Quantitative Non-Destructive Testing: The integration of non-destructive testing and probabilistic fracture mechanics

Abstract

Nowadays, the non-destructive evaluation of structural components allows the detection of cracks and other types of flaws with a high resolution. When cracks are involved in mechanical failure events, fracture mechanics provides concepts for lifetime prediction of components when component geometry, material characteristics and load intensity under steady state or impact loading are known. Under fatigue loads additionally material laws have to be observed. Bringing together these disciplines, quantitative non-destructive testing for lifetime prediction is possible. Due to measurement uncertainties related to crack size geometry, material parameters' inherent scatter and load history are not unambiguously assessable. Therefore, statistical distributions are assumed (e. g. Normal or Weibull) and probabilistic fitness for service assessment (FFS) is performed rather than a deterministic one. This concept of combining quantitative non-destructive testing and probabilistic FFS assessment works well for metals. The fracture mechanics analysis under predominantly static loading has at its core the so called Failure Assessment Diagram (FAD). Hereby, an illustrative tool for condition monitoring is supplied which is also accepted in design rules and codes. Software which addresses the criticality of cracks and other flaw types in the shell of cylindrical pressure vessels was developed. The application of the concept of probabilistic fracture mechanics using Monte Carlo simulation is demonstrated for one example from pipelines.