The principle of CompressionFit was born of necessity and developed over 40 years ago by British Gas and United Utilities (known as Swagelining or die drawing) to address the problem of failing pressure pipeline systems that were buried and entangled with other utilities throughout historic urban areas. At the time, the intended market was to replace distribution mains from 4 in through 12 in (100 mm through 300 mm) diameter. As the technology progressed through years of Research & Development and successfully completed projects, the method crossed into many pressure pipeline markets including
water, sewer force main, mining, hydrocarbons, chemicals, bulk products, and gas distribution. The technique was utilised for replacement of ageing pipes of any material in order to extend life of the asset, or new pipelines onshore and subsea as alternatives to a corrosion allowance or use of a CRA pipe material.
Limited Growth
By the mid-1990s, CompressionFit began to advance into larger diameters around the globe, including a 36 in (915 mm) diameter water transmission main replacement project completed for the Los Angeles Department of Water & Power (LADWP). However, a missing element of explosive growth was due to the lack of education and large resumé of completed projects. With cities taking a conservative approach due to the high responsibility of their infrastructure, the CompressionFit method began the slow process
of being implemented as a proven trenchless technology. Quite simply put, very few engineers or utility departments were aware of the method. Over time, an increasing number of projects were successfully completed, building an impressive resume that began to catch the attention and curiosity of utility owners. This proven track record generated interest and ‘normalized’ the CompressionFit process and the momentum began to increase.
Even as interest grew and an increasing number of larger diameter projects were undertaken, the lack of availability of larger diameter HDPE pipe sizes and wall thickness remained a challenge. Many of the large diameter projects historically installed thinner walled HDPE pipe. This was due to either unavailability of thicker walled HDPE pipe produced within the necessary timeline, or the need to reduce the pulling force to match the equipment that was available to install the HDPE.
However, fast forward to today and the CompressionFit technology now has a significant track record in America. While Murphy Pipelines experience with the method began with President Andy Mayer’s British Gas work during the early days of development, it has been over the past 15 years of tremendous dedication to education of the technology that set the stage in the US. While early work may have included pilot projects, today’s work includes award winning projects such as ASCE and Trenchless Project of the Year awards. Additionally, multiple standards now exist, including ASTM F3508 which governs the method of CompressionFit. This has allowed conservative decision makers the ability to make informed decisions on the selection of the technology.
Today almost all diameters and wall thicknesses of HDPE pipe are available. CompressionFit continues to advance in its ability to replace large diameter water transmission and sewer force mains. While the technology forges ahead in both larger diameter and thicker HDPE walls, the method remains constant in delivering expedited project schedules, 92% less excavation than open cut and provide a structural Class 5 or Class 6 solution (per ASTM F3508). “We are seeing the CompressionFit technology selected by some of the largest water and sewer programmes in the world. The method delivers value to the overall programme by maintaining the community’s way of life during construction and helping to reduce upfront planning and engineering as the technology follows the existing utility path.” commented Andy Mayer, President of Murphy Pipelines.
With advancements in polyethylene and pipe extrusion technology, HDPE pipe is now made up to 138 in (3,500 mm) diameter in the US with a wall thickness over 6 in (150 mm) (Agru America). This allows the CompressionFit and Slip Lining methods the ability to replace water and sewer force mains in any size and pressure class.
This also benefits the Slip Lining process, one of the oldest methods in trenchless. Slip Lining replaces a failing large diameter main by installing a smaller sized HDPE pipe. Potential limitations include a reduced cross-sectional area due to installing a smaller sized pipe, thus reducing flow rates and capacity. Hydraulic calculations need to be considered. For water and sewer projects that need to maximise the Internal Diameter, CompressionFit HDPE pipe lining can add value over Slip Lining.
How does CompressionFit work?
Governed by ASTM F3508, the CompressionFit HDPE pipelining technology specifies an HDPE pipe with an outside diameter larger in size than the inside of the host pipe to be replaced. After the HDPE is butt fused to correspond to the pull distance, the pipe is pulled through a reduction die immediately before entering the host pipe. This reduces the HDPE pipe temporarily below the ID of the host pipe allowing it to be inserted.
While the towing load keeps the HDPE under tension during the pull, the pipe remains in its reduced size. The HDPE remains fully elastic throughout the reduction and installation process. After installation, the pulling load is removed. The HDPE pipe expands until it is halted by the inside diameter of the host pipe. The effectively natural ‘tight’ or ‘compression fit’ exchanges an existing failing pipeline with a composite pipe in its place.
What are the Class 5 and Class 6 Designations per ASTM F3508?
Class 5 designation provides a dual wall composite pipe in place. When it is deemed that there is value remaining with the host pipe, the combination of the new HDPE plus the value of the host pipe provides a new design life. Class 6 designation provides an unequalled independent liner. The failing host can continue to deteriorate and disappear as the liner stands alone. The method uses the same HDPE pipe and wall thickness installed by other methods such as open cut, directional drilling, or pipe bursting. “The infrastructure value that the method provides to these high-volume flow application assets is significant. These include providing well over a 100-year new design life, corrosion resistance for life, ductility of withstanding water hammer/ pressure surges, smooth interior wall (C-factor of 150) increasing operating efficiencies and lowering operating costs and its resistance to extreme weather (freeze/thaw and dry/wet cycles).” commented Richard Crow, Director of Engineering and Special Project with Murphy Pipelines.
