The steam boiler is dangerous machinery and for that reason, the law is required to control all aspects of the boiler. The Factory and Machinery (Steam Boilers and Unfired Pressure Vessels) Regulations 1970 provided strict requirements on safety aspects and controls on boilers. This Code stipulates that any boiler must consolidate thirteen essential accessories so that the boilers can operate safely.
The thirteen essential accessories can be grouped into three categories. The first category is the security setting. Safety accessories include safety valves, sight gauges, pressure gauge, low water alarm, low water fuel cutoff, and fusible plug. The second category is control accessories, which incorporate bleed valves, main shutoff valve, feed check valve, and feed pumps. The final category is the legal fit, which incorporates the inspector’s test fixture, registration plate, and manufacturer’s nameplate. In this article, I would discuss some security accessories.
The safety valve is the most important safety accessory of a boiler. It is installed to prevent excessive pressure build-up in the boiler which could cause a boiler explosion. The 1970 FMA regulations require that any boiler having a heating surface greater than 100 square feet must be equipped with two safety valves, one of which must be of the direct spring type, mounted vertically as close as possible to the steam boiler casing without shut-off valve fitted. Come in. The relief capacity of the safety valves is determined by the capacity of the boiler at maximum load. Safety valves must be able to effectively discharge all steam with a pressure rise of no more than ten percent of the authorized safe working pressure (ASWP). Safety valves must be set to blow at different pressures. The first valve should open when the pressure exceeds three percent above the boiler’s working pressure, while the other valve should open at a pressure slightly higher than, but not higher than, the ASWP. A boiler’s working pressure is typically set at seven percent below ASWP. The spindles, disk and other moving parts must not be made of materials that corrode easily.
The pressure gauge is the accessory that measures the steam pressure inside the steam boiler. The Bourdon tube is the most common pressure gauge used on a boiler. The Code specifies that a pressure gauge must be installed in the vapor space and must be provided with a stopcock and siphon that develops and maintains a water seal, protecting direct contact of live steam with the Bourdon tube. A pressure gauge is usually mounted in front of the boiler in such a position that it can be conveniently read by boilermakers from the firing floor. The FMA (Steam Boilers and Fireless Pressure Vessels) Regulations of 1970 stipulate that the diameter of the dial must not be less than 6 inches and must show a pressure within a tolerance of two percent of the authorized safe working pressure . The scale on the dial of a code pressure gauge shall be graduated not less than one and one-third and not more than two times ASWP.
A fusible plug is used in addition to other forms of low water level protection. This device is not required by the ASME code, but is still included in the 1970 FMA Regulations. The fuse plug on the water tube boiler is placed 3 inches below the lowest water level, while on the fire tube boiler, the Fuse plug is placed 3 inches above the upper tubes. In the event of low water, the fusible plug will melt, the pressure inside the boiler will be released, and the sound of escaping steam will produce a loud whistle to alert the boilermakers. However, the ability of the fuse plug to put out the fire in the furnace is debatable because the steam that comes out is too small to have an extinguishing impact. The fuse plug hole is only 1/2″. The fuse plug is made of brass or bronze and contains a tapered hole. The hole is filled with tin which has a melting point of 230 degrees C. Per code , the fuse alloy must melt at a temperature of no more than 70°C above the ASWP saturated steam temperature, which corresponds to the melting temperature of tin Higher pressure would require a low level alarm This is why in a modern boiler, sometimes the fuse plug cannot be found, as it is replaced with a low water level alarm that performs exactly the same function.
