Inside Job

Inside Job

A company in Massachusetts has invented a fast and effective way of repairing pipe with carbon fiber lining. Warren Environmental of Carver, MA, recently repaired a damaged section of 42-inch water pipe in Mesa, AZ with a patented method of Pressure Infusion.

The pipe in question runs from the Pasadena Reservoir to the Val Vista Treatment Facility. It runs through a neighborhood where there’s very little clearance from the existing homes, and the pipe is 26 feet below the surface. Repairing it by trenching was ruled out.

According to Dan Warren, the inventor of the method, his company was called to Mesa in a hurry. The contractor had been trying to repair the pipe from the inside by laying-up carbon fiber by hand. “They had seven men down in the pipe for nine days,” relates Warren, “and they were failing. They were wetting it and putting it on like wall paper inside a round pipe. So it kept falling down.”

With the completion deadline looming, Warren was called in to use his new pressure infusion system.

First, in their shop, they made a tubular carbon fiber liner  – dry – no resin – on an inflatable mandrel. “We came up with a way to fold the mandrel with the carbon fiber on it. We pulled vacuum on the mandrel. The entire 110 feet of carbon fiber fit into a duffel bag. We carried it on the plane with us.”

“When we got there, everyone was a million questions, because the deadline was that night at midnight, then the liquidated damages start. ‘Where’s your equipment, where’s your equipment?’” It was in a duffel bag. Beyond that, he needed only an air compressor and the “spincasting” equipment.

First, they laid a 3/8” thick layer of epoxy on the entire inside of the pipe, using a method called spincasting. The spinning spray-head is sent down to the far end of the pipe. It sprays epoxy resin in a rotary fashion, spewing it out at a set rate controlled by a computer. The spinning head is pulled backwards through the pipe, leaving an even layer of epoxy – in this case 3/8” thick – behind it.

“It was 130 degrees down in the pipe. We pulled this liner out of a little wagon. It weighed 118 lbs. It was a controlled fold so that, as it was unwrapping, it walked itself down the pipe on its own, in 8 minutes.”

Then they turned on the air compressor, inflating the mandrel/bladder, which expanded the carbon fiber outwards to fill the entire diameter of the pipe. “We pushed the carbon fiber through the epoxy. It’s an infusion, not a wet-out. The best part is, when it gets to the head space, it keeps expanding more so you don’t trap any air, and that internal bag pushes the carbon fiber right through the epoxy.”

They held it in place several hours. Then they withdrew the bladder and shot another coat of resin on it, “to give it a glossy, beautiful finish” adds Warren.

Total time working was 6 hours. Working and curing time was 10 hours.

After 3 hours of curing, at 10:00 PM that night, Warren pressure-tested the pipe. Water normally runs through it at up to 90 psi, and the pipe had to pass an internal burst pressure test at 150 psi. It more than passed.

The resin used was Warren S‐301 epoxy, and NSF approved material with a 30-year history in water and wastewater applications. Warren reports that this past week, the resin passed a stringent environmental test, ASTM E 729-96(2007)  Standard Guide for Conducting Acute Toxicity Tests on Test Materials with Fishes, Macroinvertebrates, and Amphibians, and ASTM  E 1023-84 (2007) Standard Guide for Assessing the Hazard of a Material to Aquatic Organisms and Their Uses. In this test, microscopic marine animals are exposed to the test substance to see if they can survive for 24 hours. According to Warren, no epoxy has ever passed this test before.

Warren’s method was awarded the 2014 Joseph L. Abbott Jr Innovative Product Award by the North American Society for Trenchless Technology, based on its elimination of a) wet‐out facilities; b) the need to transport weight restricted materials; c) the need for refrigerated storage on site; and d) the need for steam or boiler trucks – all common elements of conventional cured‐in-place pipe lining systems.

While this would seem to fall more in the realm of civil engineering than architecture, there’s no reason that that technique is limited to pipes. It has implications for in situ repairs, on-site construction, and shop fabrication of structural and architectural elements of buildings, as well.

Images courtesy of Warren Environmental  except as noted.