The paper reviews advanced non-destructive testing techniques of pipeline integrity assessment mainly applied for defect detection, such as corrosion, cracks, and mechanical damage, with no disturbance to the pipeline operational services. Accordingly, the essential NDT methods reviewed will be classified as ultrasonic testing, electromagnetic inspection, radiographic testing, acoustic emission testing, and intelligent pigging. Each technique's detection accuracy, cost-effectiveness, and field applicability have been reviewed and judged. Among various comparisons done here, one points out strengths and weaknesses. At the same time, it indicates the rise of artificial intelligence for predictive maintenance, coupled with a completely different generation of IoT sensors that allow real-time monitoring. However, knowledge gaps still exist regarding standardisation, real-world validation of new technologies, and cost-efficient solutions for the complex geometries of pipelines. Finally, it concludes with recommendations for improving pipeline safety, operational reliability, and efficiency in maturing energy infrastructures
