Boiler explosion
Encyclopedia
A boiler explosion is a catastrophic failure
of a boiler
. 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 locomotive
s. Locomotive boilers are of a construction with a firebox containing the burning fuel, a boiler barrel containing boiling water under pressure, and tubes containing hot gases from the fire (a fire-tube boiler
). In these, the latter type of explosion from the furnace side is practically unknown. There can be many different causes, such as failure of the safety valve
or corrosion
of critical parts of the boiler. Corrosion at the edges of lap joint
s was a common cause of early boiler explosions.
It is particularly devastating because of the energy stored up in the heated liquid water. As an example, a basic fire-tube boiler steaming at 50 psi (344,737.9 Pa) contains water at a temperature of roughly 150 °C (302 °F). Were a catastrophic failure to occur and the vessel depressurized, most of the water would instantly flash into steam. Steam takes up 1,600 times more space than liquid water, meaning that each cubic metre of heated boiler water will expand into 1,600 cubic metres of steam and it will do so in a fraction of a second. That enormous volume of steam will expand outwardly to equalize its pressure with the atmosphere and thereby produce an explosion.
In the case of a firebox explosion, these typically occur after a burner flameout. Oil fumes, natural gas, propane, coal, or any other fuel can build up inside the combustion chamber. This is especially of concern when the vessel is hot; the fuels will rapidly volatize due to the temperature. Once the lower explosive limit (LEL) is reached, any source of ignition will cause an explosion of the vapors.
A fuel explosion within the confines of the firebox may damage the pressurized boiler tubes and interior shell, potentially triggering structural failure, steam or water leakage, and/or a secondary boiler shell failure and steam explosion
.
type with coke
, wood
, coal
or oil
used as fuel
. The water feed is by means of steam
-powered injector
s or boiler feedwater pump
s. 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 valve
s are provided to operate the pressure parts within safe
limits. The water level alarms aka water gauge are provided for corrective action by the locomotive crew. Should that gauge fail, the crew cabin will fill with scalding steam, making it near to impossible for the crew to take corrective action. For this reason the glass gauges are provided with a thick outer glass screen as additional protection. It is also common practice to provide the gauges with steam valves so they may be isolated, and to fit them in pairs, allowing one to be replaced in the event of wear or failure while the boiler remains operational.
. This practice was satisfactory for the annular joints, running around the boiler, but longitudinal joints, along the length of the boiler, diverted the boiler cross-section from its ideal, circular shape. Under pressure the boiler strained to reach, as nearly as possible, the circular cross-section. Because the double-thickness overlap was stronger than the surrounding metal, the repeated bending and release caused by the variations in boiler pressure caused internal cracks, or grooves, along the length of the joint. The cracks offered a starting point for internal corrosion, which could hasten failure. It was eventually found that this internal corrosion could be reduced by using plates of sufficient size so that no joins were situated below the water level.
(because the inner and outer walls expand at different rates under the heat of the fire), from corrosion, or from wasting as the heads of the stays exposed to the fire are burned away. If the stays fail the firebox will explode inwards. Regular visual inspection, internally and externally, is employed to prevent this. Even a well-maintained firebox will fail explosively if the water level in the boiler is allowed to fall far enough to leave the top plate of the firebox uncovered.
, a small steamboat
used to transfer passengers and cargo to and from the large coastal steamships that stopped in San Pedro Harbor in the early 1860s, suffered disaster when its boiler exploded violently in San Pedro Bay
, the port of Los Angeles
, near Wilmington, California on April 27, 1863 killing twenty-six people and injuring many others of the fifty-three or more passengers on board.
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
.
Another US Civil War Steamboat explosion was the Steamer Eclipse on January 27, 1865, which was carrying members of the 9th Indiana Artillery
. One official Records report mentions the disaster reports 10 killed and 68 injured; a later report mentions that 27 were killed and 78 wounded. Fox's Regimental Losses reports 29 killed.
s used to power machinery first came to prominence during the industrial revolution
, and in the early days 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 with 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.Fairbairn
's theoretical calculation assumes that the cylindrical vessel is much longer than its diameter. In practice, this is a viable approximation for any boiler that is a right cylinder or longer. Even for a short, squat boiler such as the Scotch
, the reduced end area due to the tubes and their staying effect on the end-plates means that the principal stress is still this hoop stress. Such investigations helped him and others explain the importance of stress concentration
s in weakening boilers.
, ASME, and others attempt to ensure safe boiler designs by publishing detailed standards. The result is a boiler unit which is less prone to catastrophic accidents.
Also improving safety is the increasing use of "package boilers." These are boilers which are built at a factory then shipped out as a complete unit to the job site. These typically have better quality and fewer problems than boilers which are site assembled tube-by-tube. A package boiler only needs the final connections to be made (electrical, breaching, condensate lines, etc.) to complete the installation.
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.
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.
Hewison (1983) gives a comprehensive account of British boiler explosions, listing 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 fell 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. Stress corrosion cracking
at the lap joint
s was a common cause of early boiler explosions, probably caused by caustic embrittlement
. The water used in boilers was not often closely controlled, and if acidic, could corrode the wrought iron
boiler plates. Galvanic corrosion was an additional problem where copper
and iron were in contact.
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 John 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.
Throughout the 20th century, two boiler barrel failures and thirteen firebox collapses occurred. The boiler barrel failures occurred at Cardiff in 1909 and Buxton in 1921; both were caused by misassembly of the safety valve
s causing the boilers to exceed their design pressures. Of the 13 firebox collapses, four were due to broken stays, one to scale buildup on the firebox, and the rest were due to low water level.
Catastrophic failure
A catastrophic failure is a sudden and total failure of some system from which recovery is impossible. Catastrophic failures often lead to cascading systems failure....
of a boiler
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
. As seen today, boiler explosions are of two kinds. One kind is over-pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
in the pressure parts of the steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
sides. The second kind is explosion in the furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
. Boiler explosions of pressure parts are particularly associated with steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
s. Locomotive boilers are of a construction with a firebox containing the burning fuel, a boiler barrel containing boiling water under pressure, and tubes containing hot gases from the fire (a fire-tube boiler
Fire-tube boiler
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...
). In these, the latter type of explosion from the furnace side is practically unknown. There can be many different causes, such as failure of the safety valve
Safety valve
A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits....
or corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
of critical parts of the boiler. Corrosion at the edges of lap joint
Lap joint
In woodworking or metal fitting, a lap joint is a technique for joining two pieces of material by overlapping them. A lap may be a full lap or half lap....
s was a common cause of early boiler explosions.
Principle
A boiler explosion is a kind of boiling liquid expanding vapor explosion.It is particularly devastating because of the energy stored up in the heated liquid water. As an example, a basic fire-tube boiler steaming at 50 psi (344,737.9 Pa) contains water at a temperature of roughly 150 °C (302 °F). Were a catastrophic failure to occur and the vessel depressurized, most of the water would instantly flash into steam. Steam takes up 1,600 times more space than liquid water, meaning that each cubic metre of heated boiler water will expand into 1,600 cubic metres of steam and it will do so in a fraction of a second. That enormous volume of steam will expand outwardly to equalize its pressure with the atmosphere and thereby produce an explosion.
In the case of a firebox explosion, these typically occur after a burner flameout. Oil fumes, natural gas, propane, coal, or any other fuel can build up inside the combustion chamber. This is especially of concern when the vessel is hot; the fuels will rapidly volatize due to the temperature. Once the lower explosive limit (LEL) is reached, any source of ignition will cause an explosion of the vapors.
A fuel explosion within the confines of the firebox may damage the pressurized boiler tubes and interior shell, potentially triggering structural failure, steam or water leakage, and/or a secondary boiler shell failure and steam explosion
Steam explosion
A steam explosion is a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or the interaction of molten metals A steam explosion (also called a littoral explosion, or fuel-coolant interaction, FCI) is a...
.
Locomotive boilers
These boilers are of a fire-tubeFire-tube boiler
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...
type with coke
Coke (fuel)
Coke is the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Cokes from coal are grey, hard, and porous. While coke can be formed naturally, the commonly used form is man-made.- History :...
, wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
, coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
or oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....
used as fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
. The water feed is by means of steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
-powered injector
Injector
ʎ̩An injector, ejector, steam ejector, steam injector, eductor-jet pump or thermocompressor is a pump-like device that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that dɯaws in and...
s or boiler feedwater pump
Boiler feedwater pump
A boiler feedwater pump is a specific type of pump used to pump feedwater into a steam boiler. The water may be freshly supplied or returning condensate produced as a result of the condensation of the steam produced by the boiler...
s. There is a safety valve
Safety valve
A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits....
included on the steam side and also one or more gauges
Sight glass
A sight glass or water gauge is a transparent tube through which the operator of a tank or boiler can observe the level of liquid contained within.-Liquid in tanks:...
to warn of low water levels. Any failure of these would result in an explosion
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...
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 valve
Safety valve
A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits....
s are provided to operate the pressure parts within safe
Safe
A safe is a secure lockable box used for securing valuable objects against theft or damage. A safe is usually a hollow cuboid or cylinder, with one face removable or hinged to form a door. The body and door may be cast from metal or formed out of plastic through blow molding...
limits. The water level alarms aka water gauge are provided for corrective action by the locomotive crew. Should that gauge fail, the crew cabin will fill with scalding steam, making it near to impossible for the crew to take corrective action. For this reason the glass gauges are provided with a thick outer glass screen as additional protection. It is also common practice to provide the gauges with steam valves so they may be isolated, and to fit them in pairs, allowing one to be replaced in the event of wear or failure while the boiler remains operational.
Grooving
The plates of early locomotive boilers were joined by simple overlapping jointsLap joint
In woodworking or metal fitting, a lap joint is a technique for joining two pieces of material by overlapping them. A lap may be a full lap or half lap....
. This practice was satisfactory for the annular joints, running around the boiler, but longitudinal joints, along the length of the boiler, diverted the boiler cross-section from its ideal, circular shape. Under pressure the boiler strained to reach, as nearly as possible, the circular cross-section. Because the double-thickness overlap was stronger than the surrounding metal, the repeated bending and release caused by the variations in boiler pressure caused internal cracks, or grooves, along the length of the joint. The cracks offered a starting point for internal corrosion, which could hasten failure. It was eventually found that this internal corrosion could be reduced by using plates of sufficient size so that no joins were situated below the water level.
Firebox
The intricate shape of a locomotive firebox, whether made of soft copper or of steel, can only resist the steam pressure on its internal walls if these are supported by stays attached to internal girders and the outer walls. They are liable to fail through fatigueFatigue (material)
'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...
(because the inner and outer walls expand at different rates under the heat of the fire), from corrosion, or from wasting as the heads of the stays exposed to the fire are burned away. If the stays fail the firebox will explode inwards. Regular visual inspection, internally and externally, is employed to prevent this. Even a well-maintained firebox will fail explosively if the water level in the boiler is allowed to fall far enough to leave the top plate of the firebox uncovered.
Steamboat boilers
SS Ada HancockSS Ada Hancock
SS Ada Hancock was a steam powered tender owned by Phineas Banning used to transfer passengers and cargo to and from large coastal steamships in San Pedro Harbor in the early 1860's...
, a small steamboat
Steamboat
A steamboat or steamship, sometimes called a steamer, is a ship in which the primary method of propulsion is steam power, typically driving propellers or paddlewheels...
used to transfer passengers and cargo to and from the large coastal steamships that stopped in San Pedro Harbor in the early 1860s, suffered disaster when its boiler exploded violently in San Pedro Bay
San Pedro Bay (California)
San Pedro Bay is an inlet on the Pacific Ocean coast of southern California, United States. It is the site of the Port of Los Angeles and the Port of Long Beach, which together form the fifth-busiest port facility in the world and easily the busiest in the Western Hemisphere...
, the port of Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...
, near Wilmington, California on April 27, 1863 killing twenty-six people and injuring many others of the fifty-three or more passengers on board.
The steamboat Sultana
Sultana (steamboat)
The SS Sultana was a Mississippi River steamboat paddlewheeler whose destruction in an explosion on April 27, 1865 was the greatest maritime disaster in United States history. An estimated 1,800 of the Sultanas 2,400 passengers were killed when three of the ship's four boilers exploded and the...
was destroyed in an explosion on 27 April 1865, resulting in the greatest maritime disaster in United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
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
Memphis, Tennessee
Memphis is a city in the southwestern corner of the U.S. state of Tennessee, and the county seat of Shelby County. The city is located on the 4th Chickasaw Bluff, south of the confluence of the Wolf and Mississippi rivers....
.
Another US Civil War Steamboat explosion was the Steamer Eclipse on January 27, 1865, which was carrying members of the 9th Indiana Artillery
9th Independent Battery Indiana Light Artillery
9th Indiana Battery Light Artillery was an artillery battery that served in the Union Army during the American Civil War.-Service:The battery was organized at Indianapolis, Indiana and mustered in December 20, 1861 for a three years service....
. One official Records report mentions the disaster reports 10 killed and 68 injured; a later report mentions that 27 were killed and 78 wounded. Fox's Regimental Losses reports 29 killed.
Use of boilers
The stationary steam engineStationary steam engine
Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars , agricultural engines used for ploughing or...
s used to power machinery first came to prominence during the industrial revolution
Industrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...
, and in the early days there were many boiler explosions from a variety of causes. One of the first investigators of the problem was William Fairbairn
William Fairbairn
Sir William Fairbairn, 1st Baronet was a Scottish civil engineer, structural engineer and shipbuilder.-Early career:...
, who helped establish the first insurance company dealing with the losses such explosions could cause. He also established experimentally that the hoop stress
Hoop stress
Circumferential stress is a type of mechanical stress of a cylindrically shaped part as a result of internal or external pressure.The classic example of circumferential stress is the tension applied to the iron bands, or hoops, of a wooden barrel...
in a cylindrical pressure vessel like a boiler was twice the longitudinal stress.Fairbairn
William Fairbairn
Sir William Fairbairn, 1st Baronet was a Scottish civil engineer, structural engineer and shipbuilder.-Early career:...
's theoretical calculation assumes that the cylindrical vessel is much longer than its diameter. In practice, this is a viable approximation for any boiler that is a right cylinder or longer. Even for a short, squat boiler such as the Scotch
Scotch marine boiler
A "Scotch" marine boiler is a design of steam boiler best known for its used on ships.The general layout is that of a squat horizontal cylinder. One or more large cylindrical furnaces are in the lower part of the boiler shell. Above this is a large number of small-diameter fire-tubes...
, the reduced end area due to the tubes and their staying effect on the end-plates means that the principal stress is still this hoop stress. Such investigations helped him and others explain the importance of stress concentration
Stress concentration
A stress concentration is a location in an object where stress is concentrated. An object is strongest when force is evenly distributed over its area, so a reduction in area, e.g. caused by a crack, results in a localized increase in stress...
s in weakening boilers.
Modern boilers
Modern boilers are designed with redundant pumps, valves, water level monitors, fuel cutoffs, automated controls, and pressure relief valves. In addition, the construction must adhere to strict engineering guidelines set by the relevant authorities. The NBICNBIC
NBIC can refer to different subjects:* Nanotechnology, Biotechnology, Information technology and Cognitive science * National Board Inspection Code...
, ASME, and others attempt to ensure safe boiler designs by publishing detailed standards. The result is a boiler unit which is less prone to catastrophic accidents.
Also improving safety is the increasing use of "package boilers." These are boilers which are built at a factory then shipped out as a complete unit to the job site. These typically have better quality and fewer problems than boilers which are site assembled tube-by-tube. A package boiler only needs the final connections to be made (electrical, breaching, condensate lines, etc.) to complete the installation.
Explosions
In steam locomotiveSteam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
boilers, as knowledge was gained by trial and error
Trial and error
Trial and error, or trial by error, is a general method of problem solving, fixing things, or for obtaining knowledge."Learning doesn't happen from failure itself but rather from analyzing the failure, making a change, and then trying again."...
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.
On land-based boilers, explosions of the pressure systems happened regularly in stationary steam boilers in the Victorian era
Victorian era
The Victorian era of British history was the period of Queen Victoria's reign from 20 June 1837 until her death on 22 January 1901. It was a long period of peace, prosperity, refined sensibilities and national self-confidence...
, but are now very rare because of the various protections
Safety
Safety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...
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
Boiler explosions generally fell 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. Stress corrosion cracking
Stress corrosion cracking
Stress corrosion cracking is the unexpected sudden failure of normally ductile metals subjected to a tensile stress in a corrosive environment, especially at elevated temperature in the case of metals. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when...
at the lap joint
Lap joint
In woodworking or metal fitting, a lap joint is a technique for joining two pieces of material by overlapping them. A lap may be a full lap or half lap....
s was a common cause of early boiler explosions, probably caused by caustic embrittlement
Caustic embrittlement
Caustic embrittlement is the phenomenon in which the material of a boiler becomes brittle due to the accumulation of caustic substances.-Cause:...
. The water used in boilers was not often closely controlled, and if acidic, could corrode the wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...
boiler plates. Galvanic corrosion was an additional problem where copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
and iron were in contact.
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 John Ramsbottom
John Ramsbottom (engineer)
John Ramsbottom was an English mechanical engineer who created many inventions for railways, including the piston ring, the Ramsbottom safety valve, the displacement lubricator, and the water trough.- Biography :...
invented a tamper-proof valve which was universally adopted. The other common cause of explosions was internal corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
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
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, though later locomotives had steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
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.
Throughout the 20th century, two boiler barrel failures and thirteen firebox collapses occurred. The boiler barrel failures occurred at Cardiff in 1909 and Buxton in 1921; both were caused by misassembly of the safety valve
Safety valve
A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits....
s causing the boilers to exceed their design pressures. Of the 13 firebox collapses, four were due to broken stays, one to scale buildup on the firebox, and the rest were due to low water level.
See also
- Steam explosionSteam explosionA steam explosion is a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or the interaction of molten metals A steam explosion (also called a littoral explosion, or fuel-coolant interaction, FCI) is a...
- Boiler safety
- Fusible plugFusible plugA fusible plug is a threaded metal cylinder usually of bronze, brass or gunmetal, with a tapered hole drilled completely through its length. This hole is sealed with a metal of low melting point that flows away if a pre-determined, high temperature is reached...
- Grover Shoe Factory disasterGrover Shoe Factory disasterThe Grover Shoe Factory disaster was an industrial explosion, building collapse and fire that killed 58 people and injured 150 when it leveled the R. B. Grover shoe factory in Brockton, Massachusetts on March 20, 1905...
- List of boiler explosions
- Lists of rail accidents
- William FairbairnWilliam FairbairnSir William Fairbairn, 1st Baronet was a Scottish civil engineer, structural engineer and shipbuilder.-Early career:...