Effect of wall thinning on deformation and failure of copper‐nickel alloy elbows subjected to low cycle fatigue

Abstract

Various industrial standards and safety regulations specify the minim number of cycles, which pressure equipment must tolerate during a single seismic event. The compliance with these standards and regulations is necessary in order to ensure safety and strength of critical structural components, eg, pressure pipe system of the primary coolant loop of nuclear reactors or condensed water supply of large hospitals or other large facilities. However, the strength can degrade with time due to flow accelerated corrosion causing wall thinning. Pipe bends are particularly susceptible to the localised corrosion, and, therefore, these structural elements need a special consideration. The current paper studies the effect of localised corrosion on low cycle fatigue behaviour of a copper-nickel elbows using experiment and finite element method (FEM). The outcomes of the study demonstrate a quite low reduction of low cycle fatigue life even at severe local wall thinning at different locations.

Low Cycle Fatigue Behavior of Elbows with Local Wall Thinning

“…The most interesting observation is the increase of fatigue life with the increase of the applied inner pressure. This behavior has also been found in carbon steel elbows, e.g., [6,20,21], and it can be explained by the inner pressure shielding effect: as the elbow specimen is pressurized, the bending moment is reduced and the overall stiffness of the structure is increased even though the displacement is maintained at an initial set value. In other words, it means that the applied bending load is relaxed by the inner pressure.…”