GB2373037A - Locating a source in a pipe, by using an inflatable plug at various locations - Google Patents

Abstract

A bag 11 at the end of a pipe 12 is inserted into a service pipe 1 and inflated at a series of positions until the unwanted fluid supply is located within a pre-determined distance. Preferably the presence of an unwanted fluid supply is detected by CCTV or a pressure gauge. Preferably the self centring bag comprises a polyurethane coated nylon outer layer, a latex rubber bladder inner layer and a semi-rigid nylon spine. Preferably the inflation pipe is medium density polyethylene. The method can be used for locating a back feed connection 5 into an old gas main 1.

Description

Method of Locating Unwanted Fluid Supply into Service Pipe This invention relates to a method of locating an unwanted fluid supply into a service pipe, in particular to a method for locating the position of a back-feed connection into an old gas main which is to be abandoned.

When old gas mains are being abandoned a problem which frequently arises is the occurrence of back-feed connections to the main which may have been overlooked or forgotten and the presence of which prevents the immediate abandonment of the main. Locating such back-feed connections can be difficult and expensive.

Gas companies have used different methods of closing or "bagging off'old gas mains over a long period. These methods vary from self centred bags to the more modem Wask 3/12 system which was developed for stopping the flow of Low Pressure Gas Systems up to 75 millibar on mains sizes ranging from about 75 mm to about 300 mm. This system uses an inflatable bag which is inserted into a live main via a sealed insertion tube. This tube is attached to the main by a base secured with chains and sealed by an appropriate sized rubber. Several years ago a method to bag off 5 cm cast iron mains and 5 cm steel runners was designed using this system. All the systems give good results in stopping the flow of gas. However, all the systems require the excavation of large work areas since they do not indicate where back-feeds are located. They only indicate the direction in which a back-feed is flowing. Present methods to locate back-feeds use closed-circuit television (CCTV) if appropriate or another large excavation with a full set of bags. Such methods however still only indicate the direction in which a back-feed is flowing. When abandoning old mains the main is bagged off, e. g. using the Wash 3/12 system, and a decay test is applied. This decay test determines if there are any consumers attached to the main and if there is a back-feed connection which will prevent the main from being abandoned. When a main is found to have a back-feed which is not shown on mains plans and there is no indication of its whereabouts it can be difficult to locate. To locate such a back-feed, standard procedure is to halve the length of the main to be abandoned and to excavate at this point where the main is again bagged off and a further decay test is made to determine the direction of the back-feed. This procedure may need to be carried out again and again until the back-feed is finally located, adding more excavations, time, customer inconvenience and cost to an original job. The use of inflatable bags in the detection of leaks in sewer pipes has been disclosed inDE-A-197 11 194 and in US-A-5 467 640. According to the present invention, we provide a method for the location of an unwanted fluid supply into an isolated service pipe by making a series of tests along the length of the service pipe to determine the approximate location of the unwanted supply, characterised in that an inflation pipe having an inflatable bag at its end is inserted along the service pipe to a first position, the bag is inflated via the inflation pipe to form a temporary seal in the service pipe, the side of this temporary seal upon which is located the unwanted fluid supply is determined, the bag is deflated and is thereafter moved to a second position along the service pipe and the inflation/sealing procedure is repeated, the procedure being further repeated if necessary, until the location of the unwanted fluid supply is determined within a pre-determined distance. The method of the invention is intended particularly for use in the location of backfeeds into gas mains which are to be abandoned, i. e. for use in the gas industry. However, it is applicable elsewhere i. e. in the location of similar back-feed pipes carrying water and other liquid into water mains, sewers etc.

In use in the gas industry, the method is preferably carried out in repeated steps until the back-feed is located to within 2 metres of its position, preferably to within 1 meter and particularly to within 0.5 metres. The procedure may be repeated as many times as in considered desirable depending on the length of the main to be abandoned.

Preferably the system is designed to operate on lengths up to 100 metres.. The inflatable bag to be used can be any suitable bag. Suitably the bag is self centering and comprises a coated nylon high visibility outer bag (preferably PU coated) with an inner latex rubber bladder and a semi rigid nylon spine with a suitable connection, e. g. a 1 to 2 cm UNF connector. Suitably, the inflation pipe is formed from medium density polyethylene (e. g. 16 mm) with a standard dimension ratio (SDR) of for example 7.

The invention is illustrated by the accompanying drawings Figures 1 to 9 which show the procedure to be adopted for locating a back-feed into a gas main which has been isolated and which is to be abandoned. Figures 1 to 9 are as follows : Figure 1 shows the isolated main in which the presence of a back-feed has been established but its exact location is not known. Figure 2 shows the main with gland assemblies attached to it. Figure 3 shows the main with standard bags installed in it through the gland assemblies. Figure 4 shows the attachment to the main of a flange assembly for the introduction of a remote bag to the main. Figure 5 shows the removal from the main of the standard bags. Figure 6 shows the initial insertion of the remote bag into the main. Figure 7 shows the initial inflation of the remote bag inside the main. Figure 8 shows the final re-positioning of the remote bag beyond the back-feed in the main. Figure 9 shows the inflation of the remote bag at its final position in the main. Figure 1 shows a gas main 1 which has been isolated using caps 2 and 3 at its ends. A pressure point 4 has been installed near cap 2 at one end. A back-feed 5 into main 1 has been identified but its location is unknown. The method of the invention is to be used to locate the junction of back-feed 5 with main 1. In Figure 2, gland assemblies 6 have been attached to main 1. These assemblies are attached to the main by flanges and have vents 7. Inside the assemblies are standard bags 8 which can be lowered into main 1 (see Figure 3). The bags 8 are lowered into main 1 and are inflated. Gas is vented through vents 7. In the drawings, two assemblies are shown. The reason for this is that the first of bags 8 stops the flow if gas but, in case some gas passes this bag, a secondary bag 8 is inserted and a vent opened between the bags 8 to ensure a satisfactory seal.

In Figure 4, cap 3, at one end of main 1, has been removed and replaced by flange 9 and pressure point 10 has been attached. Using the attachment of flange 9, remote bag 11 and its associated pipe 12 are introduced to main 1. To pipe 12 are attached pressure gauge 13 and hand pump 14 by means of which remote bag 11 can be inflated. In Figure 5, standard bags 8 have been deflated and removed into assemblies 6, leaving main 1 clear for the insertion along it of remote bag 11. In Figure 6, remote bag 11 has been inserted along main 1 to approximately the middle of the length of the main to be abandoned. In this instance, the remote bag 11 has not reached back-feed 5. Note is taken of the length of pipe 12 which has been inserted, the system is fitted with a counter on the pipe to facilitate this.

Figure 7 shows main 1 with remote bag 11 inserted as shown in Figure 6 and thereafter inflated to manufacturers'recommended pressure using pump 14. Pressure is monitored and should not fall below 20m/bar. A decay test is carried out as per field procedures; pressure should not fall below 20m/bar. The decay test will indicate in which direction along main 1 back-feed 5 is located. In this instance, remote bag 11 has not reached back-feed 5. Remote bag 11 is then deflated slowly. It is then moved further into main 1, re-positioned halfway along the remaining length of main 1 and again inflated. A further decay test is carried out. This procedure is repeated until back-feed 5 is located, i. e. until remote bag 11 is found to have passed back-feed 5 and the back-feed location has been determined within a suitable short distance, preferably within 0.5m. The final position of the remote bag is shown in Figures 8 and 9. In Figure 8, it is shown uninflated and in Figure 9 it is shown inflated.

When back-feed 5 has been located, remote bag 11 is withdrawn beyond flange 9, standard bags 8 are re-introduced into main 1 from assemblies 6, and gas is again vented through vents 7. Flange 9 and the associated assembly of remote bag 11 is removed and cap 3 is again fitted to main 1. Appropriate safety measures and tests for leakage are carried out. An excavation on the back-feed is now made and main 1 is abandoned using conventional methods. The above description relates to the case where, during the first operation of the procedure, the remote bag is inflated and a seal formed in the main between the backfeed 5 and flange 9. It is possible however that the first seal could be formed in main 1 beyond back-feed 5. A second seal would then be formed in main 1 at a position closer to flange 9.

Claims (5)

1. CLAIMS 1. A method for the location of an unwanted fluid supply into an isolated service pipe by making a series of tests along the length of the service pipe to determine approximate locations of the unwanted supply, characterised in that an inflation pipe having an inflatable bag at its end is inserted along the service pipe to a first position, the bag is inflated via the inflation pipe to form a temporary seal in the service pipe, the side of this temporary seal upon which is located the unwanted fluid supply is determined the bag is deflated and is thereafter moved to a second position along the service pipe, and the inflation/sealing procedure is repeated, the procedure being further repeated if necessary, until the location of the unwanted fluid supply is determined within a pre-determined distance.
2. 2. A method according to claim 1 characterised in that the service pipe is a gas main and the unwanted fluid supply is a back-feed.
3. 3. A method according to claim 1 or claim 2, characterised in that, the bag is formed from
4. 4. A method according to any one of the preceding claims characterised in that the pre-determined distance is 2 metres.
5. 5. A method substantially as described herein and as shown in the accompanying drawings.