Abstract
Seismic motions are likely to cause large displacements in nuclear power plants because the main mode of their piping systems is dominated by the low-frequency region. Additionally, large relative displacement may occur in the piping systems because their supports are installed in several places, and each support is subjected to different seismic motions. Therefore, to assess the seismic performance of a piping system, the relative displacement repeated by seismic motions must be considered. In this study, in-plane cyclic loading tests were conducted under various constant amplitudes using test specimens composed of SCH 40 3-inch pipes and a tee in the piping system of a nuclear power plant. Additionally, an attempt was made to quantitatively express the failure criteria using a damage index based on the dissipated energy that used the force–displacement and moment–deformation angle relationships. The failure mode was defined as the leakage caused by a through-wall crack, and the failure criteria were compared and analyzed using the damage index of Park and Ang and that of Banon. Additionally, the method of defining the yield point required to calculate the damage index was examined. It was confirmed that the failure criteria of the SCH 40 3-inch carbon steel pipe tee can be effectively expressed using the damage index.
Highlights
Energy plants, including nuclear power plants, have many piping systems that transport fluids and gases
The failure criteria for an SCH 40 3-inch carbon steel pipe tee in a nuclear power plant piping system were quantified using the damage index based on the force–displacement (P–D)
In-plane cyclic loading tests were conducted at constant amplitudes until leakage occurred
Summary
Energy plants, including nuclear power plants, have many piping systems that transport fluids and gases. A study was conducted to examine the out-of-plane failure behavior of pipe tees using component tests and finite element analysis [14] These studies highlighted the importance of defining the limit state, which is the actual failure of the vulnerable parts of piping systems, to ensure the safety of nuclear power plants [15,16]. Studies to examine the failure modes of the vulnerable parts of piping systems and to quantify leakage, which is the actual failure, have been conducted based on the results of component tests to increase the reliability of seismic fragility analysis. In-plane cyclic loading tests were conducted via displacement control using test specimens composed of a tee and pipes in the piping system of a nuclear power plant. ±80 mm. tests were conducted using three test specimens for loading amplitudes of ±10, ±20, cyclic loading
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