General
However, very little work has been done on the effect of boiler blast loading on structures. The purpose of this research is to discover a simple analytical method of predicting boiler shock load on structures through destructive testing to minimize the risks, loss of life and properties due to explosions of non-flammable liquid boilers in Bangladesh.
Research Objectives
The intensity of an explosion is related to the extent to which the explosion can perform mechanical operation. There are some technical manuals and design handbooks on the calculation of blast loads (Brode, 1955; Crowl, 1992a; Hemmatian, Casal, et al. Mills, 1987; Newmark and Hansen, 1961) which are limited to the blasting of explosives and extremely flammables. liquids.
Methodology of Work
A theoretical time history plot for the blast pressure for the front wall will then be determined (Karlos and Solomon, 2013). Load cells will be used to record the blast load on the steel sheet in order to generate an experimental time history plot.
Scope of the work
For this reason, a destructive test of an idealized steam boiler of small size (capacity 14-15 liters) will be carried out. Mild steel tubes and mild steel sheets will be used to make a total of 9 samples of steam boilers.
Organization of the Thesis
R indicates the distance between the center of the explosive charge and the target structure. 𝐻𝑒𝑥𝑝𝑑 = The heat of detonation of the actual explosive [MJ/kg] and 𝐻𝑇𝑁𝑇𝑑 = The heat of detonation of TNT [MJ/kg].
Introduction
Steam Boiler
- Classification of Boiler
- Boiler explosions
- Causes of boiler explosion
Boiler explosions lead to partial or complete collapse of the structure causing death and injury. Boiler explosions occur when any component of the boiler is not strong enough to withstand the pressure it is subjected to.
Air blast Load
Further analysis shows that the direct cause of the boiler explosion was overpressure in the combustion zone caused by water leakage from the boiler's pressure system.
Previous research on blast load testing of vessel containing flammable and non-
Hemmatian et al., (2017) compared the overpressure derived from various theoretical predictions using the TNT equivalent mass approach with the experimental data of Johnson et al. Ibrahim et al., (2019) investigated the consequences of a steam boiler explosion for boiler houses in factories throughout Egypt.
Summary of the previous study
Due to the unavailability of the systematic experimental data and the complexity of the pressure boiler explosion was described in terms of TNT equivalence. The value of gauge pressure in cylindrical tanks is not the same in the direction of the major axis.
Knowledge gaps
Various formulas for calculating peak incident overpressure are discussed in Section 3.7.2. The schematics in Figure A.5 (b) are used and the parameter values are shown in the table below.
Introduction
This chapter summarizes the characteristics of blast wave, theoretical predictions of blast using the equivalent TNT methods, determination of blast related parameters, batch energy calculation for the test boiler, etc.
Ideal blast wave characteristics
The negative phase lasts longer than the positive phase, with a minimum pressure value of Pso- and a duration of up to. The negative phase of the blast wave is generally neglected during design because the positive phase has been shown to be responsible for most structural damage.
Scaled Distance (Z)
Suppose an explosive charge of weight W1 and typical size d1, placed at a distance R1 from the point of attention, generates a blast wave of maximum pressure P, impulse i1, duration up to 1, with arrival time ta1 and that √𝑊𝑅1 . Then, according to this scaling rule, another explosive charge W2 with characteristic size d2 = 𝜆 d1, positioned at distance R2.
Explosive type and weight
The rest is released at a slower rate as the heat from the explosive products' combustion mixes with the surrounding air. Several tables describing the heat output of the most commonly used explosives (U.S. Department of the Army, 1990; Unified Facilities Criteria, 2008).
Categories of Blast-loading
- Unconfined explosions
- Confined explosion
An explosion in free air generates an initial discharge whose shock wave propagates from the center of the explosion, impacting the structure without any intermediate reinforcement. A Mach wavefront is formed when an explosive charge is detonated in air and the blast waves travel spherically outward before striking the structure after first interacting with the ground. The explosive charge is detonated near the ground surface and the blast waves impact the ground locally before propagating semi-spherically outward and striking the structure.
Each of these types of blast is associated with a particular blast loading of the structure because reflections and interference events along the propagation path can significantly modify the wave strength and thus the loading pressures. The initial wave is intensified by the non-breakable parts of the structure, and the products of the explosion are completely vented into the atmosphere, creating a shock wave (flow pressure) that propagates away from the structure.
Blast wave reflection
A fully ventilated explosion occurs within or near a barrier or enclosure structure that has one or more surfaces exposed to the atmosphere. After a limited interval, the initial wave, amplified by the fragile and non-fragile parts of the structure, and the detonation products are vented to the surroundings. The accumulation of quasi-static pressure is associated with the containment of detonation products, which consist of the accumulation of high temperatures and gaseous gases.
The particles must be able to bounce back freely in an ideal linear-elastic situation, resulting in a reflected pressure equal to the incident pressure, resulting in a doubling of the effective pressure on the surface. Depending on the structural geometry, types, size, weight, distance of the explosive and the interference of other barriers between the detonation site and the structure, the reflected pressure can be many times more than the incident pressure.
Factors affecting blast pressure
Theoretical prediction of boiler blast load
- Explosion energy calculation
- Structural blast load prediction
- Standoff distance
- Calculation of blast parameters for front wall
Threaded tape was used to make the boiler close to the back of the boiler. The test frame at BUET-JIDPUS was set up after the preparation of the boiler test. The sudden increase in the theoretical positive blast pressure (Figure 5.1 - Figure 5.9) for the different filling levels of the boiler indicates the shock wave.
Because weight of explosives is directly related to the filling degree of the steam boiler. However, the effect of distance or scaled distance is not correctly recognized in the experimental observation of the negative phase (Figure 5.11).
Introduction
Materials Used
- Mild Steel Pipe
- MS sheet for front and back side of boiler
- Nuts
- Heating Equipment
- Thermocouple and Digital Display
The average ultimate tensile strength and elongation of the MS board were found to be 611.84 MPa and 16.80%, respectively (Table 4.2). The advantage of using a threaded thermocouple and heater is that the boiler is sealed at the rear side plate. A 2000 watt electric immersion heater (pipe flange heater) connected to the rear side plate of the sample boiler was used to heat the water.
Since it has a threaded part, it can be easily attached to the boiler with the same size nut. The actual steam temperature inside the boiler sample was measured using a K-type temperature sensor of 4 inch length (Table 4.3).
Preparation of Boiler Sample
Test Setup
- Load Cells
- Data Logger
A portable data acquisition system (Figure 4.9) is used, which has 16 channels with isolation and up to 64 channels with differential inputs. In addition to the high precision of DEWETRON's fully isolated input amplifiers, the sensor calibration and correction in the software improve the measurement accuracy. In the back plate, two 3 cm holes with a center-to-center distance of 152.5 mm (6 inches) are drilled for attaching load cells. a) Front view of the test frame (b) View from the right of the test frame.
Data acquisition
The thermocouple and the heater were welded to the back of the boiler with two threaded bolts. As the charge level increases to 50% (Figure 5.4 - Figure 5.6), the predicted duration of the positive phase puff varies between 0.24 ms and 0.47 ms, and the experimental duration of the puff decreases. The main reason for this is that the negative pressure phase occurred simultaneously with the positive phase.
Due to the simultaneous occurrence of positive and negative pressure, an explicit correlation between the degree of filling and negative peak pressure could not be established (Figure 5.12b). The internal pressure in the boiler rises within a short time due to the high pressure build-up for higher filling levels.
Introduction
The findings of theoretical predictions and destructive test data for boiler bursting were compared in this chapter in terms of pressure time history, standoff distance or scaled distance, and boiler fill rate.
Comparison of theoretical pressure time-history with the pressure time-history
Comparison of blast over pressure for different standoff distances
Comparison of blast over pressure for different filling degrees
Temperature profile
The non-uniform groove on the faceplate of the boiler, as well as the failure surface, all contribute to this behavior. However, a large-scale boiler explosion test containing various flammable and non-flammable liquids can be performed for a more satisfactory understanding of the explosion pressure. Most of the boiler explosion pressure is absorbed during the rupture of the boiler (ductile failure) and only a fraction of the mechanical energy is released.
So the heat of detonation of the actual explosive (water), Hexp = E = 0.054 MJ/kg Table A.3: Calculation of scaled distance from stopping distance and TNT equivalent. If the entire response of the structure to the blast load is required, the parameters of the negative phase of the blast load must also be evaluated.
Introduction
The main objective of this study was to predict the theoretical pressure on building structures subjected to the explosion load of the boiler and to determine the explosion pressure on structures by the destructive test of a steam boiler.
Conclusions
For short distances (61 cm and 76 cm) the difference between the positive peak overpressures for the boiler explosion is negligible. An explicit connection between the filling level and negative peak pressure could not be established due to the simultaneous occurrence of positive and negative pressure. When the initial temperature in the boiler increases from 389.82 K to 400.50 K, the peak positive gauge pressure also increases from 0.57 kPa to 0.60 kPa, respectively.
Recommendations for Future Study
Task Committee on Explosion-Resistant Design of the Petrochemical Committee of the Energy Division of the American Society of Civil Engineers. From the preliminary tests the samples showed that the initial temperature inside the boiler at the time of the explosion varies between 120 °C to 135 °C. For the B60S10 boiler sample, the calculation of internal energy using exergy analysis and distance scaled by the equivalent weight of TNT are shown in the table (Table A.2 and Table A.3) below-.
Load cells together with the dynamic data logger were calibrated (Figure 4.8) using a universal testing machine and a calibrated load cell. Test data obtained from the two load cells were calibrated using the calibration equation and the average burst pressure was calculated using the average load and area (4 ft mm2) of the face plate of the test frame.
