The document discusses a novel application of horizontal directional drilling (HDD) technology for the removal of damaged high-density polyethylene (HDPE) liners from ductile iron sewer pipes in Pima County, Arizona. This innovative method, termed 'liner stripping,' allows for non-intrusive rehabilitation of sewer lines, mitigating issues caused by de-laminated liners while preparing pipes for cured-in-place pipe (CIPP) lining. The successful project highlights the economic potential and coordination required among engineers, contractors, and manufacturers in implementing trenchless technologies for infrastructure maintenance.

1. North American Society for Trenchless Technology (NASTT)
NO-DIG 2006
Nashville, TN
March 15-20, 2007
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
Paper E-2-04

2. 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.
Paper E-2-04

3. Figure 2 - Shown from the robotic camera, is a Figure 3 - The arrow indicates the early stages of
separated HDPE liner folded into the flow stream. HDPE lining separation at the ductile iron pipe joint.
Figure 4 - The circle indicates liner that has Figure 5 - Liner failure indicated by the camera
completely pulled away from the host pipe creating operator.
turbulence downstream. A by-product of this
turbulence is hydrogen sulfide gas which escalates
the degradation of the pipe.
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
Paper E-2-04

4. 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 Figure 8 - To prevent customer
camera operator to access interruption, the working section on
Figure 7 - For the the sewer line was bypassed using a
progress in the sewer line. If a directional drill to access
section requires further stripping, pump to maintain sewer flow.
the sewer main, a fifteen
the camera operator alerts the drill (15) foot section was
operator to back up and give removed from the top of the
additional attention that section of pipe.
pipe.
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 Figure 10 - The liner stripping device is assembled
hole in sections and assembled in the manhole. 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
Paper E-2-04

5. 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 Figure 12 - The robotic camera Figure 13 - WSU used a vacuum
are deployed using water trails the stripping device truck to clean the entry manhole
pressure supplied by through the showing where the pipe has and remove the cut lining chips
drill stem by a water pump been stripped of the HDPE and other debris.
connected to the directional drill. lining.
Once the arms are deployed, the
drill string is rotated and the liner
is scraped from the pipe,
preparing it for lining.
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.
Paper E-2-04

6. 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.
Paper E-2-04