20 CAR § 880-1018 – Superheater safety valves

(a)
1. (1) Every attached superheater shall have one (1) or more safety valves near the outlet.
2. (2) If the superheater outlet header has a full, free steam passage from end to end and is so constructed that steam is supplied to it at practically equal intervals throughout its length so that there is a uniform flow of steam through the superheater tubes and the header, the safety valve or valves may be located anywhere in the length of the header.
(b) The discharge capacity of the safety valve or valves on an attached superheater may be included in determining the number and size of the safety valves for the boiler, provided there are no intervening valves between the superheater safety valve and the boiler, and provided the discharge capacity of the safety valve or valves on the boiler, as distinct from the superheater, is at least seventy-five percent (75%) of the aggregate valve capacity required.
(c)
1. (1) Every independently fired superheater which may be shut off from the boiler and permit the superheater to become a fired pressure vessel shall have one (1) or more safety valves having a discharge capacity equal to six pounds (6 lbs.) of steam per square foot of superheater surface measured on the side exposed to the hot gases.
2. (2) The number of safety valves installed shall be such that the total capacity is at least equal to that required.
(d) A soot-blower connection may be attached to the same outlet from the superheater that is used for the safety valve connection.
(e)
1. (1) Every safety valve used on a superheater discharging superheated steam at a temperature over four hundred fifty degrees Fahrenheit (450° F) shall have a casing, including the base, body, bonnet, and spindle of:
  1. (A) Steel;
  2. (B) Steel alloy; or
  3. (C) Equivalent heat-resistant material.
2. (2) The valve shall have a flanged inlet connection and shall have the seat and disk of suitable heat erosive and corrosive-resisting material, and the spring fully exposed outside of the valve casing so that it shall be protected from contact with the escaping steam.
(f) Every superheater shall have adequate means of supplying sufficient steam circulation when equipment using superheated steam is out of operation or main steam valve is closed.
(g)
1. (1) Every boiler shall have proper outlet connections for the required safety valve or valves independent of any other outside steam connection, the area of opening to be at least equal to the aggregate areas of inlet connections of all of the safety valves to be attached thereto.
2. (2) An internal collecting pipe, splash plate, or pan may be used, provided the total area for inlet of steam thereto is not less than twice the aggregate areas of the inlet connection of the attached safety valves.
3. (3) The holes in such collecting pipes shall be at least one-fourth inch (1/4”) in diameter and the least dimension in any other form of opening for inlet of steam shall be one-fourth inch (1/4”).
(h) Such dimensional limitations to operations for steam need not apply to steam scrubbers or driers provided the net free steam inlet area of the scrubber or dryer is at least ten (10) times the total area of the boiler outlets for the safety valves.
(i) If safety valves are attached to separate steam drum or dome, the opening between the boiler proper and the steam drum or dome shall be not less than required above.