46 CFR 56.20-15 - Valves employing resilient material.
(a) A valve in which the closure is accomplished by resilient nonmetallic material instead of a metal to metal seat shall comply with the design, material, construction and testing for valves specified in this part.
(b) Valves employing resilient material shall be divided into three categories, Positive shutoff, Category A, and Category B, and shall be tested and used as follows:
(1) Positive shutoff valves. The closed valve must pass less than 10 ml/hr (0.34 fluid oz/hr) of liquid or less than 3 l/hr (0.11 cubic ft/hr) of gas per inch nominal pipe size through the line after removal of all resilient material and testing at full rated pressure. Packing material must be fire resistant. Piping subject to internal head pressure from a tank containing oil must be fitted with positive shutoff valves located at the tank in accordance with § 56.50-60(d). Otherwise positive shutoff valves may be used in any location in lieu of a required Category A or Category B valve.
(2) Category A valves. The closed valve must pass less than the greater of 5 percent of its fully open flow rate or 15 percent divided by the square root of the nominal pipe size (NPS) of its fully open flow rate through the line after complete removal of all resilient seating material and testing at full rated pressure; as represented by the formula: (15% / SQRT × (NPS)) (Fully open flow rate). Category A valves may be used in any location except where positive shutoff valves are required by § 56.50-60(d). Category A valves are required in the following locations:
(i) Valves at vital piping system manifolds;
(ii) Isolation valves in cross-connects between two piping systems, at least one of which is a vital system, where failure of the valve in a fire would prevent the vital system(s) from functioning as designed.
(iii) Valves providing closure for any opening in the shell of the vessel.
(3) Category B valves. The closed valve will not provide effective closure of the line or will permit appreciable leakage from the valve after the resilient material is damaged or destroyed. Category B valves are not required to be tested and may be used in any location except where a Category A or positive shutoff valve is required.
(c) If a valve designer elects to use either a calculation or actual fire testing instead of material removal and pressure testing, the calculation must employ ISA-S75.02 (incorporated by reference; see 46 CFR 56.01-2) to determine the flow coefficient (Cv), or the fire testing must be conducted in accordance with API 607 (incorporated by reference; see 46 CFR 56.01-2).