Probabilistic Analysis of Cracking Phenomenon in a Mixing Tee Under Thermal Fatigue

The paper provides a feasibility study of crack initiation and propagation in a mixing zone of an austenitic piping subjected to thermal fatigue loading. The analysis employs input data generated within the European research project THERFAT. A deterministic analysis performed using conservatively selected boundary conditions revealed high stresses in a mixing tee giving rise to fatigue damage. To account for the uncertainties, scatter and randomness of the thermal-hydraulic data and material properties, statistical data treatment and probabilistic methods are applied. Experimental measurements of temperature fluctuations obtained on austenitic thin-walled models are first employed to estimate the heat transfer coefficient. Then temperature and stress calculations are performed for a realistic piping geometry, and time to crack initiation is evaluated based on the fatigue design curves. The derived distribution function for the component life-time is compared with a deterministic assessment obtained using conservative assumptions on heat transfer conditions and material data. A possibility of crack propagation into the pipe wall is analyzed.