Abstract:
An apparatus and method for supporting pipe main repair tools in an excavation while repairs are being made requires only exposure of the top surface of a buried main and utilizes an anchoring system installed in or above the excavation and an elongate support member that spans the excavation in a generally horizontal position above the pipe main and supports an elongate tubular seal tube against the exposed surface of the pipe main. The elongate support member is secured and supported at opposite ends on the ground surface on opposed sides of the excavation by a pair of parallel laterally spaced shoring members firmly engaged on opposed sides of the excavation, or by a pair of parallel laterally spaced anchor plates firmly engaged on the ground surface on opposed sides of the excavation. The bottom end of the elongate tubular seal tube is engaged on the exterior of the pipe main and an adjustable clamping assembly mounted on the support member supports the seal tube in selective radially extending positions relative to the longitudinal axis of the pipe main. A jack mechanism between the seal tube and the adjustable clamping assembly on the support member forces the seal tube downward to seal against the pipe main. Various tools may be passed through the interior of the seal tube to perform operations on the pipe main.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional of U.S. patent application Ser. No. 08/221,891 filed Mar. 31, 1994, now U.S. Pat. No. 5,462,077 issued Oct. 31, 1995. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates generally to apparatus and methods for pipe main repair and excavation shoring, and more particularly to an apparatus and method for supporting pipe main repair tools in an excavation while repairs are being made that utilizes an anchoring system installed in or above the excavation and an elongate support member that spans the excavation in a generally horizontal position and supports an elongate tubular seal tube against the exposed surface of the pipe main through which various tools may be passed for performing operations on the pipe main. 
     BRIEF DESCRIPTION OF THE PRIOR ART 
     One of the many important tasks for a gas utility is to respond to emergencies that involve or may involve natural gas. The types of emergencies vary, but one of the more important, involves a broken or breached gas main. Gas mains can be damaged in many ways, such as breakage from excavating equipment (i.e., backhoe), excessive soil settlement, failure due to age, and washouts from broken water mains. When a gas main is breached or broken, the gas normally transported and contained within the pipe escapes to the atmosphere causing a fire or explosion hazard. If the failure is due to a washout, water can enter the main, flood the gas system, and cause a loss of service to the attached customers. In either case, the gas utility must regain control as quickly as possible by stopping the escaping gas or influx of water. Conventional methods for blocking flow in buried gas mains require extensive excavation to completely uncover the main for deployment of plugging equipment and are quite time consuming. 
     One common method for blocking flow in the main is to attach a saddle to the main and install equipment to drill into the main and insert a stopper. Typically, the saddle mounting hardware consists of bolts or chains that attach to each side of the saddle and wrap around the pipe. Some mechanical method of tightening the bolts or chains is usually supplied. To install the saddle clamping chains or hardware, soil must be excavated completely around the pipe to allow access from all sides so that the chains or hardware can be wrapped under the main, and the exterior of the pipe must be extensively cleaned to allow sealing. As a result, excavations are large and many times must be hand dug, increasing excavation time. This extra excavation and extensive cleaning adds significant amounts of time to the stopping process, thus increasing the danger from potential explosions, fire damage or the influx of water. In addition, the current drilling and stopping equipment take a long time to set up and complete the job once the main is exposed. 
     DeGiovanni, U.S. Pat. No. 4,155,373 discloses a method for shutting off gas flow in plastic pipes wherein a tubular plastic fitting is joined to the wall of a plastic gas pipe by fusion and a hole is cut through the plastic gas pipe and then a balloon-type stopper is inserted into the gas pipe and inflated. 
     Yie et al, U.S. Pat. No. 4,291,727 discloses an inflatable expandable flexible sleeve and insertion apparatus which is connected to a saddle attached to the pipeline by U-bolts. To install the saddle clamping U-bolts, soil must be excavated completely around the pipeline. 
     Minotti, U.S. Pat. No. 4,351,349 discloses pipe repair kit including an inflatable bladder and a system of conduits which are secured to the pipe exterior in longitudinally spaced relation by a plurality of two-piece clamps which extend completely around the circumference of the pipe. This method and apparatus requires a large excavation and the soil must be excavated completely around the pipeline at several locations. 
     U.S. Pat. Nos. 4,376,599 issued to Krings, 4,453,863 issued to Sutton et al, 4,787,781 issued to Bradberry, and 5,096,334 issued to Plank, all disclose various types of trench and excavation shoring apparatus. However, none suggest a method or any type of apparatus for supporting pipe main repair tools in the excavation through which various tools may be passed for performing operations on the pipe main. 
     The present invention is distinguished over the prior art in general, and these patents in particular by an apparatus and method for supporting pipe main repair tools in an excavation while repairs are being made which requires only exposure of the top surface of a buried main and utilizes an anchoring system installed in or above the excavation and an elongate support member that spans the excavation in a generally horizontal position above the pipe main and supports an elongate tubular seal tube against the exposed surface of the pipe main. The elongate support member is secured and supported at opposite ends on the ground surface on opposed sides of the excavation by a pair of parallel laterally spaced shoring members firmly engaged on opposed sides of the excavation, or by a pair of parallel laterally spaced anchor plates firmly engaged on the ground surface on opposed sides of the excavation. The bottom end of the elongate tubular seal tube is engaged on the exterior of the pipe main and an adjustable clamping assembly mounted on the support member supports the seal tube in selective radially extending positions relative to the longitudinal axis of the pipe main. A jack mechanism between the seal tube and the adjustable clamping assembly on the support member forces the seal tube downward to seal against the pipe main. Various tools may be passed through the interior of the seal tube to perform operations on the pipe main. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to provide an apparatus and method for supporting pipe main repair tools in an excavation while repairs are being made to the pipe main. 
     It is another object of this invention to provide an apparatus and method for supporting pipe main repair tools in an excavation which utilizes an anchoring system achored on the ground surface on opposed sides of the excavation and an elongate support member that spans the excavation and supports an elongate seal tube on the exterior of the pipe main through which various tools may be passed to perform operations on and inside the pipe main. 
     Another object of this invention is to provide an apparatus and method for supporting pipe main repair tools on the exterior of a pipe main at the bottom of an excavation and requires excavation of only a minimal portion of the top surface of the pipe main for installation. 
     Another object of this invention is to provide an apparatus and method for supporting an elongate seal tube on the exterior of the pipe main through which various tools may be passed to perform operations on and inside the pipe main. 
     Another object of this invention is to provide an apparatus and method for supporting an elongate seal tube on the exterior of the pipe main in selective radially extending positions relative to the longitudinal axis of the pipe main. 
     Other objects of the invention will become apparent from time to time throughout the specification and claims as hereinafter related. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section through an excavation showing an anchoring system of the apparatus for supporting pipe main repair tools in accordance with the present invention secured in the excavation above a pipe main. 
     FIG. 2 is a cross section through an excavation showing an alternate anchoring system of the apparatus for supporting pipe main repair tools in accordance with the present invention secured on the ground surface at the top of the excavation. 
     FIG. 3 is a cross section through the excavation and anchoring system of FIG. 1 showing a seal tube assembly installed on the pipe main. 
     FIG. 4 is a cross section through the excavation and anchoring system of FIG. 3 shown from the side. 
     FIGS. 5A and 5B taken together are a cross section through the seal tube assembly of the present invention. 
     FIGS. 6A and 6B taken together are a cross section through the seal tube assembly showing a cutting tool installed therein. 
     FIG. 7 is a cross section through the seal tube assembly showing somewhat schematically a sealant injection tool installed therein. 
     FIGS. 8A, 8B, and 8C taken together are a cross section through the seal tube assembly showing a bladder deployment tool installed therein with one ramp pivoted outward. 
     FIG. 9 is a cross section through the lower portion of the bladder deployment tool showing schematically both bladders deployed and inflated. 
     FIG. 10 is a cross section through the seal tube assembly showing a thread tapping and plugging tool therein. 
     FIG. 11 is an enlarged cross section showing a thread die member connected to the lower end of the thread tapping and plugging tool. 
     FIG. 12 is an enlarged cross section showing a threaded plug member connected to the lower end of the thread tapping and plugging tool. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings by numerals of reference, there is shown somewhat schematically in FIG. 1, an excavation E which has been dug to a depth sufficient to expose the upper surface of a buried pipe main M. An anchoring platform system 10 is shown deployed in the excavation E. The anchoring platform 10 has a pair of flat rectangular panels 11, or shoring members, mounted in opposed parallel relation at each end of a horizontally disposed expandable jack member 12. The jack member 12 may be either mechanical or hydraulic, and, when expanded will push against the sides of the excavation E. The opposed panels 11 are sized such that their surface area will distribute the load to acceptable levels so that the soil is not displaced a significant amount. However, the friction force between the panels 11 and the walls of the excavation E is significant and creates a firm stable platform for anchoring the elongate seal tube assembly described hereinafter. If more stability is required, stakes can be attached to the panels 11 and pushed into the surrounding soil during installation. 
     A vertical beam, or support brace 13 is secured to each panel 11 and extends upwardly therefrom to just above ground level and a quick disconnect clamp 14 is secured to the top end of each brace. A tubular horizontal cross bar 15 is removably clamped to the top ends of the vertical support braces 13 by the clamps 14 to span the excavation above the main. The horizontal cross bar 15 serves as the attachment point for the seal tube assembly through which various tools may be passed for drilling a hole in the pipe main, inserting inflatable bladders and plugging the hole, as described hereinafter. 
     FIG. 2 shows an alternate embodiment of the anchoring platform system 10A. In this embodiment, a pair of opposed anchor plate members 16 are bolted to the ground or street surface on each side of the excavation by expanding bolts 17, and a quick release clamp 14 is secured to each anchor plate. The tubular horizontal cross bar 15 is removably clamped to the top ends of the anchor plates 16 to span the excavation above the pipe main M. 
     Referring now to FIGS. 3, 4, 5A, and 5B, the exposed surface of the pipe main M is cleaned using conventional methods, and an elongate seal tube assembly 18 is positioned on the main closely adjacent the horizontal cross bar 15. The seal tube assembly 18 has an elongate tubular lower section 19 and upper section 20 each having external threads at each end. A ball valve 21 is threadedly engaged at the top end of the lower section 19. A tubular bearing member 22 formed of low friction material is secured to the interior of the lower section 19 and has vertical slots 23 along its central bore. A seal foot member 24 having an internally threaded upper end and a central bore is threadedly engaged on the bottom end of the lower section 19 of the seal tube assembly 18. The seal foot 24 has a concave bottom flange 25 with an annular seal ring groove 26 surrounding its central bore which receives a seal ring 27. The concave bottom flange 25 engages the outer surface of the pipe main M, and several interchangeable foot members are provided for fitting different diameter mains. 
     The threaded bottom end of the elongate tubular upper section 20 of the seal tube assembly 18 is threadedly engaged in the upper end of the ball valve 21 and a flange 29 is threadedly engaged on the top end. A tubular bearing member 30 formed of low friction material is secured to the interior of the flange 29 and has a resilient flat circular gland-type stripper seal 31 extending a short distance radially inward from its central bore. Circumferentially spaced wing bolts 32 are pivotally connected in slots in the outer periphery of the flange 29. A vent pipe 33 is secured in the side wall of the upper section 20 beneath the bearing 30 and seal 31 and has a valve 34 connected at its outer end to vent pressure from the interior of the seal tube assembly 18. A collar 35 is slidably received on the exterior of the upper section 20 and has a short tubular extension 36 extending outwardly therefrom. A locking lever 37 having a threaded shank extends through a tapped hole in the side wall of the short tubular extension 36. 
     As seen from the side in FIG. 4, a clamp 38 is slidably mounted on the horizontal cross bar 15. The clamp 38 can be positioned longitudinally along the horizontal cross bar 15 and then clamped into position thereon. One end of a short tubular member 39 is received in the short tubular extension 36 of the collar 35 and its other end extends through the sliding clamp 38 mounted on the horizontal cross bar 15 to connect the seal tube assembly 18 to the anchor assembly 10. 
     As best seen in FIGS. 5A and 5B, a rotatable screw jack mechanism 40 is slidably mounted on the upper section 20 between the top of the ball valve 21 and the bottom of the collar 35. The screw jack mechanism 40 has a tubular lower member 41 with a flanged bottom end 42 and an externally threaded upper portion 43. A series of lockdown bolts 44 with threaded shanks and knobs on their outer ends are threadedly engaged in tapped holes extending radially through the flanged bottom 42. The lockdown bolts 44 are screwed in and out to engage or disengage the lower section 20. A rotatable cap 45 having internal threads is threadedly received on the threaded upper portion 43 of the lower member 41. Holes 47 extend through the side wall of the cap 45 to receive a suitable tool to facilitate rotation. Rotation of the cap 45 in one direction will cause the assembled cap and lower member 41 to be drawn together and rotation in the opposite direction will cause vertical expansion. 
     The seal tube assembly 18 is manually positioned to extend normal to the longitudinal axis of the pipe main M by adjusting the sliding clamp 38 to the appropriate position on the horizontal cross bar 15. The sliding clamp 38 allows the seal tube assembly 18 to be angled to contact the main normal to the longitudinal axis of the main in the event that obstacles prevent direct vertical positioning. 
     Once the seal tube assembly 18 has been properly positioned, the short tubular member 39 is locked in place by securing the clamp 38 to secure the seal tube assembly 18 to the anchor assembly 10. The cap 45 of the screw jack mechanism 40 is rotated to vertically contract the mechanism and the screw jack mechanism is slid upwardly on the upper section 20 of the seal tube assembly 18 until the top end of the cap 45 engages the bottom end of the collar 35 and the lockdown bolts 44 are screwed in to engage the lower section 20 and securely lock the lower member 41 of the screw jack to the lower section. Then, the cap 45 is rotated to cause the screw jack members to expand vertically. The cap 45 is captured against the bottom of the collar 35 and the rotation causes a downward force to be exerted on the concave flange 25 of the seal foot 24 to push the seal foot against the pipe main M and compress the seal ring 27 to effect a sealing relation on the exterior surface of the main. Rotating locking lever 37 locks the seal tube 15 to the main M. 
     The ball valve 21 in its full-open position allows tools to be passed through the seal tube 18 but can be closed between operation to prevent blowing gas. The ball valve 21 is opened and closed by a tool T extended from the top of the excavation. 
     As shown in FIGS. 6A and 6B, after the seal tube assembly 18 has been secured to the pipe main M, an elongate tubular cutting tool assembly 48 may be lowered into the seal tube 18 through the bearing 30 and seal 31, through the open ball valve 21, and through the bearing 22 in the lower section 19. The cutting tool assembly 48 has an elongate tubular drive tube 49 which is enclosed at its top and bottom end by end plates 50 and 51. The top end plate 50 has a square bore 52. A socket plate 53 is secured to the interior of the drive tube 49 beneath the top end plate 50 and has a longitudinal square socket 54 extending downwardly from its top end. A circular hole saw 55 having a pilot bit 56 is mounted on the enclosed bottom end of the drive tube 49 and rests on the exterior of the pipe main M. A magnet 57 is secured inside the saw blade to catch the drilled material. 
     The cutting tool assembly 48 is powered by an air motor assembly 58 having a flange 59 at its bottom end which is received over the top end of the drive tube 49 and mounted on the flange 29 at the top of the upper section 20 of the seal tube 18 and secured by the wing bolts 32 which are received in slots 60 in the flange 59. The upper portion of the flange 59 is enclosed by an end wall 61 having a hexagonal bore 62 and is externally threaded 63. A rotatable cap 64 having internal threads 65 and a central bore 66 is threadedly received on the threaded upper portion 63 of the flange 59. An air motor 67 is bolted to a circular plate 68 which is rotatably retained beneath a radial shoulder 69 in the central bore 66 of the cap 64 by a snap ring 70. The plate 68 has a hexagonal extension 71 which is slidably received through the heaxgonal bore 62 in the end wall 61 of the flange 59. The drive shaft 72 of the air motor is secured to a tubular adapter 73 having a cylindrical upper end which extends rotatably through the hexagonal extension 71 and a square lower portion which is received through the square bore 52 in the top end plate 50 of the drive tube 49 and in the square socket 54 in the socket plate 53 at the upper end of the drive tube. 
     When the air motor 67 is in operation, its drive shaft 72 rotates the elongate tubular drive tube 49 which rotates the hole saw 55 and pilot bit 56. The cap 64 at the upper end of the air motor assembly 58 is used to lower the pilot bit 56 and circular saw blade 55 onto the side wall of the pipe main M. Manual rotation of the cap 64 in one direction will cause the bit and blade to be lowered vertically and rotation in the opposite direction will raise the bit and blade. As the pipe main material is cut away, it is captured by the magnet 57. The cut out piece of the side wall of the pipe main is captured in the circular saw blade 55 and may be further retained by the magnet 57 or a retainer wire connected to the pilot bit 56. The horsepower of the preferred air motor is adequate to drill through mains quickly, but is not so high as to damage bits during the drilling operation. A suitable cooling liquid may be introduced through the vent pipe 33 into the annulus between the exterior of the drive tube 49 and the interior of the seal tube 18 to flow through the slotted bearing 22 in the lower section 19 and onto the saw blade 55 during the drilling and cutting operation. The circular hole saw 55 cuts a very thin kerf, minimizing the amount of material that needs to be machined, and the low cost of such a saw allows it to be expendable such that for emergency purposes, a new saw blade can be used each time. These two factors result in drilling times of 2 to 3 minutes for most mains. 
     After a hole H has been formed in the side wall of the pipe main M, the wing bolts 32 are loosened and moved out of the slots in the flange 59 and the cutting tool assembly 48 is lifted out of the seal tube 18. The ball valve 21 can then be closed if required. 
     FIG. 7 shows the seal tube 18 supported on the pipe main M by the anchoring platform assembly 10 with a tool for applying a sealant to the interior of the pipe main installed in the seal tube. This is accomplished by a lowering an elongate tubular sealant application tool 74 into the seal tube 18. The sealant application tool 74 has a hollow tubular outer housing 75 enclosed at the top and bottom ends through which a smaller diameter tube 76 extends. The tube 76 has a hollow-cone nozzle 76A at its bottom end and is connected at its top end to a source of a viscous polymer sealant under pressure. The outer housing 75 extends through the top seal 31 and bearings 30 and 22 of the seal tube 18 and the inner tube 75 extends through a seal 75A at the top end of the outer housing and is manually raised and lowered and rotated to spray the sealant liberally onto the interior of the pipe main M. Because of its viscosity, the polymer sealant will fill small voids and imperfections in the interior surface of the main when inflatable bladders are installed (described below). 
     After the sealant has been applied to the interior of the main, the sealant application tool 74 is removed and a bladder deployment tool 77 may be lowered into the seal tube 18. FIGS. 9A, 8B, and 8C shows a double bladder deployment tool 77 having an elongate tubular upper section 78 enclosed at its top end by a wall 79 and a wall 80 a short distance above its bottom end 81. The top end of an elongate tubular lower section 82 is secured in the bottom end 81 of the upper section 78. The wall 79 at the top end of the upper section 78 has a pair of laterally spaced parallel holes 83 extending therethrough which are axially aligned with a pair of laterally spaced parallel holes 84 extending through the wall 80 at the lower end. O-ring seals 85 surround the holes 83. A vent pipe 87 extends upwardly from the top wall 79 of the upper section 78 and has a valve 88 connected at its outer end to vent pressure from the interior of the bladder deployment tool 77. 
     The interior of the lower section 82 of the bladder deployment tool 77 is divided into two compartments 82A and 82B by a vertical divider plate 89. The exterior of the lower section 82 has a reduced diameter 90 which is received through the hole H that has been cut in the side wall of the pipe main M. Each side of the reduced diameter portion 90 is cut away to form opposed elongate longitudinal openings 91 and an inverted V-shaped member 92 is secured to the bottom end of the divider plate 89. A pair of rectangular ramp members 93 and 94 are hinged at their bottom ends to the inverted V-shaped member by a spring hinge 95 to pivot relative thereto in opposed relation. The spring hinges 95 urge the top end of the ramp members 93 and 94 to normally pivot outwardly and downwardly relative to the longitudinal axis of the lower portion 90. The preferred ramp members are made of a non-sparking material for safety. 
     A pair of elongate rigid tubes 96 and 97 are slidably mounted in the parallel holes 83 and 84 in the upper section 78 and extend beyond the top and bottom ends thereof. The top ends of the tubes 96 and 97 are connected by conduit to a valve assembly 98 which is connected to a source of pressurized air and their bottom ends are connected to the top end of flexible conduits 99 and 100. The bottom ends of the flexible conduits 99 and 100 are connected to inflatable bladders 101 and 102. Each flexible bladder 101 and 102 has a small spherical ball 103 secured to its exterior opposite the connection to the conduits 99 and 100. 
     To initially install the bladders 101 and 102 in the deployment tool 77, the ramp members 93 and 94 are pivoted upwardly and inwardly against the divider plate 89 and the rigid tubes 96 and 97 are lowered so that the bottom end of the flexible conduits 99 and 100 are extended outwardly to the exterior of the lower portion 90. The bladders 101 and 102, in a deflated condition, are connected to the bottom ends of the conduits 99 and 100, folded or rolled into a generally tubular configuration, and then the tubes 96 and 97 are pulled upwardly to draw the rolled bladders into the compartments 82A and 82B such that the balls 103 are captured between the top end of the openings 91 and the outwardly biased top ends of the ramp members 93 and 94. In this position, the balls 103 prevent the spring hinges 95 from pivoting the ramp members. 
     After the bladders have been installed in their respective compartments, the bladder deployment tool 77 is lowered into the seal tube 18 until the reduced diameter portion 90 extends through the hole H in the pipe main M. Once the bladder deployment tool is in place, the two ramps 93 and 94 are released independently by pulling the tubes 96 and 97 upwardly a short distance. This retracts the ball 103 at the end of the respective bladder upwardly to clear the top end of the ramp and then the force of the spring hinge 95 urges the top end of the ramp member to pivot outwardly and downwardly relative to the longitudinal axis of the lower section 90 until they engage the interior surface of the pipe main M, as shown on the right hand side of FIG. 8C. In the deployed position, the ramps 93 and 94 are disposed at an outwardly and downwardly inclined angle. In the deployed position, the ramps 93 and 94 guide the bladders 101 and 102 into the pipe main along its longitudinal axis. The bladders 101 and 102 are deployed by pushing downwardly on the tubes 96 and 97 such that the bladders and flexible conduit extend though the openings 91 in the lower section 90 and ride outwardly on the ramps 93 and 94. 
     As shown somewhat schematically in FIG. 9, to stop the flow of gas in the pipe main using the double bladder tool 77, both bladders 101 and 102 are deployed, down stream bladder first, and are then inflated. As the bladders 101 and 102 expand inside the main which has been coated with the polymer sealant material and engage the polymer sealant material it is compressed to fill small gaps between the exterior of the bladders and the interior diameter of the main. This ensures creation of a effective seal even in mains containing debris from water seepage and corrosion products. With both bladders inflated, the seal tube 18 acts a vent pipe, safely venting any gas that leaks past the upstream bladder. The effectiveness of the inflatable bladder seal may be tested by connecting a pressure gauge to valve 88 at the outer end of the vent pipe 87 at the top of the bladder deployment tool 77. The ball valve 21 in the seal tube 18 controls the gas flow when there are no tools in the seal tube. Closing the valve prevents gas from escaping. If a seal is not established after the bladders have been deployed, a sealant may be pumped through the deployment tool to fill the void between the bladders. 
     At the conclusion of a job, the bladders are deflated and then pulled back into their respective compartments in the bladder deployment tool 77 by pulling upwardly on the tubes 96 and 97, and the bladder deployment tool is removed from the seal tube 18. 
     As shown schematically in FIGS. 10, 11, and 12, a thread tapping and plugging tool 110 may be installed through the seal tube 18 to thread the hole H which was formed in the side wall of the pipe main M and to place a pipe plug into the threaded hole. The thread tapping and plugging tool 110 is an elongate tubular member 111 enclosed at each end. A socket member 112 having a hexagonal cavity is secured to the bottom end of the drive tube 111 and has a threaded hole 113 extending laterally through its side wall. A magnet 114 is secured to the interior of the cavity. The socket 112 selectively receives a thread forming die member 115 or a threaded plug member 116. The drive tube 111 extends through the seal 31 and bearings 30 and 23 of the seal tube 18 and has a handle 119 connected to its top end. 
     A thread forming die 115 (FIG. 11) has a hexagonal stem 120 at its top end which is slidably received in the socket 112 at the bottom end of the drive tube 111 and secured thereto by a set screw 121 threadedly engaged in the threaded hole 113 in the side wall of the socket. The thread tapping and plugging tool 110 is lowered through the seal tube to place the thread forming die 115 onto the hole H which was previously cut in the side wall of the pipe main M and is rotated manually to form internal threads in the hole. After the threads have been formed, the tool 110 is rotated in the opposite direction to back the thread die 115 out of the hole and the tool 110 is removed from the seal tube 18. 
     An externally threaded plug 116 (FIG. 12) having a hexagonal stem 122 at its top end is then slidably installed in the socket 112 at the bottom end of the drive tube 111 and releasably attached thereto by the magnet 114 in the socket. The 110 is lowered through the seal tube 18 to place the threaded plug 116 into the hole H which was previously threaded and is rotated manually to threadedly engage the plug in the threaded hole. After the plug 115 has been secured, the drive tube 111 is lifted to disengage the magnet 114 in the socket 112 from plug 116 and the tool 110 is removed from the seal tube 18. It should be understood, that the plug may be provided with conventional pipe thread seal means such as pipe dope or seals. It should also be understood that the thread tapping and plugging tool may be powered by a rotary motor rather than a handle. 
     This procedure leaves the pipe main ready for immediate use once the stop-off has been completed. Other remedial work is not necessary. After the pipe plug is in place, the seal tube assembly is removed from the pipe main and the anchor system is removed from the excavation, and the excavation is then filled with soil. 
     While this invention has been described fully and completely with special emphasis upon a preferred embodiment, it should be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.