N.Y. Comp. Codes R. & Regs. Tit. 12 §§ 14-9.5

Current through Register Vol. 46, No. 53, December 31, 2024

Section 14-9.5 - Power actuated pressure relieving devices

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.

(d) When stop valves are installed in the water-steam flow path between any two sections of a forced-flow steam generator with no fixed steam and waterline:

(1) the power-actuated pressure relieving valve(s) required by subdivision (a) of this section shall also receive a control impulse to open when the maximum allowable working pressure of the component, having the lowest pressure level upstream to the stop valve, is exceeded; and

(2) the spring-loaded safety valves shall be located to provide the pressure protection requirements in subdivision (b) or (c) of this section.

(e) A reliable pressure-recording device shall always be in service and records kept to provide evidence of conformity to the above requirements.

[FN3] The power-actuated pressure relieving valve is one whose movements to open or close are fully controlled by a source of power (electricity, air, steam, or hydraulic). The valve may discharge to atmosphere or to a container at lower pressure. The discharge capacity may be affected by the downstream conditions, and such effects shall be taken into account. If the power-actuated pressure relieving valves are also positioned in response to other control signals, the control impulse to prevent overpressure shall be responsive only to pressure and shall override any other control function.

N.Y. Comp. Codes R. & Regs. Tit. 12 §§ 14-9.5