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STRIPPING OF LINERS FROM PIPES USING HDD TECHNOLOGY Harry Baum and Kwigs Bowen2 1 President, W.S.U. Inc.., Breckenridge, Colorado 2 Area Manager, Team Fishel, Chandler, Arizona ABSTRACT Horizontal directional drilling is a non-intrusive method for installing utility lines, gas pipes, water pipes, sewer lines or fiber-optic conduit below the ground without the need to open trench. Horizontal directional drills “bore” a tunnel using fixed-length drill rods that are threaded together to create what’s called a drill string. This drill string is advanced or drilled through the ground from an entrance to an exit location. This drilled bore can be drilled to precise locations because of the drilling tool’s slanted steering plate. The orientation of the tool and its slanted steering plate is what determines the direction the drill head navigates. The directional path will move when pushed through the ground without rotation. A transmitter enclosed in the drill heads housing transmits depth, digital clock rotation position, temperature and angle to a remote receiver on the surface. Maximum depth depends upon the style of the transmitter but normally 50 feet is average. Because of the flexibility HDD offers, Harry Baum, owner of W.S.U. Inc. and Steve Wentworth of Earth Tool Company LLC (manufacturer of HammerHead trenchless products) began conversations on the concept to remotely remove linings from the inside of sewer lines. As a novel concept invention Wentworth designed an umbrella like mechanical device which is attached to a directional drill. Wentworth had already designed tooling for other directional drilling uses and was able to quickly offer Baum solutions. Baum was very familiar with failed liners and the problems caused where open cut was often the only solution for removing linings. Removal of factory installed linings using custom designed tooling, deployed and actuated by a directional drill rig, is a new method. Having the ability to attach different tools to the end of rigid drill pipe opens the opportunity for other remotely operated mechanical devices. Just as a surgical tool is used to open arteries the stripping tool could open the clogged sewer arteries without open cutting the entire section. Ductile iron pipe with factory applied high density polyethylene (HDPE) liner has been widely used for sanitary sewer installations where high hydrogen sulfide gas concentrations exist. Failure of the pipes protective HDPE liner from hydrogen sulfide corrosion caused the liner to delaminate in sheets. This created the potential for problematic system backups. It was clear that the failing liner had to be removed. The removal was intended to simultaneously eliminate the potential for backup and produce a surface appropriate for relining using cured in place pipe (CIPP) methods. This paper will review a highly successful 1st attempt at using a new trenchless technology, Liner Stripping, in cooperation with Pima County Wastewater Management, Tucson Arizona. System owner engineers, contractor, sub-contractor and equipment manufacturer joined to make the job possible with the custom developed technology. The job success highlights the potential HDD drills have to service non-man entry or difficult man entry locations with custom engineered tooling. The method of “Liner Stripping,” as with all trenchless methods, will be less disruptive and less invasive than previously accepted methods or remedies to service a pipe’s

North American Society for Trenchless Technology (NASTT) NO-DIG 2006

Nashville, TN March 15-20, 2007

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interior spaces. The results demonstrate that servicing the interior of buried pipes with the attributes of an HDD drill stem is a concept that has profound potential. INTRODUCTION Recently, the Pima County Wastewater Management (PCWM) in Tucson, Arizona found itself with a perplexing problem when it tried to rehabilitate one of its ductile HDPE lined sanitary sewer pipes. In weighing possible solutions, PCWM officials permitted “Liner Stripping” of the HDPE using a horizontal directional drill HDD rig followed by CIPP lining of the sewer main. Normally HDD is used for the trenchless installation of new underground utilities not rehabilitation so this application is quite a novel concept. The Pima County wastewater conveyance system consists of nearly 3,300 miles of public separate sanitary sewers, ranging in size from 6- to 78-in. pipe diameters with an 84-in. box culvert. The Old Nogales Highway trunk sewer consists of more than 16,000 ft of 18-in ductile iron pipe with a polyethylene liner. The liner has de-laminated from the host pipe to some degree on roughly one-third of the total length of the trunk sewer line. The de-lamination on some stretches was severe enough warranting an emergency repair to remove the liner from the flow line. Pima County surrounds the high desert city of Tucson and land south to the Mexico border. Tucson sits on a remarkably flat plane consisting of fine granular soil that is susceptible to erosion. Blockage backups must be avoided when operating a pipeline or ground erosion can case sinkholes. In the 1980’s corrosion of ductile iron pipe was avoided by using a factory installed polyethylene lining. The liner .06 to .10” (1.524 to 2.54 mm) thick was intended to prevent hydrogen sulfide gas, from contacting the ductile iron sealing the odiferous gas from the iron atmosphere. Hydrogen sulfide gas is a normal byproduct of decomposition in sanitary systems. Damage to the HDPE liner around the bell and spigot may have occurred during installation or some time afterward allowing hydrogen sulfide to attack the ductile iron pipe. Oxidization built up between the liner and the interior surface of the ductile iron which caused de-bonding of the liner from the pipe. This de-bonding of the liner caused the liner to hang down inside the pipe like poorly applied wallpaper falling from the ceiling. Sewer flow velocity between the de-lamination accelerates the sewer liner degradation. This was evident when an inspection camera (figure 1) was used to inspect the line. The hanging liner (figures 2-5) reduces the annular circumferential area stalling the flow of solids which had caused backups and could continue to do so.

Figure 1 - The mobile camera inspection truck controls the operation and recording of a robotic camera. The camera documents real time information which becomes a permanent record for future use.

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Figure 2 - Shown from the robotic camera, is a separated HDPE liner folded into the flow stream.

Figure 3 - The arrow indicates the early stages of HDPE lining separation at the ductile iron pipe joint.

Figure 4 - The circle indicates liner that has completely pulled away from the host pipe creating turbulence downstream. A by-product of this turbulence is hydrogen sulfide gas which escalates the degradation of the pipe.

Figure 5 - Liner failure indicated by the camera operator.

Pima County has the additional stress of having the possibility of the backup inducing a sinkhole in one or more locations. For this reason, county officials had to find a solution that would eliminate the hanging liner and find a solution to protect the perfectly serviceable ductile iron portion of their pipe. W.S.U. Inc., in Breckenridge, Colorado, was contracted by Pima County engineers to rehabilitate the ductile iron sewer line using the custom stripping tool developed by Earth Tool Company, LLC, and manufacturer of HammerHead trenchless products based out of Oconomowoc, Wisconsin. The proximity of the line, within a railroad right of way made open-cut a daunting and undesirable method. PCWMD engineers chose the less invasive technology HDD knowing that open cut methodologies would not be acceptable. After the HDPE liner was completely removed a new CIPP liner would be applied to the bare ductile iron pipe which would produce the corrosion barrier need to make the pipe last. To insure complete removal of the HDPE liner a sewer camera recorded instantaneous progress inspection behind the rotating lining striping mechanism. HDD SOLUTION The HDD rig is setback from the intersection from the intended path end point (figure 6). This setback is determined by HDD rig rod radius specifications and the desired depth end point. The midsize HDD rig

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chosen for this application can develop 24,000 pounds of tensile and 4,000 ft. lbs. of torque. However, only a small portion of this power is required to accomplish the stripping liner removal process. A drill rod access point is excavated and the top section of pipe removed (figure 7) An inflatable plug was inserted into the sewer line and the sewer flow was by-passed around the working section (figure 8).

Figure 6 - On the surface, the directional drill operator receives radio confirmation from the camera operator to access progress in the sewer line. If a section requires further stripping, the camera operator alerts the drill operator to back up and give additional attention that section of pipe.

Figure 7 - For the directional drill to access the sewer main, a fifteen (15) foot section was removed from the top of the pipe.

Figure 8 - To prevent customer interruption, the working section on the sewer line was bypassed using a pump to maintain sewer flow.

After the trenchless bore path intersected the sewer line, the drill stem was pushed out so as to extend into a downstream manhole where the Poly Stripper mechanism was installed (figure 9). To control the long unsupported drill string a soft urethane radial or triangular pilot was used as a centering plug (figure 10) with marginal diametrical clearance. With rotation bearings housed at both ends of the centering plug stabilized the rod during high speed rotation.

Figure 9 - The stripping device is lowered down hole in sections and assembled in the manhole.

Figure 10 - The liner stripping device is assembled above ground to instruct crew members of the proper joint assembly connection down hole.

The Poly Stripper was attached just behind the centering plug. Using the HDD rig’s water pump pressure, the deployment of the radial stripper arms are controlled via bias pressure within the strippers operating

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piston mechanism (figure 11). Water pressure controls the stripper arms’ force when deployed against the liner host pipe (figure 12). Some water is bypassed around the piston chamber flushing away cuttings continuously. At the entry manhole, a screen was placed in the flow path, separating cuttings from the flow. These chips of the liner were then vacuumed up and disposed of (figure 13).

Figure 11 - The stripping arms are deployed using water pressure supplied by through the drill stem by a water pump connected to the directional drill. Once the arms are deployed, the drill string is rotated and the liner is scraped from the pipe, preparing it for lining.

Figure 12 - The robotic camera trails the stripping device showing where the pipe has been stripped of the HDPE lining.

Figure 13 - WSU used a vacuum truck to clean the entry manhole and remove the cut lining chips and other debris.

HDPE liner is scraped away from the adjacent host pipe during rotational arm deployment. Followed by the inspection camera the Poly Strippers’ progress is monitored as rotational speed is variable to approximately 250 rpm. Radio contact between the HDD rig operator and the camera operator was all the direction necessary to achieve production speed of approximately 10ft/min. By inspecting with the camera, the operator was alerted to sections that required further stripping. In addition, the camera operator could communicate the need to retract the stripper arms to de-tangle portions of the HDPE liner that had entangled the stripper arms. Several attachment cutting tools were developed, a .125” (3.175 mm) thick spring steel scraper proved superior to other designs. Each of the three stripper arms held one scraper blade which was angled slightly away from the clock wise rotation center line. Water used to make drilling fluid is common practice when directional drilling underground utilities so additional rig operator training is minimal. Repeatedly, the operator turned on the water pump, waited for water pressure to rise at the rig then began rotating the drill stripping tool. He then pulled drill pipe toward the rig until again removing drill stem and repeating the process. CONCLUSION HDD machines can provide huge economic potential to service non-man entry or difficult man entry locations with custom engineered tooling. Engineers basic working knowleadge of HDD capabilities can solve a myriad of sewer line issues. Pima County Arizona engineers were more than satisfied with the first successful performance of this experimental method. Coordination between engineers, contractor, sub-contractor and equipment manufacturer was essential in providing planning through job completion. Information supplied by Dan Cohen of WSU, a licensee of Inliner Technologies, installed ~ 5,720 lf of 18 inch ∅, 7.4mm thick CIPP using the Pulled-In-Place method of insertion per ASTM F 1743, PCWMD specifications and WSU, ISO protocol. Individual runs of CIPP were resin impregnated at WSU’s wetout facility located near Fairplay, Colorado just prior to it’s scheduled installation date. The wetout tube along with it’s corresponding calibration hose was shipped to the job site in Tucson, Arizona inside a temperature controlled, refrigerated reefer truck. The lining tube was winched into place followed by an air inversion of the calibration hose. The CIPP was then cured using steam for pressure and heat.

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Independent third party testing was performed by HTS, Inc. of Houston, TX for thickness (ASTM D 5813), flexural properties (ASTM D 790) and tensile strength (ASTM D 638). Each CIPP installation exceeded the required minimum properties in every instance. In all, the Poly-Stripper was used to clean about 5,700 feet of pipe over a two and half month period. Afterward, WSU went in and rehabbed the pipe using CIPP with the comfort in knowing the loose liner was completely removed as video proved. To date the project is considered by all involved to have been a very succuessful method for removing de-bonded liner from ductile iron pipe. Because the liner was removed completely, the corresponding CIPP liner was installed normally without any intrusive obstacles.