Boiler explosion

“ The most important points to find out in connection with any explosion are the condition of the boiler and all belonging to it immediately before the explosion, together with the locality of the first rent, the direction of the line of rupture, and the nature of the fracture; as everything occurring after the instant of the first rent is an effect and not a cause of explosion. As soon as the first rent has taken place, the balance of strain in the fabric is disturbed, and therefore the internal pressure has greatly increased power in continuing the rupture ”

“ Enough of the fragments were not recovered from the river to trace the cause of the explosion, but it is presumed that, although when the boiler was left, only 20 lbs. pressure was shown by the gauge; the fire door being left closed, the pressure must have risen to a point much above the working pressure, and to more than the boiler could bear. ”

“ Although it may be too much to suppose that boiler explosions will ever be entirely prevented, it is important that those who have Pg 68 the care of boilers should understand better what are the true causes of explosion, in order that they may know what to guard against in addition to shortness of water. This better understanding of the subject has been much retarded by the supposition that the causes of boiler explosions are beyond the comprehension of the boiler minders ”

“ If the scurf that has caused the mischief is thick and hard enough to resist the pressure for a little time, the hole enlarges, until the scurf suddenly gives way and allows the contents to issue so violently as to disturb the boiler, or at least to blow the fire out of the grate. Such was an explosion at Bilston in 1863, where a large plain cylindrical boiler, 9 ft. diameter, was heated by three large fires placed side by side along the bottom ”

“ In this case the cause of explosion was clearly the weakness of the tube, and not shortness of water. It is erroneous to suppose that if a boiler runs dry, or if the feed is turned into a red-hot boiler, there must necessarily be an explosion. If a boiler unconnected with any other runs rapidly empty, from the breaking of the blow-off pipe or any such cause, it will simply get red-hot and sink out of shape upon the fire, as may often be seen, but no explosion would happen. ”

“ External corrosion is a far more frequent cause of explosion in stationary boilers; and it arises from many causes. The most frequent cause, although the most easily detected, is leakage from the joints of the fittings on the top of the boiler, which are too frequently attached by bolts instead of rivets. This evil is much increased when the boilers are covered with brickwork, which holds the water against the plates, and hides the mischief from observation. ”

“ The repeated strain of screwing up the manhole lid, combined with the pressure of the steam, caused the lid to force its way out through the plate and blow away. This explosion occurred at Birmingham in 1865.
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The preceding examples have shown how explosions often result from faults in the construction of boilers; and the following instances illustrate the explosions caused by mischief arising during working. A boiler perhaps more than any other structure is subject to wear and tear; and let it be worked ever so carefully, it will seriously deteriorate. ”

“ When found at the part where the side flues are gathered in at the top against the boiler, it is usually occasioned by the leaking of fittings or feed pipes, or by rain being allowed to run between the boiler and the brickwork. More than one explosion has been caused by the droppings from a roof being allowed to fall upon the tops of the flues. When the corrosion is found at the point where the bottom flue walls touch the boiler, it is frequently caused by the leaking of seams that have been strained by the weight of the boiler ”

“ The explosion had taken place in the huge boiler-house of the great iron-works, a wall had been hurled down, part of the iron-beamed roof was hanging, one great barrel-shaped boiler had been blown yards away as if it had been a straw, and its fellow, about twenty feet long, was ripped open and torn at the rivets, just as if the huge plates of iron of which it was composed were so many postage-stamps torn off and roughly crumpled in the hand. ”

“ The first rent appears to have taken place where one of these plates joined the old work. The rent quickly extended along a straight seam, and the boiler was blown into three pieces. The explosion was simply caused by the boiler having been weakened by frequent repair until unable to bear the ordinary working pressure. Externally fired boilers, when so frequently patched become treacherous and uncertain, and more especially so when the seams run from end to end. ”

“ The tube collapsed over the fire, a rent taking place in the second ring of plates. The issuing steam and water caused the death of a man in front, but the shell of the boiler was not injured or moved.
The cause of the explosion was shortness of water, and as the glass gauge was set unusually low, the man in charge may have been deceived. The oval shape of the fireplace, and the laminated iron, as shown in the fracture, rendered the tube peculiarly liable to collapse. ”

“ The steam power required in ironworks so far exceeds that in any other trade, that an ironwork is half composed of boilers; the workmen are necessarily within the range of explosion of many boilers, and hence the great loss of life when such an accident occurs. The explosions of such boilers shown in Fig. 19 and Fig. 20, No. 24, 1868, and No. 31, 1868, were from external and internal corrosion respectively of the bottoms, rendering them too weak to bear the ordinary pressure.
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Fig. ”

“ Before considering in detail the causes of explosion, it is necessary to recall to mind that beyond question there is sufficient accumulated force in any working boiler to cause all the violent effects of an explosion, if this force be suddenly liberated. In Fig. 13 and Fig. 14, No. 18, 1869, and No. 63, 1866, are shown the violent effects of the rupture of vessels employed for steaming rags, which were filled with steam only. Pg 69 In ordinary boilers however there is present, besides the steam, a quantity of water heated much beyond the atmospheric boiling point ”

“ Pg 89
That the force accumulated in an ordinary boiler is enough to account for the violence of an explosion. That no form of boiler, however well constructed and fitted, is free from the liability to explosion, if allowed to get out of order; and that boilers which bear the hydraulic test may still be dangerous. That the condition of a boiler can be satisfactorily ascertained only by periodical examinations, and that no boiler should work without being thoroughly examined at short intervals. ”

“ Pieces of plate have in some cases been erroneously pronounced to be deteriorated by work, which have been taken from situations in the boilers where they were not exposed to any action of fire that could cause overheating; and therefore in reality the injury could only have taken place when the boiler was being made, by burning the iron in bending it to the required shape. A frequent cause of fatal injury to boilers is injudicious repair, whereby the crossing of the seams is destroyed, as in the explosion at Wolverhampton in 1865, previously referred to and shown in Fig. ”

“ Certain mechanical empirics and impractical quasi-scientists have at various times attempted to surround the cause of boiler explosions with a halo of mystery. But our most accomplished scientists who have made the subject a special study, and our best mechanical experts who have devoted years of patient experiment and research to the investigation of boiler explosion, attribute the terrible phenomenon to intelligible causes alone. The conclusions of the practical part of the mechanical world are well summed in one sentence in one of the annual reports of the Master Mechanics’ Association. ”

“ Then let the boiler cool down before putting in fresh water. Banking the fire is better than drawing or dumping it, as either of these make the heat greater for a moment or two, and that additional heat might cause an explosion. Dashing cold water upon the fire is also very dangerous and in every way unwise. Again, do not open the safety valve, for that also, by relieving some of the pressure on the superheated water, might cause it to burst suddenly into steam and so cause an explosion. ”

“ It is fortunate, however, that the error is usually upon the safe side of indicating more than the actual pressure.
Any boiler that has been standing idle for a few weeks or months is a dangerous thing to enter, and no one should attempt it until it has been thoroughly ventilated by taking off all the man hole and hand-hole plates and throwing water into it. This is due to the presence of a gas which is generated from the refuse and mud, or scale, which, to a greater or less degree, remains in all boilers. Contact with fire is certain to result in an explosion. ”

“ So few persons comparatively have the opportunity of examining boilers after explosion, that the most erroneous ideas have prevailed, and theories have been advanced which would soon be dissipated by practical experience or by reading accurate reports. ”

“ In most cases of explosion of this class of boiler the bottom was torn off, owing to the angle iron round it being weakened by the alternate bending backwards and forwards under each variation of pressure, as all the sides and the bottom must be constantly springing when at work. Such was the explosion at Chester in 1822, and many others. This shape was soon improved in its steam generating powers by making the sides concave instead of flat, as shown in Fig. 12., so that the heating surface was greater and also in a better position to receive the heat from the flame in the flues. ”

“ Perhaps no boilers have worked for a greater number of years than the Plain Cylindrical boilers, many specimens being in existence and apparently in good order which were put to work fifty or sixty years ago. When such boilers have been too much or injudiciously Pg 72 repaired, they are treacherous and uncertain; but their rupture and explosion occur not so much on account of fault of shape, as from the simple reason that like willing horses they are easily overworked. ”

“ Although boilers do explode from the softening of the plates by Pg 67 overheating in consequence of shortness of water, yet it is very doubtful whether the turning on of the cold water at such a time is ever the cause of explosion. The feed water being always introduced at the bottom of the boiler, as in Fig. ”

“ It is sometimes asserted that corrosion cannot be the cause of an explosion, because the corroded place would simply give way and let off the steam harmlessly, or at least the boiler would not be displaced from its seating. When the corrosion is only local, and surrounded by sound plates of sufficient strength to arrest the extension of the fracture, this may be the case, as in an explosion at Sheffield in 1865, shown in Fig. ”

“ Several instances have occurred of explosion of Portable Crane Boilers. Their small size has led to their condition being disregarded, under the idea that scarcely any pressure could burst them. In practice it is found however that they are often exposed to greater pressure than other boilers, because the fire is large and quick in proportion to their size; and they often have to stand for a considerable time with the steam up, and their exposed position and long intervals of rest add to the chances of corrosion, as shown by the example in Fig. ”

“ First as to faults of construction which fall under the department of the boiler maker or repairer. One of the most apparent causes of explosion in stationery boilers is the loss of strength occasioned by frequent repair, not only from the injury done to the old plates by removing rivets, but from the want of bond in the new work. This has lead to many of the explosions of the Plain Cylindrical boilers, such as are shown in Fig. ”

“ Probably four-fifths of the boiler explosions which have taken place on the Mississippi River during the last eighty years—and there have been hundreds of such—were the result of these conditions: low water in the boilers, exposing the plates until red-hot, then throwing in water and "jumping" the steam pressure faster than the engines or safety-valve could release it, followed by the inevitable giving away of the whole fabric of the boiler, wrecking the steamer, and usually killing and scalding many of the passengers and crew. ”

“ The early explosions were so palpably due to the weakness of the boilers, which compared with those of the present day were most ill constructed, that no one Pg 9 thought of any other cause than the insufficient strength of the vessel to bear the expansive force of the steam contained in it. When the advantages of high-pressure steam became recognized, and the boilers were improved so as to bear the increased strain, the tremendous havoc caused by an explosion led many to think that something more must be required than the expansive force of the steam to produce such an effect ”

“ Low water is dangerous from the fact that it leaves parts of the boiler to be overheated and the strength of iron rapidly decreases in such a case. In fact, an explosion caused by low water might be expected to be less disastrous than if the water was higher, other conditions being equal, from the fact of there being less water at a high temperature ready to flash into steam at the moment of liberation. ”

“ The famous British engineer, Fairbairn, asserted the principle: A steam-boiler should be so constructed as not to be liable to explosion. [3] The modern water-tube boiler of good design combines the principle that a steam-boiler should not be liable to disruptive explosion with that which asserts that, if rupture does occur, it shall be in minimum degree dangerous. It was asserted by the writer, a generation ago, that this class must ultimately displace the older forms of 'shell-boiler' which are liable to destructive explosion. ”