PROBABILITY OF NO-FAILURE OPERATION OF THE SURFACE PART OF OIL-CONTAINING REINFORCED CONCRETE MARINE STATIONARY PLATFORMS OF GRAVITATIONAL TYPE

Abstract

The development of offshore hydrocarbon deposits in Russia contributes to the introduction of new types of stationary offshore gravity-type platforms. The construction of these facilities should be technically and economically feasible, while ensuring the required reliability and durability. One of the reliability criteria is a guaranteed forecast of the life cycle of the platforms, which may cause the platform to stop working prematurely for repair and restoration work. Therefore, the search for optimal methods of life cycle assessing is an urgent task. An assessment of the impact of operating environments on reinforced concrete platforms showed that chloride ions and carbon dioxide in the zone of variable moistening of the trunk part of the caisson have the greatest impact. The article provides an analysis of foreign regulatory and technical documents in the field of ensuring the durability of concrete and reinforced concrete in comparison with the domestic standard. The latter showed significant lags in requirements for primary protection measures, namely in ensuring the density of concrete, cement consumption, etc. The results of the analysis of the life cycle of reinforced concrete when exposed to carbon dioxide taking into account the «Duracrete» model for the surface part of the «Berkut», «Astokhskaya-B» and «Pelytun-Lunskaya-A». The parameters of the life cycle of the platform were determined, i.e. the reliability index and the risk probability, which showed that with a protective layer thickness of 50 mm, a complete loss of reliability will occur in 100 years, the intersection of the reliability index curves and the probability of risk will occur in the period of 30 - 40 years. In order to clarify the beginning of the first repair work, the authors proposed an additional definition of the «probability of no-failure operation» of the offshore platform. Calculations have shown that this period may occur 25 years after the start of operation.