Several repair and replacement methods were considered. There would be the potential for both hori-zontal movement due to parallel trenches, vertical movement due to weakened beam support from perpendicular trenches under the cast iron pipe, and new traffic loads associated with the water main construction. Joint sealing methods that had not been proven reliable for the substantial movement anticipated were eliminated as maintenance alternatives. The choices would be to either replace the pipe or to use cured-in-place lining to ensure joint integrity even after the water pipe construction. Re-placement was ruled out because of the lack of adequate right-of-way space to add a new line (unless of course, the existing pipe was extracted), the increased risk of damaging other buried facilities while trenching in the new large-diameter pipe, because of the estimated relative high cost of a new pipe. Cured-in-place lining offered a number of benefits. Fewer excavations would be needed, so restoration liabilities and costs would be reduced, disruption to traffic and businesses would be limited, the risk of damaging other buried utilities would be all but eliminated, and the cost of renewal would be consid-erably less than replacement. KeySpan was one of the early pioneers in lining and felt confident that Progressive Pipeline Management, the contractor and the starline® liner product would meet their needs.
The KeySpan 20 inch cast iron pipe lining project, about 7000 feet, represents the longest gas lining job in the U.S. The 20 inch main was located in Brooklyn, NY, mostly along a busy thoroughfare, Flushing Avenue. About 5000 feet of the main operated at 15 psig and the other 2000 feet at low pres-sure (inches water column). Once lined, all of this primary gas supply artery would be operated at 15 psig. Sections of the pipe would be replaced if they were extremely close to the water pipe or would be too shallow once other construction and grading work was completed. The lining project was compli-cated because KeySpan restricted the length of some inversions (typically 500 - 700 feet) to as short as 250 feet to limit customer outages and due to work-time restrictions that required the lining was completed early in the day. The flexibility of the product was demonstrated when successfully lining sections of pipe that had 4-6 offsets. Even ancillary tools, cleaning equipment and robots performed outstandingly in preparing the pipe and in reinstating services. Lining started in October 2003, paused due to weather, then, resumed in March before finishing in April 2004. KeySpan was pleased with results of the lining job and expects to operate this large-diameter main for many years to come. "We expect to have more of these types of projects and based on the success we've with starline®, lining the pipe will be considered a viable if not a preferred maintenance option" says Susan Fleck, KeySpan.
Background
starline Trenchless Technology, LLC was formed in 1999 as a joint venture of GRI and Karl Weiss GmbH & Co. KG of Berlin, Germany, following a GRI worldwide search for promising pipe rehabili-tation technologies for the U.S. natural gas industry. Research and testing conducted by GTI and oth-ers has resulted in significant improvements, and with a new North American licensee since 2003, Progressive Pipeline Management, lining has continued to grow.
Benefits
With starline® technology, aging gas mains and services are returned to their original leak-free integ-rity through the use of high-strength flexible fabric liners installed in the pipes with a special inversion process, without the need for long trenches.
This lining process, unlike open-trench gas-line replacement, enables utilities to reduce the need for traffic control and minimize excavation and pavement and landscape restoration - tasks that can ac-count for up to 70% of the cost of gas-line rehabilitation. The system also eliminates the risk involved with digging around other buried utilities in the right of way. Unlike straight or rigid liners, cured-in-place liners can be installed through bends, fittings, and where there may be variations in internal pipe diameters. A 500-foot section of gas main typically can be disconnected, cleaned, lined, and recon-nected in only 24 hours.
The starline® process benefits gas utilities by:
- Eliminating existing and potential leaks with no significant reduction in pipe capacity
- Reducing pavement removal and site excavation by more than 90%, compared to traditional open-cut methods
- Extending the useful life of the existing pipeline
- Reducing customer/public inconvenience
With the starline® process, after disconnection of gas piping, the pipes are cleaned and inspected using a sand-blasting process to remove scale, dust, and residue. Ultra-high-pressure water jetting or sand-blasting can be used to remove any tar-like material. Cleaning is followed by a camera inspection. The liner is then impregnated with a solvent-free adhesive resin and inverted into the pipe using a single entry point. By using internal pressure, the liner is turned inside out (inversion process), expanded to fit tightly on the pipe wall. The adhesive is then cured in place, tightly adhering the liner to the pipe wall. Extensive pressure testing is then completed. Following the lining process, a robot is used to open any gas main services internally, eliminating the need to dig up each service connection.
Lining Applications
starline® products can be used to rehabilitate both gas services and mains.
The starline® technology is available for lining services with diameters of ¾" to 2½" up to 200 feet in length. Up to five offsets (or five 90-degree bends) can be lined uniformly and wrinkle-free. The operating pressure of a service liner rehabilitated using the starline®200 technology can range from inches of water column to 60 psi. Depending on the size of the rehabilitation crew, three to four ser-vices can be lined per day if a warm-curing method is used.
Natural gas mains (up to 60 psi) are rehabilitated with the starline® technology. For use in pipes from 4 inches to 24 inches in diameter, pipe segments, which are not easily accessible to construction vehicles, can be lined by using mobile lining equipment. The actual lining procedure can be completed in approximately one hour for sections up to 700 feet, with the total process taking from 12 to 24 hours. The pressure drum can be disconnected from the line so that additional sections can be rehabili-tated with a single set of installation equipment in one working day. The specially developed cleaning technique and proprietary resin adhesive allow the fabric hose to be uniformly bonded to the interior wall of the pipe, ensuring the high quality of the rehabilitation.
Status
"The starline® story underscores how with effective industry guidance, new technology can be devel-oped into products that really impact how utilities do business" says Allen Spivey. Progressive Pipe-line Management brings to the process its patented pipe-cleaning technology and established working relationships with the gas industry. They work collaboratively with the utility as well as the local con-tractor and continues to build a respectable reputation among users and fellow contractors. Still, eve-ryone knows there is room for improvement. GTI has been charged with testing and demonstrating the performance of a high-pressure liner (rated at a MAOP of 250 psi for 2004 commercial introduction) and in developing methods to reduce the time required to complete a liner installation. Progress has been made on both efforts.