This paper addresses implementation of ultrasonic (UT) process qualification by performance demonstration as imposed by the ASME Boiler and Pressure Vessel Code Section XI, Appendix VIII. The intended audience for the present paper is an engineer with a good knowledge of NDE, but a limited knowledge of the ASME Codes and Standards. The starting point for application of UT performance demonstration is described in a paper published in this journal just over a decade ago by Cowfer and Hedden. That paper addressed the application of ultrasonic performance demonstration to qualify an examination process for ASME Code Section XI inservice inspection. The present paper provides a brief summary of papers specifically selected to provide the reader with a concise update of progress in UT performance demonstration since the earlier paper. Given that qualification, the reader should not expect new information in this present paper. The papers selected have been mostly selected from those presented at ASME Pressure Vessels and Piping Conferences, from 1995 to 2002, addressing the subsequent development and application of the UT performance demonstration process. The emphasis is on work performed for nuclear utilities under the Performance Demonstration Initiative (PDI), for application to Section XI inservice inspection. However, material also is included describing parallel work in the European Community, and applications of UT performance demonstration in Sections I and VIII of the ASME Boiler and Pressure Vessel Code, for use of UT in place of RT for new construction, are included.

In 1996, Code Case 2235, which allows ultrasonic examination of welds in lieu of radiography for ASME Section VIII Division 1 and Division 2 vessels, was approved by the ASME B&PV Code Committee. This Code Case has been revised to incorporate: 1) a reduction in minimum usable thickness from 4″ (107.6 mm) to 0.5″ (12.7 mm), and 2) flaw acceptance criteria including rules on multiple flaws. A linear elastic fracture mechanics procedure has been used in developing the flaw acceptance criteria. This paper presents the technical basis for Code Case 2235.

Section III of the ASME Boiler and Pressure Vessel Code requires radiographic testing (RT) of pressure boundary welds. RT is performed to detect flaws that might be created in welds as they are fabricated. Current Section III acceptance standards require rejection and repair of flaw indications characterized as cracks, lack of fusion, or incomplete penetration regardless of the size of the indication or the structural significance of such indications on fitness for service (FFS). The current Section III requirements have been effective in meeting the design objective of preventing pressure boundary failures. However, the rules are sufficiently conservative that not only are structurally significant flaws excluded, but they also exclude more benign indications that have no impact on structural integrity. This approach has resulted in repairs for even minor flaws that have no FFS impact. In addition to the cost of performing these unnecessary repairs, the repairs may have contributed to service induced cracking because of the higher residual stresses from the repair. Clearly, there is a need to revisit the Section III inspection and repair rules so as to distinguish between structurally unacceptable flaws and benign flaws that have no FFS impact. This paper describes the technical basis for the proposed Section III Code Case that uses the FFS approach to eliminate the need for weld repairs for minor flaws that have been shown to have no structural impact. Specifically, the Code Case will provide the option to use qualified volumetric inspection to size the flaw indications accurately and define acceptance criteria to determine flaw sizes that are judged to have little structural significance. In addition to describing the requirements of the proposed Code Case, this paper also describes the technical basis for the flaw acceptance criteria and the results of ultrasonic (UT) qualification testing to demonstrate the capability to detect and characterize fabrication flaw indications.