Fluid related safety.
The boiler operates with steam pressures in the range of 200 bar or even more. The steam temperature is also high in the range of 600 °C. This will be the condition inside the water and steam tubes and connected parts. On the furnace side the outside of the tubes, the gas temperatures can be as high as 1400 °C. The water or steam carrying tubes, the drum and other connected parts have to be strong enough to withstand these temperatures and pressures. Imagine what will happen if the tubes or pipes burst open at this pressure and temperature. The result will be a catastrophic accident which can also lead to fatalities.
Design and Manufacturing stage.
To prevent such failures every detail from the metallurgy of the steel used, strength calculations for each part, manufacturing and welding procedures are subject to strict adherence to code compliances. Every part is tested and results documented to ensure compatibility with the codes. Hydro tests at pressure of 1.5 to 2 times the operating pressure at the end of the construction phase ensure that all parts can withstand the high pressure conditions.
Abnormal operating conditions.
The pressure parts can withstand these high temperatures and pressures under normal operating conditions. If due to an abnormal operating condition the pressure of the boiler rises beyond control, then the parts will become weak and the chance for a failure is very high. Safety valves prevent such abnormal pressure increase in the boiler. When there is an abnormal increase in pressure the safety valves will automatically open and let out the steam to the atmosphere.
The furnace of the boiler is made of water carrying tubes. Heat transfer takes place in these tubes to produce steam. If there is not enough water in these tubes, the tubes will overheat and fail. Water level is the key parameter in boiler operation. This is continuously monitored. In case the water level falls to less than the minimum, control systems will cut off the fuel supply to the boiler thereby cutting of the heat input into the boiler and preventing any damage.
‘Boiler and Pressure Vessel code’ of the ASME is one the most commonly used codes. All over the world design, manufacturing and operation of a boiler follow these codes or equivalent regulations. Most of the countries these are mandatory by law.