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In a previous study [1], the seismic behavior of a piping system with local thinning elbow caused by liquid droplet impingement erosion (LDI) was evaluated using hybrid seismic testing method in Central Research Institute of Electric Power Industry (CRIEPI). In those studies, torsional buckling and wrinkles occurred at locally wall thinning elbow under large amplitude seismic motion of eight times the design basis earthquake based on the allowable stress level. It was concluded that buckling should be considered as a failure mode. In this study, the torsion buckling under out-of-plane bending of locally wall thinning elbows could be demonstrated by finite element analyses. Torsion buckling deformation agreed well with test result and the critical buckling deformation was clarified by comparing parameter analyses. The buckling formula was proposed to prevent the torsion buckling of locally wall thinning elbow.

The earthquake-proof safety of piping systems with local wall thinning due to liquid droplet impingement erosion (LDI) was evaluated using a hybrid experiment which has been incorporated a numerical analysis of the whole system with a static loading test of elbow pipe model. Seismic performance effects of wall thinned elbow were clarified by comparing three cases of different thickness elbow models such as no defect, 50% defect and 75% defect. No damage was observed for in-plane and out-of-plane bending of elbows in the 75% condition under a seismic load equal to five times the design basis earthquake required to reach allowable stress level. In addition, torsion buckling occurred and through wall crack penetrated by cyclic loading under eight times large amplitude the above mentioned seismic motion.Copyright © 2014 by ASME

Pipe wall thinning is a one of the major degradation mechanisms in aged nuclear power plants (NPPs). In Japan, the seismic safety of wall thinning piping system during earthquake must be evaluated in aged NPPs. Seismic safety of piping systems with wall thinning had been investigated by other researchers using shaking table tests of reduced scale and numerical analyses. However, there exist the limitations such as the scale effect of pipe model for shaking table tests and the limit of the evaluation for numerical analysis concerning the criteria of pipe integrity. By the way, elbow can be one of the most important elements to evaluate the seismic safety of piping system. So, in order to evaluate seismic safety of piping systems with wall thinning elbow, hybrid tests have been conducted, in which the seismic response of the whole piping system is treated as a numerical model, and the real piping is used only for the element on which the transformation and damage locally concentrated. The through-wall crack only occurred in the case of a uniform thinning model although cracks didn’t penetrate in the non thinning model and the local thinning model. In the experimental condition, the failure mode of wall thinning elbow under seismic loadings had been low cycle fatigue, and effectiveness of this evaluation method has been demonstrated.

Flow accelerated corrosion (FAC) is one of the pipe wall thinning phenomena. There are a few prediction equations for FAC under the two-phase flow condition, but their accuracy is uncertain. In this study, these equations are summarized. A new prediction equation is proposed, in which the liquid film velocity near the wall is taken into account. Also, FAC experiments with water-steam two-phase flow are performed. The thinning rate is predicted by calculation and compared with the experimental value.Copyright © 2013 by ASME

Flow accelerated corrosion (FAC) and liquid droplet impingement erosion (LDI) are the main pipe wall thinning phenomena in piping system of power plants in Japan. Authors have promoted the development of prediction method to evaluate local thinning trend by FAC/LDI. To apply the method to pipe wall thinning management in power plants, it is required to be transformed into practical tools for easy usage. In Japan, discussion is being made to considerate the introduction of prediction tools into wall thinning management based on wall thickness measurement at present. Authors have simplified their FAC/LDI models to predict wall thinning trend one-dimensionally along piping layout, and applied to actual thinning data of power plants. With PWR’s FAC data and BWR’s LDI data, maximum thinning rate for each pipe elements were roughly predictable with considerable accuracy. Especially for high thinning rate data, which is important in plant management, the model was able to evaluate within the factor of 2. By installing this model, prediction software “FALSET” was developed, equipped with practical functions for the management. With the further verification and improvement of each function, there are prospects for this software to be utilized as a management tool in power plants.

Liquid droplet impediment erosion (LDI) is a pipe wall thinning phenomena that a droplet accelerated by steam flow attacks pipe surface. It is difficult to evaluate LDI behavior in the system of NPP. Therefore, in current pipe wall thinning management, the pipe element is replaced conservatively when it is recognized to become thinner by pipe wall thinning measurement result. If LDI behavior at each point of the system can be estimated, it is possible to measure the pipe wall thickness and replace the pipe element at an appropriate time, in accordance with reasonable pipe wall measurement schedule. CRIEPI has constructed the evaluation system for LDI by using flow dynamics. This paper is concerned with the following items: • the applicability of the LDI evaluation system by a comparative verification between pipe wall thinning rate calculated by LDI system and that by actual measurement result; • establishment of remaining life assessment method of pipe in LDI environment by using LDI model.Copyright © 2009 by ASME

An evaluation system for liquid droplet impingement erosion (LDI) has been developed to predict the LDI location and the wall thinning rate. The results from previous studies and knowledge are organized and the LDI evaluation system that involves the “1. Flow Evaluation Step” and “2. LDI Evaluation Step” is suggested. The flow evaluation step includes the mass flow rate evaluation, flow distribution evaluation and droplet behavior evaluation. The LDI evaluation is conducted with LDI sensitivity function. The LDI sensitivity was test-evaluated in the steam piping model. The results show that the 1st and last elbows have higher LDI sensitivity because of the velocity condition. We also found that the droplet collision frequency is important when evaluating the LDI sensitivity.Copyright © 2009 by ASME