Experimental investigation of boiler blast load on building structures

Abstract

Boilers are commonly used in many industries including the RMG sector of Bangladesh to perform numerous industrial processes. Explosion of steam boilers has become a common menace in the last few years in the context of Bangladesh. Moreover, numerous BLEVE (Boiling liquid expanding vapor explosion) incidents have occurred across the world, resulting in fatalities and injuries. Most of the researchers studied the blast due to explosives and extremely flammable fluids and developed different models on blast pressure prediction. Non-flammable fluid (e.g., water) as the filling liquid in steam boilers may behave differently from other explosives and flammable fluids. The equivalent TNT method is considered for the theoretical prediction of boiler blast load. Initially, the internal energy inside the boiler during the explosion is calculated using the exergy concept (thermodynamic availability) and converted to equivalent TNT mass. Finally, a theoretical pressure-time history of the sample boiler is plotted for the front wall considering different standoff distances and filling degrees. An experimental investigation of boiler blast is conducted in this study utilizing water heater to have a precise conception of the actual explosion scenario by developing a time-history diagram. A total of nine idealized small-scaled steam boiler samples were prepared for destructive testing, considering standoff distances of 61 cm, 76 cm and 91 cm with filling degrees of 40%, 50% and 60% respectively. The scaled distances of these samples varied from 1.255 m/kg0.333 to 2.156 m/kg0.333. For controlled testing a cross shaped groove was cut at the front plate of these boilers. For capturing impact load and internal temperature inside the boiler two load cells, dynamic data logger and temperature sensor were used. The actual explosion depicts a gradual increase in pressure to the peak positive overpressure, followed by a negative phase. The experimental blast waves have a prolonged blast phase and a lower positive peak overpressure than the theoretical prediction. As the standoff distance increases, the positive peak overpressure rapidly decreases. For a 40% filling degree and at a standoff distance of 61 cm, the positive peak overpressure amounts to 0.6 kPa (approx.). However, it declines rapidly beyond a 76 cm standoff distance and becomes 0.48 kPa (approx.). The behavior is comparable to filling degrees of 50% and 60%. Moreover, peak overpressure stays near enough for high degrees of filling even with a small standoff distance. However, for a constant standoff distance, minimal increment of peak overpressure is found for the increment of boiler filling degrees.