REMAINING LIFE ANALYSIS FOR A PRESSURE-VESSEL SUBJECTED TO CYCLIC LOADS BASED ON FRACTURE-MECHANICS

Fracture mechanics has evolved into an engineering tool able to solve problems related to the safety of structures containing defects. In practice, however, a wide choice of parallel methods as well as unsolved discrepancies in the theory requires engineering judgement and pragmatism. In this paper a practical case study is presented, concerning a maintenance strategy assessment performed on a welded pressure vessel. The pressure vessel is analysed in terms of leak-before-break arguments, proof test logic, fatigue initiation life, defect initiation and unstable growth critical sizes, fatigue crack propagation that leads to fracture or leakage, as well as probabilistic methods based on defect size distributions and NDE detection probabilities. The paper deals with some background to the theories employed, the different steps of the assessment methodology, as well as with the interpretation of the result to design a practical and safe maintenance strategy.