FATIGUE DIAGRAMS OF RESTORED WELDED COMPOUNDS OF MARINE STATIONARY PLATFORMS FOR OIL AND GAS PRODUCTION ON THE SHELF

Abstract

Background The world is actively developing offshore oil and gas fields. Various offshore structures are actively used for offshore mining, including offshore stationary platforms. During operation, these platforms are subjected to various influences (wave, wind, ice, etc.), which leads to the occurrence of variable stresses. The acting alternating stresses activate fatigue processes in welded joints. Therefore, knowledge of the stress state of the welded joints of offshore stationary platforms is the key to understanding the fatigue processes occurring in them. The author shows that the theory of strength used to assess the stress state of welded joints of offshore platforms does not fully reflect the actual stress state in the welded joints of the platform due to the fact that inhomogeneities in the stress state of the welded joint and the presence of local points with an increased stress concentration in it are not taken into account. In addition, the issue of assessing the residual life of welded joints after their repair has not been resolved. It is obvious that different repair technologies for welded joints will provide a different value of their resource. Aims and Objectives The aim of the work was to conduct experimental studies that allow us to study the fatigue parameters of welded joints of marine stationary platforms repaired by various technologies. Based on this information, the author set the goal of constructing fundamentally new fatigue diagrams of repaired welded joints, which will allow in the future to calculate the residual life of these joints. In this case, the question of the influence of local factors such as the diameters of the elements being welded, their wall thickness, the contact angle of the connected elements and other factors on the local stress concentration was studied. Methods To solve the problems specially designed experimental plants were used. In order to accumulate primary fatigue fractures, initial fracture was carried out at these plants, then the welded joint was restored using various repair technologies. Then repeated destruction was carried out. The information obtained as a result of the experiments was processed. The experimental method for studying the residual life of repaired welded joints remains one of the most accurate methods for obtaining information. Results Based on the studies, it can be concluded that for almost all repair technologies, the endurance limit will be almost at the same level (from 13 to 15 MPa), however, the base of the fracture cycles of fatigue diagram will have completely different values, which suggests that with a further determination of the residual life, its various values will be obtained for each of the described repair technologies.