New York Codes, Rules and Regulations › Title 12 - DEPARTMENT OF LABOR › Chapter I - Industrial Board Of Appeals › Subchapter A - The Industrial Code › Part 14 - Construction, Installation, Inspection And Maintenance Of High Pressure Boilers; Construction Of Unfired Pressure Vessels › Subpart 14-9 - Power Boilers: New Installations › Safety Valves and Safety Relief Valves › Section 14-9.5 - Power actuated pressure relieving devices

Current through Register Vol. 46, No. 28, July 10, 2024
For a forced-flow steam generator with no fixed steam
						  and waterline, equipped with automatic controls and protective interlocks
						  responsive to steam pressure, safety valves may be provided in accordance with
						  section
						  14-9.9 
						  of this Subpart or the following protection against over-pressure shall be
						  provided:
(a) One or more
						power-actuated pressure relieving valves [FN3] shall be provided in direct
						communication with the boiler when the boiler is under pressure and shall
						receive a control impulse to open when the maximum allowable working pressure
						at the superheater outlet, as shown in the master stamping, is exceeded. The
						total combined relieving capacity of the power-actuated relieving valves shall
						be not less than 10 percent of the maximum design steaming capacity of the
						boiler under any operating condition as determined by the manufacturer. The
						valve or valves shall be located in the pressure part system where they will
						relieve the overpressure. An isolating stop valve of the outside-screw-and-yoke
						type may be installed between the power-actuated pressure relieving valve and
						the boiler to permit repairs provided an alternate power-actuated pressure
						relieving valve of the same capacity is so installed as to be in direct
						communication with the boiler in accordance with the requirements of this
						paragraph. Power-actuated pressure relieving valves discharging to intermediate
						pressure and incorporated into bypass and/or startup circuits by the boiler
						manufacturer need not be capacity certified. Instead, they shall be marked by
						the valve manufacturer with a capacity rating at a set of specified inlet
						pressure and temperature conditions. Power-actuated pressure relieving valves
						discharging directly to atmosphere shall be capacity certified and ASME Code
						stamped.
(b) Spring-loaded safety
						valves shall be provided, having a total combined relieving capacity, including
						that of the power-actuated pressure relieving capacity installed under
						subdivision (a) of this section, of not less than 100 percent of the maximum
						designed steaming capacity of the boiler, as determined by the manufacturer,
						except when the alternate provisions of subdivision (c) of this section are
						satisfied. In this total, no credit in excess of 30 percent of the total
						required relieving capacity shall be allowed for the power-actuated pressure
						relieving valves actually installed. Any or all of the spring-loaded safety
						valves may be set above the maximum allowable working pressure of the parts to
						which they are connected, but the set pressures shall be such that when all of
						these valves (together with the power-actuated pressure relieving valves) are
						in operation the pressure will not rise more than 20 percent above the maximum
						allowable working pressure of any part of the boiler, except for the steam
						piping between the boiler and the prime mover.
(c) The total installed capacity of
						spring-loaded safety valves may be less than the requirements of subdivision
						(b) of this section provided all of the following conditions are met:
(1) The boiler shall be of no less steaming
						capacity than 1,000,000 lb/hr and installed in a unit system for power
						generation (i.e., a single boiler supplying a single turbine-generator
						unit).
(2) The boiler shall be
						provided with automatic devices, responsive to variations in steam pressure,
						which include no less than all the following:
(i) a control capable of maintaining steam
						pressure at the desired operating level and of modulating tiring rates and
						feedwater flow--in proportion to a variable steam output; and
(ii) a control which overrides subparagraph
						(i) of this paragraph by reducing the fuel rate and feedwater flow when the
						steam pressure exceeds the maximum allowable working pressure by 10 percent;
						and
(iii) a direct-acting
						overpressure-trip-actuating mechanism, using an independent pressure sensing
						device, that will stop the flow of fuel and feedwater to the boiler, at a
						pressure higher than the set pressure of subparagraph (ii) of this paragraph,
						but less than 20 percent above the maximum allowable working
						pressure.
(3) There
						shall be not less than two spring-loaded safety valves and the total rated
						relieving capacity of the spring-loaded safety valves shall be not less than 10
						percent of the maximum designed steaming capacity of the boiler as determined
						by the manufacturer. These spring-loaded safety valves may be set above the
						maximum allowable working pressure of the parts to which they are connected but
						shall be set such that the valves will lift at a pressure no higher than 20
						percent above the maximum allowable working pressure.
(4) At least two of these spring-loaded
						safety valves shall be equipped with a device that directly transmits the valve
						stem lift action to controls that will stop the flow of fuel and feedwater to
						the boiler The control circuitry to accomplish this shall be arranged in a
						"fail-safe" manner (see Note).
Note:"Fail-safe" shall mean a circuitry arranged as
						  either of the following:
Note:
(1)
						Energize to trip: There shall be at least two separate and independent trip
						circuits served by two power sources, to initiate and perform the trip action.
						One power source shall be a continuously charged DC battery. The second source
						shall be an AC-to-DC converter connected to the DC system to charge the battery
						and capable of performing the trip action. The trip circuits shall be
						continuously monitored for availability. It is not mandatory to duplicate the
						mechanism that actually stops the flow of fuel and feedwater.
Note:
(2) De-energize to trip: If the circuits are
						arranged in such a way that a continuous supply of power is required to keep
						the circuits closed and operating and such that any interruption of power
						supply will actuate the trip mechanism, then a single trip circuit and single
						power supply will be enough to meet the requirements of this
						subparagraph.
(5) The
						power supply for all controls and devices required by this subdivision shall
						include at least one source contained within the same plant as the boiler and
						which is arranged to actuate the controls and devices continuously in the event
						of failure or interruption of any other power sources.