In the present work, structure health monitoring (SHM) of welded steel pipes was used to diagnose their state via vibration based damage detection techniques. The dynamic quantities such as Frequency Response Functions (FRFs), mode shapes and modal parameters from structural vibration to detect damage were measured, set on linear averaging mode, with a maximum frequency of analysis of 3.2 kHz. Two most commonly used welding techniques were used, namely: shielded metal arc welding (SMAW) and gas

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... tungsten arc welding (GTAW). Static tests were performed to assure the quality of welded steel pipes. These tests include three point bending test (3PB), face bending, and tensile testing. In addition, X-ray images were utilized as a non-destructive testing (NDT). The results showed for non-cracked pipes, having the first three modes, the higher damping frequency and the lower damping ratio. This reflects the difficulty of dissipating energy at higher frequencies. Also, it was found that SMAW gives higher damping ratio (7.418%) as compared to GTAW joints (7.220). So, the latter joints have higher stiffness than former ones. The results demonstrated that the FRFs technique is a potentially powerful tool for damage detection and health monitoring of welded steel structural pipes.