Session: 01-05: Nuclear Plant Operation, Modification, Life Extension, Maintenance and Life Cycle - V

Paper Number: 135012

135012 - Remote Impact Acoustic Inspection of Structures Using Water Jet Impacts 

Abstract: 

Many nuclear structures worldwide have exceeded 40 to 50 years since their construction, reaching a critical period where the concrete components, with a typical lifespan of 40 to 50 years, require comprehensive inspection. While conventional concrete structures are inspected by workers using hammers, nuclear structures may necessitate remote inspection due to their design, making it difficult for workers to approach specific areas. This study introduces a method developed with the specific goal of remote impact acoustic inspection of structures.

As an alternative to impact acoustic inspections, infrared thermography is a well-known technique. This method leverages the phenomenon where internal defects, such as delamination or debonding within a structure, impede heat transfer during temperature elevation caused by sunlight. Consequently, defective areas exhibit higher surface temperatures compared to the surrounding regions. So, the applicability of infrared thermography is limited to structures exposed to direct sunlight.

To overcome this limitation, the present research introduces a method that employs pulsed water jet streams to impact structures. By discharging water flows from a nozzle with a diameter ranging from 1mm to 5mm at speeds between 30 m/s and 40 m/s for a duration of 0.01 s, the water transforms into a mass that collides with the structure. The impact acoustic signals are then gathered for inspection. Distinctive acoustic signals are generated in the presence of anomalies, enabling the identification of structural abnormalities. A noteworthy aspect of this method is its capability to conduct tests from a distance of several meters between the impact device (nozzle) and the structure, allowing inspectors to perform inspections remotely. Furthermore, when integrated into mobile devices such as suspended platforms, the automation of inspections becomes achievable.

In this study, periodic water jet discharges at 0.1-second intervals enabled impact acoustic inspections at a frequency of 10 Hz. Moving the impact points at a speed of 1 m/s allowed inspections at 10 cm intervals. At this testing speed, the rate was 0.1 m² per second, achieving 6 m² per minute. The effectiveness of this inspection approach was demonstrated by detecting a 300mm diameter disk-shaped void defect within a 900 mm x 900mm x 300 mm concrete specimen. Test conditions included a 5 mm nozzle diameter, water pressure of 1 MPa, a 3 m distance between the specimen and the nozzle, and an average impact point velocity of 20 cm/s. The impact acoustic signals from the void defect exhibited distinct characteristics compared to the intact regions. The proposed method is termed "the water jet impact acoustic method," showcasing its capability for remote impact acoustic inspections regardless of the varying distance from the inspection surface.

Presenting Author: Kazuya Mori Kumamoto University

Presenting Author Biography: Name: Dr. Kaziya Mori

Date of Birth: November 23, 1960

Place of Birth: Japan

Education:

1985: Graduated from the Graduate School of Kyushu University
1991: Ph.D. in Engineering
Career:
Dr. Mori began his career by joining a technical college in Japan, specializing in mechanical engineering. His research focused on the fields of destructive mechanics and non-destructive testing. Later, he transitioned to Kumamoto University, progressing from the position of Assistant Professor to Professor.

In recent years, Dr. Mori has been dedicated to developing a remote non-destructive testing method utilizing the phenomenon of water collision. This innovative approach promises advancements in the field of non-destructive testing.

Entrepreneurship:
In 2019, Dr. Mori founded a company dedicated to non-destructive testing. He is actively working on bringing practical applications to the forefront, pushing the boundaries of conventional testing methods.

Personal Life:
Apart from his professional pursuits, Dr. Mori has a passion for travel. Additionally, he enjoys hobbies such as touring, snowboarding, and diving. These activities not only serve as recreational outlets but also contribute to his well-rounded and adventurous lifestyle.

Authors:

Saeko Tokuomi Kumamoto University
Kazuya Mori Kumamoto University
Yasutaka Ohshima Kumamoto University