Application of Ultrasonic Non-Destructive Testing for Weld Inspection in Nigerian Pipeline Infrastructure

Pipeline weld integrity is a critical safety and environmental concern in Nigeria's hydrocarbon transmission network, where weld defects contribute to a significant proportion of pipeline failures. Ultrasonic testing is the most widely used non-destructive technique for volumetric weld inspection in the oil and gas industry. This study evaluates the application of manual and phased array ultrasonic testing for detecting planar and volumetric weld defects in 12-inch API 5L X65 pipeline specimens provided by the Nigerian Gas Company's pipeline maintenance department. Artificial defects including side-drilled holes, flat-bottom holes, and fatigue cracks are introduced into weld specimens by electrical discharge machining. Inspection is performed using a 5 MHz single-crystal probe for manual UT and a 64-element phased array probe for PAUT, following ASME V Article 4 procedures. Probability of detection curves are constructed from 40 defect specimens per defect type. Results indicate that PAUT achieves a probability of detection of 0.95 for planar defects above 3 mm height, compared to 0.87 for manual UT. Volumetric defects above 5 mm diameter are detected with equal reliability by both methods. The study provides performance qualification data for ultrasonic inspection procedures applicable to Nigerian pipeline assets. Keywords: ultrasonic testing, weld inspection, pipeline, phased array, non-destructive evaluation