Practical Application of Probabilistic Fracture Mechanics for Structural Integrity Management

Abstract

Abstract This paper describes an approach to the estimation of time dependent structural reliability of crack like features based upon codified fracture mechanics (e.g. BS7910, API579) techniques. A numerical simulation methodology is used to consider statistically defined through life wave load effects generated using recognized hydrodynamics codes and statistically defined defect, structural geometry and material property data, in estimating probabilities of structural failure. The approach outlined in this paper may be used to support through life integrity management of pipe, platform and ship structures subjected to uncertain variable amplitude loading. An FSO double bottom hull structure cracking scenario is used in this application of fracture mechanics in the prediction of the probability of achieving a given fatigue life considering the crack growth and final failure using an automated analytic tool. The streamlined analysis tool will be described along with its inherent assumptions and approximations in demonstrating the sensitivity of the structural reliability estimates to the problem data and assumptions. The process employed and results presented are considered unique in terms of their ability to describe the time dependent nature of fatigue reliability considering a range of defect types and structural geometries. The paper provide guidance and demonstrate through a practical application, the utility of fracture mechanics in considering structural reliability in developing critical flaw sizes to support inspection and repair criteria. The same techniques will also be used to define inspection intervals while considering the influence and significance of uncertainties in load and material properties. In presenting this sample application, the intended future application and further development of this technology is presented for discussion.