Non-Destructive Evaluation of Coating Thickness Using Water Immersion Ultrasonic Testing

Jiannan Zhang,Jin-Hak Yi,Young H Kim,Azamatjon Kakhramon Ugli Malikov,Younho Cho,Weibin Li,Jeongnam Kim

doi:10.3390/coatings11111421

Jiannan Zhang, Jin-Hak Yi + Show 5 more

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https://doi.org/10.3390/coatings11111421

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Abstract

The coating is applied to prevent corrosion on the surface of ships or marine structures, and the thickness of the coating affects its anti-corrosion effect. As a result, non-destructive testing (NDT) is required to measure coating thickness, and ultrasonic NDT is a convenient and quick way to measure the thickness of underwater coatings. However, the offshore coating’s energy attenuation and absorption rates are high, the ultrasonic pulse echo test is difficult, and the testing environment is harsh. Because of the coating’s high attenuation, the distance of the optimal water delay line designed based on the reflection coefficient of the vertically incident wave is used. To accurately measure the thickness of the coating material, TOF of the reflected echo on the time-domain waveform was evaluated. The experimental results show that, when compared to caliper measurements, the coating thickness measured by the proposed method has a lower error and can be used for accurate measurement. The use of ultrasonic water immersion measurement is almost limitless in terms of size, location, and material of the object to be measured, and it is expected to be used to measure the thickness of the surface coating of ships or marine structures in the water.

Highlights

Published: 20 November 2021Coatings are widely used as anti-corrosion layers in ships or marine structures [1].When the thickness of the coating and its uniformity directly affect the anti-corrosion effect [2], it may cause safety problems for ships or marine structures, and lead to accidents
When the coating material of a ship is applied to the surface of a metal structure, the thickness of the coating material can be even thinner, which increases the difficulty of the assessment of coating thickness
The results show that, the four experiments can measure the coating thickness with an error of less than 1%, the thickness error measured by the best delay line theory is the smallest, which is only one-third to two-halves of the error of the other three experimental results

Summary

Introduction

Coatings are widely used as anti-corrosion layers in ships or marine structures [1]. When the thickness of the coating and its uniformity directly affect the anti-corrosion effect [2], it may cause safety problems for ships or marine structures, and lead to accidents. It is very important that the thickness in the coating must be monitored regularly, but in practical applications, the coating is obviously thinner, especially on the surface of marine structures [3]. Non-Destructive Testing (NDT) is an effective method for assessing the structural integrity of these and identifying any thickness degradation, deviations or defects [4]. Appropriate non-destructive testing techniques need to accurately detect, locate, and measure structural parameters, such as thickness and defects, in a non-invasive manner, and use the results to plan wisely for future use and maintenance. In order to deal with these situations, many researchers and engineers have developed many new NDT technologies, such as ultrasonic (UT) techniques, radiograph (RT), magnetic flux leakage (MT), electromechanical

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