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Boiler explosions are catastrophic failures of boilers. As seen today, boiler explosions are of two kinds. One kind is over-pressure in the pressure parts of the steam and water sides. The second kind is explosion in the furnace. Boiler explosions of pressure parts are particularly associated with steam locomotives. Locomotive boilers are of a construction with a very small hand-fed furnace, a boiler barrel containing boiling water under pressure, and tubes containing superheated gases from the fire (a fire tube boiler). In these, the latter type of explosion from the furnace side is practically unheard of.
These boilers are of a smoke tube type with wood, coal or oil used as fuel. The water feed is by means of steam-powered injectors or boiler feedwater pumps. For storage of fuel and water a separate tender is often provided, adding to the length of the locomotive. This tender usually has a sloping floor for easy flow of fuel toward the locomotive cab and firebox therein. There is a safety valve included on the steam side and also one or more gauges to warn of low water levels. Any failure of these would result in an explosion of the pressure parts with consequent injury to operating personnel, apart from the damage to equipment. The consequences are more severe due to the restricted working space and constant movement of the locomotives.
Safety valves are provided to operate the pressure parts within safe limits. The water level alarms are provided for corrective action by the locomotive drivers.
The steamboat Sultana was destroyed in an explosion on 27 April, 1865, resulting in the greatest maritime disaster in United States history. An estimated 1,700 passengers were killed when one of the ship's four boilers exploded and the Sultana sank not far from Memphis, Tennessee.
The boiler was thought to be the victim of bad construction. Sometimes known as 'the leaky woes'
Use of boilers
In the very early days, locomotives used reciprocating steam engines to move the wheels. High-pressure boilers became widespread after the pioneering work of Richard Trevithick in his attempts to improve the efficiency of the steam engine invented by James Watt. Trevithick developed one of the first locomotives Pen-y-darren in the early 1800s, and was later followed by George Stephenson. Standing steam engines used to power machinery were essential during the industrial revolution, and there were many boiler explosions from a variety of causes. One of the first investigators of the problem was William Fairbairn, who helped establish the first insurance company dealing wth the losses such explosions could cause. He also established experimentally that the hoop stress in a cylindrical pressure vessel like a boiler was twice the longitudinal stress. Such investigations helped him and others explain the importance of stress concentrations in weakening boilers. The use of steam engines and boilers has been almost eliminated in present day locomotives worldwide. However, references are made here to the experiences of early boilers.
The following information is given for comparison only. These are mainly land based industries for driving steam turbines working as prime movers.
Modern boilers are more sophisticated and larger, constructed for stationary use. These boilers are both water tube and high-pressure types. These types are more sophisticated with all necessary protections, primarily used in land based industries and thermal power stations, particularly of power-generating utilities. The installation in these provides sufficient space for operator movement for them to be in a safe place in case of emergency, such as boiler or furnace explosions, as compared to early locomotive boilers.
In steam locomotive boilers, as knowledge was gained by trial and error in early days, the explosive situations and consequent damage due to explosions were inevitable. However, improved design and maintenance markedly reduced the number of boiler explosions by the end of the 19th century. Further improvements continued in the 20th century, but other methods of prime movers for locomotives had come into practice, such as diesel engines, which proved to be much safer, convenient, and economical.
On land-based boilers, explosions of the pressure systems happened regularly in stationary steam boilers in the Victorian era, but are now very rare because of the various protections provided, and also because of regular inspections compelled by governmental and industry requirements. Furnace side explosions do happen occasionally, in spite of provisions requiring furnace side explosion doors, wrecking the whole boiler mostly due to operators bypassing the operating instructions.
Locomotive boiler explosions in the UK
Hewison (1983) gives a comprehensive account of British boiler explosions, listing no less than 137 between 1815 and 1962. It is noteworthy that 122 of these were in the 19th century and only 15 in the 20th century.
Boiler explosions generally fall into two categories. The first is the breakage of the boiler barrel itself, through weakness/damage or excessive internal pressure, resulting in sudden discharge of steam over a wide area. Boiler plates have been thrown up to a quarter of a mile (Hewison, Rolt). The second type is the collapse of the firebox under steam pressure from the adjoining boiler, releasing flames and hot gases into the cab. Improved design and maintenance almost totally eliminated the first type, but the second type is always possible if the traincrew do not maintain the water level in the boiler.
Boiler barrels could explode if the internal pressure became too high. To prevent this, safety valves were installed to release the pressure at a set level. Early examples were spring-loaded, but Ramsbottom invented a tamper-proof valve which was universally adopted. The other common cause of explosions was internal corrosion which weakened the boiler barrel so that it could not withstand normal operating pressure. In particular, grooves could occur along horizontal seams (lap joints) below water level. Dozens of explosions resulted, but were eliminated by 1900 by the adoption of butt joints, plus improved maintenance schedules and regular hydraulic testing.
Fireboxes were generally made of copper, though later locomotives had steel fireboxes. They were held to the outer part of the boiler by stays (numerous small supports). Parts of the firebox in contact with full steam pressure have to be kept covered with water, to stop them overheating and weakening. The usual cause of firebox collapses is that the boiler water level falls too low and the top of the firebox (crown sheet) becomes uncovered and overheats. This occurs if the fireman has failed to maintain water level or the level indicator (gauge glass) is faulty. A less common reason is breakage of large numbers of stays, due to corrosion or unsuitable material.
Of the 20th century accidents, just 2 were boiler barrel failures (at Cardiff 1909 and Buxton 1921), and both were caused by misassembly of the safety valves so that the boiler reached a pressure far higher than designed. Of the 13 firebox collapses, 4 were due to broken stays, 1 to scale buildup on the firebox and the remaining 8 were low water level.
List of locomotive boiler explosions
(in chronological order)
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Boiler_explosion". A list of authors is available in Wikipedia.|