Design and testing of composite tubes subjected to external pressure in oil well environment
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Carbon fiber reinforced polymers are advanced materials with unique material properties that are being used in an increasingly number of industrial applications. In well intervention the high stiffness to weight ratio as well as the chemical resistance is being utilized to make a semi-stiff rod for logging purposes. The carbon rod has several advantages over its competitors, but the performance can be further improved for use in the horizontal sections of the well. As a solid carbon rod, the submerged weight causes the rod to press against the bottom of the casing generating friction which prevents the desired reach. By making the rod hollow, the submerged weight will reduce significantly and the rod will stay buoyant in the casing, hence extending the reach.The main focus of this study was to find and develop manufacturing methods for a continuous rod consisting of an inner layer of pure hoop and an outer layer of longitudinal fibers. One of the suggested methods included a filament wound hoop layer using a PPS thermoplastic impregnated carbon fiber tape with lay-up configuration corresponding to the previous tested rods based on epoxy resin. The PPS-rod was then tested with external overpressure and axial compression, the same tests performed on the epoxy-rod. The rods are considered as thick-walled tubes and had an outer diameter equal to 15mm, which is the same as the current solid rod in field operation, and inner diameters at 12 mm. They were made using the filament winding machine at NTNU. The epoxy-rod was made with resin bath to ensure a good and even impregnation of the fibers, while a gas torch was used to melt the PPS-tape.Two rods were produced using a custom setup in the filament winding machine. Due to the provisional setup it is obvious the process and quality need more development. The rods were leaking under low pressure, and when sealed, the failure load was inconsistent and about 35% of the failure load of the rod with made with epoxy. Microscopy shows many voids and cracks so the poor results are easily explained.Although the results could not be used to determine the potential of a rod based on a PPS matrix, the manufacturing method was proved to be a feasible way to produce a rod with the desired layup. The rod extracted easily from the mandrel and a continuous process seems feasible. Tensile tests on laminates of the PPS impregnated tape showed satisfying material properties.A study of different layups for the rod has also been conducted. Rods with layups [±45°] and [±80°/±9°] has been wound and tested with external overpressure and axial compression. Compared with the previously tested [±80°]-rod they showed marginally less pressure capacity, but at the compression test the [±80°/±9°] layup proved to be the best configuration due to its longitudinal fibers.Future work based on this study should focus on improving the manufacturing method of the PPS-rod. An adhesion test should also be conducted to determine how the PPS hoop rod bonds with a pultrusion resin. Temperature resistance is also an issue not discussed in this study and needs to be investigated as well as long term testing and the effect of creep.