Reliability-Based Optimization of Multi-Component Welded Structures

Abstract

Sufficient safety of welded structures against fatigue damage is achieved through the use of several safety procedures, design of the structure, quality control of the welding procedure during fabrication, and inspection for fatigue cracks with subsequent repair of detected cracks. Each safety procedure has a certain cost, and it is important to minimize the total expected cost over the lifetime of the structure. The present paper presents a probability-based optimization procedure defining optimal initial design, quality of welding procedure at fabrication, time of inspections, quality of inspections, and length of weld to be inspected at each inspection for a continuous weld. The cost considered in the optimization is cost-related to initial design, cost of fabrication, cost of inspection, expected repair cost, and expected failure cost. The probabilistic optimization problem is formulated for a homogeneous continuously welded structure containing hazardous material for which no leakage is permissible. The weld seam considered has multiple potential crack initiation sites from weld defects, where all the crack initiation sites are exposed to the same stochastic loading condition. Two models are applied to define the distribution of weld defects over the weld seam: a model where the locations of the crack initiation sites are known, and a model where the locations and number of crack initiation sites are unknown and described through a homogeneous Poisson distribution process. Uncertainties in the long-term stochastic load process, the fatigue strength, and the crack size of the different initial defects are considered in the procedure.

Risk-Based Fatigue Design Considering Inspections and Maintenance

“…The framework is applied to the optimization of the thickness, inspection times and inspection quality of a jacket 4 Mendoza, July 27, 2020 joint. Cramer and Friis-Hansen (1994) use this model to address optimal design, fabrication and inspection length for welded components with several hot-spots. Moan et al (1993) proposes a relaxation of the design Palmgren-Miner's sum as a function of the inspection program.…”

Incorporation of risk and updating in inspection of fatigue-sensitive details of ship structures

“…Consequently,uncertainties should be incorporated within the risk-informed decision making and updating. During the past few decades, the field of ship structural reliability assessment has been developed considerably (Cramer and Friis-Hansen 1994;Mansour et al 1996;Wirsching et al 1987;Lukic and Cremona 2001a;Ku et al 2004;Kwon and 3 Frangopol 2012;Rabiei and Modarres 2013). In its most broad terms, structural reliability is a measure of the probability of a system's survival givena limit state.…”

System Effects in Generic Risk-Based Inspection Planning

“…The effect of dependencies of one hot spot on another has been investigated in some studies, see e.g. Moan and Song [4], Cramer and Friis-Hansen [5], Faber and Sorensen [6] and Lotsberg et al [7]. In Faber et al [8] an informal decision analysis is proposed where the number of considered elements is reduced in a consistent and systematical way.…”