Ichiro Komura

The Influence of structures of Nickel Base Alloy Weld Metals on Flaw Detectability by Ultrasonic Test

Ultrasonic Test (UT) method is the most appropriate method in many kinds of non-destructive test methods because of capabilities for detection and depth sizing of flaw. But it is generally said that the flaw detection in nickel base alloy welds is more difficult than that in ferritic steel welds because of dispersion and attenuation of the ultrasonic wave. Therefore, influences of welding conditions on flaw detectability and signal to noise ratio (SN ratio) of UT in nickel base alloy welds were investigated. Tested weld joints were prepared with multi-pass gas tungsten arc method. Partial weld joints were applied to weaving or magnetic stirring when that welded. Specimens having an electrical discharge machining slit in weld metal or in heat affected zone were tested by a longitudinal wave of 5 MHz in frequency and 45 degree in incident angle. Obtained results are as follows. Welded joints having columnar structures with the same growth direction showed high SN ratio that means good flaw detectability. Effective welding conditions, which make the columnar structure to be the same growth direction, were found to be the application of weaving or magnetic stirring. Same growth direction in columnar structures means same angle between the columnar structure growth direction and the ultrasonic wave propagating direction. Then, ultrasonic wave has almost same velocity in the weld metal, and the acoustic impedance will be almost same. High SN ratio may be caused by above phenomena. The SN ratio of weld joints by different base metal can be well explained by the difference of acoustic impedance at the boundary columnar structure and base metal.

Study of a methodology of identifying important research problems by the PIRT process

In this paper, we propose a new methodology of identifying important research problems to be solved to improve the performance of some specific scientific technologies by the phenomena identification and ranking table (PIRT) process which has been used as a methodology for demonstrating the validity of the best estimate simulation codes in US Nuclear Regulatory Commission (USNRC) licensing of nuclear power plants. The new methodology makes it possible to identify important factors affecting the performance of the technologies from the viewpoint of the figure of merit and problems associated with them while it keeps the fundamental concepts of the original PIRT process. Also in this paper, we demonstrate the effectiveness of the new methodology by applying it to a task of extracting research problems for improving an inspection accuracy of ultrasonic testing or eddy current testing in the inspection of objects having cracks due to fatigue or stress corrosion cracking.

Research on Ultrasonic Inspection of Cast Austenitic Stainless Steel Piping

Japan Nuclear Energy Safety Organization (JNES) has been carrying out the research program entitled “Nondestructive Inspection Technologies for the Cast Stainless Steel Piping” since 2009FY to comprehend the unique ultrasonic wave propagation in the Cast Austenitic Stainless Steel (CASS) and to confirm detection and sizing capability for cracks in the material by currently available ultrasonic testing techniques. The research is also intended to provide inspection staff with the fundamental information of ultrasonic wave propagation in CASS, for educational purpose.In this research program, specimens whose material, size, dimension and welding method are identical to the main coolant piping system in Japanese pressurized water reactors (PWRs) are examined. Results from the study on the capability for inspection of CASS and the unique wave propagation phenomena such as beam skewing are discussed in this paper.Copyright

A project aiming at the enhancement of NDT{\&}E of stress corrosion cracking

This paper introduces a research project the authors have proposed. The project aims to gather non-destructive testing data of stress corrosion cracking specimens and present them as benchmark data freely available to researchers in the field. Round-robin test using seven austenitic stainless st eel plate specimens with artificial stress corrosion cracki ng is carried out, and they are measured using various non-destructive testing methods. The data measured are made available together with the results of destructive tests to confirm the true profile of the cracking.

Subharmonic wave analysis in crack using the developed FEM

As the first step of the improvement of developed FEM code to extend the subharmonic wave generation at nano scale gap crack, we investigated the basic crack model for accurate simulator of subharmonic behavior using the voxel mesh FEM code.

Optimum inducement of eddy current for NDE of deep lying defects: An analytical approach

A line-current model is proposed to calculate eddy current induced by rectangle coils. Eddy current induced by rectangle coils are analytically calculated using this model, and a coil configuration to induce eddy current deeper into a conductive material is proposed. Optimum excitation frequency is also calculated.