Updating the Distributions of Uncertain Parameters Involved in Fatigue Analysis

Abstract

Fatigue is an important failure mode in offshore jacket platforms. To evaluate the fatigue damage, these platforms are periodically inspected during their lifetime. Regarding fatigue damage, the information from inspection consists of crack measurement. A Bayesian framework can be used to update the probability distribution of the crack size. The main purpose of this study is to develop a framework to update the probability distributions of all uncertain parameters involved in the fatigue crack growth analysis. This methodology maximizes the benefit of the inspection results by updating several uncertain parameters involved in the fracture mechanics approach. Two sets of cracks are used to obtain the updated distributions for uncertain parameters; prior cracks and simulated reality cracks. By comparing these cracks, the updated distributions for uncertain parameters are obtained. The updated crack size distribution can be used to update the estimation of the probability of failure. To demonstrate the developed framework, a tubular joint in a specific jacket platform is considered and the framework is applied for that joint. The results of the developed methodology indicate that the updated distributions of uncertain parameters shift towards the simulated reality distributions.

Determining Factors of Fixed Offshore Platform Inspections in Indonesia

“…Fixed offshore structures are commonly used for various purposes in offshore industries, especially oil exploration [1,2]. Since the first commercial production in 1971 of offshore areas, until now, Indonesia has had 613 units of fixed offshore platforms: 54.65% of these are more than 20 years old and 24.63% are 16-20 years old [3].…”

Fatigue Crack Monitoring of T-Type Joints in Steel Offshore Oil and Gas Jacket Platform

“…To assess fatigue damage, these platforms are regularly inspected over their life span. Fatigue damage inspection information mainly includes crack measurements [ 49 ]. Moreover, the fatigue reliability evaluation of welding joints is carried out using two different methods, the first is based on stress life curve, also called linear damage accumulation law, the second is based on the fatigue crack growth analysis, as well as failure standards [ 49 , 50 ].…”

“…Fatigue damage inspection information mainly includes crack measurements [ 49 ]. Moreover, the fatigue reliability evaluation of welding joints is carried out using two different methods, the first is based on stress life curve, also called linear damage accumulation law, the second is based on the fatigue crack growth analysis, as well as failure standards [ 49 , 50 ]. The first method is used during the design phase, to evaluate the reliability of the existing or planned design structure solutions [ 51 ].…”