Abstract:
A method of cleaning a pipeline for transporting a fluid without interrupting the fluid flowing through the pipeline, including applying suction to remove a mixture of the fluid and debris from the pipeline, separating the debris from the fluid, and re-injecting the fluid separated from the debris into the pipeline.

Description:
The present application is a national stage application of the PCT application Ser. No. PCT/GB98/00525 filed Mar. 10, 1998, which claims priority to the Great Britain Patent Application No. 9705182.5 filed Mar. 13, 1997. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an improved method for cleaning a pipeline, in particular a gas main, and to an improved apparatus for carrying out the method. 
     DISCUSSION OF THE BACKGROUND 
     Gas mains can contain a substantial amount of debris, for example light dust through to heavy scale, or foreign bodies and other intruding material. This material needs to be removed in particular before any internal inspection or repair is carried out and because it reduces the carrying capacity of the main. 
     SUMMARY OF THE INVENTION 
     It is known to clean gas mains in a decommissioned state. but this has the disadvantage that the gas supply to the customers supplied by that main has to be interrupted while the cleaning is being carried out, thus causing inconvenience and difficulties to these customers. 
     It is an object of the present invention to provide a method of cleaning a pipeline, in particular a gas main in which the above disadvantages are reduced or substantially obviated. It is a further object of the present invention to provide an apparatuis for carrying out the cleaning method. 
     The present invention provides a method of cleaning a pipeline for transporting a fluid, in particular a gas, more particularly a gas which forms an explosive mixture when mixed with air, which method comprises removing debris from the pipeline by means of a collecting device and a removal unit, characterised in that the pipeline is cleaned in a commissioned state, without interrupting the flow of fluid through the pipeline, by removing a mixture of fluid and debris from the pipeline by means of suction, separating the debris from the fluid and re-injecting the cleaned fluid into the pipeline. 
     In particular, the present invention provides a method of cleaning a pipeline for transporting a fluid, in particular a gas, more particularly a gas which forms an explosive mixture when mixed with air, which method comprises the steps of 
     (i) inserting into the pipeline to be cleaned a device for scraping the internal wall of the pipe and collecting the debris deposited by this scraping, together with loose debris in the pipe; 
     (ii) propelling the collecting device, together with the collected debris, along the pipeline to a collection point; 
     (iii) introducing a removal unit in the pipeline for location close to the collecting point and 
     (iv) removing debris from the pipeline by means of this removal unit 
     characterised in that the pipeline is cleaned in a commissioned state, without interrupting the flow of fluid through the-pipeline, and the removal unit comprises a suction head which is powered by a vacuum unit located in a cleaning unit, which cleaning unit is connected to the pipeline to be cleaned at a first point, close to the collection point for debris, and at a second point downstream (with respect to the direction of fluid flow) of the first point, and a mixture of gas and debris is removed by suction from the pipeline at the first point, passed through the cleaning unit, the debris is separated out from the gas/debris mixture as it is passed through the cleaning unit and the cleaned gas is returned to the pipeline at the second point. 
     In a preferred embodiment of the method according to the invention, the cleaning unit is provided, close to its first connection point. with an inlet for purging gas, and purging gas is supplied to the cleaning unit during the cleaning process. 
     The present invention further provides a cleaning unit for use in the pipeline cleaning method according to the invention, characterised in that the cleaning unit comprises, connected in series, first means for connecting the cleaning unit to the pipeline, first valve means, one or more separation stages for mechanical separation of debris from the gas/debris mixture, a blower for creating suction, second valve means connected in parallel with the blower, third valve means. a non-return valve, and second means for connecting the cleaning unit to the pipeline. 
     The cleaning unit according to the present invention preferably further comprises a plurality of sensors for measuring the pressure at a plurality of points in the cleaning unit, and control system for registering the output of the sensors, determining whether a hazard condition exists and taking appropriate action. 
     The control system is preferably designed to indicate where in the cleaning system, a hazard condition has originated. The control system is particularly preferably adapted to allow the cleaning system only to operate within pre-set system parameters. 
     The present invention further provides a trailer unit which comprises a cleaning unit mounted on a trailer, within a housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of a method according to the invention, and a preferred embodiment of a cleaning unit according to the invention will now be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic diagram, showing a preferred embodiment of a cleaning unit according to the invention, connected to a pipeline and 
     FIG. 2 is a perspective view of a cleaning unit according to the invention mounted in a housing unit on a trailer for transport, and connected to a gas main. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As can be seen from FIGS. 1 and 2, the cleaning unit shown generally at  10  comprises a pipe  2  detachably connected in a fluid tight manner at both a first access point  4  and a second access point  6  to a gas main  8 . At access point  4  the pipe  2  may be insertable into the main  8  by a selectively variable amount. An openable and closable inlet  12  for purging gas is provided in the pipe  2  close to the point  4 . A first manual valve  14  and first automatic valve  16 , with pneumatic control, are provided in the pipe  2  downstream (with respect to the gas flow) of point  4 . On the downstream side of the first automatic valve  16 , a first separation stage  18  is located. This first separation stage  18  comprises a cyclone separator  20  connected by means of a manual valve  22  to a disposal chamber  24 , which is vented to the atmosphere via a further manual valve  26 . Opening the valve  22 , periodically, allows separated debris to drop from the cyclone separator  20  into the chamber  24 . Opening the valve  26 , periodically, allows the debris to discharge from the chamber  24 . 
     Downstream of the first separation stage  18 , a second separation stage  28  is located. The second separation stage  28  comprises a filter  30  connected by means of a manual valve  32  to a disposal chamber  34  which receives separated debris when the valve  32  is opened periodically. The chamber  34  is vented to the atmosphere via a further manual valve  36  when opened periodically. The filter  30  is a coarse filter, which may be made of wire mesh. 
     Downstream of the second separation stage  28 , a fine filter  38  is located. The filter  38  is a fine filter, which may be made of paper. 
     Downstream of the filter  38 , the pipe  2  divides into two branches, a first branch  2 ′ leading to a Roots blower  40 . The blower  40  is driven by a diesel powered engine  42  to which it is connected by means of a safety coupling  44 . Diesel fuel is supplied to the engine  42  by means of a fuel valve  46 . The second branch  2 ″ leads via a second automatic valve  48  back to the first branch  2 ′, downstream of the blower  40 . The function of the second automatic valve  48 , which as will be explained later, is spring-loaded ‘fail-open’ is to protect the blower  40  from damage due to build-up of excess pressure downstream of the blower  40 . 
     The pipe  2  then returns via a third automatic valve  50 , a non-return valve  52  and a manual valve  54  to the second connection point  6  where it is connected to the gas main  8 . The function of the non-return valve  52  is to ensure that the gas flow cannot reverse. 
     A plurality of sensors S 1  to S 5  are positioned along the pipe  2  to sense the pressure at the points where they ire connected. A first sensor S 1  is positioned betwveen the first automatic valve  16  and the first separation stage  18 , a second sensor S 2  is positioned between the first separation stage  18  and the second separation stage  28 , a third sensor S 3  is positioned between the second separation stage  28  and the filter  38  a fourth sensor S 4  is positioned between the filter  38  and the blower  40  and a fifth sensor S 5  is positioned between the blower  40  and the third automatic valve  50 . 
     The sensors S 1  to S 5  are connected to a central control and monitoring unit (not shown). 
     As can be seen more clearly in FIG. 2, a suction head shown generally at  56  and mounted on an inner tube (not shown) is introduced into the gas main  8  at the first connection point  4 . The inner tube on which the suction head  56  is mounted is controlled by means of a jack  58 . 
     For ease of transport, the cleaning unit  10  is preferably mounted on a trailer  60  within a housing  62 . 
     Preferably debris from a length of the main  8  between the access points  4  and  6  is scraped or otherwise suitably propelled by appropriate means towards the access point  4 , whilst the main is live, so this debris is gathered at a single place in the main at or adjacent to the access point  4  for extraction by the suction head  56 . 
     In operation, prior to start-up of the cleaning process, the first and second manual valves  14  and  54  are closed, as are the first and third automatic valves  16  and  50 . The first and third automatic valves  16  and  50  are spring loaded ‘fail-shut’, i.e. in the closed position when the system is not in operation. The second automatic valve  48  is open when the system is not in operation and closed when it is in operation: i.e. it is spring loaded ‘fail-open’. 
     As the cleaning process is started, the cleaning unit  10  is initially purged with gas which is injected into the pipe  2  via the inlet  12 , so that the whole system is filled with gas and there is no air present. 
     The manual valves  14  and  54  are then opened and the control unit opens the automatic valves  16  and  50 , the fuel valve  56  and shuts the automatic valve  48  and then the diesel engine  42  is started, to operate the blower  40 . The engine  42  is hand-cranked, for safety reasons, as an electric starter might produce sparks which could ignite the gas. The fuel valve  46  is a solenoid operated valve which is linked to the control system, so that the control system can shut-down the diesel engine  42  in an emergency, by closing down the fuel supply to the engine. 
     While the cleaning system is in operation, the sensors S 1  to S 5  continually monitor the gas pressure to ensure that it is above atmospheric pressure and below a maximum set operating pressure, which is substantially equal to the pressure in the gas main. Any loss in pressure below atmospheric pressure or increase above the set operating pressure indicates to the control system that there is an emergency, caused for example by a blockage in the system and the control system shuts down the cleaning process. 
     In the event of an emergency, the following close down sequence is followed; 
     (i) the diesel supply to the diesel engine  42  is shut down; 
     (ii) the second automatic valve  48  is opened to bypass and thus protect the blower  40  by allowing gas pumped thereby to circulate through the pipe branch  21 ″ and valve  48  and back to the blower to ensure there is no excessive pressure build-up whilst the system is in the process of shutting down; 
     (iii) after a set time, typically 5 seconds, the control system closes the first and third automatic valves  1  and  3  and the cleaning system stops operation. 
     By monitoring the outputs of the sensors S 1  to S 5,  the control system is able, in an emergency shut-down as described above, to indicate to the operator where the problem has arisen, which is helpful in achieving a more rapid solution to the problem. 
     The control system is further designed not to allow the cleaning system to operate outside of the system set parameters. 
     For example, the control system can be set to allow the cleaning system to operate with a maximum pressure differential across each of the filters  30 , 38 , thus detecting when a filter is blocked or becoming blocked. 
     Either access point  4  or  6  may be specially drilled or may be a known access point normally provided to a gas main. The access points  4  and  6  are sealed after the cleaning procedure is completed and the pipe  2  is detached from the access points.