Fatigue behavior of high-strength steel-pipe in offshore pipeline

Introduction. An approach to the development of a method for assessing the fatigue strength of an offshore high-strength steel pipeline has been presented. The effect of fatigue caused by cyclic loads has been well studied, the combined destructive effect of fatigue and corrosion has not been studied enough, although it has unexpected consequences and significantly reduces the life of the structure. The synergistic effect of both fatigue and corrosion acting simultaneously makes it difficult to determine the exact interaction between the two, but it is safe to assume that the corrosion fatigue is more than just a simple superposition of the two negative effects. While we can improve the fatigue strength of a material through heat treatment and alloying, if the material is in a corrosive environment the advantage gained can easily be completely neutralized, as the corrosive mechanism in play usually dictates the endurance limit in such a case. In fact, the difference in fatigue strength is most noticeable at lower stress values. Materials and methods. The most common approaches are based on mathematical models for assessing the durability of structures under low-cycle loading. The work was carried out with reference to existing and future offshore projects. Results. One of the advantages of the proposals developed are the requirements for testing the fatigue strength of offshore subsea pipelines of high-strength steel with a longitudinally oriented defect. The Load of the offshore pipeline is 0.766 % of the operating load, excluding accidental loads. These requirements are submitted for consideration to the Russian Maritime register of Shipping. Conclusions. In of civil engineering, ensuring the reliability of offshore subsea pipelines of high-strength steel with a longitudinally oriented defect under low-cycle loading is an urgent problem and is of theoretical and practical interest. The results were obtained by combining the calculated and - the empirical approach according to the method for assessing low-cycle fatigue of the offshore pipeline structure. Calculations show the need to monitor the state of the structures of the offshore underwater pipeline.