The gas industry now can save up to 50 to 70 percent of its cost repairing iron pipe joints with a new, durable, safer and faster technology than the conventional ones, thanks to an extensive evaluation by Cornell University researchers.

After a two-year comprehensive study of anaerobic methacrylate sealants by two Cornell experts, the gas industry can be assured that the new technology can be adopted on a widespread basis.

The anaerobic sealant technology, developed about 10 years ago, has been used in Great Britain, but American gas officials were worried that the new sealants would not hold up as long as conventional methods, especially under North American conditions. They also wanted to understand how these sealants work so that better and more durable sealants can be developed in the future. To test the technology, a joint panel of gas industry officials turned to Anil Netravali, a fiber and polymer scientist and associate professor of textiles and apparel, and Thomas D. O'Rourke, a geotechnical engineer and professor of civil and environmental engineering.

"Our analysis determined that the new technique of injecting anaerobic sealants is, indeed, an effective and reliable method for repairing leaks in the cast iron joints of gas distribution piping and can stand up to environmental stresses, such as heavy traffic, weather and aging, for up to 50 years," said Netravali, who teaches courses in the physical properties of fiber-forming polymers and fibers in Cornell's College of Human Ecology.

The researchers' conclusions also open the door for the industry to combine these sealants with a much less disruptive and safer method of exposing joints using keyhole and vacuum excavation technology, says O'Rourke, a member of the Geotechnical Engineering Group at Cornell's School of Civil and Environmental Engineering in the College of Engineering. He teaches courses in geoenvironmental engineering, earth support systems and rock mechanics, and he studies earthquake engineering, ground failures, lifeline systems, infrastructure rehabilitation and underground construction technologies.

The conventional encapsulation method to repair leaks typically involves excavating a large hole to expose the entire joint to give workers plenty of room to sandblast, clean and seal it. Also with encapsulation, the keyhole and vacuum method utilizing anaerobic sealants needs a much smaller hole to expose only about one-third the joint, no sandblasting and very little cleaning. Soon, internal robotic devices introduced from a single excavation are expected to enhance this technology by injecting the sealants into joints up to 50 to 60 feet in either direction underground, thereby minimizing excavations and further maximizing the savings.

Netravali and O'Rourke, working with postdoctoral associate Sanyog Pendharkar in the Fiber Science Program in the Department of Textiles and Apparel and graduate students Adam Tonkinson, Debanik Chaudhuri and Selcuk Toprak in civil engineering submitted their 400-page report to the industry early this month (May).

The researchers interviewed field utility engineers who had worked with the anaerobic sealants; evaluated stresses and deformation of joints to determine how the joints held up under heavy traffic and temperature changes and increased stiffness after sealant injection; conducted mechanical aging tests on joints under simulated field conditions; reviewed the sealant properties and current testing procedures; conducted extensive tests to assess the long- and short- term performance of the sealants; and established criteria for future sealant evaluation and testing procedures.

The new sealant technology involves injecting the methacrylate-based anaerobic compounds in a pipe joint through a small hole. The sealant gets absorbed and transported by the jute packing present in the joint, the researchers said. The jute packing acts as a reservoir for metal ions, available in the form of iron, rust particles and debris that have penetrated the fibers from the pipe surfaces. The metal ions, in turn, act as a catalyst for the formation of a rubber-like polymer that solidifies throughout the jute fiber matrix and develops adhesive bonds with surfaces in the joint.

The gas industry operates approximately 62,000 miles of cast iron gas pipe, with joints at 12-foot intervals, totaling some 30 million pipe joints. "Leaks can develop at these locations, and the industry devotes millions of dollars, considerable time and effort to maintain these joints and pipes," Netravali said. In the New York City metropolitan area alone, there are nearly 5,000 miles of gas pipe line.

Next, the researchers plan to evaluate and analyze the use of new polymer linings as a way to renovate gas mains without replacing them.

The study was funded by the Gas Research Institute, the Consolidated Edison Co. of New York Inc., Brooklyn Union and Consumers Gas of Toronto, Ontario.