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Organic “High-Build” Spray-in-Place Liners – An Emerging Class of Rehabilitation Methods
The Polyurea is applied onto the pipe surface using a robotic application system or by conventional hand-applied procedures in multiple thin layers to build a pipe inside a pipeline with wall thickness between 20 and 1000 mils (0.5 and 25 mm) or greater (Figure 2). Examples of the technology are the PolySpray Structural Liner. Polyurea coating typically utilizes two layers of approximately 90 mils (180 mils total thickness). Flow can be reinstated in as little as 60 minutes, allowing same day return to service. An example of a polyurea coating is PCSI Polyurea Manhole Coating.
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Fig 2. Twenty-four inch corrugated metal pipes coated with different formulations of polyurea awaiting testing at the Trenchless Technology Center
Polyurea and 100 percent solid polyurethane form a new class of organic “high-build” coating systems. These products, which are able to be built to substantial thicknesses within minutes, feature a very quick curing time that supports same day return to service and exhibit pressure ratings adequate for most municipal water mains, making them attractive rehabilitation methods for municipalities looking for short downtime for potable waterlines and force mains (Johnson et al., 2002). However, for this potential to materialize, appropriate qualification and service testing for pressure pipe applications needs to be performed, long-term performance characteristics established and design procedures developed. Procedures for operation maintenance, installation of new services and emergency repairs of rehabilitated pipe sections are also concerns that must be addressed before these technologies can come to fruition.
The following sections describe the results of testing 28 panels of 100 percent solid polyurethane and polyurea under varying thickness subjected to a uniformly incremented water pressure until failure (burst-test). These tests are part of a comprehensive research initiative undertaken by the Trenchless Technology Center which is aiming at the development of an extensive database, and subsequently a predictive model, for organic “high-build” spray-in-place liners. It is anticipated that this research effort will support the establishment of a design procedure for these products.