Processing and characterization of high performance piping materials for geothermal applications

Abstract

Polymer composite based pipes are being recently utilized in transportation of geothermal fluids.The utilization of composites is due to their resistance to aggressive chemicals and hot-wet environment with relatively high specific strength and design flexibility.Exposure of materials to wide range of temperatures and humidity level, while under the action of load, may degrade them and cause to severe reduction in their properties and service life.Understanding the complex degradation mechanism of the composites exposed to a variety of temperature and fluid chemistry (including geothermal fluid) is essential to improve their durability.This research focuses on the investigation of interactions between geothermal fluid and composite piping materials made of various matrices and the mechanism of degradation in these composites.The matrix materials include polyester, epoxy and graphite particle added epoxy materials.In this study, E-glass fiber reinforced polymer composites were fabricated by employing filament winding and tube rolling techniques.Fabricated composites and neat polymers were exposed to dry environment, distilled water and geothermal fluid of Balçova geothermal field until the saturation of weight gains due to water uptakes.In addition, the specimens with neat polymers were prepared to simulate and follow the degradation of matrix materials under hot-wet environments.Once the saturation occurred, the specimens were subjected compressive mechanical testing.For both dry and wet specimens, the mechanical testing was performed to obtain stress-strain behavior, modulus of elasticity, strain at failure values and energy absorption during the loading.The results were compared to evaluate the degradation of the properties due to various exposures.Moreover, the thermal conductivity of the various composites fabricated in this research was measured to determine the heat losses and temperature distribution within the materials.The temperature distribution within the cross-section of the pipes for various materials was analyzed using a finite element-modeling tool, LUSAS for uninsulated pipes.The heat loss occurring during the transportation of hot geothermal fluid was calculated as a case study to compare composites and traditional metal piping.It was found that polyester composite pipes have higher mechanical performance under axial and radial compression as compared to the composite with epoxy matrices. For all the composite types, some considerable degradations were measured due to exposure to hot-wet environments.The extend of degradation was less for graphite particles added epoxy composite pipes that exhibited the lowest water uptake values. The graphite particles incorporated into the matrix affected the water uptake and thermal conductivity of the epoxy.The water uptake of polyester matrix composite pipes was the highest that might be related to the most extensive degradation of polyester based composite.Moreover, it was found that the thermal conductivity of the composites is much lower than traditional materials.The graphite particles cause reduction in thermal conductivity, simultaneously in heat loss for uninsulated pipes.However, if the isolation is used, heat loss is not sensitive to pipe material.