20 CAR § 880-1007 – Blowoff piping

(a)
1. (1) A blowoff as required herein is defined as a pipe connection provided with valves through which the water in the boiler may be blown out under pressure, excepting drains such as are used on water columns, gauge glasses, or piping to feedwater regulators, etc., used for the purpose of determining the operating condition of such equipment.
2. (2) Piping connections used primarily for continuous operation, such as deconcentrators on continuous blowdown systems, are not classed as blowoffs, but the pipe connections and all fittings up to and including the first shutoff valve shall be equal at least to the pressure requirements for the lowest set pressure of any safety valve on the boiler drum and with the corresponding saturated steam temperature.
(b)
1. (1) A surface blowoff shall not exceed two-and-one-half-inch pipe size, and the internal and external pipes, when used, shall form a continuous passage, but with clearance between their ends and arranged so that the removal of either will not disturb the other.
2. (2) A properly designed steel busing, similar to or equivalent to those shown in the ASME code, or flanged connection shall be used.
(c) Each boiler shall have a bottom blowoff pipe fitted with a valve or cock in direct connection with the lowest water space practicable.
(d)
1. (1) The minimum size pipe and fittings shall be one inch (1”) and the maximum size shall be two and one-half inches (2 1/2").
2. (2) The minimum size of pipe and fittings may be one-fourth-inch for boilers with one hundred square feet (100 ft²) of heating surface or less.
(e) Straight-run globe valves of the ordinary type or valves of such type that dams or pockets can exist for the collection of sediment shall not be used on such connections.
(f) Straightway Y-type globe valves as shown in the ASME code or angle valves may be used in vertical pipes or horizontal runs of piping provided they are so constructed or installed that the lowest edge of the opening through the seat shall be at least twenty-five percent (25%) of the inside diameter below the center line of the valve.
(g)
1. (1) Return connections of the same size or larger than the size herein specified may be used, and the blowoff may be connected to them.
2. (2) In such case, the blowoff must be so located that the connection may be completely drained.
(h) All integral economizers, waterwalls, or water screens forming parts of a steam boiler shall be equipped with drain or blowoff valves conforming to the requirements herein described.
(i)
1. (1) A bottom blowoff cock shall have the plug held in place by a guard or gland.
2. (2) The end of the plug shall be distinctly marked in line with the passage.
(j) The blowoff valve or valves and the pipe between them and the boiler shall be of the same size except where a larger pipe for the return of condensation is used, as described above.
(k) All fittings between the boiler and valves shall be of steel for pressures not less than one hundred twenty-five pounds per square inch (125 psi).
(l) In all cases, the valves and fittings from the boiler to and including the required stop valves shall be equal at least to the requirements of the ASME code for pressure one and one-quarter (1.25) times the maximum allowable working pressure of the boiler or one and one-quarter (1.25) times the lowest set pressure of any safety valve on the boiler drum, except that for pressures not exceeding one hundred pounds per square inch (100 psi), the valves and fittings shall be equal at least to the requirements of the ASME code, as adopted, for one hundred twenty-five pounds per square inch (125 psi).
(m) For pressure exceeding one hundred pounds per square inch (100 psi), the valves shall:
1. (1) If of cast iron, be equal at least to the requirements for two hundred fifty pounds (250 lbs.) as given in the ASME code, as adopted; and
2. (2) If of steel construction, shall be equal to the requirements of the ASME code, as adopted.
(n) For pressures over two hundred pounds per square inch (200 psi), the valves or cocks shall be of steel construction equal at least to the requirements for three hundred pounds per square inch (300 psi) as given in the ASME code, as adopted.
(o) On all boilers, except those used for traction and/or portable purposes, when the allowable working pressure exceeds one hundred pounds per square inch (100 psi), each bottom blowoff pipe shall have two (2) slow-opening valves or one (1) slow-opening valve and a quick-opening valve or cock complying with the above requirements.
(p) “Slow-opening” valve means one which requires at least five (5) three-hundred-sixty-degree turns of the operating mechanism to change from full-closed to full-opening and vice versa.
(q)
1. (1) On a boiler having multiple blowoff pipes, a single master valve may be placed on the common blowoff pipe from the boiler, in which case only one (1) valve on each individual blowoff is required.
2. (2) In this case, either the master valve or the individual valves or cocks must be of the slow-opening type.
(r) Two (2) independent slow-opening valves, or a slow-opening valve and a quick-opening valve, or a cock may be combined in one (1) body provided the combined fittings are the equivalent of two (2) independent slow-opening valves, or a slow-opening valve and a quick-opening valve, or a cock so that the failure of one (1) to operate could not affect the operation of the other.
(s) The drain or blowoff valves for waterwalls or water screens forming parts of a boiler shall conform to the requirements herein.
(t) The bottom blowoff pipes of every traction and/or portable boiler shall have at least one (1) slow-opening or one quick-opening blowoff valve or cock conforming to the above requirements.
(u) A bottom blowoff pipe when exposed to direct furnace heat shall be protected by firebrick or other heat-resisting material so arranged that the pipe may be inspected.
(v) An opening in the boiler setting for a blowoff pipe shall be arranged to provide free expansion and contraction.