Polyurethane sealing discs on cleaning pigs-characterization and dynamic behaviour
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Pipeline pigging enhances flow rate and corrosion control. Pigging is made possible by the sealing element of the pig, of which polyurethane is the chief material used. Polyurethane raw materials are; polyols, isocyanates, water, methylene chloride, catalyst, chain extenders, colourants, air and additives. These raw materials are combined on 'systems' rather than a straight-forward formula, and are formulated to achieve predetermined properties in order to suit end applications. The main aim of this thesis is to develop a deeper understanding of keeping pipeline as much as possible to the as-built condition, as efficient and predictable seal discs facilitate safe and efficient pigging. Keeping maximum continuous flow reduces cost and also increase the life span of the pipeline. This is achieved by the understanding precisely shore grade 65, 75 and 85 used for pigging operations. The structure of this thesis is divided into four parts. The first part involves the determination of the material properties of shore grade 65, 75 and 85 at temperatures of 20°C, 40°C, 60°C, 70°C and 80°C. The material properties of shore grade 65, 75 and 85 are achieved from the stress-strain curve of the polyurethane at the different temperature using tensile test machine. Shore grades are heat treated to the required temperature of minimum of 12 hours in an oven or refrigerator before the tensile test. The second part of the thesis is using the stress - strain data as an input into finite element material database, hence finite element model of the seal discs geometry is created to determine resulting deflection, static reacting forces on the wall. This was achieved by the application of step incremental displacement on the pig discs into the 8’’ pipeline in order to generate the static behavior of pig of shore grade 65, 75, & 85 at different temperature. The third part of the thesis involves the use of stress-strain data to perform transient dynamic analysis of seal discs with shore grade 65, 75 and 85 at 20 °C. This is to determine resulting deflection, and “kinetic reacting forces on the wall”. This was achieved by the application of differential pressure on the pig so as to drive it into the 8’’ pipeline in order to generate the dynamic behavior of pig (shore 65, 75, & 85) at 20 °C. Finally, a verification test on the time travel of pig (shore grade 65, 75 & 85) on a test rig 8’’x12m long was performed in IK AS facility Forus.
Master's thesis in Offshore technology : marine and subsea