Boilers, steam safety valve

Section 38 of the Factories Act 1961 defines a steam boiler as a any closed vessel in which for any purpose steam is generated under pressure greater than atmospheric pressure . Economizers used to heat water being fed to such a vessel and superheater for heating steam are also included. Every boiler must be fitted with the recommended safety measures (e.g. safety valve, stop valve, water gauge, low-water alarms, pressure gages, etc.). 

Safety Valve normally used for steam service, but suitable for gases or vapors. When used in steam generation and process steam service the valves conform to the ASME Power Boiler Code as well as the ASME Pressure Vessel... 

The pressure gauge and associated shut-off valve, the boiler vent cock valve, main steam stop valve, and safety valve can be observed rising above the crown sheet of a FT boiler (the highest point of the boiler), normally in a line running the length of the boiler. 

Water tube boilers have a pressure gauge, vent cock, and drum safety valve on the top of the steam drum. Where superheaters are fitted, the steam takeoff line leads to the superheater, which is followed by a superheater safety valve, automatic nonreturn valve, and stop valve with a pressure-equalizing line and valve. 

Safety valves are spring-loaded valves of various designs, typically with a steam huddling chamber feature that increases the total force of the steam, thereby causing the valve to pop up (pop-type SV) rather than rise slowly in response to increased pressure. Boilers operating at higher pressures (say, 600-3,000 psig) tend to have super-jet SVs. 

Stop valves are fitted to each main or auxiliary discharge steam outlet, close to the boiler (but not in front of a safety valve or superheater connection). They are employed to place a boiler in or out of service. Gate-type stop valves of outside stem and yoke valve (OS Y) design often are employed because they indicate whether they are open or shut by the (out/in) spindle position. 

CANDLE.—Read, in connection with the processes described at pages 430,431 —The operations of saponification of the fat, and decomposition of the lime-soap by sulphuric acid, have been hitherto effected in open vessels, under the ordinary pressure of the atmosphere. An improvement on this plan has been recently proposed by M, Delapchiek, of Besangoo, who substitutes dose vessels in Order to saponify the fat. Wash and decompose the lime-soap under a pressure of about twenty-two pounds to the square inch, by which the operations are considerably facilitated, and their duration shortened. The products by this process are said to be superior to those obtained in open vessels, and a considerable economy of flaid is effected. The apparatus consists essentially of a horizontal boiler, with a man-hole and two safety valves at the top, The heat is furnished by a large steam-pipe, running in a depression along the bottom of the boiler. The... 

Nuclear Boiler Assembly. This assembly consists of the equipment and instrumentation necessary to produce, contain, and control the steam required by the turbine-generator. The principal components of the nuclear boiler are (1) reactor vessel and internals—reactor pressure vessel, jet pumps for reactor water circulation, steam separators and dryers, and core support structure (2) reactor water recirculation system—pumps, valves, and piping used in providing and controlling core flow (3) main steam lines—main steam safety and relief valves, piping, and pipe supports from reactor pressure vessel up to and including the isolation valves outside of the primary containment barrier (4) control rod drive system—control rods, control rod drive mechanisms and hydraulic system for insertion and withdrawal of the control rods and (5) nuclear fuel and in-core instrumentation,... 

Around 1830 Timothy Hackworth developed an open-ended Safety Valve for the steam trains and boilers that were first being built around that time, which was the start of the Safety Valve design as we know it today. However, the steam installations didn t really become much safer with the safety devices then in use (Figure 1.3). 

Korea KS B 6216 Spring-loaded safety valves for steam boilers and pressure vessels... 

The resistance to heat and steam in combination with resistance to aging allows silicone rubbers to be used as seals in steam-heated irons, in safety valves in boilers, etc. 

If De Luc liked to think of steam boilers in the clouds, perhaps Hutton had pistons deep within the Earth As Davies also notes, the Earth/heat-engine analogy is reinforced by Hutton s treatment of volcanoes as a kind of safety valve. Hutton put it this way ... 

A boiler rupture occurs if steam flow output is prevented or restricted and the temperature and pressure in the boiler increases. If some form of safely device is not provided or is inadequate to limit the pressure to a safe value, the boiler will rupture. Boilers are required to be equipped with safety valves to relieve pressure if they exceed set values. Low points in some boilers are provided with fusible plugs. During normal operations, the plugs are covered with water which keeps them cool. If the water level drops and they are exposed, the plugs melt and create another vent for pressure relief. Boilers also have low-water shutoff devices which block in the burner fuel when the steam drum water drops below a certain level. 

Waste Heat Boilers, Steam Drum, and Superheater safety valves, level indicators, vents, fittings, non-retum valves, water gauge glass (should be visible from control room) position of blowdown vessel ... 

Stmctural saddle supports and woik platforms may be obtained from the vendor. Vendor shall supply all standard fittings and valves for feed water, blowdown, vent, safety, as well as steam stop valves, instmmentation, level controllers with low-level alarms, and boiler feed water pumps with motors. All of these shall be supplied with test certificates and approval of statutory authorities. 

On the other side the German Boiler Rule imposed a global safety valve capacity of 200% per steam generator realize on the German units by two 100% pilot operated safety valves. (One 100% safety valve + one 100% relief valve)... 

Oum s Process.—The ol ect of this process is to combine silicates of soda or potash with soap, under pressure, whereby a more perfect union is stated to be effected, and the same method is said to be applicable to ordinary soaps. For yellow soap Mr. Dunn takes tbe materials in tne usnal proportions,—say, tallow 7, palm-oil 3, lesin 3 parts, and caustic soda leys at 21 B. from 140 to 150 g ons. These are placed in a steam boiler (Fig. 20), which is furnished with a man-hole, safety-valve, and all other appendages of such an apparatus, with a thermometer pping into a chamber of meronty. At A is a feed-pipe, and at b a... 

These valves are each sized to pass a steam flow of 945,292 Ib/hr at 1308 psia. This limits steam generator pressure to less than 110% of steam generator design pressure during worst case transients. The secondary safety valves consist of two banks of 10 valves with staggered set pressures. The valves are spring-loaded safety valves procured in accordance with ASME Boiler and Pressure Vessel Code, Section III (see Table 5.2-1). Parameters for the secondary safety valves are given in Table 5.4.13-2. 

Overpressurization of the Reactor Coolant System (RCS) and steam generators is precluded by means of primary safety valves, secondary safety valves and the Reactor Protection System (RPS). Pressure relief capacity for the steam generators and RCS is conservatively sized to satisfy the overpressure requirements of the ASME Boiler and Pressure Vessel Code, Section III. The safety valves in conjunction with the RPS, are designed to provide overpressure protection for a loss-of-load incident with a delayed reactor trip. 

The System 80+ Standard Design, steam generators, and reactor coolant system are protected from overpressurization in accordance with the guidelines set forth in the ASME Boiler and Pressure Vessel Code, Section III. Peak reactor coolant system and secondary system pressures are limited to 110% of design pressures during a worst case loss load event. Overpressure protection is afforded by primary safety valves, secondary safety valves, and the Reactor Protection System. 

On lever-type safety valves the weight must be locked to the lever. Every part of every steam boiler shall be of good construction, sound material and adequate strength and free from patent defect and with its fittings and attachments properly maintained. 

The boiler (including economiser and superheater if fitted) must be thoroughly examined by a competent person when it is under normal steam pressure. This examination should be made on the first occasion when the steam is raised after the examination when the boiler is cold, and must consist of ensuring that the safety valve is adjusted so as to prevent the boiler being worked at a pressure greater than the maximum... 

All boilers should have a safety valve so adjusted as to prevent the boiler being worked at a pressure greater than the safe operating limit, a suitable stop valve, steam pressure gauge, at least one water level gauge, means for attaching a test pressure gauge and be provided with a low water alarm device. The nature and frequency of examination of boilers will be specified in the written scheme of examination. 

Occasional serious boiler accidents continued to happen through the twentieth century. Another workplace tragedy occurred at the New York Telephone Company, New York, on October 3,1962, when a boiler explosion left 23 dead and 94 injured. The failed boiler was fairly low-pressure, and weighed seven tons empty. The boiler operator had reportedly started the boiler then left the building to have lunch. In addition, however, three different safety systems were not operational. First, the operator started the boiler with the steam shutoff valve on the steam supply header pipe in the closed position. Second, a pressure switch had been inadvertently unplugged by a maintenance worker. Third, a pair of safety valves on top of the boiler apparently did not function when they exceeded pressure limits. 

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