and Mill Furnaces, leading in some cases to the supposition that this
form of boiler is more liable to explosion than others. They were not
adopted however in the iron-making districts without great care and
consideration, and there does not seem ground for attributing special
danger to them. The causes of the five explosions referred to of these
boilers were manifest, and would have led to the explosion of any form
of boiler; the loss of life however was great, because the situation
of the boilers was among a large number of workmen. 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 Figs. 19 and 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.
[Illustration: _Fig. 21._]
[Illustration: _Fig. 22._]
[Illustration: _Fig. 24._]
Those shown in Figs. 21 and 22, No. 23, 1870, and No. 53, 1869, were
from the collapse of the central tubes, which were weakened by external
and internal corrosion respectively. In Fig. 24, No. 35, 1868, the
shell was in bad order from over work and receiving too much heat from
four large furnaces, one of these especially causing a constant mass of
flame to impinge upon a single plate, which resulted in a seam rip.
[Illustration: _Fig. 23._]
[Illustration: _Fig. 25._]
[Illustration: _Fig. 26._]
[Illustration: _Fig. 27._]
The greatest number of explosions and the greatest loss of life and
personal injury have been in the case of Cornish and Lancashire
boilers, or others with internal flues. In the county of Cornwall
itself there have been many explosions, as often from the rupture of
the shell, Fig. 23, No. 58, 1869, as from the collapse of the tube,
Fig. 25, No. 35, 1869. The temporary patching on some of these old
boilers was most extensive, Fig. 26, No. 52, 1869, and the only wonder
really was that they held together as long as they did. The belief that
shortness of water is the only cause which can lead to the collapse of
tubes is so strong, that the boiler minders have often been condemned
almost unheard in cases of explosion, as if there were no room for
doubt that their neglect was the cause. Explosions from weakness of
tubes are not however confined to Cornwall, as for example in Fig.
27, No. 42, 1868, where the flue was oval and very weak: although it
was supposed that shortness of water caused the accident, from the
idea that nothing else could account for it. The strain caused by the
varying temperature of the internal tubes in Cornish or Lancashire
boilers, and the difficulty of staying their flat ends so as to make
them sufficiently secure without being too rigid to allow for the
expansion of the tubes, render them liable to corrosion or "furrowing"
in particular lines of strain, the destructive action of which is
very rapid; while the large quantity of brickwork around the outside,
necessary to form the external flues, also renders them liable to
corrosion in the parts most difficult of access. In this favourite
form of boiler therefore careful and frequent examination in every part
is more needed than in boilers of simpler form and setting; and the
increasing number of explosions among these boilers seems to establish
that they are only trustworthy if frequently examined and kept in
perfect order.
[Illustration: _Fig. 28._]
[Illustration: _Fig. 29._]
[Illustration: _Fig. 30._]
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. 28, No.
14, 1869. The large manholes without strengthening rings, that are so
often put in these boilers, have been the cause of explosions such as
that shown in Fig 29, No. 57, 1866.
[Illustration: _Fig. 31._]
The same remark applies to some of the portable or agricultural
boilers which have exploded, such as those shown in Figs. 30 and 31,
No. 43, 1868, and No. 12, 1869.
Much mischief is often caused by bad imitation of well planned boilers.
Thus in boilers of the Cornish form, the ends are made sometimes so
rigid as to give no allowance for the expansion of the tube, and the
result is such continued strain as to cause constant leaking and the
consequent risk of fracture. In furnace boilers the tops of the crowns
of the inside tubes are often made flat, as in Fig. 37, instead of
being domed; or the inside tube is of undue size, as in Fig. 21, No.
23, 1870, see page 73. Furnace boilers have been made with the omission
of the stays that are so peculiarly necessary in that form, whereby
both ends have been left free to bulge outwards with the pressure, as
in Fig. 32.
[Illustration: _Fig. 37._]
[Illustration: _Fig. 32._]
[Illustration: _Fig. 33._]
[Illustration: _Fig. 34._]
[Illustration: _Fig. 35._]
Cornish boilers are often altered to the plain cylindrical form,
without compensation being made for the loss of strength caused by
the removal of the tube; this has led to such explosions as shown in
Fig. 33, No. 47, 1869, where two tubes where taken out, and Fig. 34,
No. 42, 1867, where one tube was taken out. One of the most frequent
and serious causes of loss of strength is the repairing of externally
fired boilers. Not only are the patches sometimes only bolted on in a
temporary manner, as in Fig. 35, No. 29, 1869, but even where they are
rivetted on there is an entire want of bond or crossed joint, as in the
case of the exploded boilers shown in Figs. 15, 16, and 17, see page
70 and 71, No. 10, 1869, and Fig. 36.
[Illustration: _Fig. 36._]
[Illustration: _Fig. 38._]
An attempt is made in Fig. 38 to show the effect of wear and tear
of boiler plate in an ordinary upright furnace boiler, such as is
shown in Fig. 37. The external surface is exposed to intense heat
and consequently expands, while the internal surface is kept cool by
contact with the water and expands to a much less degree. The continued
repetition of this process produces the same effect of cracking the
surface as that seen in the anvil blocks of steam hammers; and the
strength of the plate is reduced in proportion to the destruction of
the continuity of its surface. The deleterious effect of this process
is much increased if the boiler is subject to alternate heating
and streams of cold air on opening the fire-doors. To avoid it the
flame should have room to spread over as large a surface as possible,
without impinging on one particular point, and the firing should be
as regular as possible; and hence the greater freedom from injury in
boilers mechanically fired or heated by gas. The above action is quite
distinct from the overheating of the plates that occurs when no water
is in contact with them, which simply softens them and reduces their
strength, as in Fig. 39. It is believed that many boilers suffer from
overheating without being short of water: and an attempt is made to
show this action in such an upright boiler as is represented in Fig.
37, page 78, by the enlarged section of the side shown in Fig. 40.
The flame is shown impinging on a limited surface, as before, and
the steam rises so rapidly from the inner surface as to maintain a
continuous stratum of steam between the iron and the water, and the
plate consequently becomes overheated at that part. When the intense
flame subsides by an alteration of the working of the furnace, the
stream of steam diminishes, and the water returns and suddenly cools
and contracts the plate, but often not before it has commenced to get
out of shape. This has perhaps led to the explosion shown in Fig. 59,
No. 37, 1868, page 82. The same thing may happen to the crowns of tubes
of internally fired boilers when over fired, as in Fig. 41. Success
has attended the use of internal linings to boilers, arranged so as
to ensure a rapid circulation over the most heated parts, and also to
catch all the mud and loose scale.
[Illustration: _Fig. 39._]
[Illustration: _Fig. 40._]
[Illustration: _Fig. 59._]
[Illustration: _Fig. 41._]
[Illustration: _Fig. 42._]
[Illustration: _Fig. 43._]
[Illustration: _Fig. 44._]
In order to enable boiler minders to make proper periodical
examinations, it is necessary that care should be taken to arrange
both the boilers and the flues with that view; and this can be done
without materially injuring the efficiency of the boiler. Ordinary
plain cylindrical boilers can be entered easily, as in Fig. 42; and
although the small spaces between the tubes and the shells of Cornish
and Lancashire Boilers, as shown in Fig. 43, render the complete
examination troublesome, there is no difficulty in seeing those parts
most likely to need examination, such as the crowns of the tubes and
the end plates and angle iron. It is in the external flues that greater
accommodation is needed, as in many cases these are so narrow that the
boiler is quite inaccessible without pulling down the brickwork, as in
Figs. 44 and 45. The loss of heating effect caused by the use of wider
flues is so little, that it is far outweighed by the greater security
obtained from the more efficient examination that is thereby rendered
practicable. The flues of the plain cylindrical boiler are easily
made wide enough for a man to pass through them. The flues of Cornish
and Lancashire boilers should be made as shown in Figs. 46 and 47, so
that a man can enter them without such inconvenience as in Fig. 48.
One point of danger being the use of wide mid-feather walls, on which
corrosion is apt to take place, these should be narrowed and the weight
of the boiler supported on side brackets; the top of the mid-feather
and side walls can then be constructed with sight holes as at A A in
Figs. 49 and 50, so as to give the means of examining the plates near
each seam by simply removing loose bricks.
[Illustration: _Fig. 45._]
[Illustration: _Fig. 46._]
[Illustration: _Fig. 47._]
[Illustration: _Fig. 48._]
[Illustration: _Fig. 49._]
[Illustration: _Fig. 50._]
[Illustration: _Fig. 51._]
[Illustration: _Fig. 52._]
[Illustration: _Fig. 53._]
[Illustration: _Fig. 54._]
[Illustration: _Fig. 55._]
The explosions of fourteen Domestic or Heating-Apparatus Boilers are
included in the list of explosions, Table III; and some notice is
required to be taken of these, because they have led to the loss of the
lives of those who could not be expected to know their construction or
how to guard against accident; and as these boilers are seldom seen or
examined after they are once set, they should be the more carefully
constructed. In one or two cases these boilers were of a rectangular
shape, as in Fig. 51, No. 41, 1868, ill adapted to bear internal
pressure, and yet placed in connection with cisterns in the roofs of
lofty houses, so as to expose them to a hydrostatic pressure almost
up to their bursting strength without any addition of steam pressure.
The most usual cause of explosion is the lighting of the fire during
frosty weather in a house that has been left vacant, so that steam
pressure accumulates in the boiler whilst the exit is frozen up, as was
the case in Fig. 52, No. 6, 1870. The cast-iron boilers commonly used,
Fig. 53, end of 1869, are capable of bearing but little pressure; and
the wrought iron boilers, as in Fig. 54, No. 7, 1870, are found often
so badly welded as to be but little stronger; but even if they were as
strong as they could be made, the stoppage of the pipes by ice would
lead to explosion. Steam pressure may be guarded against by a safety
valve; but as this may become set fast in a little time, it would
be far better to avoid all chance of steam accumulation by such an
arrangement as that shown in Fig. 55, where the circulating boiler is
placed within an open-topped boiler behind the kitchen fire, and only
receives its heat through the hot water surrounding it, and therefore
cannot itself become sufficiently hot to generate steam.
* * * * *
[Illustration: _Fig. 56._]
A few remarks may be useful as to those faults arising in working
which fall under the department of the boiler minders. Not a few of
the explosions during the last four years have occurred from acts of
simple carelessness, such as where a blow-off pipe was left open,
so that the boiler was nearly emptied of water while at work; or in
another case where two boilers were fed at the same time through a
common pipe without a back valve, and the water from one "kicked" over
into the other. Undue pressure has been allowed to accumulate by safety
valves being tied down, as in the agricultural boiler, Fig. 56, No. 16,
1867; or by an extra weight being put upon the safety valve, as in an
instance where three bricks were fastened to the lever and the fires
were lighted earlier than usual, under the idea that an accumulation
of steam could be raised during the night to make a good start in the
morning. Another explosion was caused by working a boiler at more than
three times its proper pressure to meet a temporary emergency. In not a
few cases of explosion there was no pressure gauge on the boiler, or
the gauge was out of repair in consequence of being placed on the steam
pipe, so that it vibrated with every stroke of the engine; as in the
examples shown in Figs. 24 and 16, No. 35, 1868, No. 32, 1870, pages 70
and 74.
[Illustration: _Fig. 57._]
Corrosion has been the direct cause of many of the explosions. In one
or two cases the corrosion was known to exist, but the renewal of the
boiler was too long delayed, as in Fig. 57, No. 8, 1869, in others it
took both owners and minders by surprise, as in Fig. 1, No. 12, 1870,
page 63. It is said that to produce rapid rusting of iron there must be
present oxygen, water, and carbonic acid; and as all these are present
in a boiler flue when there are leaks, it is not surprising that so
many cases occur of explosions from corrosion.
* * * * *
Much mischief is often done by the injudicious use of compositions in
the boiler that are designed to prevent incrustation, especially where
there is no blow-off cock or where its use is neglected. A hard deposit
on the boiler plates is, in the writer's opinion, not so injurious as
the soft and muddy deposit produced by the use of such compositions.
A hard scale is equivalent to thickening the plate; and although this
is sufficiently mischievous, the injury to the plates is much more
rapid when a thicker but spongy deposit entirely prevents contact of
the water and impedes the transmission of the heat. An attempt to
illustrate this is given in Fig. 58, which is an enlarged view of a
portion of such a boiler as is shown in Fig. 37. The money spent in
boiler compositions would be better applied in securing a supply of
proper water, or in filtering and purifying the water before it enters
the boiler.
[Illustration: _Fig. 58._]
The writer has had to mention only faults in boilers; but it is not
to be inferred that all boilers are working in actual danger. A very
small percentage perhaps are so; but without periodical examination
no one can feel sure of the condition of any boiler. It is not likely
that explosions in future will be from exactly the same causes as those
now described, because the known faults will be avoided. For instance
no new Balloon, Wagon, or Butterley boilers are now made; and the
peculiar faults and the weakness of the tubes in Cornish and others of
the better classes of boilers are now so well known as to be generally
avoided; and as information spreads, many evils will become things of
the past.
As periodical examination has been so strongly advocated, it might seem
natural to desire that it should be enforced by government authority;
but this is by no means recommended. A select parliamentary committee
has been recently investigating the subject, with a view to ascertain
whether that would be desirable, but has adjourned for the session
without coming to any decision on this point. Even if a perfect
system of government inspection could be contrived and perfectly
administered, it would have the effect of taking the responsibility
from the owners, who are the natural guardians of the safety of their
boilers. Although the loss of 70 lives per annum by boiler explosions
is sufficiently deplorable, the deaths by railway accidents are more
than three times that number; yet very little inspection of railways
is held to be necessary, and that inspection takes place chiefly before
the commencement of working or after accidents. A coercive system
may introduce more evils than it cures, especially as at present so
much difference of opinion exists respecting the causes of boiler
explosions. In the opinion of the writer, far more real good arises
from the calm discussion of the facts and from the spread of correct
information by such societies as this Institution, than from enforcing
by law any action which is not perhaps believed by the majority of
steam users to be at all necessary or useful. It has been at times
suggested to increase the power and responsibility of coroners in
holding inquests upon those killed by boiler explosions, by requiring
them to obtain scientific evidence and to insist that the causes of
the explosions shall be added to the verdicts of juries. But it is
believed that this would only encumber an important institution,
because a jury who might well decide whether a person had been killed
by any criminal carelessness would not be a suitable tribunal to
decide between possibly conflicting scientific evidence; and also,
as an inquest may result in a verdict of manslaughter, the eliciting
of information on such an occasion is checked by the natural fear of
inadvertently involving some one in so serious a charge. The public
at large, and steam users generally, would gain more information and
guidance from the scientific evidence itself than from the verdict
of a coroner's jury; and it is believed much good has resulted in
preventing locomotive boiler explosions by publishing the reports of
the government inspecting engineers, who have gained their knowledge
of the facts in conversation with all those concerned, and have added
recommendations which have been promptly acted upon.
The writer's object has been that the boilers found most convenient and
best suited for the different purposes for which they are used should
be made to work with safety, rather than that reliance should be placed
upon the qualities of any particular kind of boiler or fittings. No
form of boiler at present admits of absolute reliance upon its freedom
from risk.
The following general conclusions appear to arise from the
consideration of the records of boiler explosions.
1. That the force accumulated in an ordinary boiler is enough to
account for the violence of an explosion.
2. 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.
3. 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.
4. That the cost of periodical examination is so little as to be far
outweighed by the greater security obtained; and that the settings of
all boilers should be constructed with a view to facilitate examination.
5. That the surest way to make systematic examination general is to
spread as widely as possible correct information as to the facts and
ascertained causes of boiler explosions, and to inform boiler owners
and minders what dangers to guard against; and that this is preferable,
and more likely to lessen explosions than enforcing any system of
inspection by legal enactment.
TABLE I.
_Summary of Records of Steam Boiler Explosions_
_up to 30th June, 1870,_
_showing Description of Exploded Boilers._
+------------------++-----------------------++-----------------------+
| Description of || Explosions up to June || Explosions in the 4 |
| Boiler. || 1866. || years from June 1866 |
| || || to June 1870. |
+ |+--------+--------+-----++--------+--------+-----+
| ||English.|Foreign.|Total||English.|Foreign.|Total|
+==================++========+========+=====++========+========+=====+
|Marine || 57 | 203 | 320 || 12 | 64 | 76 |
+------------------++--------+--------+-----++--------+--------+-----+
|Cornish, || 140 | 1 | 141 || 84 | 3 | 87 |
|Lancashire, or || | | || | | |
|others with || | | || | | |
|internal flues || | | || | | |
+------------------++--------+--------+-----++--------+--------+-----+
|Locomotive || 91 | 29 | 120 || 10 | 68 | 78 |
+------------------++--------+--------+-----++--------+--------+-----+
|Plain Cylindrical || 114 | 2 | 116 || 54 | 3 | 57 |
|externally fired || | | || | | |
+------------------++--------+--------+-----++--------+--------+-----+
|Balloon, || | | || | | |
|Haystack, Wagon, || 62 | 2 | 64 || 5 | 2 | 7 |
|Butterley, || | | || | | |
|British-Tube || | | || | | |
|Elephant, or || | | || | | |
|Trevithick || | | || | | |
+------------------++--------+--------+-----++--------+--------+-----+
|Portable, || | | || | | |
|Agricultural, || 28 | 1 | 29 || 17 | 17 | 34 |
|Upright, Crane, || | | || | | |
|or very small || | | || | | |
+------------------++--------+--------+-----++--------+--------+-----+
|Heating, Kitchen, || 14 | .. | 14 || 22 | 14 | 36 |
|Domestic, Rag || | | || | | |
|Steamers, &c. || | | || | | |
+------------------++--------+--------+-----++--------+--------+-----+
|Furnace-upright || 10 | .. | 10 || 8 | .. | 8 |
+------------------++--------+--------+-----++--------+--------+-----+
|Not sufficiently || 203 | 29 | 232 || 7 | 175 | 182 |
|described to be || | | || | | |
|classified || | | || | | |
+==================++========+========+=====++========+========+=====+
|Totals || 719 | 327 |1046 || 219 | 346 | 565 |
+------------------++--------+--------+-----++--------+--------+-----+
TABLE I (continued)
+------------------++--------------------------+
| Description of || Total Explosions |
| Boiler. || up to June, 1870. |
| |+--------+--------+--------+
| ||English.|Foreign.| Total. |
+==================++========+========+========+
|Marine || 69 | 327 | 396 |
+------------------++--------+--------+--------|
|Cornish, || 224 | 4 | 228 |
|Lancashire, or || | | |
|others with || | | |
|internal flues || | | |
+------------------++--------+--------+--------+
|Locomotive || 101 | 97 | 198 |
+------------------++--------+--------+--------+
|Plain Cylindrical || 168 | 5 | 173 |
|externally fired || | | |
+------------------++--------+--------+--------|
|Balloon, || | | |
|Haystack, Wagon, || 67 | 4 | 71 |
|Butterley, || | | |
|British-Tube || | | |
|Elephant, or || | | |
|Trevithick || | | |
+------------------++--------+--------+--------+
|Portable, || | | |
|Agricultural, || 45 | 18 | 63 |
|Upright, Crane, || | | |
|or very small || | | |
+------------------++--------+--------+--------+
|Heating, Kitchen, || 36 | 14 | 50 |
|Domestic, Rag || | | |
|Steamers, &c. || | | |
+------------------++--------+--------+--------+
|Furnace-upright || 18 | .. | 18 |
+------------------++--------+--------+--------+
|Not sufficiently || 210 | 204 | 414 |
|described to be || | | |
|classified || | | |
+==================++========+========+========+
|Totals || 938 | 673 | 1611 |
+------------------++--------+--------+--------+
TABLE II.
_Summary of Records of Steam Boiler Explosions_
_up to 30th June, 1870,_
_showing Causes of Explosions._