November 15, 2012Replacing utilities in urban areas presents challenges to all stakeholders. Easement issues, street closures, traffic congestion, disturbing surface works and customer inconvenience are all areas of concern that communities must address. City administrators, engineers and residents are starting to demand more efficient and less disruptive methods of replacement to ease these concerns. As pipelines are coming to an end of their useful life, replacement methods such Swagelining are being selected to add value to all stake holders involved.
Over the past 20 years, many North American communities have begun implementing programs to replace failing gravity sewer and water distribution pipelines. A combination of construction methods, including trenchless technologies such as CIPP and pipe bursting have come to the forefront to replace these smaller diameter pipelines in a cost-effective, efficient and environmentally friendly manner.
While much work is still to be done, the next major focus by communities is to address failing medium and large diameter water transmission and sewer force mains in the diameter range of 16 to 72 in. These systems form the major artery of a community’s pipeline network. Failure of large transmission mains poses a substantial risk to public safety; such a failure can result in an initial explosive force of between 20 and 200 tons of dynamite and the release of pressurized water with an initial velocity of 90 mph. As we have unfortunately seen recently in the media, when these pipelines fail, the effect to a community can be catastrophic. The failure of a 36-in. transmission main is not equivalent to the failure to the segment of a 6-in. main servicing 10 customers. One single repair can cost well into the millions of dollars. Additional adverse effects include major sink holes, flooding, environmental damage, significant inconvenience of businesses, street closures on major roads and regrettably loss of life. Some communities have specific types of large diameter pipelines more susceptible to failure, such as that of PCCP installed in the 1970s to mid-1980s. During this time period, PCCP manufacturers used a higher strength wire (Class IV). This newly extruded wire turned out to be very susceptible to hydrogen embrittlement, which can result in sudden breaks in the wire and subsequent failures.
Just as the industry has seen various trenchless technologies come to the forefront to rehab smaller diameter pipelines, Swagelining technology is emerging as a leading candidate to renew and replace mid- to large-diameter water transmission and sewer force mains. Developed more than 30 years ago by British Gas and United Utilities (then known as North West Water) to address the problem of failing pipeline systems that were buried and entangled with other utilities throughout urban and rural areas, the principle of Swagelining was developed. It is considered by the pipeline industry as the benchmark in polymer lining technology for its ability to deliver cost-effective lining solutions in every environment. With an extensive list of work across the globe, the technology has been proven in many extreme projects spanning three decades onshore and subsea. Projects have been completed for water, sewer force main, mining, hydrocarbons, chemicals, bulk products and gas distribution.
Specifying an HDPE pipe with an outside diameter larger in size than the inside of the host pipe, Swagelining reduces the HDPE pipe temporarily below the ID of the host pipe, allowing it to be inserted. While the towing load keeps the liner pipe under tension, it remains in its reduced size. The HDPE pipe remains fully elastic throughout the reduction and installation process. As the liner pipe is not permanently deformed by Swagelining, the release of the towing load after insertion is the catalyst for the liner to start reverting back toward its original size. As its original size is larger than that of the host pipe, the HDPE pipe expands until it is halted by the inside diameter of the host pipe. The HDPE pipe has been prevented from continuous expansion back to its original state. This produces a residual strain that is locked in the liner and keeps it pressed tight against the inside of the host pipe, even with no internal pressure from the product conveyed. A digital animation that illustrates this concept is available at www.Swagelining.com.
The effectively natural ‘tight’ or ‘compression fit’ produced by Swagelining is accepted as exchanging an existing failing pipeline with a composite pipe in its place. The HDPE provides the very long-term corrosion protection barrier for the corroding pipe while the structural strength required to maintain pipeline operating pressure is delivered through the existing pipe. In circumstances where the host pipe can no longer provide pressure retaining capability, Swagelining can insert a structural HDPE for almost any size of pipeline diameter.
Replacing large diameter pipelines have unique engineering and construction requirements, and as such may limit the number of construction methods feasible to be employed. As large diameter mains can be located in high profile areas, attaining easements for relocation is often not an option. Maintaining the existing pipeline alignment eliminates the need for utility relocates and easement concerns. In rural and environmentally sensitive areas, following the existing utility path reduces environmental concerns and permitting. In addition to following the existing utility path, one of Swagelining technology’s key attributes is the resulting ‘compressive tight’ fit of the HDPE. This allows for the maximum bore path as all annular space is eliminated and rules out the need for grouting. The ‘compressive fit’ is also important to maintain the HDPE against vacuum collapse or when no pressure is conveyed.
On the jobsite, typical production ranges from 1,000 to 5,000 ft in one continuous pull. This is critical to speed installation when many projects are undertaken during dry weather periods of limited shut down. The long pull distances also contribute to minimizing excavations, including reducing the number of connection points required. As the HDPE installed is one long continuous fused pipeline, the reduction in connection points reduces the potential for leakage to occur in the future.
Over the years, the Swagelining technology has been selected to renew numerous medium and large diameter water transmission and sewer force main projects throughout the United States. This work includes some recent high-profile work in Texas and Colorado (See the sidebar for an overview). These projects demonstrate the unique engineering and construction characteristics required that ultimately lead to the Swagelining technology being selected. While many construction methods were considered during the pre-design phase, fundamentally the Swagelining technology was selected as being the most advantageous long-term solution.
With more than three decades of history, the Swagelining technology is problem solving with joined up engineering, research and development, advanced HDPE materials and connectors to deliver long-term solutions to renew the life of medium and large diameter water transmission and sewer force mains.
Todd Grafenauer is the educational director for Murphy Pipeline Contractors, a national leading contractor in static pipe bursting and Swagelining technologies.
Swagelining in Texas and Colorado
Two recent swagelining projects highlight the unique engineering and construction requirements that ultimately lead to the selection of the technology.
W ith a 30-in. water transmission main traveling through the heart of a major Texas community, the design engineering team needed to select a construction method to renew the existing cast iron main installed in 1927. The transmission main was located in a tight utility corridor and through major intersections. As the pipeline is a major artery of the city’s pipeline network, the transmission main moves water from a pump station to feed the north end of the city. Even of more importance than maintaining the existing utility path was maintaining the existing flow and capacity of the pipeline. A resulting ‘compressive’ fit of the HDPE provides the same or better flow rate due to the new C-factor of the smooth walled pipe material. The HDPE also provided a long-term design life, in excess of 100-plus years. The last requirement of the project was to complete the work within a short, dry weather period. With installation distances exceeding 1,800 ft in continuous pull lengths, the project was completed well under the allotted time.
With a 24-in. RCP raw water inverted siphon pipeline in Colorado moving mountain runoff to a reservoir, the pipeline is a necessity of life for nearby town residents. The engineering design challenges included the pipeline was located in an environmentally sensitive area starting from Salt Lick Gulch on the north side of I-70, and then traveling through the inverted siphon located under I-70, a major freeway. As the inverted siphon consisted of bends that could not be accessed, it was vital that the installation be completed in one continuous pull. The siphon could also only be renewed during a limited period of time during the summer dry season. With the Swagelining technology being selected, the technology eliminated costly and environmentally damaging excavations as the raw water main was renewed in one continuous pull. The small footprint of the excavations also eliminated timely and costly permits. In addition, the ‘tight’ fitting HDPE will provide a long-term design life to ensure the water supply of the siphon to the reservoir.