Detection of Buried Non-Metallic (Plastic and FRP Composite) Pipes Using GPR and IRT

DETECTION OF BURIED NON-METALLIC (PLASTIC AND FRP COMPOSITE) PIPES USING GPR AND IRT Jonas Kavi Pipelines are crucial in transporting petroleum products, natural gas, and water from production facilities to consumers under high pressure and long service life. In addition to being the primary means of transporting water from treatment facilities to consumers, pipelines also account for the transportation of more than half of the 100 quadrillions Btu of energy commodities consumed in the United States annually. The important role played by energy pipelines in the US economy and standard of living of citizens requires that these assets be safely maintained and appropriately expanded to meet growing demand. Pipelines remain the safest means of transporting natural gas and petroleum products, nonetheless, the pipeline infrastructure in the US is facing major challenges, especially, corrosion of steel/metallic pipes and excavation damage of onshore pipelines (leading to oil spills, explosions, and deaths). Problems associated with corrosion of metallic pipelines can be avoided by using non-corrosive materials such as PVC (Polyvinyl Chloride) or other plastics for water, sewer, or low pressure gas lines and Glass Fiber Reinforced Polymer composite (GFRP) for transporting high-pressure oil and natural gas. But buried nonmetallic pipelines such as GFRP and PVC material are not easily detectable using the conventional techniques employed by construction crews to detect buried metallic pipes, which can lead to increased excavation damage during building/construction and rehabilitation works. This research investigated alternative strategies for making buried non-metallic pipes (CFRP, GFRP, and PVC) easily locatable using Ground Penetrating Radar (GPR). Pipe diameters up to 12" and buried with up to 4 ft. of soil cover were investigated. The findings of this study will help address the detection problem of non-metallic pipelines and speed the adoption of composite pipes by the petroleum and natural gas industry. The research also investigated the possibility of locating buried pipes transporting hot fluids using Infrared Thermography (IRT). Results from the study have shown that, using carbon fabric and aluminum foil/tape overlay on non-metallic pipes (GFRP or PVC for this study) before burying significantly increases the reflected GPR signal amplitude, thereby making it easier to locate such pipelines using GPR. The reflected GPR signal amplitude for pipe sections with carbon fabric or aluminum foil overlays was found to have increased by a factor of up to 4.52 times, and 2.02 times on average across all the pipe sections tested, from the baseline (unwrapped) pipe sections. The research also highlights the importance of using the correct antenna frequency for detecting buried pipes in wet soil conditions. Wet soils with high electrical conductivity and dielectric constants have higher radar signal attenuations that significantly affect the penetration depth and returned signal amplitudes from buried objects. A 200 MHz frequency antenna was found in this study to be ideal for locating the buried pipes in all soil moisture conditions. The 200 MHz antenna was able to detect buried pipes up to the maximum 4 ft. depth of soil cover that was studied experimentally. Numerical estimation using the same soil from the experiment shows that this antenna can penetrate up to a depth of at least 5.5 ft. in very wet clay soils with volumetric water content of 0.473. After evaluating the attenuation characteristics of different radar antennae, it was found that material/ohmic attenuation is constant across a range of antenna frequencies; the increase in GPR signal attenuation associated with higher antenna frequencies was found to be a result of scattering attenuation from subsurface inhomogeneity/clutter. Scattering attenuation is however usually ignored in literature, resulting in erroneous estimation of radar signal attenuation. Finally, laboratory study proved that, heat from a buried pipeline transporting hot fluid can propagate through the soil to the surface and be detected using IRT. Additionally, a 6" diameter steam pipe with a 6" minimum insulation and buried with 2.5 – 3 ft. of soil cover was easily detected in varying soil moisture conditions during different seasons throughout the year using IRT in the field environment. The successful application of IRT in detecting this pipe proves the potential for using this technique in locating buried pipes transporting hot fluids such as steam or petroleum products from production wells or refinery plants.