Grease-like coupling agent based on metal ionization method for low-frequency ultrasonic NDT

In long-distance NDT based on ultrasonic guided waves with low-frequency excitation, the most commonly used industrial coupling agents are grease-like coupling agents. However, these agents show the poor performance in NDT, because they can cause more acoustic energy loss and lower acoustic transmissivity. In the study, to improve the acoustic transmission property of grease-like coupling agents, a new method was proposed to combine different metal ions like Li+, Na+ and Ca2+ with base grease, thus forming new grease-like coupling agents. By comparing with the ultrasonic transmitting property of the regular coupling agents, selects a premium ultrasonic grease-like coupling agent. In the experimental results, when low-frequency ultrasonic guided waves transmitted through the lithium-based coupling agent, except the slight delay of peak response time, pulse signals showed the higher energy transmission efficiency with the better pulse vibration waveforms in the iron medium than other oil-based coupling agents. The newly developed grease-like coupling agent can be easily prepared at a lower cost. Importantly, the new coupling agent can improve the energy transmission performance and greatly enhance the sensitivity of ultrasonic flaw detection.