Replacing mains

Abstract: A method is provided for replacing a length of a branch gas main 1 joined to a spine main 2 with a length of replacement main 7 having an outer diameter smaller than the inner diameter of the branch main. In the method access is gained to the bore of the branch main and one end of the replacement main 7 is fed along the branch main 1 via the access point and towards the spine main 2 until the branch main 1 has been replaced. During and after the feeding step gas is prevented from entering any clearance 20 between the mains 1 and 7 by means of a head 9 attached to the leading end of the main 7. After the feeding step a sealant 25 is injected into the branch main 1 to form a seal within the clearance 20.

Description: The present invention relates to replacing an existing main with a replacement main. Gas, water and sewage mains may need to be replaced when they develop leaks or for other reasons. Leaks may develop at joints as a result of leak paths appearing within the joints in the case of cast iron gas mains or as a result of cracks in the wall due to corrosion or mechanical damage in cast iron and other materials, e.g. ductile iron and steel, cement, brickwork or plastics. In the case where the main to be replaced is a branch main joined to a fluid-carrying spine main, present techniques of mains replacement necessitate an excavation being made at the junction between the branch main and the spine main to gain access thereto. This is frequently in the middle of a busy thoroughfare and the excavation may lead to disruption of both pedestrians and traffic. WO-A-90/07672 discloses a method for replacing an existing gas service pipe with a replacement service pipe. In one method the replacement service pipe has at its forward end a sealing portion in the form of a tubular body having several spaced annular vanes for sealing with the internal wall of the existing service pipe when the replacement pipe is inserted into the existing pipe via a gland arrangement. The vanes provide a barrier to the flow of gas from forward of the sealing portion to the annular gap which is formed between the replacement pipe and the existing pipe. An adaptor is connected to the ends of both the existing pipe and replacement pipe remote from the sealing portion. The adaptor has an injection nipple via which a flowable settable sealant is injected from outside of the replacement pipe into the annular gap, whereby the gap is filled with sealant. The method enables an existing service pipe to be restored to non-leak capability without excavating and removing the pipe. It is an object of the present invention to provide a method by which an existing main can be replaced by a replacement main in such a way that such disruption can be minimised. Another object of the invention is to provide a replacement main for feeding into an existing fluid carrying main. A further object of the invention is to provide a head for use in replacing an existing fluid carrying main with a replacement main. According therefore to one aspect of the present invention we provide a method for replacing a length of a branch main joined to a spine main with a length of replacement main, the length of the replacement main having: an outer wall of smaller diameter than the diameter of the inner wall of the branch main, one end which has two spaced annular vanes disposed around and extending from the outer wall of the replacement main, and an injection point or nozzle in the wall of the replacement main and located between the two vanes via which sealant can be injected between the vanes, the method comprising gaining access to the bore of the branch main at an access point, feeding said one end of the length of replacement main into the length of branch main via the access point and towards the spine main until the length of branch main has been replaced, with the two spaced annular vanes extending to the inner wall of the branch main and defining therebetween, together with the outer wall of the replacement main and the inner wall of the branch main, an annular clearance, and then injecting through the injection point or nozzle sealant supplied via the bore of the replacement main into the annular clearance at a point closer to the one end of the replacement main than to the access point, so that the sealant forms a seal at a point closer to the one end of the replacement main than to the access point. According to another aspect of the present invention, we provide a replacement main for feeding into an existing fluid carrying main, the replacement main having an outer wall of smaller diameter than the inner wall of the existing main, one end of the replacement main having spaced annular vanes disposed around and extending from the outer wall of the replacement main, the replacement main being characterised by having two such vanes and an injection point or nozzle in the wall of the replacement main and located between the two vanes via which sealant can be injected between the vanes, so that on feeding the replacement main into the existing main through an access point an annular clearance is formed between the two spaced vanes, the outer wall of the replacement main and the inner wall of the existing main, the injection point or nozzle being adapted for releasable connection to a hose to extend along the bore of the replacement main and be connected to a sealant source for supplying sealant to the injection point or nozzle for discharge into the annular clearance, when the replacement main is located within the existing main, at a point closer to the one end of the replacement main than to the access point. According to a further aspect of the present invention, we provide a head for use in replacing an existing fluid carrying main with a replacement main having an outer wall of smaller diameter than the diameter of the inner wall of the existing main, the head comprising a tubular body for connection to one end of the replacement main and the tubular body having an outer wall of smaller diameter than the inner wall of the existing main and spaced annular vanes disposed around and extending from the outer wall of the tubular body, the head being characterised by having two such vanes and an injection point or nozzle in the wall of the tubular body and located between the two vanes via which sealant can be injected between the vanes, so that on feeding the replacement main with the head connected to it into the existing main through an access point an annular clearance is formed between the two spaced vanes, the outer wall of the tubular body and the inner wall of the existing main, the injection point or nozzle being adapted for releasable connection to a hose to extend along the bore of the replacement main and the tubular body and be connected to a sealant source for supplying sealant to the injection point or nozzle for discharge into the annular clearance when the head is located within the existing main. Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:- Figure 1 shows a length of a sub-ground branch main joined to a sub-ground spine feeder main carrying fluid, in this case gas, Figures 2 to 7 show the steps in an embodiment of a method according to the invention for the replacement of the branch main with a length of replacement main, Figure 8 is an amplified longitudinally sectioned view of Figure 5. Figure 9 is an amplified longitudinally sectioned view of Figure 7, and Figures 10 to 12 show the final three steps of a method for replacing a branch main lying between two spine feeder mains which are adjoined by the branch main. Referring to Figures 1 to 9 of the drawings, Figure 1 shows a length of branch main 1 joined to a spine main of the same or larger diameter 2 both of which mains are located underneath the ground. The spine main 1 may be carrying gas, water or sewage although the invention is particularly suitable for the replacement of gas-carrying mains. In Figure 1 the spine main 2 is a district feeder main, the branch main 1 leading off therefrom and terminating in a closed end 3. In Figures 10 to 12 however, the branch main 1 is also fed from a further spine main (not shown) at the other end of the branch main 1. The steps shown in Figures 2 to 7 and described in relationship thereto apply to the branch main 1 shown in Figure 1. In the first step of each embodiment of the method (Figure 1) the spine-main distal end 3 of the branch main 1 is exposed by excavation, this end being remote from the spine main 2. Alternatively, an excavation can be made between the spine main and distal end 3 to any convenient point, as required. In this version of the method (Figure 2) a part 4 of the branch main 1 is exposed at a convenient point which in this case is close to the end 3 and is sealed off from the flow of gas by the known technique of "bagging off". Here a pair of removable inflatable rubber bags 5, 6 respectively are inserted into the main 1 at spaced apart positions and are inflated as shown temporarily to block the bore of the main 1. In the next step of this method (Figure 3) the end 3 of the main 1 is removed by sawing or other well known technique to provide an access point for the replacement main 7 to the bore of the branch main 1. A full bore known-type gate valve or damper plate 8 is then connected as shown to the now open end of the branch main 1 and with the valve 8 closed the bags 5 and 6 are deflated and removed through their insertion holes which are plugged or sealed as conventional. A length of replacement main 7 of length sufficient to line or replace the entire length of the branch main 1 from its junction with the spine main 2 to its end 3 is selected, the main 7 being of a suitable synthetic material, preferably polyethylene. The main 7 may comprise discrete lengths fused together or a coil of such material. The outer diameter of the main 7 is smaller than the inner diameter of the branch main 2 to permit the replacement main 7 to be inserted into and fed along the branch main 1. As shown in Figure 3 the replacement main 7 terminates at its leading end in a head 9 which in effect forms an integral part of the main 7. The head 9 may also be of a suitable synthetic resin material e.g. polyethylene in the form of a moulding and comprises a tubular body with a through-going bore, a rear portion 10 for connection to the end of the replacement main and a front portion 11 having two annular vanes 12 and 13 spaced apart along and disposed around the outer wall of the head 9. While a head having two vanes is described there may be more than two if desired or necessary. In use of the head 9, the vanes 12 and 13 form a close or tight fit with the inner wall 14 of the branch main 1 so as to provide a gas-tight barrier to the flow of gas along any clearance between the inner wall 14 of the branch main 1 and the outer wall 15 of the replacement main 7 when the latter is inserted into and pushed along the branch main 1. The external diameter of the vanes may be equal to or greater than the internal diameter of the existing main to achieve the close or tight fit. The head 9 may be attached to the replacement main 7 in any convenient fashion for example by fusion, adhesive or as a force fit within the end of the main 7. Referring to Figures 8 and 9 in particular, extending through an aperture in the wall of the head 9 located between the vanes 12 and 13 is an injection nozzle 30 which is force fitted or glued to the head 9. The inlet end 31 of the nozzle 30 terminates inside the bore of the head 9, while the outlet end 32 of the nozzle 30 terminates between the vanes 12 and 13. Before, however, the head 9 is attached to the leading end of the main 7, this end is inserted through a known-type gland box or pig trap 16 (Figure 3). The gland box 16 has an entry wall 17 formed of elastomeric components which form a hole through which the end of the replacement main 7 may be inserted, the edge forming the hole providing a flexible seal for the outer wall 15 of the main 7. Once the leading end of the main 7 has been inserted into the gland-box 16 and pushed clear of its mouth 18 the head 9 can be attached to the leading end of the main 7. After this step the head 9 is pulled back into the gland-box 16 as shown in Figure 3. The other end of the replacement main 7 is closed by a known type cap with fitted purge valve 19 (Figure 3) to provide means by which any air within the main 7 can be removed by purging as will be described subsequently. Referring to Figure 4, in the next stage of the method the gland-box 16 is connected to the valve 8, the valve 8 is opened and the main 7 is pushed from the gland-box 16 into the branch main 1. As shown, particularly in Figure 8, to prevent in use ingress of dirt and other debris into the head 9 during insertion into the branch main 1, the bore of the head 9 may be temporarily blocked by a conventional inflatable rubber bladder 37 which can be positioned near the front end of the head 9 as shown. The bladder 37 is inflated (and deflated) by means of a hose 38 which extends rearwardly through the head 9 and through and out of the far end of the replacement main as will be described in more detail subsequently. The bladder 37 is inflated before the head 9 is inserted into the gate valve 8. The bladder hose 38 extends rearwardly through the head 9, the replacement main 7 and a known type pipe gland 39 to a source of compressed air (not shown). The vanes 12 and 13 prevent gas from the spine main 2 entering any clearance 20 between the outer wall 15 of the replacement main 7 and the inner wall 14 of the branch main 1. Pushing of the main 7 towards the spine main 2 can be effected by hand or mechanically by means of a conventional pipe pusher machine. The replacement main 7 is pushed along the branch main 1 until the head 9 reaches and enters the spine main 2 (Figure 5). The main 7 is then retracted a short distance until the head 9 is securely located in the branch main 1. This point can be determined by monitoring the pressure in the clearance 20 which will be positive when the head 8 is inside the spine main 2 but will drop to zero when the head 8 is once again inside the branch main 1. Alternatively or in addition the head could incorporate a TV camera or probes to detect the spine main 2. The head 9 could be retracted still further if it is desired to replace a shorter section of branch main 1. The purge valve 19 is opened to permit gas to purge any air from the main 7 and then the valve 19 is closed. The gland-box 16 is then disconnected from the valve 8 and is slid along the main 7 towards the purge valve 19. Next, the valve 8 is disconnected from the end 21 of the branch main 1 and this too is slid along the main 7 towards the valve 19. Alternatively, both valve and gland box can remain joined and be slid along the main still connected and then be disconnected from each other. Referring to Figure 5, it will be seen that the replacement main 7 is blocked by the inflated bladder 37. With the head 9 positioned as shown (in Figures 5 and 8) within the branch main 1, there is formed between the inner wall 33 of the branch main 1, the vanes 12 and 13 and the outer wall 34 of the head 9 lying between the vanes 12 and 13, an annular chamber 35 in which the sealant may be injected via the nozzle 30 as shown in Figure 9. In this way a seal may be formed with a relatively small amount of sealant. The sealant is supplied to the nozzle 30 by means of a flexible e.g. polyethylene hose 36 which as shown in Figure 8 is connected to the inlet end 31 of the nozzle 30. The hose 36 extends rearwardly through the head 9, the replacement main 7 and the pipe gland 39 to a suitable sealant pump (not shown). The pipe gland 39 forms a seal between the replacement main 7 and the hoses 36 and 38. The pump (not shown) which pumps sealant along the hose 36 to the nozzle 30 where it is discharged into the annular chamber 35. When this chamber 35 is full as indicated by an increase in pumping pressure, the hose 36 may be removed from the nozzle 30 and then removed from the replacement main. To this end the hose 36 is connected to the nozzle 30 by a breakable-type connection whereby the hose 36 may simply be snapped off from the nozzle 30 after the clearance has been filled with sealant. At this stage, a suitable sealant 25 is pumped along the hose 36 to emerge into and fill the annular chamber 35 and form a seal therein as shown in Figures 6 and 9. The sealant 25 may be a cementitious grout, cement, epoxy or anaerobic sealant to provide a secondary gas-tight permanent seal in addition to that formed by the vanes. After the sealant has been allowed to set, the hose 36 is snapped off from the nozzle 30 and removed from the main 7 via the pipe gland 39. Then the bladder 37 is deflated and removed via its hose 38 through the pipe gland 39. A so-called "squeeze off" (not shown) is then applied to the main 7 between the end 21 of the branch main 1 and the purge valve 19 by means of a pair of known type squeeze rolls which squeeze the main 7 flat to prevent gas reaching the valve 19. With the squeeze off still applied the gland box 16, valve 8 and pipe gland 39 are slid off the end 24 of the main 7 and then the end of the replacement main 7 is closed by means of a cap (not shown) so that the position in Figure 7 is reached. The cap may be of a synthetic resin material e.g. polyethylene and which is fused or adhered to the main 7 in any suitable manner. The head 9 may be dispensed with if the replacement main 7 itself is fitted with the nozzle 30 and vanes 12 and 13. These could be fitted to the main 7 at the factory where the main is produced and supplied to the user complete with nozzle hose 38 connected to the nozzle 30. Referring to Figures 10 to 12 where parts and components similar to those shown in Figures 1 to 9 bear similar reference numerals a branch main 50 lies between two spine mains, only one 51 being shown, the main 50 adjoining the spine mains at either end. Previously to the stage shown in Figure 10, a section of the branch main 50 located at a point between the spine mains where traffic and pedestrian disturbance is minimal is removed by sawing or other technique to gain access to the bore of the branch main 50. At either side of the section before its removal bags similar to those shown in Figures 2 and 3 are inserted to temporarily block the bore of the main 50 to each spine main. After removal of the section and in consequence thereof a first length 52 of branch main 50 is formed between the first spine main 51 and the open end 53 of the length 52 and a second length 54 of branch main 50 is formed between a second spine main (not shown) and the open end 55 of the length 54 as shown in Figure 7. Each of the lengths 52 and 54 of branch main may be replaced by suitable corresponding lengths 56 and 57 of replacement mains of a material similar to that previously described, each of the lengths 56 and 57 having outer diameters smaller than the internal diameter of the branch main 50. The lengths of branch main are replaced by the technique shown in Figures 2 to 9 previously described. In Figure 10 both lengths of branch main have been replaced by the technique described in Figures 2 to 5. In the position shown in Figure 10 the corresponding purge valves, gland-boxes and valves have been removed from the lengths 56 and 57 after a squeeze off has been applied by respective squeeze rolls 22 and 23, the ends of the lengths 56 and 57 lying adjacent to each other and the ends being open. Next with the squeeze off still applied (Figure 11) the ends 58 and 59 of the lengths 56 and 57 are connected together by any convenient means such as by butt-fusion or as shown in Figure 11 by means of a known type electrofusion sleeve 60. Finally (Figure 12) the squeeze offs are removed. In this way gas or other fluid can flow between the spine mains by way of the replacement mains. The technique described in Figures 10 to 12 can be used with advantage to replace any branch main which is too long to be replaced by a single length of main, the site for any necessary excavation being selected so as to provide a minimum of disruption to traffic and pedestrians.

Claims: A method for replacing a length of a branch main joined to a spine main with a length of replacement main, the length of the replacement main (7) having: an outer wall (15) of smaller diameter than the diameter of the inner wall (14) of the branch main, one end (11) which has two spaced annular vanes (12, 13) disposed around and extending from the outer wall (15) of the replacement main, and an injection point or nozzle (30) in the wall of the replacement main and located between the two vanes (12, 13) via which sealant can be injected between the vanes, the method comprising gaining access to the bore of the branch main at an access point (21), feeding said one end of the length of replacement main (7) into the length of branch main (1) via the access point and towards the spine main (2) until the length of branch main has been replaced, with the two spaced annular vanes (12, 13) extending to the inner wall (14) of the branch main and defining therebetween, together with the outer wall (15) of the replacement main and the inner wall of the branch main, an annular clearance (35), and then injecting through the injection point or nozzle (30) sealant supplied via the bore of the replacement main into the annular clearance at a point closer to the one end (11) of the replacement main than to the access point (21), so that the sealant forms a seal (25) at a point closer to the one end of the replacement main than to the access point. A method as claimed in claim 1, in which the access point (21) is that end of the branch main (1) opposite to the spine main (2). A method as claimed in claim 1, in which the branch main (50) lies between and adjoins the said spine main and another spine main, and the access point lies between the spine mains. A method as claimed in claim 3, employing another length of replacement main (57) having: an outer wall with a smaller diameter than the diameter of the inner wall of the branch main (50), one end which has two spaced annular vanes (12, 13) disposed around and extending from the outer wall of the another replacement main, and an injection point or nozzle (30) in the wall of the another replacement main and located between the two vanes via which sealant can be injected between the vanes, the method further comprising feeding said one end of the another length of replacement main into the branch main by way of the access point (55) and towards the other spine main until the length of branch main between the access point and the other spine main has been replaced, with the two spaced annular vanes (12, 13) extending to the inner wall of the branch main and defining therebetween, together with the outer wall of the another replacement main and the inner wall of the branch main, an annular clearance (35), injecting sealant through the injection point or nozzle (30) supplied via the bore of the another length of replacement main (57) into the annular clearance between the outer wall of the another length of replacement main and the inner wall of the branch main at a point closer to the one end of the another length of replacement main than to the access point, so that the sealant forms a seal at a point closer to the one end of the another replacement main than to the access point, and joining the other ends (58, 59) of the lengths of replacement main (56, 57) together. A method as claimed in any of the preceding claims, in which the sealant is injected via the access point. A method as claimed in any of the preceding claims, in which the sealant is transported along the bore of the replacement main and/or the another replacement main to the injection point(s) or nozzle(s). A method as claimed in any of the preceding claims, in which during the step(s) of feeding the, and/or the another, replacement main into the branch main and prior to injecting the sealant, the vanes (12, 13) form a barrier to prevent fluid from entering the or each annular clearance (20) defined between the replacement main(s) and the branch main. A replacement main for feeding into an existing fluid carrying main, the replacement main (7) having an outer wall (15) of smaller diameter than the inner wall of the existing main, one end of the replacement main having spaced annular vanes (12, 13) disposed around and extending from the outer wall of the replacement main, the replacement main being characterised by having two such vanes (12, 13) and an injection point or nozzle (30) in the wall of the replacement main and located between the two vanes via which sealant can be injected between the vanes, so that on feeding the replacement main into the existing main (1) through an access point an annular clearance (35) is formed between the two spaced vanes (12, 13), the outer wall (15) of the replacement main and the inner wall (14) of the existing main, the injection point or nozzle (30) being adapted for releasable connection to a hose (36) to extend along the bore of the replacement main and be connected to a sealant source for supplying sealant to the injection point or nozzle for discharge into the annular clearance, when the replacement main is located within the existing main, at a point closer to the one end of the replacement main than to the access point. A replacement main as claimed in claim 8, in which the vanes (12, 13) provide a barrier to prevent fluid from entering the annular clearance (20), defined between the replacement main and the existing main when the replacement main is located within the existing main. A replacement main as claimed in claim 8 or claim 9, in which the main is of synthetic resin. A replacement main as claimed in claim 10, in which the main is of polyethylene. A head for use in replacing an existing fluid carrying main with a replacement main having an outer wall of smaller diameter than the diameter of the inner wall of the existing main, the head comprising a tubular body (9) for connection to one end of the replacement main (7) and the tubular body having an outer wall (34) of smaller diameter than the inner wall (33) of the existing main and spaced annular vanes (12, 13) disposed around and extending from the outer wall of the tubular body, the head being characterised by having two such vanes (12, 13) and an injection point or nozzle (30) in the wall of the tubular body and located between the two vanes via which sealant can be injected between the vanes, so that on feeding the replacement main (7) with the head connected to it into the existing main through an access point an annular clearance (35) is formed between the two spaced vanes (12, 13), the outer wall (34) of the tubular body and the inner wall (33) of the existing main, the injection point or nozzle (30) being adapted for releasable connection to a hose (36) to extend along the bore of the replacement main and the tubular body and be connected to a sealant source for supplying sealant to the injection point or nozzle for discharge into the annular clearance when the head is located within the existing main. A head as claimed in claim 12, in which the vanes (12, 13) provide a barrier to prevent fluid from entering the annular clearance (20), defined between the replacement main and the existing main when the head is connected to the replacement main and located within the existing main. A head as claimed in claim 12 or claim 13, in which the tubular body is made of a synthetic resin. A head as claimed in claim 14, in which the body is of polyethylene. A head as claimed in claim 15, in which the body is a moulding.

Inventors: ELGAR ANTHONY DENNIS, PARKES ADRIAN SYDNEY, SALES BRIAN THOMAS, ELGAR, ANTHONY DENNIS, PARKES, ADRIAN SYDNEY, SALES, BRIAN THOMAS
Applicants: BRITISH GAS PLC
Application year: 1991
Main classification: F16L55
IPC codes: F16L1, F16L55