scope:

These rules apply to materials, design, fabrication, inspection and examination of internal and external valve items for Class 1, 2, and 3 line valves. Internal and external valve items are those items of a valve other than valve bodies, valve bonnets, valve items welded to valve bodies and bonnets (but not including internal permanent attachments), and bolting which joins valve bodies and bonnets. As an alternative to the requirements of Section III, internal permanent attachments, disks, and those valve items covered by NB-3546.3(a) may be constructed in accordance with the requirements of this Case.

Category as used herein is the grouping of various internal and external valve items for the purpose of applying the rules of this Case. Categories for typical valve types are shown in Figs. 1 through 10. The figures are not to scale, and are not intended to convey any preference for valve type or design, but are provided as a guide to the Manufacturer to identify the various internal and external items of a valve for categorization. In determining categories for valve items of valve types not specifically illustrated, a valve or valve detail which is most nearly representative shall apply. Categories 1 and 2 are those valve items presently covered by Subsections NB, NC, and ND. Categories 3 through 8 are internal and external valve items which may be constructed in accordance with this Case.