Reliability Centered Strategy for Mooring Integrity Management

Abstract

Petrobras has operated offshore production units on the Brazilian coast for over 25 years. Over time, its facilities are expected to degrade due to the variety of mechanisms of damage that the offshore environment provides. Mooring systems are among the assets that present degradation throughout the operation and understanding the integrity behavior of this system throughout its lifetime is extremely important for operational safety. Mooring lines installed in floating production units of Petrobras have a wide range of operating ages (2 to 30 years) and a diversity of mooring systems (Spread mooring semisubmersible, single point mooring FPSO and spread mooring FPSO). To optimize integrity management, a reliability-centered strategy was developed using available field data of mooring lines installed in floating production units of Petrobras. The database created for this study covered failure data, maintenance, and operational parameters of mooring line components installed between 1992 and 2021. Life data analysis was used to evaluate how the failure probability evolved with the lifetime. Therefore, the Weibull parameters of each mooring line component were estimated. The strategy aims to improve reliability and optimize life cycle cost, reducing corrective maintenance and avoiding production loss as a result. The results show that different mooring line components have different failure rate behaviors during their lifetime. Also, parameters such as mooring system type (single point mooring or spread mooring), the position of mooring lines (due to environmental conditions), and the presence of cathodic protection are important to predict the level of degradation of the components. Through the scenarios evaluated, it was possible to define critical systems where preventive maintenance should be done and the optimal time, to improve life cycle cost and reliability.