MSS SP-121

Abstract

This Standard Practice provides procedures and guidelines for testing and evaluation of valve stem packing materials and material combinations. This testing provides qualification by verifying the adequacy of specific packing material combinations for service within defined limits of size, pressure, temperature, and cyclic duty. Such specific combinations generally represent products of individual manufacturers, although generic qualification of raw materials may be demonstrable in certain cases. <br>It is intended that this Standard Practice apply to qualification of stem packings for Class 150 through 4500 ASME B16.34 or equivalent steel or special alloy valves (including intermediate classes and Standard, Special, and Limited Class ratings) with rotating/rising and non-rotating/rising stems, as traditionally used in globe and gate valves. Other valve stem types (e.g. quarter-turn) may involve additional considerations not within the scope of this Standard Practice.The requirements herein apply to qualification of traditional compression packings. Rod seal elements such as "O" rings, "V" rings, and similar proprietary seals are not within the scope.Stem packings may be prequalified by experience or by test programs conducted prior to publication of this Standard Practice if a qualification report is prepared based on documented evidence. <br>This Standard Practice is intended to provide experimental qualification of packing materials and materials combinations for service with water, steam, and other common liquids, vapors, and gases. Some of the procedures identified in detail use water and steam as test fluids, but air or nitrogen may also be used with appropriate modifications in testing and data acquisition methods. <br>General Note: More chemically aggressive line fluids may damage packings and degrade sealing performance. Packings qualified in accordance with this Standard Practice may not be satisfactory for applications with such fluids. <br>Environmental pollution regulations (e.g. fugitive emissions) or limitations on leakage of hazardous or toxic fluids may require additional or different qualification tests that are outside the scope of this Standard Practice. <br>This Standard Practice is not intended to apply to packings for valves developed for and predominantly used in instrument piping systems.