Okla. Admin. Code § 380:25-5-10 – Safety valves

(a) The use of weighted-lever safety valves or safety valves having either the seat or disk of cast iron are prohibited; valves of this type of construction shall be replaced by direct, spring-loaded, pop-type valves that conform to the requirements of ASME Code Section I.
(b) Each boiler shall have at least one ASME/National Board certified safety valve, and if it has more than 500 square feet of water-heating surface, or an electric power input of more than 1,100 kw, it shall have two or more safety valves of the same type.
(c) The valve or valves shall be connected to the vapor space of the boiler, independent of any other steam connection, and attached as close as possible to the boiler without unnecessary intervening pipe or fittings. Every safety valve or safety relief valve shall be connected so as to stand in an upright position, with spindle vertical. Where alteration is required to conform to this requirement, owners, or users shall be allowed reasonable time in which to complete the work as permitted by the Chief Boiler Inspector.
(d) No valves of any description shall be placed between the safety valve and the boiler nor on the discharge pipe, if used. When an escape pipe is used, it shall be at least the full size of the safety valve discharge and fitted with an open drain to prevent water lodging in the upper part of the safety valve or safety valve discharge pipe; it shall be located close to the safety valve outlet or the discharge pipe shall be anchored and supported securely. All safety discharges shall be so located or piped as to be carried clear from walkways or platforms.
(e) The safety valve capacity of each boiler shall be such that the safety valve or valves will discharge all the steam that can be generated by the boiler without allowing the pressure to rise more than 6% above the highest pressure to which any valve is set, and in no case to more than 6% above the maximum allowable working pressure.
(f) One or more safety valves on every boiler shall be set at or below the maximum allowable working pressure. The remaining valves may be set within a range of 3% above the maximum allowable working pressure, but the range or setting of all the safety valves on a boiler shall not exceed 10% of the highest pressure to which any valve is set.
(g) When two or more boilers, operating at different pressures and safety valve settings, are interconnected, the lower pressure boilers or interconnected piping shall be equipped with safety valves of sufficient capacity to prevent overpressure, considering the maximum generating capacity of all boilers.
(h) In those cases where the boiler is supplied with feed water directly from water mains without the use of feeding apparatus (not to include return traps), no safety valve shall be set at a pressure greater than 94% or the lowest pressure obtained in the supply main feeding the boiler.
(i) If the safety valve or safety relief valve capacity cannot be computed or if it is desirable to prove the computations, it may be checked in any one of the three following ways, and if found insufficient, additional capacity shall be provided:
1. (1) By making an accumulation test, which consists of shutting off all other steam discharge outlets from the boiler and forcing the fires to the maximum. The safety valve capacity shall be sufficient to prevent a rise of pressure in excess or 6% of the maximum allowable working pressure. This method should not be used on a boiler with a superheater or reheater;
2. (2) By measuring the maximum amount of fuel that can be burned and computing the corresponding evaporative capacity (steam generating capacity) upon the basis of the heating value of this fuel. These computations shall be made as outlined in the Appendix of the ASME Code, Section I;
3. (3) By measuring the maximum amount of feedwater that can be evaporated. When either of the methods outlined in Section 380:25-5-10(i)-(2) & (3) is employed, the sum of the safety valve capacity shall be equal to or greater than the maximum evaporative capacity (maximum steam generating capacity) of the boiler.