IMPROVED MEANS AND APPLIANCES FOR PREVENTING CORROSION IN BOILERS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Alfred Rosling Bennett at the Office
of the Commissioners of Patents on the 11th July 1882.
ALFRED ROSLING BENNETT, of Todholes, near Kilbarchan, in the County of
Renfrew, Telegraphic Engineer, "IMPROVED MEANS AND APPLIANCES FOR
PREVENTING CORROSION IN BOILERS,"
"
It is well known that when two or more metals or other conductors of electricity
are in contact with each other, and also in contact with a liquid consisting of, or
holding in solution, chemicals having greater affinity for some of the metals or
conductors of electricity so in contact than for others, a current of electricity is set
up, and that the metals or other conductors of electricity which are most attacked
or affected by the liquid are gradually reduced to other states by combination
with the chemicals contained therein. It is likewise well known that it is the
custom of constructors of boilers for steam engines to attach pipes, tubes, and other
fittings appurtenances composed of other metals than the boiler itself directly to
the boiler, so that a current of electricity, if such were applied, would pass freely
between them, from the boiler to the fitting, and vice versa, notwithstanding that
the two metals, in addition to being in contact with each other, are also when the
boiler is in operation, in contact with a liquid frequently holding in solution
chemicals which, under such circumstances, enter more freely into combination
with one metal than the other.
The first part of my Invention is founded on the fact that iron and steel, of
which boilers for steam-engines are as a rule constructed, are electro-positive to
copper and brass, of which tubes, pipes, and other boiler fittings are usually
composed, when in contact with such solutions as are generally contained in boilers,
especially those of sea-going steam vessels; and that consequently the iron and
steel of the boiler are wasted away by the voltaic action due to their contact, in
the presence of a chemical solution, with the copper and brass of the tubes, pipes,
and other fittings.
To prevent this wasting, it is necessary to render impossible voltaic action
between the iron and steel of the boiler, and the copper and brass, or other dis-
similar metal, of the fittings. This I accomplish by interposing a nonconductor
of electricity between the boiler and every fitting not composed of the same
metal as the boiler itself, in such a manner that if a current of electricity were
F

page_text: applied to the boiler when empty, it would not pass to the fittings, and vice versa,
that is to say I electrically insulate the boiler from all conductors of electricity
other than the one of which it is itself composed.
It is also necessary to prevent any exterior metallic connection between the
boiler and its fittings, such as might be afforded by both being in contact with the
sides or decks of an iron vessel, or with the iron flooring of the boiler or engine-
room. I therefore electrically insulate the boiler, both internally and externally,
from all conductors of electricity other than the one of which it is itself composed,
and from all decks, floorings, or other masses of metal capable of conveying a
current of electricity between the boiler and any of its fittings. For example, if
an iron boiler and a condenser containing copper tubes were in metallic communi-
cation with each other, either directly by means of their connecting pipes, or
indirectly by means of an iron deck or flooring, voltaic action would ensue to the
injury of the boiler. But if the boiler and condenser were insulated from each
other so that a current of electricity applied to the one would not pass to the
other, voltaic action would not take place.
The second part of my Invention is based on the fact that iron and steel will
not rust when immersed in solutions of the caustic alkalies and that in such
solutions iron and steel cease to be electro-positive to copper and brass, as is well
known,
Consequently, under certain circumstances to be more fully ascertained and
described in the final Specification I prevent corrosion of iron or steel boilers by
keeping the water used therein highly alkaline by the addition thereto of large
quantities of caustic potash or caustic soda, either with or without insulating the
boilers from their fittings.
"