D.C. Mun. Regs. tit. 12, r. 12-E1025
Insert a new Section 1025 in the Mechanical Code to read as follows:
Maximum allowable working pressure. The maximum allowable working pressure on the shell or drum of a miniature boiler shall be determined in accordance with the following equation:
(TS x t x E) ÷ (R x FS) = Pm
where:
Pm = Maximum allowable working pressure (psi) (kPa)
TS = Ultimate tensile strength of shell plates (psi) (kPa)
t = Minimum thickness of shell plate in weakest course (inch)
(mm)
E a = Efficiency of longitudinal joint, per Section VIII, Division 1,
Part UW, paragraph UW-12, "Joint Efficiencies" of the ASME Code
E a = Efficiency for tube ligaments between openings as calculated in
Section I, Part PG, paragraphs PG-52 and PG-53 of the ASME Code
R = Inside radius of the weakest course of the shell or drum (inch) (mm)
FS = Factor of safety required by Chapter 10 of the Mechanical Code
a. Where there are both riveted joints and tube ligaments to consider, the lowest calculated efficiency, E, shall be used.
Parts and equipment. Each miniature boiler shall be equipped with the following parts and equipment that shall meet the requirements of Sections 1025.2.1 through 1025.2.13, as applicable.
Feed pump. Each miniature boiler operating at a pressure in excess of 25 pounds per square inch (psi) (172 kPa) shall be provided with at least one feed pump or other approved water- feeding device.
Exception: Where the steam generator is operated as a closed system with no extraction of steam, in lieu of a feeding device, a suitable connection or opening, not less than 1/2 inch (13 mm) nominal pipe size, shall be provided to fill the generator when cold.
Feed water and blow-off connections. Each miniature boiler shall be fitted with feed water and blow-off connections that shall not be less than 1/2 inch (13 mm) iron pipe size, unless operated on a closed system. The feed pipe shall be provided with a check valve and a stop valve. The blow-off shall be fitted with a valve or cock and shall be in direct connection with the lowest water space practicable. When the boiler is under pressure, feed water shall not be introduced through the openings or connections used for the column, the water gauge glass or gauge cocks. All valves, pipe fittings and appliances shall be rated at a minimum of 125 pounds per square inch (psi) (862 kPa) standard pressure.
Water gauge glass and gauge cocks. Each miniature boiler shall be equipped with a water gauge glass and one or more gauge cocks. The lowest permissible water level shall be at a point one-third of the height of the shell.
Exceptions:
Steam gauge. Each miniature boiler shall be equipped with a steam gauge having its dial graduated to not less than 1 1/2 times the maximum allowable working pressure. The gauge shall be connected to the steam space or to the steam connection to the water column by a brass or bronze composition siphon tube, or equivalent device that will keep the gauge tube filled with water.
Safety valve. Each miniature boiler shall be equipped with a sealed, spring loaded, "pop" safety valve not less than 1/2 inch (13 mm) diameter connected directly to the boiler. To ensure the safety valve is unrestricted, each valve shall have a substantial lifting device by which the valve disk can be lifted from its seat when the pressure in the boiler is at least 75 percent of full working pressure. All safety valves shall be mounted with their spindles vertical and shall be accessible.
Safety valve identification. The safety valve shall be plainly marked by the manufacturer with the following information:
Minimum relieving capacity. The minimum relieving capacity for the safety valve shall be determined on the basis of 3 pounds of steam per hour per square foot (lb/hr/ft2) (14.65 kg/hr/m2) of heating surface and shall be sufficient to discharge all the steam that can be generated by the miniature boiler without allowing the pressure to rise to more than 6 percent above the maximum allowable working pressure.
Standard stop valve. Each steam line from a miniature boiler shall be provided with a 125 pounds per square inch (psi) (862 kPa) standard stop valve located as close to the boiler shell or drum as practicable.
Blow-off connections. Each miniature boiler shall be provided with a blow-off connection that shall not be reduced in size and shall be extended to a safe point of discharge.
Whenever, in the judgment of the code official, a safe point of discharge is not available, a blow-down tank shall be provided. The blow-off shall be fitted with a valve or cock and shall be connected directly to t he lowest water space practicable.
Automatic low-water fuel cut-off. Each miniature boiler mechanically- fired by any fuel other than gas shall be provided with an automatic low-water fuel cut-off, so located as to automatically cut off the fuel supply in case the water level falls below the bottom of the water glass.
Gas-fired boilers. The burners of gas-fired miniature boilers shall conform to the listing requirements of the American Gas Association. Such burners shall be equipped with an automatic fuel-regulating governor regulated by the steam pressure. The governor shall be so constructed that, in the event of its failure, there can be no possibility of steam from the boiler entering the combustion chamber or the gas supply pipe. A manual stop cock or throttle valve shall be provided, located in the inlet pipe ahead of the fuel-regulating governor. Each gas- fired miniature boiler shall be equipped with a 4- inch (102 mm) vent or flue, extended to an approved location outside of the building or connected to a chimney, in accordance with the Fuel Gas Code. Where the horizontal run of the vent is more than 10 feet (3048 mm), its size shall be increased to 6 inches (152 mm).
Replacement. All miniature boiler replacements shall conform to the requirements of the Mechanical Code for new installations.
Retubed boiler inspections. Each retubed miniature boiler shall be inspected and approved by the code official before the boiler is again put in service.
Used boilers. Each used miniature boiler brought into the District of Columbia shall be inspected and approved by the code official before being installed. Installation shall require a permit pursuant to Section 1001.3 and Section 105 of the Building Code.
Installation Permit. Moving a miniature boiler and reinstalling it in the same or another building shall require a boiler installation permit.
D.C. Mun. Regs. tit. 12, r. 12-E1025