Probabilistic Approach for Determination of Thick Pressure Vessels Reliability

The study conducted for this paper attempts to provide a method for evaluating the integrity, condition, and behaviour of pressure vessels based on the fact that all significant parameters provide some form of stochastic distribution. It is possible to reduce the uncertainty in the assessment of the integrity of pressure equipment by evaluating the findings of the probabilistic approach in comparison to the conventional deterministic approach. Samples were taken from different parts of the vessel, different orientations of the initial notch and tests were performed in different laboratories. Testing of statistical hypotheses on the normality of the sets and the equality of the results was performed. The random variables included in the integrity assessment are considered as statistical distributions. The analysis included parameters obtained from experimental research such as yield strength, critical stress intensity factor and crack growth rate. The recording of the real characters of operating stresses depending on the production technology was performed. The analysis is carried out on thick-walled pressure vessels of the material grade 40Mn6. All results were used to define the failure function and the reliability function for two cases of load action and for hypothetical crack growth until reaching the critical length. The dependability level and reliability function limit values may be defined through experimental studies and then used to predict the remaining life, inspection intervals and fitness-for-service in the most realistic way possible.