Section 162.018-4 - Construction and workmanship(a) Safety relief valves shall be of either the internal or external spring-loaded type, suitable for the intended service.(b) Safety relief valve body, base, bonnet and internals shall be designed for a pressure of not less than the set-pressure of the valve.(c) All safety relief valves shall be so constructed that the failure of any part cannot obstruct the free and full discharge of vapors from the valve.(d) The nominal size of a safety relief valve shall be the inside diameter of the inlet opening to the individual valve disk. No safety relief valve shall be smaller than 3/4 inch nor larger than 6 inches. Safety relief valves shall have flanged or welded end inlet connections and either flanged or screwed outlet connections, except outlets exceeding 4 inches in diameter shall be flanged.(e) Safety relief valves shall be of the angle or straight-through type, fitted with side or top outlet discharge connections.(f)(1) Springs shall not show a permanent set exceeding 1 percent of their free length 10 minutes after being released from a cold compression test closing the spring solid.(2) Springs may not be re-set for any pressure more than 10 percent above or 10 percent below that for which the valve is marked.(3) If the operating conditions of a valve are changed so as to require a new spring under paragraph (f)(2) of this section for a different pressure, the valve shall be adjusted by the manufacturer or his authorized representative.(g) The design and construction of safety relief valves shall permit easy access for inspection and repair.(h) Safety relief valves shall be tapped for not less than 1/4 inch pipe size drain at the lowest practicable point where liquid can collect.CGFR 52-43, 17 FR 9540, Oct. 18, 1952