Papers by Author: Katsumasa Miyazaki

Abstract: If multiple discrete flaws are detected, alignment and combination rules are used to determine whether the flaws should be treated as non-aligned or as coplanar, and independent or combined flaws. Alignment and combination rules for multiple flaws are provided in Fitness-for-Service (FFS) procedures of many codes and standards in the world. However, these alignment and combination rules defined in the FFS are different. This paper aims to give overview of alignment and combination rules for multiple flaws in FFS procedures. In addition, experimental data on flat plates with parallel planar flaws are compared with the alignment rules of these FFS procedures.

Abstract: To achieve a rational maintenance program for aged Light Water Reactor components, it is important to establish and to improve the flaw evaluation criteria. The current flaw evaluation criteria such as ASME Boiler and Pressure Vessel Code Section XI are focused on Class 1 piping which usually shows relatively higher toughness. On the other hand, flaw evaluation criteria suitable for Class 2, 3 piping with moderate-toughness are also required because some Class 2, 3 piping systems are as important to plant safety analysis as Class 1 piping. In this study, both analytical and experimental studies were conducted to provide the evaluation method of fracture loads for acceptance criteria for Class 2, 3 piping. Pipe fracture tests by four-point bending were conducted on circumferentially cracked carbon steel pipes with moderate-toughness. The Net-Section Collapse criterion overpredicted experimental maximum loads for through-wall-cracked pipes, which suggested the necessity of Z-factor. Three-dimensional finite element analysis and simplified analysis based on the reference stress method were conducted to complement the limited pipe fracture tests. It was ascertained that the reference stress method always gave moderately conservative fracture loads compared with the finite element analysis and pipe fracture tests as well. Z-factor for Class 2, 3 piping was then derived and formulated using the reference stress method. Z for Class 2, 3 piping was affected by radius-to-thickness ratio, and was higher than Z for Class 1 piping in the present codes.

Abstract: JSME Code on Fitness-for Service for Nuclear Power Generation Facilities defines allowable subsurface flaws for Class 1 ferritic vessels in the Acceptance Standard. When detected subsurface flaws are located near vessel surface, the subsurface flaws are transformed to be surface flaws for assessment of acceptability in JSME Code. This paper describes inconsistency of the subsurface flaws transforming to surface flaws and introduces an improvement method for the subsurface flaws.