilation system where the fluid is maintained in the pipe exit element at a pressure sufficiently below the ambient pressure of water at the distal end of the pipe element to create a pressure differential along the scraper large enough to cause water to be vented from the outlet member at the distal end of the pipe element, whereby the scraper is pushes along the pipe element towards the distal end thereof. It will be appreciated that when the pipeline contains other liquids, for example petroleum, having a density other than water (fresh water or sea water, as appropriate), then the pressure of the used fluid ventilation system should take these differences into account. in density and the effects thereof on the pressure load or loads within the pipeline and the fluid ventilation system as will be discussed further hereinbelow. The pressure differential created through the scraper is preferably large enough to overcome any loss of energy due to friction (between the scraper and the pipe element and / or between the fluid and the pipe and / or the input element and / or outlet of the pipe element) as the scraper is pushed along the pipe element towards the distal end thereof. Preferably, the pressure differential created through the scraper is large enough to cause the scraper to be pushed along the pipe element at an average, predetermined speed, or within a predetermined speed range. The pipe element can follow a substantially horizontal path or can be arranged at an angle (for example on an inclined seabed). Alternatively, only part of the length of the pipe element can be arranged at an angle, or the pipe element can follow a wavy path on a corrugated seabed. The input element preferably comprises an inlet valve having an open position in which water, or any other fluid, can flow towards the proximal end of the pipe element, and a closed position in which the liquid can not flow towards the proximal end of the pipe element. The outlet element preferably comprises an outlet valve having a closed position in which the fluid of the fluid ventilation system can not flow towards the distal end of the pipe element, and an open position in which the fluid content of the Pipe element, namely air / gas or liquid, can flow out of the distal end of the pipe element (towards the fluid ventilation system). Optionally, one or both of the inlet and outlet valves may be used to control the rate of flow of water to the pipe and / or gas or liquid out of the pipe. For the avoidance of doubt, it should be noted that the input element and the output element referred to above are generally related to the direction of the scraper path and not to the flow direction of any fluid, for example hydrocarbons, which may flow through the pipe element during submarine use. In addition, the proximal end and / or the distal end of the pipe element can be provided with input elements and / or output elements respectively through which the scraper can be introduced or removed respectively from the pipe element. It will be appreciated that the output element, for example, can be provided in a lock element of the removable tubing end, often known as a "scraper receiver", which incorporates the outlet valve, or alternatively, can be provided in a separate portion of the distal end of the tubing. pipe element towards the outlet valve. Similarly, the input element may be provided in a "scraper launcher" at the proximal end of the pipe element that incorporates the inlet valve, or it may be provided in a portion spaced from the proximal end of the pipe element to the valve. entry. When the pipe element is initially substantially filled with air at atmospheric pressure (or, alternatively, another gas having a density less than the density of the water), the method preferably comprises connecting the outlet valve of the pipe element to a system of fluid venting comprising a conduit, preferably in the form of a hose, connected directly or indirectly to the surface or buoy of medium depth, or surface, the system includes ventilation outlet elements, conveniently in the form of a ventilation outlet in the same buoy, through which the air of the pipe element can be ventilated or discharged, towards the surrounding water. The ventilation outlet element can alternatively be at one end of the hose.

Preferably, the vent outlet element is disposed at a water level higher than the proximal end (inlet valve) of the pipe element. The pressure on one side of the scraper (namely the side closest to the distal end of the pipe) is thus always lower than the pressure on the other side (which, at any time, is at the hydrostatic pressure in the pipe, to the depth of the scraper below the surface), creating a differential pressure through the scraper. As long as the pressure differential is large enough to overcome any frictional loss, the scraper will be pushed along the pipe element until it reaches the distal end thereof. The higher the vent outlet element above the proximal end of the pipe element, the greater the pressure differential, the differential being the larger when the vent outlet element is on the surface. The advantage of a buoy disposed in a part of the way to the surface, the so-called "medium depth" buoy, is to avoid the limitations associated with running a hose all the way from the seabed to the surface (where the pipeline is located). installed on the seabed). It will be appreciated that the upper end of the hose could, instead of being attached to the buoy, be supported on the platform or vessel on the surface of the sea, when this option is available.

The height of the ventilation outlet element above the proximal end of the pipe element is advantageously chosen so as to reach a desired speed of travel of the scraper along the pipe element under the action of the resulting pressure differential. For example, when the vent outlet element is in the buoy, several different scraper speeds can be achieved by varying the height of the buoy. The inlet valve can be opened before opening the outlet valve, causing the scraper to be pushed along the pipe element until the air in the pipe element, in front of the scraper, is compressed to a pressure more or less equal to the water pressure behind the scraper. The outlet valve can then be opened to connect the pipe element to the vent outlet element, causing the scraper to be pushed the rest of the way along the pipe element, to the distal end thereof. This procedure tends to minimize the risk of back pressure from the vent outlet element - particularly in the medium depth buoy - forcing the water to the outlet end of the air-filled pipe. Alternatively, and preferably, the vent outlet element is provided with a one-way valve mechanism whereby the fluid of the pipe element can only be vented when the fluid pressure from the pipe element exceeds the pressure of the water in the ventilation outlet element, and the inlet valve and outlet valve open simultaneously, or the outlet valve opens before opening the inlet valve. In these cases, the air in front of the scraper is compressed until it reaches the environmental pressure of the water in the ventilation outlet element, at this point the one-way valve opens to allow the fluid to be vented from the ventilation system of the fluid. When the scraper is to be transported along a pipe filled with liquid, the method preferably comprises connecting the outlet valve of the pipe, by means of a pipe, preferably in the form of a hose, directly or indirectly to a surface buoy or of medium depth, whether the duct or the buoy has ventilation outlet elements therein, via which the contents of the pipeline can be discharged to the surrounding water, and introducing gas, which may be air, or alternatively another fluid having a density less than the density of the water, in the hose that connects with the outlet valve to the ventilation outlet element. The effect of introducing the air or other fluid into the hose creates a pressure differential between the proximal and distal ends of the pipe, the scraper placed in the middle is thus pushed along the pipe until it reaches the distal end thereof. The hose, buoy and source of air or other fluid that is introduced into the hose together form the fluid ventilation system. Advantageously, air is introduced into the hose by pumping, or otherwise injecting, pressurized air into the hose via an inlet, preferably a valve inlet, provided in the hose for this purpose. Alternatively, air can be pumped into the hose via an array of multiple valves that comprise the pipe's outlet elements, or by pumping the air directly into the pipeline via a convenient inlet provided therein for this purpose. The travel speed of the scraper along the pipeline can be controlled by the amount of air that is pumped into the hose. The air can be pumped into the hose by a pump on a surface or platform container or, perhaps less conveniently, by an underwater pump that compresses air. Alternatively, pressurized air cylinders arranged on the seabed can provide the source of pressurized air. The last arrangement avoids the need for a surface support vessel while the pumping is taking place. In some cases when the method of the invention is being used to push a scraper along a pipe filled with gas or air, the scraper may not travel directly to the distal end of the pipeline because some (marine) water has entered into the portion of the pipe in front of the scraper (ie between the scraper and the distal end of the pipe). This may occur when some water from the near (inlet) end of the tube is pressed past the sides of the scraper and / or when the water gets into the pipe via the hose and buoy and / or the outlet valve. In this situation, the technique described above for pushing the scraper along a pipe filled with liquid (which involves introducing air or a fluid of lower density than the water in the pipe) can be used as a supplementary procedure to complement the path of the pipe. scraper towards the distal end of the pipe. This supplementary procedure can be controlled automatically and, preferably, remotely, for example, from a surface container, platform, or underwater device. The method or methods described above for pushing a scraper along a pipe filled with liquid, namely water, can also be used after the method to push a scraper into a pipe filled with air, in order to push a second, third, or additional, scrapers along the pipeline when these additional scrapers are separated from each other, and from the first scraper, by water or another liquid. Although the latter method involving the introduction of air or compressed gas into the hose may involve the use of a pump (unless pressurized gas cylinders are used), this method has several potential advantages over the aforementioned methods of the prior art. of scraping a pipe that involve the use of pumps. For example, the need for a surface support container to support or control pumping at the inlet end of the pipe throughout the scraping process is avoided in the present invention in which any support container that may be required during the Scraping process will be required above the farthest (exit) end of the pipe. This method will then be particularly advantageous when, for example, the near end (inlet) of the pipe is inaccessible to a support container. According to another aspect, the invention comprises a fluid ventilation system for use for venting fluid from an underwater apparatus containing fluid, the system comprising a buoy element and a conduit having one end thereof for connection, in use , with an outlet of the underwater apparatus so that it is in fluid communication or thereof, and another end for linking the buoy element, and vent outlet elements via which the fluid can exit the fluid ventilation system, being provided the vent outlet elements with valve elements formed and accommodated to be in the closed position, substantially preventing the fluid from flowing to the fluid ventilation system through the vent outlet element, when the internal pressure in the exhaust system fluid venting is less than the external pressure of the vent outlet element, and being in an open position, allow The fluid in the fluid ventilation system is ventilated therefrom, when the internal pressure in the fluid ventilation system is less than the external pressure in the vent outlet element, and in an open position, allowing the fluid in the fluid ventilation system to be vented therefrom, when the internal pressure in the fluid ventilation system is greater than the external pressure in the vent outlet element, whereby, in use, the fluid in the underwater apparatus is vented from it to the fluid ventilation system when the fluid is at a higher pressure than the internal pressure in the fluid ventilation system from which, in turn, the fluid ventilates when it is at a higher pressure than the external pressure in the ventilation outlet element thereof. This fluid venting system can, for example, be used to push a scraper along an underwater pipeline, in which case one end of the pipe is connected to an outlet at one end of the pipe and the other end is connected to the pipeline. buoy, thus allowing the fluid in the pipe to be vented from it. The fluid ventilation system may further include at least one source of compressed air (or, alternatively, another fluid having a lower density than water), for connection to said conduit, the conduit preferably being provided with input elements of air to be coupled with the source of compressed air. The buoy is preferably hollow, and can generally be bell-shaped, or balloon shaped, having an inlet connected to one end of the duct, and a narrow outlet end comprising the vent outlet element. The valve member in the vent outlet element conveniently comprises a check valve that controls the flow of fluid through the buoy. Alternatively, the vent outlet element may be provided at the free end of the conduit that may be suspended from a surface buoy, or medium depth. In another possible embodiment, an end downstream of the conduit is connected to the outlet member of the pipe and an upper end is mounted on, and in fluid communication with, a ventilation damping chamber which is suspended from the buoy, the Ventilation outlet element provided in the buffer chamber. It will be appreciated that underwater ventilation of the contents of the pipe element offers many advantages. By locating the vent outlet element under the water the present invention can take advantage of density differences between the ambient water and a gas, for example, air that is vented from the pipe element in order to create the necessary pressure differential to through the scraper to drive it along the pipe element. In the case of a pipe element initially filled with waterby introducing air bubbles into the fluid ventilation system, the fluid density in the ventilation system can be effectively reduced below that of the ambient water, again allowing the necessary pressure differential to be achieved. It is by using the valve elements formed and accommodated to prevent ambient water from entering the ventilation outlet element of the fluid ventilation system as these pressure differentials can be achieved and maintained. Furthermore, it will be appreciated that the fluid ventilation system described above could be used in other applications in which it is desired to vent the fluid content of an underwater apparatus, not only in the aforementioned method to push a scraper along the pipeline. Preferred embodiments of the invention will now be illustrated, by way of example only, and with reference to the accompanying drawings in which: Figure 1 schematically illustrates a method of pushing a scraper through an underwater pipeline filled with air in accordance with the invention; Figure 2 illustrates a modified version of the method illustrated in Figure 1; Figure 3 is a cross-sectional view of the buoy shown in Figures 1 and 2; Figure 4 schematically illustrates a method of pushing a scraper through an underwater pipeline filled with water; Figure 5 illustrates the different pressures acting on the pipe arrangement shown in Figure 4, where the pipe is arranged at an angle with the horizontal; Figure 6 shows a modified underwater pipeline (in cross section) with which the method illustrated by Figures 4 and 5 can be used; Figure 7 is a partial cross-sectional view of a fluid ventilation system according to an embodiment of the invention; and Figure 8 illustrates the apparatus for injecting chemicals or dyes into a pipe. Figure 1 illustrates a submarine pipe 1 (in cross section along its main axis) lying substantially horizontally on the seabed 2 and containing air at atmospheric pressure PA. The proximal and distal ends 4, 6 of the pipe are sealed by respective lock arrangements 7, 8 which are provided with an inlet valve 3 and an outlet valve 5 respectively. The pipe also contains a scraper 9 that is inserted therein at the proximal end 4, usually before sinking the pipe to the seabed. The inlet valve 3 is closed before placing the pipe, to prevent water W from entering the pipe at the proximal end thereof. The outlet valve is connected to one end 13 (the "lower" end) of a hose 10 and the other end 14 (the "upper" end) of which is mounted on a buoy 11 floating on the surface of the sea 12. It will be appreciated that Figure 1 is not drawn to scale, the pipe being usually disposed well below sea level, in some cases more than one thousand meters below the surface. The pipe 1 itself can comprise a single pipe, or a plurality of individual pipes extended end to end. The buoy 11 is shown in cross section, in greater detail, in Figure 3. The buoy 11 is generally bell-shaped having a hollow interior 15 in which the upper end 14 of the hose extends (via an opening 20 in FIG. the buoy, the hose 10 being in sealing engagement with the buoy 11), as shown. An inner portion 16 of the buoy 11 is provided with a narrow outlet end 17 that functions as a vent outlet and in which at least one one-way check valve is adjusted to control the flow of the fluid (water or air) to through it. The valve 18 operates to prevent the flow of water in the hollow interior, or "buffing volume" 15 of the buoy 11 when the external pressure of the water in the vent outlet 17 of the buoy exceeds the pressure in the damper volume 15, to allow the fluid (in Figure 1, namely air), to exit the buoy, via the outlet 17, when the pressure in the damper volume 15 exceeds the external pressure of the water at outlet 17. The sea water W it thus prevents it from entering the cushioned volume 15, and therefore the upper end 14 of the hose, by the check valve 18. One or more of these other check valves 19a, 19b (indicated in broken lines in Figure 3) ) can be included in the vent outlet 17 and / or the upper end of the hose 14 to further reinforce the buoy against the ingress of seawater through the narrowed outlet 17. Additionally, the upper end 14 of the hose 10 is available very close a of the exit 17 in the buoy 11. In this way, the point of "air intake" is greater than the point of "air outlet" so that if some water from the sea manages to enter the buoy 11 it is little likely to enter hose 10, and in any case, will be ejected from the buoy when resuming air overpressure. The hose 10 and the buoy 11 are connected to the outlet valve 5 before the pipe sinks into the seabed. The outlet valve is in its open position, preventing seawater from entering the pipe via the distal end of the pipeline through the check valves in the buoy. The advantage of having the outlet valve open when the pipeline is installed at the bottom of the sea is that no further intervention is required at the distal end of the pipe to initiate the "scraping" process which will be described. The method of pushing the scraper 9 along the pipe initially filled with air 1, according to the embodiment of the invention illustrated in Figure 1, in which the pipe 1 is substantially horizontal, comprises opening the inlet valve 3 so as to allow the hydrostatic head of water at the inlet 3 to lead the scraper 9 along the pipe, the air in the pipe being vented therefrom, via the hose 10, towards the buoy 11 (the outlet valve 5 is already open, as described above). The invention works due to the hydrostatic pressure Pw of the water load on one side of the scraper (equal to pgHw, where p is the density of the water, g is the acceleration due to gravity, and Hw is the depth of the inlet valve 3 below the surface of the sea) being greater than the pressure in the other side of the scraper, which is the atmospheric pressure Pa, the resulting pressure differential through the scraper carries it forward to the distal end 6 of the pipe 1. In this method, when both the inlet and outlet valves 3, 5 the air pressure at the front of the scraper (ie, between the scraper and the distal end 6 of the pipe) is open, it is prevented from rising to the external water pressure at the water depth of the pipe. Since there is no pressure build-up in front of the scraper it will continue to travel along the pipe (in the direction indicated by the arrow in Figure 1) until all the air has been expelled from it. Figure 1 in fact shows the scraper 9, still in the process of being pushed along the pipe 1, having been pushed part of the way along it from the proximal end 4 of the pipe, with the valve entrance as well as the exit 3, 5 open. Figure 2 shows a modified implementation of the method illustrated in Figure 1. In this embodiment, buoy 11 is a buoy called "medium depth" disposed at a depth H3 below sea level 12. This will work in a similar manner to the method of Figure 1, although this time the differential pressure through the scraper 9 is equal to the difference in pressure between the hydrostatic pressure Pj (equal to pgHj) in the inlet valve 3 and the hydrostatic pressure P3 in the depth H3 below level 12 (where P3 = pgH3). Assuming that this differential pressure is sufficient to overcome any frictional loss (due to friction between the scraper and the pipe, and associated with the flow of fluid through the pipe) the scraper 9 will be driven forward under the action of the differential. of pressure created. When the inlet valve 3 is opened, the air pressure in front of the scraper will only accumulate until it equals the hydrostatic pressure P3 at outlet 17 in the buoy, after which the check valve (s) in the buoy will open and The air will be vented outside the buoy, thus continuing the scraper traveling along the pipe until all the air has been expelled from it. An advantage of this method is that it avoids the need to carry a hose from the seabed all the way to the surface 12. Moreover, the depth H3 in which the buoy is disposed can be used to determine the speed with which the scraper 9 will be pushed along the pipe 1. If the situation arises in which the ventilation hose 10 is subjected to an external pressure sufficiently greater than the internal pressure in the hose 10 that the pressure of collapse of the If the hose was exceeded, the hose could collapse on itself. This can happen during the operation of the apparatus of Figures 1 and 2, for example when the pipe is filled with air and the inlet valve 3 is first opened so as to cause the scraper to begin to traverse towards the distal end of the pipe. The pipe. Until the air in front of the scraper is pressurized upward to the hydrostatic pressure of the outlet valve in the buoy, the pressure in the ventilation hose 10 may be sufficiently lower than the surrounding underwater hydrostatic pressure for collapse to occur. the hose. This collapse of the hose could, in the worst case scenario, lead to damage to the hose, and / or prevent or delay the scraper 9 from driving further along the pipe 1 until the hose has been replaced. hose, and represurizado or "descolapsado". In order to avoid these problems, the pressure of the hose 10 can be deliberately maintained at a predetermined level all the time. This can be done by, for example, connecting a subsea cylinder 49 of pressurized gas (e.g., pressurized gas Ap) to a dedicated inlet 50 (indicated, in outline in Figure 2) provided in a lower portion of the ventilation hose , a one-way valve 51 being incorporated in the dedicated inlet 50, this valve opens when the hose pressure drops below the predetermined level. By way of example, in the embodiment of Figure 1, if the ventilation hose is at an underwater depth of approximately 1000 meters, the ambient pressure of the water Tw surrounding the ventilation hose will be approximately 100 bar. If the hose collapses when it is subjected to a differential pressure Pc of, say 10 bar, between the outside and the inside of the hose, then in practice as long as the pressure Ph in the ventilation hose is maintained by Above Pw-Pc (ie above 90 bar) all the time, hose collapse will be prevented. When, for example, the check valve CV1 on the buoy 26 is at, say, 950 meters below the water, the pressure enters the outlet of CV1 being 95 bar, and the lower end of the ventilation hose is at 1000 meters under the water, in practice as long as the pressure in the hose Ph, is maintained at, say, 93 bar, the collapse of the hose will be avoided. In this example, the fluid in the vent hose can only exit the buoy when it is at a pressure greater than (95 bar + pressure required to physically open the check valve (s) 18, 19a, 19b). In most cases the pressure required to physically open the valves themselves will be negligible. Another embodiment of the present invention is illustrated in Figure 4. Parts equal to those of Figures 1 and 3 are indicated by like reference numerals. Here, the horizontal pipe 1 is filled with seawater when the scraper is inserted into the proximal end 4 of the pipe (which is illustrated in reverse orientation to that of Figures 1 and 2). According to this method, pressurized air Ap is injected into the hose 10 connected to the buoy 11 at the lower end 13 of the hose. Instead of air, alternatively a fluid (gas or liquid) having a lower density than water can be used. With the both inlet 3 and outlet 5 open valves, a pressure differential is created through the scraper 9, leading the scraper forward (in the direction indicated by the arrow in Figure 4). The air must be injected into the pipe 1 at a pressure at or above the hydrostatic pressure of the water load at the depth Hw of the inlet valve 3 (and / or the outlet valve 5) of the pipe 1. However, as the pressurized air moves up the hose 10, the hydrostatic pressure acting on it decreases and the air expands (as shown in Figure 4), so that the pressure in the hose at any height given is less than the pressure outside the hose at that height. This result is that, with the inlet and outlet valves 3, 5 open, (and assuming that the inlet and outlet valves are at the same depth Hw below the surface 12), and the pressurized air that is being injected in the hose, the pressure P ^ e ^ to water charge in the hose (equal to pxgHw, where px is the average amount of fluid in hose 10 at any time) is less than the water charge pressure Pt (p ^ H ^ where pw is the density of seawater W) in the inlet valve 3 and thus there is a differential depression along the scraper that pushes the scraper forward. (Note that another reduction in the pressure inside the hose is likely to result due to the impulse transfer of the accelerating gas to the water in the hose 10). Instead of the surface buoy 11 illustrated in Figure 4, a buoy of medium depth could be used, as in Figure 2 (see Figure 5, and below). A check valve 22 can be provided at the point where the air is injected into the hose 10, to stop the contents of the hose (initially sea water) entering the pressurized air source. The source of pressurized air (not shown) can be a pump located on a surface support vessel, or it can be a subsea pumping unit. In the most preferred embodiment, the pressurized air comes from a compressed air storage facility, for example gas cylinders stored in the seabed. Figure 5 illustrates a water-filled pipe 1 in which the method according to Figure 4 is implemented, but where the pipe is not in a substantially horizontal position as in Figure 4, but is disposed on an inclined seabed 2. So that the scraper 9, at a depth H2, continues to move at a desired scraper speed vp, then: Pw9Hl = Pw9 (H H2) + Pw9H3 + P? 9 (H4-H3 >; + PW9H5 + (friction losses, to vp) Where pw is the density of seawater; px is the density (average) of the contents of the hose (a mixture of seawater and air, or other low density fluid); g is the acceleration due to gravity; the "friction losses" represent the pressure losses associated with the friction forces arising between the scraper and the pipe (and / or associated with the fluid flow in the pipe) when the scraper is traveling at a velocity vp; Hj is the depth of the inlet valve 3, at the proximal end 4 of the pipe 1; H3 is the depth of the buoy 11; H4 is the depth of the lower end 13 of the hose, where it connects with the distal end 6 of the pipe; and H5 is the difference between H2 and H4 (ie H2-H), as shown in Figure 5. In this way, the total pressure in the fluid ventilation system (ie pwgH3 + pxg (H4-H3) ) is less than PW9H4 less friction losses, the scraper will move (initially) and in fact will accelerate along the pipeline. Figure 6 shows a modification to the arrangement shown in Figures 4 and 5. In Figure 6, to avoid localized pressure buildup a pressure vessel 24 with a "cushion volume" 25 therein, and which incorporates the point of gas injection, is coupled between the lower end 13 of the hose 10 and the outlet valve 5 of the pipe. In this embodiment the outlet valve 5 at the distal end 6 of the pipe may be in the form of a check valve which prevents the contents of the pipe, in front of the scraper 9, from being pressurized by the air or other fluid A_injected in the pressure vessel 24. A pressure meter 26 can be connected to the pressure vessel 24, if desired, to monitor the pressure in the damped volume 25. It will be appreciated that a pressure vessel arrangement similar to that of Figure 6 will be It could be used when injecting gas into the hose is used in connection with the methods of Figures 1 and 2 (to scrape a pipe initially filled with air) in order to avoid collapse of the hose. Other additional features can be incorporated into the systems described above, particularly (but not exclusively) a submarine compressed air storage facility. For example, a remote control system may be included to control the injection of compressed air into the hose 10; the fluid flow rate monitoring apparatus for monitoring the flow of the fluid through the outlet valve 5 and / or the inlet valve 3, and another control system linked with the outlet and / or inlet valves 5 , 3 to control the flow of the fluid therethrough; monitoring apparatus for measuring the total amount of gas and / or water entering and / or leaving the pipe 1, the monitoring system being related to one or more of the aforementioned control systems. Another possible feature of the system would be an automatic activation system, to activate the injection of compressed air into the hose 10, which includes a sensor to detect any liquid in the pipe 1 in front of the scraper 9 and activate the injection of compressed air when the detects another liquid (This would be applicable when the pipe is initially filled with air and compressed air injection is used to complete the scraping process, if any liquid enters the pipe, as described hereinafter). Another possible feature would be a control system related to the scraper 9 and / or any additional scraper in the pipe 1, which cooperates with the fluid ventilation system (comprising the hose 10, the buoy 11 and the source of compressed air) to control (automatically) the advance of the scraper 9 along the pipe 1. The gas injection point, instead of being in the hose 10, may be in the pipe 1, or in the pressure vessel 25. scraper receiving unit (not shown) may be attached to distal end 6 of the pipe, and this unit could alternatively incorporthe gas injection point. (A scraper release unit may also be attached at the proximal end 4 of the pipe). The buoy 11 in any of the embodiments described above may additionally be provided by one or more of a buoy connected to the hose, as described above. It will further be appreci that in the embodiments described above, the hose and buoy could be replaced by a convenient, flexible or otherwise conduit having its upper end mounted or supported on a surface platform or other construction / support available in the surface, or at the desired depth below sea level. It will be appreci, however, that the hose and buoy arrangement provides the simplest, most convenient way to implement the invention. The same buoy does not need to be hollow; the upper end 14 of the hose 10 may instead function as a vent outlet 17 via which the hose fluid is vented, providing a check valve at this upper end of the hose. In the last mode, the upper end of the hose can be fixed directly to the buoy, or it can be suspended from the buoy (for example via a connecting wire) so that it is disposed at the desired depth below the surface of the sea. In each case the buoy can be a shallow or medium depth buoy. Another possibility would be to mount the upper end of the hose in a ventilation chamber that is suspended from a buoy element, the ventilation chamber having a construction similar to the buoy illustrated in Figure 3. This arrangement is shown in Figure 7. In this arrangement the fluid ventilation system consists of a hose having an end 61 connected to the valve outlet 5 of the distal end 7 of the pipe 1 (or a scraper receiving unit attached to the end of the pipe and in communication with the pipe). fluid therewith) and the other end 63 mounted in a ventilation damping chamber 62. The end 63 mounted in the ventilation damping chamber has a one way check valve 64 provided therein. The chamber 62 (shown in cross-section for the purpose of revealing the interior of the hose 60) has two vents 65, 66 which also each have a one-way check valve 67, 68 for controlling the flow of fluid through it. The ventilation chamber 62 operates in a manner similar to the buoy 11 shown in Figure 3, the three check valves 64, 67, 68 operate in a manner similar to the check valves 18, 19 in the buoy ventilation system of Figure 3, but in this case the fluid ventilation system also includes a buoy 70 which floats on the surface of the water and from which the ventilation damping chamber 62 is suspended, as shown. A cable 72 is also provided, which extends between the pipe 1 and the chamber 62 to help keep the chamber in a stable position above the pipe 1. The depth H3 of the ventilation outlets 65, 66 below the The surface of the water determines the speed of the path of the scraper along the pipe 1. The buffer chamber 62 in Figure 7 provides a "damping volume" or "buffer zone" similar to that provided by buoy 11 of the Figure 3. The flow of fluid into the buffer chamber 62 outside the upper end 63 of the hose 60 can only exit the system via the ventilation outlets 65, 66 of the damping chamber 62. The advantages provided by this damping volume already have been described. Another reason why the buffer zone is important is because, in practical applications, the check valves may not act instantaneously to pressure inversions. In this way, if a low pressure were present in the hose 60 (in relation to the surrounding environment) the buffer zone would prevent water from entering the upper end of the hose. Any ambient water entering the buffer zone (via the exits of the buffer chamber 62) during this pressure drop will be ejected upon resuming the overpressure in the hose 60. In addition, it will be appreciated that the method described with reference to the Figures 5-6 can be used as a supplementary process, after carrying out the method described with reference to Figure 1 or Figure 2 for a pipe initially filled with air, in order to complete the scraping process where a liquid it has managed to enter the pipe 1 in the volume in front of the scraper (i.e. between the scraper 9 and the outlet valve 5). The aforementioned methods are applicable to flexible pipes, as well as to rigid pipes. Another possible feature of the methods described above and apparatuses may be the use of a filter at the inlet 3 of the pipe in which the seawater enters the pipe to push the scraper forward along the pipe. The filter would be adapted to filter the water entering the pipe, preferably before it enters the pipe. further, devices can be provided to introduce chemical products into the pipeline. Chemicals are typically introduced into the pipe, behind the scraper, for the prevention of pipe corrosion and / or dyes that can be used to assist in the detection of leaks during the pipe pressure test. A convenient apparatus for introducing these chemicals is illustrated in Figure 8. Figure 8 shows the proximal end 8 of pipe 1 (or a scraper launch unit connected to pipe 1 and in fluid communication with it), with a valve inlet 80 thereto which is connected to the outlet of a series of three containers or boxes 82, 83, 84 in which water soluble chemicals are contained. These three containers are in fluid communication with each other and are linked, via a connecting conduit with valves 85 to a filter unit 86. A valve 87 in this connection conduit, and the valve 80 between the boxes containing chemicals 82 -84 and pipe 8, are used to control the opening of the pipe to the external hydrostatic pressure. With these two valves open, and when the pressure in the fluid ventilation system in fluid communication with the pipe at the other end thereof is sufficiently low to cause the sea water to be pulled into the pipe, the water is pulled through the filter unit 86 where it is filtered before passing to the containers of chemical products. The water-soluble chemicals in them are pulled into the pipe 1, behind the scraper 9. There is no particular requirement for the shape of the container or the water soluble chemicals therein, but the following characteristics are desired in the system: (1) The surface area of chemicals exposed to the water flow should remain approximately constant to ensure that the rate at which chemicals are introduced into seawater is constant with respect to the water flow rate from sea towards the pipeline; (2) The surface area and the flow path through which seawater flows through the containers should be designed to achieve, over the expected range of water flow rates, the dose ratios of chemicals required; (3) The design of the filter unit and containers shall minimize the pressure losses associated with the flow of water through them; (4) The filter unit should have a sufficiently large surface area to be unlikely to be blocked, - (5) Containers should maintain sufficient chemicals to maintain the required dose of chemicals throughout the scraping process; (6) Other valves can be provided to control and / or isolate the flow of water in and out of the containers.

Claims (33)

1. CLAIMS 1. A method for pushing a scraper (9) along a pipe element in the seabed substantially filled with air (1) having input elements (3) at a proximal end (4) thereof and output elements (5) at a distal end (6) thereof, and a scraper (9) disposed therein at least a distance away from the distal end, the method comprising the steps of opening the entry element (3) to allow entry of water to the pipe element at a pressure generally corresponding to the ambient water pressure at the proximal end (4) of the pipe element, and coupling the outlet element (5) of the pipe element to a fluid ventilation system that it comprises a conduit (10) connected to a buoy element (11), and ventilation outlet element (17) via which the air of the pipe element can be ventilated, wherein environmental water is substantially prevented from entering the fluid ventilation system and The buoy element supports the vent outlet element (17) at a height sufficiently above the seabed to maintain air in the fluid ventilation system at a sufficiently low pressure to create a pressure differential across the scraper (9) large enough to cause substantially all the air in the pipe element, in front of the scraper, to be vented 4? from the distal end (6) of the pipe element to the fluid ventilation system, whereby the scraper is pushed along the pipe element towards the distal end thereof. A method according to claim 1 wherein, after substantially all of the air in the pipe element (1) has been vented from the pipe element, the element further includes introducing into said pipe (10) a fluid having a density less than that of water, so as to maintain the fluid in the fluid ventilation system at a pressure sufficiently below the ambient water pressure at the distal end (6) of the pipe element to create a differential of pressure through the scraper large enough to cause any amount of water that has entered the pipe element, in front of the scraper, to vent from the outlet element (5) at the distal end of the pipe element to the fluid ventilation system , to complete the path of the scraper towards the distal end of the pipe element. 3. A method for pushing a scraper (9) along a pipe element in the bed filled with substantially air (1) having an input element (3) at a proximal end (4) thereof and an element outlet (5) at a distal end (6) thereof, and a scraper (9) disposed at the distal end (6) of the pipe element towards the fluid ventilation system, by means of which the scraper is pushed as far as possible. length of the pipe element towards the distal end thereof. A method according to claim 1 wherein, after substantially all of the air in the pipe element (1) has been vented from the pipe element, the element further includes introducing into said pipe (10) a fluid having a density less than that of water, so as to maintain the fluid in the fluid ventilation system at a pressure sufficiently below the ambient water pressure at the distal end (6) of the pipe element to create a differential of pressure through the scraper large enough to cause any amount of water that has entered the pipe element, in front of the scraper, to vent from the outlet element (5) at the distal end of the pipe element to the fluid ventilation system , to complete the path of the scraper towards the distal end of the pipe element. 3. A method for pushing a scraper (9) along a pipe element in the bed filled with substantially air (1) having an input element (3) at a proximal end (4) thereof and an element of outlet (5) at a distal end (6) thereof, and a scraper (9) disposed therein at least a distance away from the distal end, the method comprising the steps of opening the input element (3) to allow water to enter the pipe element (1) at a pressure corresponding in general to the environmental pressure of the water at the proximal end (4) of the pipe element, and coupling the outlet element (5) of the pipe element to a fluid ventilation system (10, 11, 17) having a vent opening open to atmospheric pressure, so as to create a pressure differential across the scraper (9) sufficiently to cause substantially all of the air in the pipe element (1), in front of the scraper, to be vented from the end distal (6) thereof, whereby the scraper is pushed along the pipe element towards the distal end thereof. 4. A method according to claim 3, wherein the fluid ventilation system comprises a conduit (10) having one open end coupled to the outlet element (5) of the pipe element and the other open end maintained above the surface of the water (12) and open to atmospheric pressure. A method according to any one of claims 1 to 4, wherein the pressure differential created through the scraper (9) is large enough to cause the scraper to be pushed along the pipe element (1). ) within a predetermined speed range of the scraper. A method according to any one of claims 1 to 5, wherein the pressure differential created through the scraper (9) is large enough to cause the scraper to be pushed along the pipe element (1) at a predetermined average speed. A method according to claim 1 or 2, wherein the vent outlet element (17) is held by the buoy element at a predetermined depth (H3) below the surface so that it reaches a desired speed of scraper travel along the pipe element. 8. A method according to claim 2, wherein the fluid introduced into the conduit is compressed air. A method according to claim 2 or claim 8, wherein the fluid is pumped into the conduit (10) by a pump in a surface support container or platform. A method according to claim 2 or claim 8, wherein the compressed gas (Ap) is injected into the conduit (10) from a subsea compressed gas storage facility. 11. A method according to claim 10 in. where the submarine compressed gas storage facility comprises at least one cylinder of compressed gas disposed in the seabed. 12. A method according to claim 1, which includes monitoring the pressure in the conduit (10) and injecting compressed gas (Ap) into the conduit when the pressure therein falls below a predetermined value at which the collapse of the conduit, whereby collapse of the conduit is substantially prevented. A method according to claim 1 or claim 2, wherein a lower end of the conduit is connected to the outlet element (5) of the pipe element (1) and an upper end of the conduit is mounted on, and in fluid communication with, a ventilation damping chamber (62) which is suspended from the buoy (70), the ventilation outlet element (65, 66) being provided in the ventilation damping chamber. 1 . A method according to claim 1 or claim 2, wherein the buoy element comprises a buoy (11) disposed on the surface of the water. 15. A method according to claim 1 or claim 2, wherein the buoy element comprises a buoy (11) disposed at a depth below the surface of the water. 16. A method according to claim 18 or claim 19, wherein the lower end of the conduit is connected to the outlet element (5) of the pipe element (1) and an upper end of the conduit (10) is connected to the buoy (11), and the vent outlet element (17) is provided in the buoy. 17. A method according to claim 14 or claim 15, wherein the vent outlet element is provided in the conduit (10). 18. A method according to claim 17, wherein the lower end of the conduit (10) is connected to the outlet element (5) of the pipe element (1) and an upper end of the conduit is suspended from the buoy (11). ), the ventilation outlet element being provided at the upper end of the duct. A method according to any of the preceding claims wherein the water flowing into the pipe element (1) through the inlet element (3) is pulled through the filter element (86) before flowing to through the entry element. A method according to any one of the preceding claims wherein the water flowing into the pipe element (1) through the inlet element (3) is pulled through the container element (82)., 83, 84) that has water soluble chemical substances, before flowing through the input element. 21. A fluid ventilation system for use in venting a fluid from an underwater apparatus containing fluid (1), the system comprising a buoy element (11, 70) and a conduit (10, 60) having one end (13, 61) thereof for connection, in use, with one outlet (5) of the underwater apparatus to be in fluid communication therewith, and another end (14, 63) for linking to the buoy, and venting the outlet element (17, 65, 66) via which the fluid can exit the fluid ventilation system, the vent outlet element being provided with automatic valve elements (18, 67, 68) formed and accommodated to be in a closed position, substantially preventing fluid from flowing to the fluid ventilation system through the vent outlet element, when the internal pressure in the fluid ventilation system is less than the external pressure in the element exit of ve Nitilation, and to be in an open position, allowing fluid in the fluid ventilation system to be vented from it, when the internal pressure in the fluid ventilation system is greater than the external pressure in the outlet element of ventilation, whereby, in use, the fluid in the underwater apparatus (1) is vented therefrom to the fluid ventilation system when the fluid is at a pressure greater than the internal pressure in the ventilation system of the fluid from which, in turn, the fluid is vented when it is at a higher pressure than the external pressure in the ventilation outlet element (17, 65, 66) thereof. 22. A fluid ventilation system according to claim 21 for use in pushing a scraper along an underwater pipeline (1), thereby allowing the fluid in the pipeline (1) to be vented from an outlet at one end of the pipe and outside the fluid ventilation system when the valve element (18) is in the open position. 23. A fluid ventilation system according to claim 21 or claim 22, wherein the vent outlet element comprises an outlet (17) provided in the buoy member (11). 24. A fluid ventilation system according to claim 21 or claim 22, wherein the vent outlet element comprises an outlet provided in the conduit (10). 25. A fluid ventilation system according to any of claims 21 to 24, wherein a lower end (61) of the conduit (60) is adapted for its connection for the outlet of the subsea apparatus (1), and one end upper (63) of the conduit is mounted on, and in fluid communication with, a ventilation damping chamber (62) which is suspended from the buoy element (70), the vent outlet element comprising at least one outlet (65). , 66) in the ventilation damping chamber. 26. A fluid ventilation system according to any of claims 21 to 24, further including at least one source of compressed fluid (Ap), the fluid having a density less than the density of the water, for connection to the conduit (10). , 60). 27. A fluid ventilation system according to claim 26 further comprising a pressure vessel (24) coupled between the compressed fluid source and the conduit (10). 28. A fluid ventilation system according to claim 26 or claim 27, further comprising a control system for controlling the injection of the compressed fluid (Ap) into the conduit. 29. A fluid ventilation system according to any of claims 26 to 28, wherein the compressed fluid is compressed gas (Ap). 30. A fluid ventilation system according to claim 29, when dependent on claim 28, wherein the control system comprises compressed gas injection elements and pressure sensor elements (26) for capturing the pressure in the conduit (10) and for activating the compressed gas injection element for injecting compressed gas (Ap) into the conduit when the pressure in the conduit falls below a predetermined level at which collapse of the conduit may occur, whereby substantially the collapse of the canal is avoided. 31. A fluid ventilation system according to any of claims 21 to 30, wherein the buoy element (11) is hollow and generally bell-shaped having an inlet (20) connected to an upper end (14). ) of said duct, and a narrow outlet end (16) comprising the ventilation outlet element (17), * r "and wherein the valve element comprises a valve of 10 retention (18) that controls the flow of fluid through the buoy element (11). 32. A fluid ventilation system substantially described herein and with reference to Figure 3 of the drawings. 33. A fluid ventilation system substantially as described herein and as reference to Figure 7 of the drawings.