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-alloy and/or fine grained steel. For the testing of welds in other steel materials this document gives guidance. For coarse-grained or austenitic steels, ISO 22825 applies in addition to this document.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 discontinuities for acceptance purposes based either on 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.