ISO 11666:2018规定了铁素体钢全熔透焊接接头的两个超声波验收等级，即验收等级2（AL 2）和验收等级3（AL 3），分别对应于ISO 5817:2014质量等级B和C。ISO 5817:2014质量等级D的验收等级不包含在本文件中，因为这种焊接质量通常不需要超声波检测。 这些验收水平适用于根据ISO 17640进行的测试。 ISO 11666:2018适用于厚度为8 mm至100 mm的全熔透铁素体钢焊缝的测试。 它也可用于其他类型的焊缝、材料和厚度，前提是在进行试验时，对部件的几何结构和声学特性进行了必要的考虑，并且可以使用足够的灵敏度，以使本文件的验收水平得以应用。本文件中使用的探头的标称频率在2 MHz和5 MHz之间，除非衰减或对更高分辨率的要求需要其他频率。重要的是考虑使用这些接受水平与频率范围以外的频率仔细。

ISO 11666:2018 specifies two ultrasonic acceptance levels known as acceptance level 2 (AL 2) and acceptance level 3 (AL 3) for full penetration welded joints in ferritic steels, which correspond to ISO 5817:2014, quality levels B and C. An acceptance level corresponding to ISO 5817:2014, quality level D is not included in this document, as ultrasonic testing is generally not requested for this weld quality. These acceptance levels are applicable to testing carried out in accordance with ISO 17640. ISO 11666:2018 applies to the testing of full penetration ferritic steel welds, with thicknesses from 8 mm to 100 mm. It can also be used for other types of welds, materials and thicknesses, provided the tests have been performed with necessary consideration of the geometry and acoustic properties of the component, and an adequate sensitivity can be employed to enable the acceptance levels of this document to be applied. The nominal frequency of probes used in this document is between 2 MHz and 5 MHz, unless attenuation or requirements for higher resolution call for other frequencies. It is important to consider the use of these acceptance levels in conjunction with frequencies outside this range carefully.