Test results and calculations concerning crack propagation under cyclic thermal chock loading on a pressure vessel nozzle

Abstract

Abstract The mechanical-technological and nondestructive tests to determine the state of the HDR pressure vessel revealed that no significant defects were present. For this reason it was proposed to weaken the pressure vessel purposefully by cyclic thermal shock applied locally in the A2 nozzle region as to bring about defined natural defects for the purpose of NDE measurements and fracture mechanics analysis. Throughout the duration of the test, operating variables and changes under thermal shock loading, such as strain, temperature and crack openings were recorded. After a total of 1751 thermal shock cycles had been attained a limited destructive test was made on nozzle A2 for the purpose of determining the actual geometry of individual cracks. For precalculation of crack propagation cyclic, stress intensity factors were determined on the basis of 2D and 3D linear elastic FE stress analysis. The crack growth was determined by integrating the Paris correlation. The results of the thermal shock test series V66 on HDR nozzle A2 show that further investigations into the behaviour of components which are cracked and exposed to pressurized water under superimposed static and cyclic load components are necessary in order to obtain crack propagation assessment criteria valid for the crack front.