ASME Section III Subsection NF Linear Current and Future Concepts

Over the past thirty years Subsection NF of the ASME Boiler and Pressure Vessel Code, Section III, has been transformed from a basic set of structural rules to evaluate and qualify component supports to a dynamic Code that recognized the difference between pressure retaining and structural elements. Initially, with the publication of the 1974 Edition of the ASME Code, Subsection NF identified essentially two different types of supports, Plate & Shell and Linear. Plate & Shell supports were evaluated using in effect the same rules in Subsections NB, NC and ND for pressure retaining elements. Linear supports, on the other hand, were an odd group. The ASME Code was a pressure Code providing rules for pressure retaining components such as vessels, piping, valves, pumps, tanks etc. In 1963, when the first Edition of ASME Section III for nuclear plants was published, there wasn’t any place for non-pressure retaining elements such as component supports. This continued for eleven years until supports made their debut in the 1974 Edition of Section III (actually the 1973 Winter Addenda to the 1971 Edition). At this time the AISC Manual for Steel Construction was the premier set of rules for the design and construction of steel structures. Since many supports were comprised of structural steel elements due to the nature of loading (thermal and seismic) at nuclear power plants, the AISC Code seemed to be the ideal set of rules to adopt for the construction of supports. Additional requirements for temperature and seismic considerations were incorporated in Subsection NF to account for supports on nuclear plants.