This Small Business Innovation Research Phase I project presents a patent-pending new approach for on-site pipe manufacturing that can reduce time, overhead costs, materials costs, leakage, and corrosion when compared with other pre-manufactured pipes in the industry. Phase I of this research activity will focus on developing and mechanizing the technique for assembling the pipe using sandwich composite construction, and then evaluating the short-term behavior of the honeycomb-fiber reinforced polymer (FRP) composite sandwich (HCS) pipe under various loading and environmental conditions. Performance limits that will be considered include key failure modes of buckling, deflection and internal pressure. Testing will include a sand bed for buried pipes, internal and external pressure tests which will reveal how the stiffness of the pipe, which is fabricated from composite materials, compares to the stiffness of the composite materials in a flat panel. The data collected will provide useful design information regarding the behavior of the pipe, as well as demonstrate the feasibility of manufacturing and installing such a product.
The broader impact/commercial potential of this project is enormous, considering the versatility and low cost of the pipes, in addition to the corrosion resistance that they provide. The ability to produce pipelines on-site has far-reaching implications for remote locations and developing nations which have little to no infrastructure for natural gas discovery and water delivery systems. As the viability of this product is proven, there are quite a few variations that can be tested, such as using the pipe vertically and filling it with concrete for piles and columns in various construction industries. Other possible uses include underwater pipelines and transmission lines for the oil and gas industries, or even as low cost, mobile, temporary pipelines for mining and fracking operations around the globe. As the mobile manufacturing units are developed and the process becomes more efficient, the resulting cost savings, not only in terms of the pipe itself but also on equipment and freight costs, will be substantial. This, in addition to the long-term savings from reduced leakage and maintenance of these pipelines, will lead to an industry shift towards this greener, more efficient technology.
Construction of pipelines has traditionally required manufacturing of the pipe in segments that are 20-40 ft long; these pieces are shipped to the job site and connected together to form a long pipeline. The connection or the joint in the pipelines is a major source of leakage. Additionally, for larger diameter pipes, transportation of the segments to the job site can be costly. As a result, pipeline factories that are close to the job site have an advantage over the competitors that have to ship their finished pipes a longer distance. We have developed a new pipe called StifPipe® that uses carbon or glass Fiber Reinforced Polymer (FRP) products. Unlike metals, these materials do not corrode and offer a long service life. FRP is constructed of fibers (or fabrics) of glass or carbon that are saturated with a resin and cure quickly. Once cured, the materials have a tensile strength that is 3-4 times that of steel. To lower the cost of the pipe, the wall of the pipe includes a lower cost spacer that is sandwiched between the CFRP or GFRP skin layers. The sandwich construction technology has been used in the aerospace industry for decades but its application to build a pipe is a novel idea. Construction of the pipe consists of providing a mandrel, wrapping 1 or more layers of FRP fabric around the mandrel, applying a honeycomb sheet, and wrapping additional layer(s) of FRP (Fig. 1). Once the epoxy cures in a few hours, the pipe segment can be removed. The pipe is very strong and weighs less than 10% of a comparable steel pipe. This NSF SBIR project focused on demonstrating the feasibility of StifPipe® as a viable alternative for pipe construction. The ultimate goal is to develop a Mobile Manufacturing Unit (MMU) that would allow the construction of the pipe on site to virtually any length, thus the name InfinitPipe®. The MMU should be able to produce pipes at a rate of 1 ft per minute. If successful, InfinitPipe® would eliminate or reduce many of the problems associated with current pipelines, e.g. leaking joints, high transportation cost, welding and assembly in the field, construction delays while waiting for the pipe segments to be built in the plant, etc. The technology would revolutionize the pipeline industry by allowing us to participate in projects in far and remote locations. A few containers of raw material and a relatively small MMU that can also be shipped in a container are all that is needed to build miles of pipeline. With an eye on the ultimate goal of fast manufacturing in the field, we had to make several major changes to our design. These included: a) switching from an ambient temperature cure resin to one that could be cured faster at an elevated temperature (e.g. 3 minutes at 300F); b) replacing the honeycomb with a 3D fabric that is much easier to be automatically wrapped around the mandrel; c) using an HDPE sheet as the first layer of the pipe; this layer can be welded to create a thin tube or pipe that is wrapped with FRP for additional strength and stiffness. Nearly twenty specimens of different sizes were constructed and tested, including many 12-in. diameter samples that were tested at the Louisiana Tech Trenchless Technology Center. The ASTM D2412 tests is aimed at determining the overall stiffness and rigidity of the pipe. These tests demonstrated that the pipe has sufficient stiffness and can be designed as a free-standing pipe or as a liner to repair existing pipes and culverts. A 14-ft long segment of the pipe was buried in a soil box and the soil around the pipe was compacted before overburden pressure was applied to the sample. This test also proved to be successful with the pipe exhibiting minimal deflection. A numerical model for the pipe was also made and tested under various loads; both those results and the Charpy impact tests indicated that the behavior of this pipe is similar to that of a steel pipe. lastly, the pipe was subjected to internal hydrostatic pressure. But the specimen started to leak at a pressure of 80 psi; this was due to a defective weld in the HDPE liner and it can be easily fixed. Nevertheless, the 80 psi is more than sufficient for many gravity flow applications, e.g. sewer pipes and culverts. All of these results indicate that the proposed pipe is a viable alternative to conventional pipes. We have started the develpment of the MMU and plan to complete a fully working prototype in Phase II of this project.
