Masakazu Hisatsune

Ductile Fracture Behaviour of Class 2 and 3 LWR Piping and Its Implications for Flaw Evaluation Criteria

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.

Failure Behavior of Pipe Having Local Wall Thinning in Downstream Region of Orifice

Monotonic four-point bending tests were conducted using pipe specimens having orifice undergoing local wall thinning. The effects of local wall thinning on the fracture behaviors of pipe were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area were l = 100 mm in eroded axial length, d/t = 0.5 and 0.8 in eroded ratio, and 2θ = 180° in eroded angle. The area undergoing local wall thinning was subjected to either tensile or compressive stress. Failure type could be classified into ovalization, local buckling, and crack initiation, depending on eroded ratio, and stress at the eroded area. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors. The crack initiation point could be successfully predicted by the criterion proposed by Miyazaki et al..Copyright

Fracture and Deformation Behaviors of Tee Pipe With Local Wall Thinning Under Monotonic Bending

Monotonic four-point bending tests were conducted using tee pipe specimens having local wall thinning. The effects of local wall thinning on the fracture behaviors of tee pipes were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area were l = 100 mm in eroded axial length, d/t = 0.5 and 0.8 in eroded ratio, and 2θ = 90° in eroded angle. The area undergoing local wall thinning was subjected to either tensile or compressive stress. Fracture behaviors of the tee pipes were compared with those of straight pipes. It was found that fracture type could be classified into ovalization, local buckling, and crack initiation, depending on pipe shape, eroded ratio, and stress at the eroded area. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors.Copyright

Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities: Part 1 — The Work Schedule of Project and a Seismic Design of Crossover Piping System

This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities” [1]–[4]. This part describes the work schedule of this project and the summary of a seismic design for crossover piping system.Since the Southern Hyogo Prefecture Earthquake in 1995, a seismic isolated design has been widely adopted for Japanese typical buildings. The Japanese government accepted utilizing seismic isolation technology for nuclear power facilities with the 2006 revision of the “Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor Facilities”. Under these backgrounds, the Japan national project with the participation of all electric power companies and reactor vendors has been started from 2008 to develop seismic isolation systems of nuclear power facilities under the support of the Ministry of Economy, Trade and Industry.In the design of seismic isolated plant, the crossover piping systems, such as Main Steam line and other lines related to the safety system have the important roles for overall plant safety. Therefore, the design of multiply supported piping systems between isolated and non-isolated buildings is one of the major key issues.This paper focuses on the seismic response analysis of Main Steam crossover piping between seismic isolated Reactor Building and non-isolated Turbine Building. Multiple input response spectra and time history analyses of the crossover piping have been performed and the structural integrity of piping and the validity of the multiple input analysis method have been verified based on comparisons with the results obtained by conventional response spectrum analysis using enveloped floor response spectrum.Copyright

Effect of Local Wall Thinning on Low Cycle Fatigue Behaviors of Elbow with Internal Pressure : Estimation of Fatigue Life based on Revised Universal Slope Method

Low−cycle fatigue tests and finite element analysis were conducted using100A elbow specimens made of STPT410 with local wall thinning in order to investigate the influences of local wall thinning on the low−cycle fatigue behaviors of elbows with internal pressure.Local wall thinning was machined on the inside of the elbow in order to simulate metal loss by flow−accelerated corrosion. The local wall thinning located in three different areas,called extrados,crown and intrados.Eroded ratio(eroded depth/wall thickness)was0.5 and0.8.The elbow specimens were subjected to cyclic in−plane bending under displacement control with internal pressure of0 or9MPa.Fatigue failure was classified into two types.The one is the type of fatigue crack initiation and another is the type of crack initiation after local buckling.In the type of fatigue crack initiation,fatigue crack initiated at crown and propagates to the axial direction.In the type of crack initiation after local buckling, at first local buckling occurs and secondary,crack initiates at the same place and propagates to the circumferential direction.The low−cycle fatigue lives of elbows were predicted conservatively by the revised universal slope method.

Failure Behavior of Carbon Steel Pipe Having Local Wall Thinning Near Tee Joint

Monotonic four-point bending tests were conducted using tee pipe specimens having local wall thinning. The effects of local wall thinning on the failure behaviors of tee pipes were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area were l = 100 mm in eroded axial length, d/t = 0.5 and 0.8 in eroded ratio, and 2θ = 90° and 180° in eroded angle. The area undergoing local wall thinning was subjected to tensile stress. It was found that fracture type could be classified into ovalization or crack initiation, depending on eroded ratio. Three-dimensional elasto-plastic analyses were also carried out using finite element method to discuss the effects of position and geometries of wall thinning in both tee pipes and straight pipes.Copyright

Approach to Establish Flaw Evaluation Method for Class 2 and 3 Light Water Reactor Pipes

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 from the viewpoints of in-service inspection request, reduction of operating cost, and systematization of consistent code/standard. In this study, both analytical and experimental studies were conducted to provide the allowable flaw sizes for acceptance standards as well as the evaluation method of fracture loads for acceptance criteria for Class 2, 3 piping. An approach to identify the allowable flaw sizes for acceptance standards was newly proposed using the failure assessment curve, and allowable flaw sizes for Class 2 3 piping were tentatively derived based on the approach. Cracked pipe fracture tests together with finite element analysis and simplified fracture analysis were also conducted using typical moderate-toughness pipe materials. The experimental and analytical results were reduced to the Z-factor to predict fracture loads of Class 2, 3 cracked piping.Copyright

Ductile Fracture Behavior of Carbon Steel Cracked Pipes With Moderate-Toughness

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 and Class 3 piping with moderate-toughness are also required because some Class 2 and Class 3 piping systems are as important to plant risk analysis as Class 1 piping. In this study, fracture experiments by four-point bending were conducted for circumferentially cracked pipes. Tested pipes were made of moderate-toughness carbon steel, STPT410 carbon steel. Ductile fracture behavior and load-carrying capacity were compared with those from elastic-plastic fracture mechanics analysis. As a result, it was ascertained that ductile fracture behavior could be well predicted by fracture mechanics analysis using J-integrals. A Z-factor approach applicable to moderate-toughness pipes was also discussed.Copyright