ISO 17635:2016 gives guidelines for the choice of non-destructive testing (NDT) methods for welds and evaluation of the results for quality control purposes, based on quality requirements, material, weld thickness, welding process and extent of testing. ISO 17635:2016 also specifies general rules and standards to be applied to the different types of testing, for either the methodology or the acceptance levels for metallic materials. Acceptance levels cannot be a direct interpretation of the quality levels defined in ISO 5817 or ISO 10042. They are linked to the overall quality of the produced batch of welds. Requirements for acceptance levels for NDT comply with quality levels stated in ISO 5817 or ISO 10042 (moderate, intermediate, stringent) only on a general basis and not in detail for each indication. Annex A gives correlations between quality, NDT and acceptance level standards. Annex B gives an overview of the standards linked to quality levels, acceptance levels and NDT methods.