Recent developments in ASME code rules for ultrasonic examination of welds in nuclear power plant components

Since publication of Appendix I of Section XI of the ASME Boiler and Pressure Vessel Code in June 1973, the Code requirements for inservice inspection have incorporated a number of revisions. The rules of Appendix I, for ultrasonic examination of vessel welds, have been refined, simplifying application of the rules without sacrificing stringency. In addition, rules for ultrasonic examination of welds in ferritic piping, Appendix III, have been prepared. Provisions for non-mandatory application of these rules to welds in austenitic piping are included; however, the Task Group hesitated to include the austenitic welds because of the well-documented anomalies experienced in their examinations, both because of geometric conditions commonly found in a pipe in the vicinity of a weld, and because of changes sometimes encountered in ultrasonic response due to variations in the metallurgical structure of both the base material and weld. With the recent increase in experience in repeated inservice inspections in a number of nuclear power plants, the background for preparing Code ultrasonic examination rules is becoming increasingly firm. In addition to this, it has been possible to obtain objective evaluations of the rules. Industry organizations (PVRC and EPRI) are conducting evaluations of examinations of specimens containing 'real'weld flaws. Examinations of specific specimens have been conducted under field conditions by a series of teams from the various manufacturing and service firms; a series of tests is then concluded with sectioning of the specimens to verify the precise nature of the reflectors. In such ways the Code committees continue to seek, not rules that are completely generalized, nor rules that require state-of-the-art achievement, but rules that are meaningful in relation to the size and nature of flaws that are detrimental to the safety of the structure being examined. (author)