This document specifies the application of the phased array technology for the semi- or fully automated ultrasonic testing of fusion-welded joints in metallic materials of minimum thickness 6 mm. It applies to full penetration welded joints of simple geometry in plates, pipes, and vessels, where both the weld and the parent material are low-alloyed carbon steel. Where material-dependent ultrasonic parameters are specified in this document, they are based on steels having a sound velocity of (5 920 ± 50) m/s for longitudinal waves, and (3 255 ± 30) m/s for transverse waves. It is necessary to take this fact into account when testing materials with different velocities. Steels with other velocities should be tested under testing level D. For coarse-grained or austenitic steels ISO 22825 applies. This document provides guidance on the specific capabilities and limitations of the phased array technology for the detection, location, sizing and characterization of discontinuities in fusion-welded joints. Phased array technology can be used as a stand-alone technology or in combination with other non-destructive testing (NDT) methods or techniques, for manufacturing inspection, pre-service and for in-service inspection. This document specifies four testing levels, each corresponding to a different probability of detection of imperfections. This document permits assessment of discontinuites for acceptance purposes based on either amplitude (equivalent reflector size) and length or on height and length. This document does not include acceptance levels for discontinuities. This document is not applicable for automated testing of welds during the production of steel products covered by ISO 10893-8, ISO 10893-11 and ISO 3183.