Abstract:
A method of replacing an existing underground pipe, especially a sanitary sewer line, uses a boring machine that advances a drill string of hollow rods through the existing pipe. The method includes the steps of mounting a rotary cleaning tool on a distal end of the drill string, moving the cleaning tool progressively through the underground pipe while rotating the drill string in order to clean the inside of the pipe, flushing debris loosened by the cleaning tool from the pipe using a pressure fluid, removing the cleaning tool from the drill string and mounting a camera assembly on the distal end of the drill string, moving the camera and drill string through the underground pipe on the drill string and inspecting the inside surface of the pipe with the camera, removing the camera from the drill string and replacing it with a pipe destroying apparatus, moving the pipe destroying apparatus through the pipe to destroy the existing pipe, and then installing a replacement pipe along the same line as the destroyed existing pipe. This permits a single piece of equipment, such as a directional drill rig, to perform several different functions as part of the pipe replacement process.

Description:
RELATED APPLICATIONS 
     This application is a conversion of U.S. Provisional Application Serial No. 60/279,837, filed Mar. 29, 2001, the disclosure of which is incorporated herein for all purposes. 
    
    
     TECHNICAL FIELD 
     The invention relates to a method and apparatus for cleaning and inspecting underground pipes and conduits in order to facilitate repair and replacement of such under ground pipes. 
     BACKGROUND OF THE INVENTION 
     A known technique for replacing sanitary sewer lines and various other underground conduits and pipes is to burst or expand the existing pipe and then pull a replacement pipe through the expanded bore. In one variation of this process, a horizontal directional drill advances a drill string with pipe bursting or splitting tool affixed to the end of the drill string. The system may include a impact device mounted at the end of the drill string such as a rotary impactor (see U.S. Pat. No. 5,782,311) or a pneumatic impact tool that delivers cyclic impacts to the bursting or splitting tool. The replacement pipe is attached to the bursting or splitting tool and pulled through the bore behind it. 
     It is common practice to clean an existing sanitary sewer pipe prior to a line replacement operation. Lateral connections, for example to residences, must be accurately located and marked to avoid excessive excavation. However, in many cases, existing underground pipelines will have an accumulated buildup of solids, grease, and wax-like materials that may interfere with the inspection, bursting, splitting and/or replacement operations. The accumulated buildup may also prevent or interfere with locating pipe joints, which in the case of cast iron pipes may require particular attention during the splitting operation. 
     In the past, sanitary sewers have been cleaned with specialized equipment including high pressure water jets operating at 2000 psi. This method of cleaning requires the use of a jet truck, i.e., a truck specially equipped with one or more specialized pumps designed to deliver moderate volumes of water at extremely high pressures, a high pressure hose to reach the area or areas to be cleaned, and nozzles specially designed to direct the high pressure water into a jet capable of cutting the materials. The nozzles are radially spaced and angled rearwardly so that the discharge of water through the nozzles creates a reaction force to propel the high pressure hose through the pipe being cleaned. A “soup” of suspended solids, grease and water flows downstream through the pipeline. In some cases the jet truck will vacuum this soup from a manhole, the same manhole the spray head was introduced from. 
     This invention makes opportunistic use of the presence of a horizontal drilling machine using a rigid drill string during a pipe bursting and replacement operation. Conventionally, horizontal directional boring machines are used only for the pipe bursting and replacement stage of the operation. The present invention provides accessories by which other useful steps can be carried out using the directional boring machine, including cleaning and inspecting existing pipes. 
     SUMMARY OF THE INVENTION 
     The invention provides a method of replacing an existing underground pipe, especially a sanitary sewer line, using a boring machine that advances a drill string of hollow rods through the existing pipe. Such a method includes the steps of: 
     (a) mounting a rotary cleaning tool on a distal end of the drill string; 
     (b) moving the cleaning tool progressively through the underground pipe while rotating the drill string in order to clean the inside of the pipe; 
     (c) flushing debris loosened by the cleaning tool from the pipe using a pressure fluid; 
     (d) removing the cleaning tool from the drill string and mounting a camera assembly on the distal end of the drill string; 
     (e) moving the camera and drill string through the underground pipe on the drill string and inspecting the inside surface of the pipe with the camera; 
     (f) removing the camera from the drill string and replacing it with a pipe destroying apparatus; 
     (g) moving the pipe destroying apparatus through the pipe to destroy the existing pipe; and 
     (h) installing a replacement pipe along the same line as the destroyed existing pipe. The existing pipe can be destroyed by any known method appropriate to the material the pipe is made from, such as pipe bursting or pipe slitting and spreading. According to preferred forms of the invention, the pressure fluid is supplied through the drill string and ejected from the cleaning tool as the cleaning tool advances through the existing pipe. 
     The existing pipe is typically a sanitary sewer line having a number of lateral line connections. As such, step (e) preferably involves determining the locations of the lateral line connections to the existing pipe, such as by connecting a sonde to the camera and marking the position of the lateral above ground by detecting the sonde&#39;s position when the camera shows a lateral connection. For this purpose, the camera is typically a video camera that provides a live feed of the pipe interior and has a built in light source. 
     According to a preferred form of the invention, steps (a) to (c) are performed as the drill string is extended from an entrance to an exit at opposite ends of the existing pipe. The entrance and exit may be openings in a pit or manhole. Step (d) is then performed while the distal end of the drill string is near the exit, and step (e) is performed as the drill string is retracted from the exit back to the entrance. In this manner the existing pipe is cleaned, flushed and then inspected in one down and back cycle of the drilling machine. The same drilling machine is then used for the subsequent steps of destroying the existing pipe, replacing it with a new pipe, and optionally de-beading the new pipe after lateral connections have been welded on. 
     The pipe inspection and cleaning aspects of the invention can also be used separately when the occasion requires and specialized equipment is not available. A method for inspecting an inside surface of a pipe using a horizontal boring machine that advances a drill string of hollow rods through the pipe includes the steps of attaching a camera to a distal end of the drill string, moving the camera through the underground pipe on the drill string, and imaging the inside surface of the pipe with the camera while the camera is inside the pipe. A method of cleaning an underground pipe includes the steps of mounting a rotary cleaning tool on a distal end of the drill string, moving the cleaning tool progressively through the underground pipe while rotating the drill string in order to clean the inside of the pipe, and flushing debris loosened by the cleaning tool from the pipe using a pressure fluid. 
     The invention further provides a pipe cleaning tool useful in such a method adapted to be mounted on the end of a drill string and advanced through an underground pipe with a horizontal drilling machine to clean the pipe. Such a tool includes a generally cylindrical body including a front nose section, a plurality of side flats at intervals around the circumference of the body, and a rear connecting portion configured for connecting the pipe cleaning tool to the drill string. A flexible flap mounted on each of the flats extends tangentially from the body and is configured to scrape along the inside of the pipe as the cleaning tool is advanced through the pipe. The body further includes fluid passages for communicating through the drill string with a source of a pressure fluid, and a plurality of nozzles connected to the fluid passages for ejecting the pressurized fluid in a radial direction as the tool is advanced through the pipe. 
     The invention also provides an apparatus for inspecting a pipe. Such a device includes an electronic camera and an elongated carrier body having a recess adapted to receive the camera therein, an end connecting portion configured for mounting the carrier body on a drill string, and an opening whereby the camera can be positioned to capture an image through the opening. The camera is preferably a video camera and transmits its signal through a cable to a video display above, permitting the operator to inspect the condition of the line interior and locate lateral branch lines. These and other aspects of the invention are described in the detailed description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustration of a pipe cleaning operation wherein a pipe section between two manholes is being cleaned in a method according to the invention; 
     FIG. 2 is a first side view of a cleaning tool according to the invention; 
     FIG. 3 is a second side view of the cleaning tool of FIG. 2; 
     FIG. 4 is sectional view taken along line A—A of FIG. 3; 
     FIGS. 5 and 6 are front and rear views, respectively, of the cleaning tool of FIG. 2; 
     FIG. 7 is a perspective view of a camera assembly according to one aspect of the invention, the camera assembly being mounted on a sonde housing; and 
     FIG. 8 is a partial lengthwise section of the camera assembly of FIG.  7 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a pipe inspection operation wherein a pipe section  12  extending between first and second manholes  14  and  16  is to be cleaned and inspected. In the operation, an operator, using a conventional directional boring machine  10 , drills an entry bore  18  from the surface on an arcuate path, intersecting existing pipe  20  with a drill string  22  in a tangent manner, preferably at an existing exposed location such as at a first manhole  14 . Alternately, instead of boring in an arcuate path, directional boring machine  10  may be placed in an access pit excavated adjacent to the start of a pipe section  12  to be replaced. The particular tool to be used in the operation is installed on the drill string  22  in manhole  14  and the drill string is positioned inside of the existing pipe section  12  that is due for replacement. 
     In accordance with a method of the invention, a cleaning tool  24  is installed on the free end of the drill string  22  in manhole  14 . Using the high pressure fluid pump mounted on the horizontal direction drilling machine (hereafter HDD), pressurized cleaning fluid is supplied to the tool through drill string  22  to tool  24  which delivers a spray to the interior of the pipe section  12  to clean and wash the accumulated grease and solids from the pipe. The spray may, for example, be water plus a grease-cutting surfactant or detergent. In the embodiment illustrated in FIG. 1, tool  24  is attached to the front end of a sonde housing  21 , which in turn is mounted on drill string  22 . 
     Turning to FIGS. 2 through 6, cleaning tool  24  includes a generally cylindrical shaped body  26  including an annular groove  28  positioned midway along its length. Body  26  includes a forwardly rounded (semi-spherical or bullet shaped) nose section  30  ahead of groove  28  to aid in inserting and guiding tool into and through pipe section  20 . As best shown in FIGS. 4 and 6, a splined recess or socket  32  extends into body  26  at the rear of tool  24  and is configured to receive the male end of a splined connection or joint such as described in Wentworth U.S. Pat. No. 6,148,935, the contents of which are incorporated by reference herein. Alternatively, tool  24  may be connected to drill string  22  with any number of conventional joints known in the art including, for example, a standard API threaded joint. 
     Nose  30  has a plurality of radially spaced flats or mounting surfaces  36 . Flats  36  are located ahead of groove  28  but rearwardly spaced from tip  40  of nose  30 . A flexible cleaning paddle or flap  38  is mounted on each of flats  36  such that a forward end  44  of each flap  38  abuts a forward endwall  42  of each flat  36 . Each of flaps  38  includes a forward end  44 , a rear end  46  a leading side  48  and trailing side  50  and an angled side portion  52  between forward end  44  and a trailing side  50 . As shown, each of flaps  38  is configured to extend tangentially outward from nose section  30  so that trailing side  50  scrapes the interior of pipe  20  as tool  24  is rotated, cleaning grease and solids from the interior surface of pipe  20 . Side section  52  is angled at approximately 45° relative to forward end  44 , and rear end  46  extends past the associated flat  36 , overlying a minor portion of groove  28 . The use of angled side  52 , as opposed to joining forward end  44  and trailing side  50  at a right angle, allows flaps  38  to gradually engage grease and solids built up on the interior of pipe  20  as tool  24  is advanced, and tends to reduce the forces applied to the flap and prevent breakage. To further prevent breakage, flaps  38  are preferably formed from a hard, flexible plastic material exhibiting a high level of abrasion resistance. 
     As shown, three flaps  38  are mounted on flats  36  with flaps  38  spaced equiangularly (at 0°, 120° and 240°) from each other around the circumference of nose section  30 . It will be appreciated that a greater or lesser number of flats  36  and flaps  38 , spaced at different and/or non-uniform intervals may be employed. For example, a tool  24  designed for small diameter pipes may only include two flaps  38 , spaced 180° apart. 
     Each of flaps  38  includes one or more (two shown) countersunk apertures  54  that align with threaded bolt holes  59  for receiving a threaded fastener such as a cap screw  58  that is screwed into threaded hole  59  in body  26  to secure flaps  38  to tool  24 . As will be appreciated, mounting flap  38  on flat  36  as illustrated protects screws  58  and the portion of flap  38  through which cap screws  58  extend from abrasion as tool  24  is rotated and advanced in pipe  20 . Additionally, as illustrated, each flap  38  is mounted such that the forward end  44  of each flap  38  abuts a forward endwall  42  of flat  36  to help prevent the forward ends  44  of flaps  38  from catching on obstructions in a pipeline as tool  24  is advanced into the pipe, thereby minimizing the possibility that a flap will be torn off of tool  24  in operation. 
     Body  26  includes an axially extending fluid passage  60  and threaded apertures  62  that communicate with drill string  22  secured in recess  32  to allow a pressurized fluid such as water to pass through body  26  and apertures  62  to one or more nozzles  64 . In the illustrated embodiment, tool  24  is provided with three nozzles in groove  28 , each positioned midway between adjacent flaps  38  at equal intervals (60°, 180° and 240°) around the circumference of groove  28 . Nozzles  64  are positioned in recesses  65  in groove  28  to protect the nozzles from abrasion and from hanging up on obstructions during the cleaning operation. 
     Nozzles  64  are each directed at different angular orientations to eject the pressurized fluid evenly around the circumference of the tool and are angled rearwardly (e.g., 5 to 45°) to create a flow in a rearward direction to wash out the pipe interior as the drill string advances from through pipe  20  from an entry zone (manhole  14 ) to an exit zone (second manhole  16 ). In one embodiment wherein a Vermeer Navigator® horizontal drilling machine is employed, approximately 50 gpm of water at 150 psig. is supplied through the drill string to nozzles  64  to suspend and flush grease and solids from pipe  20  as tool  24  is advanced. Solids and grease scraped from the interior of pipe  20  are thus slurried with water or a mixture of water and a surfactant and flow back past tool  24  to manhole  14  where the mixture may be vacuumed or pumped out of the manhole if the volume of slurry warrants. 
     Tool  24  provides several advantages over conventional high pressure water blasting techniques for cleaning underground horizontal pipes. Tool  24  utilizes equipment, in particular the horizontal drilling machine, that is necessarily on site, eliminating the need for special high pressure water blasting equipment. Further, tool  24  is driven with a rigid drill string, the tool can be forced through accumulations of grease and solids in a pipe that a conventional water blasting apparatus may not be able to penetrate. The use of flaps  38  further provides a scraping action against the interior of a pipe being cleaned that tends to dislodge accumulated materials faster than a conventional water blasting apparatus that relies on one or more narrow streams of high pressure water to cut accumulated material from the inside of the pipe. In applications were the material to be removed is sufficiently soft, water soluble and/or of sufficiently small volume, flaps  38  may be omitted. In other applications the horizontal drilling machine may be equipped with a pump capable of delivering a water pressure sufficient to cut though the build up in which case the flaps may also be unnecessary. The flushing operation may be carried out at the same time as rotary cleaning, or thereafter. 
     In many cases, after the cleaning operation is completed, it is advantageous to visually inspect the interior of the pipe. One important reason for visual inspection of the pipe is to accurately determine the locations where lateral pipe runs are connected to the main pipeline. In the case of a sanitary sewer, these joints typically comprise a connection to a house or other building that must be replaced after the new pipe has been installed. Replacing such lateral connections generally requires excavating and replacing the joint to reconnect the lateral pipe run. Determining the location of the joint through a visual inspection of the interior of the pipe facilitates this process and reduces the amount of excavation required. 
     Conventional techniques for inspecting the interior of a horizontal underground pipe in this manner utilize a camera mounted on a powered robot or tractor equipped with a powered ground drive such as wheels or tracks or pulled with a cable. A cable is attached to the robot or tractor to transmit signals from the camera to a recording device such as a video recorder and the location of lateral connections is determined by the footage of cable extended into the pipe or through the use of a radio frequency transmitter carried by the robot. In the case where a transmitter is used, the location of the crossover is determined by locating the robot with a receiver carried on the surface when the camera transmits an image corresponding to the location of a lateral connection. 
     The use of a robot or tractor to carry a camera through an underground pipe for inspection purposes has disadvantages. The robot or tractor is an expensive piece of additional equipment that must be brought on site and maintained. Since a robot or tractor relies on wheels or tracks for mobility, such units are subject to becoming jammed or stuck in the pipeline, requiring excavation or similar measures to retrieve the unit. 
     Referring to FIGS. 7 and 8, in one aspect of the invention, a camera assembly  70  is mounted on the end of a drill string for inspecting an underground pipe, preferably after the pipe has been cleaned. As best shown in FIG. 8, camera assembly  70  includes a generally cylindrical carrier body  72  with a splined recess or socket  74  extending into the rear of carrier body  72  that is configured to receive the male end  76  of a splined connection or joint such as described in Wentworth U.S. Pat. No. 6,148,935. As shown, carrier body  72  is removably coupled to sonde housing  21  with such a joint by a retainer such as a roll pin that interlocks sonde housing  21  and body  72 . Alternatively, carrier body  72  may be connected to drill string  22  with any number of conventional joints known in the art including, for example, a standard API threaded joint. Carrier body  70  is substantially smaller in diameter than the pipe to be inspected and includes one or more forwardly inclined side surfaces  78  extending forwardly from a supporting heel  79  to aid in guiding carrier assembly  72  smoothly through the pipe to be inspected. 
     A video camera  80  is mounted in a central, longitudinally extending cavity  82  in carrier body  72  for inspecting the pipeline. As illustrated, camera  80  is installed in cavity  82  through a forwardly facing opening  81  in carrier body  72  and secured with a threaded collar  84 . Opening  81  provides camera  80  with a forward field of view through which camera  80  may image the walls of a pipe as it advances through the pipe. A cutout  83  is formed in a sidewall  85  of carrier body  72  to further enable camera  80  to image the wall of a pipe as the camera passes through the pipe if camera  80  is equipped for side view imaging. One such camera suitable for use in the practice of the invention is the Pearpoint model 455 TwinView Dual Sensor Auto Upright Digital color camera manufactured and sold by Pearpoint, Inc., 72055 Corporate Way, Thousand Palms, Calif. 92276. The Pearpoint Model 455 includes LED light heads and clock/counter clockwise side-view rotation capability. In the illustrated embodiment, camera  80  can provide an image from both the front and side vantage points. It may be advantageous to reposition the camera to permit other views, such as a rear view of there the drill string has been. 
     Signals from video camera  80  are transmitted to the operator through a camera cable  87  which passes from the rear of camera  80  through a protective conduit  86 , positioned in an axially extending slot  86  in carrier body  72 . As shown, camera cable  87  is coupled to an extension cable  88  with a cable connector  90  which allows the camera assembly to be readily connected and disconnected to cable  88  when the camera is installed and removed from the drill string. In order to protect the connector from decoupling during operations, one or more tethers  92  are connected to cable  88  with a tubular holder  94  and secured to camera carrier body  72 . 
     In operation, after pipe section  12  has been cleaned with tool  24 , the tool is removed and camera assembly  70  is mounted on the end of drill string  22 . Preferably, camera assembly  70  is mounted on drill string  22  so that the camera will be pulled though the bore as the drill string is retracted through pipe section  12 . Cable  88  is connected to camera cable  87  and camera assembly  70  is pulled though the bore as drill string  22  is retracted from manhole  16  to manhole  14 , allowing camera  80  to acquire and transmit images of the pipe interior to the operator on the surface, who view the camera images on a video display. This allows the operator to determine the location of lateral connections and pipe joints either by measuring the footage of cord extended. Cable  88 , which extends out in front of the camera  70 , may be marked with length gradations  91  for this purpose, in the manner of a tape measure. In the alternative, camera assembly  70  is mounted on sonde housing  21  with sonde  100  generating a signal detectible with a walkover receiver on the surface above the pipe section. Using the walkover receiver, in conjunction with the images supplied by camera  80 , an operator can quickly and easily locate lateral connections and pipe joints and mark them on the surface such as with a flag or spray paint. Similarly, depending on the conditions, it may be possible to transmit the image data with the camera forming part of a wireless network rather than use a cable to transmit the images to the surface. After the inspection is completed, the camera assembly is uncoupled from drill string  22  and disconnected from cable  88  after which cable  88  is retrieved from pipe section  12 , completing the inspection operation. 
     After the cleaning and/or inspection processes are completed, pipe  12  may be replaced using a number of conventional bits, reamers, pipe bursting devices and pipe pullers, by bursting or slitting the existing pipe and then pulling in the replacement pipe. The bore may be completed either at a pipe exit pit or existing exit structure beneath the ground surface such as a manhole. Lateral connections are then made by excavating at the locations found earlier and joining the laterals (branch lines) to the new pipe. If desired, in accordance with the method of the invention, the operator then reenters the new pipe with the drill string and de-beads the fuse joints of the new product pipe using a drill stem mounted on a debeading device as known within the industry. Such a device acts as a reamer to shear the beads from the inside of the pipe using a circumferential motion. If desired, the operator may then perform a final camera inspection of the installed pipe using camera assembly  70 . 
     While certain embodiments of the invention have been illustrated for the purposes of this disclosure, numerous changes in the method and apparatus of the invention presented herein may be made by those skilled in the art, such changes being embodied within the scope and spirit of the present invention as defined in the appended claims. The camera, for example, need not be provided with the specialized housing described, and could be pulled through the pipe connected to the end of the drill string by a tether. The terminal or distal end of the drill string, as used in the claims, means the end of the foremost of a series of identical hollow drill rods, or a starter rod, sonde housing or other component that may be interposed between the attachment of the invention and leading rod of the drill string.