Structural Reliability Applications in Developing Risk-Based Inspection Plans for a Floating Production Installation

Abstract

This paper outlines the essential steps taken in performing structural reliability calculations during the process of laying out a risk-based inspection program. The structural reliability analysis described in this paper essentially takes the deterministic finite element method (FEM) stress/fatigue analysis results, coupled with uncertain degradation mechanisms (e.g. corrosion rate, crack propagating parameters, etc.), and tracks the time-varying structural reliability index of the structural components under consideration. This can then be used to determine the timing for inspection of structural components. For the assessment of structural strength, an efficient and straightforward method is proposed to calculate the time-variant reliability index. This method is verified by an example problem and compared to the random process first-passage reliability solutions. Load combination issue is briefly discussed, in which an approach stems from the ABS Dynamic Loading Approach (DLA) coupled with concepts from Turkstra’s rule. This proposed simplistic load combination approach is verified through an example problem in which the result is compared to the solution calculated from a more sophisticated approach. Establishment of target reliability levels is also briefly discussed. For the assessment of fatigue behavior for welded connections, both S-N curve based and fracture mechanics based reliability methods are discussed. Their usefulness will be discussed in terms of both inspection interval as well as selecting the proper sampling percentage of connections to inspect. Statistical correlation among a group of similar connections is discussed to assist the selection of appropriate locations in the population of the aforementioned sampling. The usefulness of fatigue reliability analysis is also demonstrated by an example problem.

Structural Reliability Applications In Risk-Based Inspection Plans And Their Sensitivities To Different Environmental Conditions

“…The details on the probabilistic distributions for R B and S B can be found in [1]. R B and S B are the model uncertainty factors for the resistance and load calculations, respectively.…”

“…Details of a structural reliability methodology applicable to risk based inspections on a ship-shaped floating production vessel have been published in a companion paper [1]. From that paper, a flow chart of this methodology is shown in Figure 1.…”

“…For the example vessel considered in [1], direct seakeeping and global finite element analysis were conducted to identify representative high-stressed structural components of all types for further structural reliability analyses. The model plot of this global finite element analysis is shown in Figure 2.…”

Flexible Approaches to Risk-Based Inspection of FPSOs

“…These cases represent the more comprehensive approach to RBI plan development [11], [12]. The approach for both the Structural Reliability Assessment (I) and Structural Reliability Assessment (II) cases are generally the same, but there are some significant differences in the structural analysis which result in variations in the reliability analyses used to set inspection frequencies and scopes.…”

“…The American Bureau of Shipping (ABS) has been involved in the development of and the assistance with implementation of a multi-level risk-based inspection methodology [7][8][9][10] ranging from a simplified approach using standard design analysis data up through to a sophisticated approach that relies on additional probabilistic analyses [11][12]. The level selected depends on a number of factors including inspection objectives, condition of the asset, availability of design analysis information, etc.…”