Thinned Pipe Management Program of Korean Nuclear Power Plants

Abstract

Local wall thinning and integrity degradation caused by several mechanisms, such as flow accelerated corrosion (FAC), cavitation, flashing and/or liquid drop impingements, are a main concern in carbon steel piping systems of nuclear power plant in terms of safety and operability. Thinned pipe management program (TPMP) had been developed and optimized to reduce the possibility of unplanned shutdown and/or power reduction due to pipe failure caused by wall thinning in the secondary side piping system. This program also consists of several technical elements such as prediction of wear rate for each component, prioritization of components for inspection, thickness measurement, calculation of actual wear and wear rate for each component. Decision making is associated with replacement or continuous service for thinned pipe components. Establishment of long-term strategy based on diagnosis of plant condition regarding overall wall thinning is also essential part of the program. Prediction models of wall thinning caused by FAC had been established for 24 operating nuclear plants. Long term strategies to manage the thinned pipe component were prepared and applied to each unit, which was reflecting plant specific design, operation, and inspection history, so that the structural integrity of piping system can be maintained. An alternative integrity assessment criterion and a computer program for thinned piping items were developed for the first time in the world, which was directly applicable to the secondary piping system of nuclear power plant. The thinned pipe management program is applied to all domestic nuclear power plants as a standard procedure form so that it contributes to preventing an accident caused by FAC.

Calculation of Steel Pipeline Corrosion Depth at the Galvanic Corrosive Element Operation

“…In the published works containing descriptions of the methods for calculating the rates of corrosion wear on the basis of operational control data, it is noted that the calculation is empirical. The studied methods take into account factors that significantly increase the calculating error [13][14][15][16]. It has been proved by researchers that the main role in assessing the safety of pipelines operation in the presence of cracks in the insulation coating belongs to studies of the corrosion rate and depth.…”

Repeated measurements and quality of estimates in the analysis of NPP pipeline erosion-corrosion wear

“…The ECW rate of a component of equipment or a pipeline, calculated from the results of one-time control of wall thicknesses, contains many uncertainties (Baranenko et al 2016) that reduce the accuracy of estimates (Bridgeman and Shankar 1991;Lee et al 2003;Moolayil 2007Moolayil , 2008; Baranenko et al 2010). These factors include as follows:…”

Evaluation about Detection of Defects in the Nuclear Piping Loop System Using Lock-in Infrared Thermography

“…The wall-thinning defect progresses without any sign of damage and commonly occurs in the base metal as well as in the weld, making it difficult to detect the defect through the conventional operation test. For this reason, nuclear power plants operate a separate wall-thinning defect management program and accordingly carry out wall-thickness test for parts with high possibility of wall-thinning defects [3,4]. For inspection of the pipe thickness, ultrasonic test is most commonly used but it takes a lot of time since it has to measure the thickness at all lattice points.…”