Extra-High-Resolution UTCD Solution for Small-Diameter Pipelines – Introducing Extended Depth Sizing

Abstract Depth sizing beyond 4 mm for crack-like anomalies has been made available recently for large-diameter ILI tools. For small-diameter pipelines (OD ≤ 12 inches), additional challenges to the measurement performance had to be considered and addressed by the inspection tool design before an extended depth sizing could be provided in a robust and reliable manner. The sharp circumferential curvature of small-diameter pipes has a focusing effect on the ultrasonic beam, thus altering the characteristics of the sound pressure distribution and signal strength. For small-diameter pipelines, the ultrasound propagation angle in the pipe wall can significantly differ for internal and external axial anomalies because of the difference between the curvature radius of the outer and inner pipe surface (OD vs. ID). Small-diameter pipelines generally have a limited tolerance for variations of the incidence angle. Therefore, UT-C inspections of small-diameter pipes are generally more sensitive to the operating conditions and to sound velocity variations of the coupling medium (due to temperature variations during the run). This article discusses the above limitations in detail and presents technical solutions for realizing high-performance UT-C tools for small-diameter pipelines. Furthermore, the paper presents the performance qualification procedure and results of new generation of extra-high-resolution UTCD tools for 6″, 8″ and 10″ pipeline diameters. The UTCD performance qualification is based on so-called “extended depth sizing” method, resulting in discrete depth sizing even for anomalies deeper than 4 mm. This method incorporates both direct and indirect corner echo amplitudes into the depth sizing.