The deteriorating state of the nation’s infrastructure is now more apparent during ongoing times of economic duress as roads deteriorate without being repaired and pipes older than their design life burst. But it also offers opportunities and the developer of a new pipe-repair technology believes the system can not only stop leaks but offer structural integrity to all types of pipe, including pressurized steel lines.
The system, developed by Mo Ehsani, professor emeritus of civil engineering at the University of Arizona, Tucson, uses fiber-reinforced polymers—carbon and glass laminate—that are coiled around an inflatable bladder on wheels. The device is inserted into a pipe and inflated at the point of rupture, pressing the resin-impregnated laminate against the inner pipe wall where it cures in place. The application device can be moved through great distances of pipe, allowing repairs to be done without surface excavation and the disruptions to traffic and commerce that go with it.
Coiled PipeMedic laminate being taken into a pipe.
Called PipeMedic and located in Tucson, Ehsani says the system differs from other pipe-lining systems that work similarly. “Those are very good for stopping leaks but they are not designed to take loads,” he says. PipeMedic laminates provide tensile strength from 60,000 psi to over 155,000 psi and can be applied to a wide range of pipe diameters, he says.
Standard pipelining systems use the “wet-lay” method where lining is coated with resin onsite, and either applied manually to the damaged area or with hot air, which unfurls the lining against the pipe not unlike putting your hand through a rolled-up sock. However, strength cannot be determined until after installation when the resin is fully cured.
Ehsani’s solution is to produce the lining in a manufacturing facility where prefabrication allows the product to be strength-tested and given rigidity. Samples can be sent to the jobsite ahead of schedule, giving construction managers plenty of time to test whether the lining meets specifications. That can be important when critical pipe systems are shut down for repairs, he notes. "You don’t lose time mixing and applying resins,” he says.
Various layers of fabric can be incorporated into a single sheet of super laminate.
Ehsani describes the product as a “superlaminate” because carbon fibers crisscross with layers of glass laminate. It then is saturated with resin, pressurized and heat-treated to create strips of extreme thinness, from 0.010 in. to 0.025 in.
Its thinness promotes easy coiling for transportation and application and because its elastic memory wants the laminate to flatten, it naturally springs against the pipe surface when its restraints are loosened at the point of repair.
Ehsani says PipeMedic has been in “earnest” development for about five years. “It is simple to explain but to actually make such a thin uniform laminate is not that easy,” he says.
But the product already is making an impact. The Gas Technology Institute has given official approval for its use in pressurized gas lines after an emergency fix last January on 100-year-old, 700-ft-long , 16-in.-diameter, cast-iron pipe owned by utility PSE&G in Paterson, NJ. The pipe’s location, at some points reaching 24 feet below grade under residential property, active railroad tracks and commercial property, precluded excavation.
Coiled laminate wraps around balloon-type application device, which inflates and presses the liner against pipe wall.
The contractor was comfortable with relining the pipe but the job was complicated by a stretch beneath the railroad tracks divided by a drip pot and a length of vertical standpipe. The drip pot is a device to collect excess fluids, a remnant of the pipe’s earlier use as an outlet to a gas manufacturing plant. The standpipe ran from the bottom of the pot through the line and to the surface giving workers access to extract the liquid.
Contractor Progressive Pipeline Management and PSE&G devised a robotic device to enter the pipe, cut away the standpipe and apply the carbon-fiber sleeve. But the resulting 24-inch gap was too long a distance for a standard liner, which could not produce the needed strength and integrity.
But Ehsani’s superlaminate could and became the first application of PipeMedic. GTI cleared the product after testing showed no sign of structural failure when subjected to pressure as high as 250 psi. Ehsani says that is about one-third the ultimate strain of the PipeMedic laminates.
Epoxy is used to adhere the laminates to pipe walls, but Ehsani notes that carbon placed on steel creates a high potential for galvanized corrosion. In those cases, a layer of glass fabric is first applied to the pipe wall to act as a barrier. Ehsani says his laminates can be produced with a glass veil to allow the material to be applied directly to the steel pipe wall, a measure that can save a lot of construction time in the field.
The laminate is produced in flat sheets and packaged in 4-ft by 150-ft rolls and can be installed in 4-ft widths or cut to specification. They can be installed in rings or in a continuous spiral pattern. To maintain structural integrity, crews must overlap each ring and it must be done in the direction of the flow to ensure liquid does not penetrate the laminate.
Because the spiral application lends itself to robotic application, which Ehsani says can maintain and repeat geometrical parameters needed to build a cylindrical tube inside the pipe. He now is collaborating with two University of Arizona engineers to create a robot for spiral and individual ring installation.
“The target applies to small pipes where humans cannot get in,” says Ricardo Sanfelice, assistant professor in UA’s Dept. of Aerospace and Mechanical Engineering, who is working with Professor Parviz Nikravesh on the device. Parviz is working on the robot’s design and Sanfelice is collaborating on controls. They hope to have a third prototype ready for testing on a 25-in.-diamter pipe by the end of spring 2012, says Sanfelice.
To make such a thin uniform laminate is not that easy.
Mo Ehsani, professor emeritus of civil engineering at the University of Arizona