Ultrasonic testing (UT) has developed as a principal technology for crack detection in liquid pipelines, with its effectiveness well-recognized across various industry standards. In liquid pipelines, UT shear waves are commonly employed, utilizing measurement techniques such as pulse-echo and pitch-and-catch for the accurate detection, identification, and sizing of cracks. The reliability of this technology has been thoroughly validated. largely due to the inherent presence of a coupling medium—the transported liquid—which facilitates efficient ultrasonic wave propagation.
Applying UT in liquids is simpler due to the speed of sound and acoustic impedance of the coupling medium. However, the application of UT in gas pipelines presents unique challenges, due to the low speed of sound and low acoustic impedance. Recent research has demonstrated that it is feasible to adapt UT for gas pipelines by utilizing gas as the coupling medium, with a significant shift from traditional shear waves to the use of Lamb waves. This advancement has led to the development of a novel crack detection tool specifically designed for gas pipeline environments.
This paper presents a comparative analysis of UT crack detection technologies in both liquid and gas pipelines, emphasizing the operational principles, advantages, and limitations of each approach. Key similarities include the fundamental reliance on ultrasonic wave propagation for flaw detection, while major differences arise from the choice of wave mode and the nature of the coupling medium. The discussion highlights recent innovations in Lamb wave application for gas pipelines and outlines future directions for enhancing crack detection reliability across gas pipeline environments.