BS EN 12952-10:2002 – Water-tube boilers and auxiliary installations — Part 10: Requirements for safeguards against excessive pressure
5 Requirements
5.1 Steam boiler
5.1.1 Each steam boiler and each isolatable heated compartment (e.g. reheater, superheater, economizer) shall be provided with at least one suitable safety device which shall ensure against excessive pressure. The total certified discharge capacity of all safety devices mounted on the boiler shall be at least equal to the maximum continu- ous rating (MCR) of the boiler. The suitability of the safety device shall be demonstrated by a hot test on the as- sembled boiler. The number and type of safety devices to be installed shall be specified by the manufacturer and shall meet the requirements of this clause. At least one of the following safety device shall be considered suitable:
a) direct-loaded safety valves in accordance with prEN 1268-1or;
b) assisted safety valves in accordance with prEN 1268-1 or;
c) supplementary-loaded safety valves in accordance with prEN 1268-1 or;
d) pilot-operated safety valve (POSV) in accordance with prEN 1268-1 or prEN ISO 4126-4, consisting of a main valve, controlled by signals from 3 pilot valves;
e) controlled safety pressure relief system (CSPRS) in accordance with prEN 1268-5, consisting of a main valve, controlled by signals from 3 sensing lines.
The safety device shall be capable of operating when the signal from only one pressure sensing line is avail-able.
The size and position of the pressure sensing lines shall ensure that the risk of loss of function is reduced to a minimum.
The mechanical and electrical parts of the pilot and control unit which are used to actuate the main valves shall still be functionally fit even in the case of an assumed individual defect.
It shall be possible to prove the reliability of the safety pressure relief device by functional testing on the plant.
In case of assisted, supplementary loaded safety valves, POSV and CSPRS shall be allowed to control one or more main valves by the same control unit.
5.1.2 The minimum flow diameter of safety valves or main valves of POSV or CSPRS for boilers with a volume ≤ 10 litres shall be at least 6 mm and for volumes > 10 litres shall be at least 15 mm.
5.1.3 In the case of boilers without superheater(s) the safety valves or main valves of POSV or CSPRS shall be connected to the steam space.
NOTE If the total required discharge capacity is q m and the drumspace is simultaneously protected by n safety devices ( n > 1) the discharge capacity of each of them should be at least q m /( n + 1).
5.1.4 In the case of once-through steam generators the safety valves or main valves of POSV or CSPRS shall be located at the steam outlet of the boiler.
5.1.5 In the case of superheaters that cannot be isolated the following shall apply:
1) Safety devices in accordance with 5.1.1 located at the superheater outlet shall be of sufficient capacity to prevent the allowable wall temperature of the superheater from being exceeded.
BS EN 12952-10:2002 – Water-tube boilers and auxiliary installations — Part 10: Requirements for safeguards against excessive pressure