1068

THE COLLIERY GUARDIAN.

November 20, 1914.

replace the ordinary toe rivets of the gusset stays. These
provide flexibility in the end plate, but guard against
any undue movement of the plate. The adoption of
corrugated flues tends to prevent grooving ih the end
plates of Lancashire boilers, as such flues possess a con-
siderable amount of flexibility. In locomotive type
boilers, grooving is frequently met with. Instances of
this, however, with illustrations, were given in the issue
of the Colliery Guardian for April 12, 1912.

Although most commonly met with in the end plates
of Lancashire boilers, or in the roots of the angle irons
connecting the end plates to the tubes, grooving is occa-
sionally met with at the circumferential and longitudinal
seams. In the former case, the defect cannot be
regarded as a dangerous one, because the end plates are
attached to the shell not only by the internal tubes, but
also by the gussets at both back and front ends. Even
then, should the grooving extend completely through
the plate, there is little possibility of an explosion taking
place. As regards grooving at the seams, the case is
very different, particularly in connection with externally
fired boilers. Should a groove extend for a consider-
able distance along a circumferential or a longitudinal
seam, it is liable to result in an explosion, as there are
no stays to prevent the parts being blown violently
apart. This is particularly the case with the longitu-
dinal seams, because it will be remembered that a boiler
is only one-half as strong longitudinally as circumferen-
tially. Grooving at longitudinal seams is, indeed, the
worst of all the defects considered.

A defect sometimes confused with grooving, but
one which may be brought about in an entirely
different manner, is “ furrowing ” or “ channell-
ing.” This defect is somewhat similar to grooving,
but differs in that it is of greater width. As
its name implies, it takes the form of a furrow or
channel, which generally runs for some distance along
a seam or joint. It is met with both internally and
externally. In the latter case, it is due to leakage at
a joint or seam.

All the forms of internal corrosion described in the
foregoing are liable to be met with in boilers fed with
corrosive water. We have already. mentioned that
internal corrosion is usually caused by the acid action
of the feed water. Hence, by introducing into the feed
water some alkali, the acid action may often be
neutralised, and corrosion thus prevented. Soda ash,
for example, is largely employed for this purpose, and
in perhaps the majority of cases proves to be effectual.
Most of the boiler compositions on the market consist
mainly of soda, with certain ingredients added. It is
not advisable to use such compositions without first
ascertaining from a chemist that they are suitable for
the particular water to be treated, as many of them are
not only useless, but distinctly harmful. No boiler
composition is suitable for all feed waters, and yet in
the majority of cases it is taken for granted that such
is the case. The proper reagents for any particular
water can only be correctly determined from a chemical
analysis of the water. In addition to neutralising the
corrosive action bf the feed water, a boiler composition
should prevent the formation of hard scale on the boiler
plates. It should be carefully borne in mind that the
use of a suitable composition does not, as is often sup-
posed, do away with the necessity for frequent clean-
ing : the most it can do (besides preventing corrosion)
is to convert hard scaly deposits into soft ones, which
can be easily removed from the plates, or to cause
scale-forming matter which would otherwise become-
caked hard on the plates to be deposited in a soft con-
dition on the bottom of the boiler.	«

Chemical treatment of boiler feed waters is best
carried out in special apparatus outside the boilers, i.e.y
in water softeners, as obviously the boiler is not the
place in which to deposit scale-forming matter, etc.
The expense of installing a special water softening plant,
however, is heavy, and hence internal treatment is in
the majority of cases resorted to, but where there are
many boilers, it will generally pay to instal such a plant.
Many successful installations are in use in various
parts of the country.

To minimise the risks of internal corrosion, the boiler
plates should be kept free of thick scale, as otherwise
serious defects will be liable to escape detection. For-
tunately, it is generally found that when a feed water
is corrosive, little trouble is experienced from scale and
deposit, because the acids in the water appear to attack
any deposit which may be formed.

A layer of scale on the plates will, of course, serve to
preserve the plates from internal wasting. Where a
firm has two sources of water available, one corrosive
and the other limy, it may prove advantageous to feed
the boilers for a time with the limy water until a thin
layer of scale has formed on the plates, after which the
other water may be used until the lime has disappeared,
and so on.

Although the presence of acids in the feed water is
the usual cause of internal corrosion, trouble is some-
times experienced with waters which are exceptionally
pure. The water from Loch Katrine, in Scotland, the
town supply for Glasgow, for example, is one of the
purest in the world, but yet it occasionally gives rise to
“ pitting.” This is caused by the presence of dissolved

gases in the water. All natural waters derived from
rain or streams absorb from the atmosphere carbon
dioxide. This gas, by forming a salt with the iron of
the boiler plates, renders the oxygen in the water active;
the oxygen combines with the iron, forming an oxide of
iron, and the pitting is due to this action. In boilers
where the circulation is defective, the tendency of the
plates to corrode, due to the presence of dissolved gases
in the feed water, is greater than is the case with boilers
where the circulation is good. Thus Lancashire boilers
are more liable to suffer than water tube boilers. The
reason for this is that if the circulation is good, the
bubbles of gas, instead of being allowed to remain
attached to the plates to do their destructive work, are
swept off by the circulating or convection currents.
Boilers which are laid off for a period, and not emptied
of their water, are very liable to suffer from dissolved
gases, as there is nothing to remove the bubbles of gas
from the plates. It is not always realised as it should
be that an idle boiler is quite as liable to suffer from
internal corrosion as one which is in service, unless cer-
tain precautions are taken to preserve it- When a
boiler is to be laid off for a certain length of time, there
are two methods which may be adopted to guard against
internal corrosion. The first, known as the “ wet ”
method, is to fill up the boiler with water, and then to
seal up the various openings carefully. This method

1 may be employed when the period of stoppage is a short
one. It is not altogether effectual in preventing internal
corrosion, but is certainly far better than leaving the
water in the boiler at the ordinary working level, in
contact with air. The other method, known as the
“ dry ” method, consists in first running off all the
water, thoroughly cleaning and drying the plates, and
placing a quantity of quicklime inside the boiler. After
this, the openings should be sealed up to exclude the
external air. The lime serves to absorb all traces of
moisture. After a certain length of time, it should be
examined, and if found slaked, renewed.

The “ dry ” method should always be adopted in the •
case of boilers which are to be laid off for a considerable
length of time, as it is far more effectual in preventing
internal corrosion than the “ wet ” method. The
practice of coating the plates over with paraffin to pro-
tect them should be strictly avoided, as it is a very
dangerous one, and has been the cause of many serious
accidents.

As the presence of acids in boiler feed waters is the
principal cause of internal corrosion, it may be interest-
ing to consider some of the means by which the waters
become charged with acids. Large numbers of
boilers take their feed supply from canals and rivers,
on the banks of which are situated works and factories
of various kinds. Many of these discharge various
kinds of refuse into the water, which, in consequence,
becomes polluted. In the case of works manufacturing
iron wire, for example, what is known as “ pickling ”
water is largely used, this being a weak solution of “ oil
of vitriol,” or sulphuric acid. After use, the “pickling”
water is discharged into the river or canal, which, in
consequence, becomes more or less acid in character.
Again, dye works, galvanising shops, chemical works,
etc., discharge refuse containing acids into the water.
The water used for feeding boilers in Sheffield is ren-
dered very corrosive in this way, and large numbers of
the boilers become worn out by internal corrosion in a
comparatively short space of time.

The use of animal or vegetable oils for lubricating the
engine cylinders is frequently responsible for acidity in
the feed water. These oils become decomposed by heat
in the cylinders, and as a result'fatty acids are formed,
which eventually find their way to the boilers, being
carried along with the steam exhausted from the
cylinders. It is much better to use only the best
mineral oils for lubricating the engine cylinders, as
these are much less liable to decompose and form acids
under the influence of heat.

Some feed waters contain certain salts, which, under
the influence of the heat in the boiler, decompose with
the formation of acids. Thus, magnesium chloride,
which is a constituent of some waters, decomposes at
the temperatures met with in steam boilers, with the
formation of muriatic or hydrochloric acid. This acid
is a very corrosive one, and rapidly corrodes away the
boiler plates.

It is often possible to test acidity in boiler feed waters
by means of blue litmus paper, which, on being
immersed in a sample of the water, turns red, if the
acidity is sufficiently strong. Similarly, alkalinity may
be tested by means of red litmus papers, which turn blue
again if the alkalinity is strong enough. The Litholine
Company, of Manchester, who supply reagents suitable
for various classes of water, provide with their reagents
the red litmus papers, with the object of enabling the
engineer-in-charge to test whether or not he has added
sufficient Litholine to render the originally acid water
alkaline.

In conclusion, some reference should be made to
electrolytic or galvanic action in steam boilers, which
action is probably responsible for many cases of internal
corrosion. If two different metals be immersed in a
liquid which acts chemically on both of them, the two
metals become corroded. Thus, if a piece of zinc and a
piece of iron be immersed in a weak solution of sulphuric
acid, the acid will attack and corrode both the zinc
and the iron. If the two pieces be placed in contact
with each other, or connected by a copper wire, wrhat
is known as a “ galvanic couple ” is formed, and a
current of electricity flows along the wire. It. will now
be found that the corrosive action is concentrated at the
zinc, which consequentlv corrodes away, whilst the iron
remains unaffected. The current of electricity is the
result of a difference of electrical potential being set up
in the circuit. In a steam boiler it seems more than
likely that differences of electrical potential exist
between different parts of the shell, because the steel

of which the boiler plates are made is a complex mixture
of elements and compounds. These differences of
potential set up galvanic action between different parts
of the same plate, with the result that certain parts of
the plate become corroded. This galvanic theory
readily accounts for the peculiar localisation of pitting,
certain parts being affected, whilst others are not.

Corrosion caused by galvanic action may often be pre-
vented by suspending blocks of zinc inside the boiler, and
connecting these up with the shell plates. By so doing
galvanic action is set up between the zinc and the iron
of the plates, and the corrosive action then becomes con-
centrated at the zinc, the iron thus being preserved at
the expense of the zinc. It is important that the con-
nection between the iron and the zinc be maintained,
as otherwise the galvanic action will cease, and the iron
will then be attacked as well as the zinc.

h

APPLICATIONS TO AVOID OR SUSPEND
PATENTS.

An application has been made by Mr. E. Mills, of 9,
Harper-street, The Manor, Willenhall, Staffordshire, to
avoid or suspend a patent granted in 1911 to W.
Reinhard, of Crefeld. An abridged description is
given below:—

Improvements in Props or Stemples for Mines
(No. 27415/11.—In the specification of Letters Patent
No. 20472 A.D. 1909, there is described a mine propping
device or stempie provided with two wedges, one for
raising a slotted head,
which holds a portable
ioof supporting rail, and
the other for pressing
the rail in the head
against the roof. In the
case of .seams of varying
thickness the prop exten-
sion obtainable by means
of this double wedging
operation is insufficient.
The invention meets this
difficulty by substituting
for the wedge which
raises the head, a screw
spindle inserted into a
tubular part of the prop,
upon which rests a nut
working on the said
spindle. This device of
a screw spindle and nut
for raising a rail sup-
porting head at the top
of a pillar is not in
itself new. The tubular

member is preferably flared at the bottom, for insertion
of the wooden spike. The improved prop is illustrated
in the accompanying drawing, in which fig. 1 is a
longitudinal section, and fig. 2 a plan view of the nut.
In raising the prop the head d is lifted by hand and
pressed against the joist, and the nut is then screwed
down till it rests on the tube edge. The prop can then
be made fast by striking the wings k of the nut c with a
hammer or pick.



Partnership Dissolved.—The London Gazette announces
the dissolution of the following partnership :—W. R. Blair,
C. S. Dunkley, M. V. Thomas, and Edith I. Thomas, coal
merchants, at Wellfield-road, Cardiff, under the style of the
Pentwyn Coal Company, and at Tymawr-road, Llandaff
North, near Cardiff, under the style of E. Chick and Com-
pany.

Grimsby Coal Exports. — Returns for the week ending
November 13 show that the coal shipped from Grimsby was
as follows :—Foreign : To Copenhagen, 355 tons; Gefle,
4,904; Helsingborg, 1,713; Landscrona, 1,647; Malmo,
4,128; Odense, 1,379; Ronne, 841; Rotterdam, 1,364;
Solvesborg, 1,404; Stockholm, 2,168; and Ystad, 1,443,
making a total of 21,346 tons foreign, against 26,149 tons
foreign and 99 tons coastwise during the corresponding week
of last year.

Coaling German Cruisers.—The Buenos Ayres correspon-
dent of the Journal of Commerce states that the German
cruiser “ Eleonore Woermann ” recently at that port began
to load coal and stores to such an extent that public opinion
among the British community was roused. The port autho-
rities were appealed to, and she was officially declared to
have only 2,800 tons of coal aboard, the rest of her loading
being fresh water, general cargo, and stores. He says she
is not the only German vessel that has been stealthily filling
up here. The steamer “ Sierra Cordoba ” left a few days
ago, her papers being made out for Bremen, a port that she
is as likelv to reach as any other under existing circum-
stances, whilst the steamer “ Gotha ” has also taken on a
large quantity of coal. The question naturally arises as to
whence all this fuel is obtained, and it will come as a sur-
prise to many to learn that indirectly it is part of the output
of British pits. The whole of the electric light and power
of Buenos Ayres is generated by a very large German com-
pany, and in the first week of the war a special permit was
granted to British coaling companies covering the mainten-
ance of existing contracts with this concern, an act of
deference on the part of the British Government to the
Argentine authorities in general, and the needs of Buenos
Ayres in particular. The “ Sierra Cordoba ” has already
got clear away, and any day may see the “ Eleonore Woer-
mann ” and the “ Gotha ” follow her, despite the fact that
the former vessel has been forced to discharge 800 tons into
lighters alongside. There is no question as to the Argen-
tine Government’s wish to be both neutral and impartial,
but in all matters connected with shipping its officials are
far from practical, and although the regulation runs that
coal sufficient to carry a vessel to the next port, which is
Santos, may be shipped, an authorisation for 350 tons of
fuel may, by the addition of a “ 0 ” and the connivance of
junior employees, be converted into quite a useful cargo for
a German cruiser debarred from obtaining fresh bunkers
in the ordinary way of business.