Failure Pressure Assessment of the Circumferentially Flawed Heat Exchanger Tubes

Abstract

Since the structural integrity of thin-walled tubes in the heat exchanger is crucial from the viewpoint of safety and reliability, the integrity evaluation for flawed tubes is quite important. Accurate estimation of the failure pressure is a key element of the structural integrity assessment. With regard to the prediction of the failure pressure, most of preceding researches have been focused on the limit load approach. However, the integrity assessment scheme based on the elastic plastic fracture mechanics concept has not been settled despite of its accuracy and efficiency. In this paper, three-dimensional finite element analyses assuming elastic plastic material behavior are carried out for the thin-walled tubes with various sizes of the circumferential flaws. As for the flaw location, both the top of tube sheet and transition regions are considered. The flaw instability is evaluated by comparing the driving force with the fracture toughness of the tube material. Analysis results show that the elastic plastic fracture mechanics approach accurately predicts the failure pressures compared to the experimental data. Thus, it is thought that the elastic plastic fracture mechanics concept can be applied to the integrity assessment of the heat exchanger tubes with the circumferential through-wall flaws.