North Carolina Administrative Code › Title 13 - LABOR › Chapter 13 - BOILER AND PRESSURE VESSEL › Section .0400 - GENERAL REQUIREMENTS › Section 13 .0405 - PRESSURE RELIEF DEVICES

Current through Register Vol. 39, No. 2, July 15, 2024
(a) Boilers and
				pressure vessels shall be protected from overpressurization by a pressure
				relief device. All pressure relief devices installed on any boiler or pressure
				vessel shall be constructed and stamped in accordance with the Accepted Design
				and Construction Code as defined in Rule .0101 of this Chapter.
(b) All pressure relief devices shall be
				stamped and capacity certified by the manufacturer indicating compliance with
				the National Board. The stamping shall include the set pressure and the
				relieving capacity.
(c) High
				pressure boilers with over 500 square feet of heating surface and electrically
				fired boilers having an input in excess of 1100 kW shall be provided with a
				minimum of two safety valves. For high pressure boilers with a combined bare
				tube and extended water-heating surface area exceeding 500 square feet, one
				safety valve is required if the design steam generating capacity of the boiler
				is less than 4,000 pounds of steam per hour.
(d) Safety valves and safety relief valves
				for heating boilers shall have a seat diameter of not less than ½ inch,
				and not more than 4 ½ inches.
(e) Pressure relief devices shall have a set
				pressure and relieving capacity in accordance with the requirements of the
				Accepted Design and Construction Code for the type of equipment on which the
				pressure relief device is installed. At least one pressure relief device shall
				have the set pressure set at not greater than the maximum allowable working
				pressure of the boiler or pressure vessel. The relieving capacity shall not be
				less than the minimum required relieving capacity indicated on the
				manufacturer's name plate or stamping, or as otherwise required by the Accepted
				Design and Construction Code. Safety relief valves installed on water heaters
				shall be of the combination temperature and pressure relieving type, or as
				permitted by the Accepted Design and Construction Code for modular water
				heaters.
(f) All safety valves
				installed on high pressure boilers shall be installed on top of the boiler, or
				in the case of watertube boilers on top of the upper drum, with the spindle in
				the vertical position. All safety valves and safety relief valves installed on
				heating boilers shall be on top of the boiler or on an opening at the highest
				practicable part, as determined by industry standards, of the side of the
				boiler, but in no case shall the safety valve be installed below the normal
				operating level for a steam boiler. Safety valves and safety relief valves
				installed on hot water heating boilers, hot water supply boilers, and steam
				heating boilers shall be installed with the spindles mounted in the vertical
				position. Safety relief valves for water heaters may be installed with the
				spindles mounted in either the vertical or horizontal position. In no case may
				pressure relief devices be mounted on appurtenances, unless permitted by the
				Accepted Design and Construction Code for modular heaters.
(g) The distance between the pressure relief
				device outlet nozzle on the boiler and the pressure relief device inlet shall
				be kept to a minimum consistent with the size of the pressure relief device and
				the pipe sizes required. In no case shall any valves or stops be installed in
				the inlet piping to the pressure relief device or in the discharge piping from
				the pressure relief device. The boiler outlet and the piping between the boiler
				outlet and the pressure relief device shall have a cross sectional area of not
				less than the cross sectional area of the pressure relief device
				inlet.
(h) Discharge piping from
				the pressure relief device outlet shall be the same size, or larger, than the
				outlet pipe connection on the pressure relief device and shall be extended full
				size to a safe location. A safe location shall be interpreted to mean a
				location within six inches of the finished floor of the mechanical room, to a
				location outside the building terminating a safe distance above the building
				roof or to a location outside the building within six inches above the finished
				grade. For vessels such as organic fluid heaters where the medium presents a
				hazard, the discharge shall be to a containment vessel large enough to hold all
				anticipated pressure relief discharges. When pressure relief device discharge
				piping is routed vertically, piped drainage shall be provided by the use of
				drip pan elbows installed on the outlet of each pressure relief device
				served.
(i) Multiple pressure
				relief devices may be piped to the point of discharge using a common discharge
				header pipe. The header pipe size shall have a diameter sufficient to provide
				an equivalent cross-sectional area equal to or larger than the sum of the
				cross-sectional areas of the pressure relief device outlets to which it is
				connected.
(j) Pressure relief
				devices on pressure vessels may be installed with the spindle in the vertical
				or horizontal position. The pressure relief device inlet, discharge piping, and
				the requirement for piping the discharge to a safe location shall be the same
				as noted for boilers. The requirement for discharge piping is optional for
				pressure vessels used to store compressed air, inert gasses, water, or other
				fluids no more hazardous than water.
(k) Pressure relief devices for direct fired
				pressure vessels and for those used as air compressor storage tanks shall be
				installed directly on the pressure vessel with no intervening valves. Pressure
				relief devices for all other pressure vessels may be installed directly on the
				pressure vessel or in the piping system.
(l) A stop valve may be installed between a
				pressure vessel and the pressure relief device if one of the following is
				satisfied:
(1) the stop valve is normally
				locked in the open position, and may only be closed when there is an attendant
				stationed at all times at the stop valve when it is in the closed position for
				testing purposes; or
(2) isolating
				the pressure relief device from the pressure vessel by closing the stop valve
				also isolates the pressure vessel from the source of pressure.