A Process for the Protecting of Tubes, Pipes, and Reservoirs of Steam Generators by the Application of Silver.
Year: 1899

page_text: Date of Application, 29th Apr., 1899
Complete Specification Left, 27th Jan., 1900-Accepted, 28th Apr.,
1900
PROVISIONAL SPECIFICATION.
A Process for the Protecting of Tubes, Pipes, and Reservoirs of Steam
Generators by the Application of Silver.
I, EUGENE JULES MARIE LA COMBE, of 41, Rue de la Rampe, Brest, in the
Republic of France, Professor of Mathematics, do hereby declare the nature of
this invention to be as follows:-
My invention relates to a process for the protection of steel boiler
tubes; feed reservoirs; supply pipes and steam conduits in steam
generators, and generally speaking of all parts traversed by the
steam or water, for the purpose of protecting their walls against
any alteration arising either from the accidental admission of sea water
into the evaporating apparatus or from the lubricants with which it is necessary
to supply the various parts of the engine, the elements of which are caused to
enter the feed water from all sides notwithstanding the employment of filters,
and which, at the working temperature of the engine, either attacks the walls
of the tubes and necessitates frequent renewals, or obstructs the conduit pipes
and thus causes explosions.
My process consists in applying a layer of silver upon the steel tubes or other
parts which are in contact with the water to be vaporised or with the steam.
I have been led to adopt this method because these tubes are now frequently
raised to a temperature of 200° C., for the purpose of producing steam at high
pressure; at this temperature silver is the only metal which is not altered in
any manner and which adheres strongly to the steel to which it has been
applied, especially when such application has been made by the means which
I will now describe.
At this high temperature of 200°, it is not only the heat properly so called
which is to be feared; but at this temperature all the mineral and other fats
which may be contained in the boiler are converted into a kind of black mud
which attacks the metals. At a temperature approximating 2000, silver is the
only metal which resists the action of this black mud; I have in fact ascertained
that silver could not be attacked as a result of the doubling of these fats at this
high temperature unless the formation of a double salt into which a silicate
entered took place, which is impossible under the circumstances.
It will thus be readily understood how valuable is the application of silver to
the internal surfaces of steel tubes, as tubes so treated resist the corrosive action
of fats in the conditions which have been explained.
I have also ascertained that from a temperature of 100°, chloride of sodium in
solution in water renders the deposits of calcareous salts and of magnesium
salts arising from the evaporation of water very mobile upon a surface of silver,
whilst, on the contrary, these deposits form a high adherent tartar upon tubes
of steel or other metals. As a result of the silvering of boiler tubes, the admission
of sea water need no longer be feared; on the contrary, it will be advantageous
to a certain extent, since under these circumstances the marine salt in com-

page_text: bination with the coating of silver is an auxiliary for preventing the adherence
of deposits.
In order to effect this application of silver upon steel tubes, a very thin
layer of copper is first of all caused to adhere to the walls of such tubes; the
internal walls if the water circulates internally, and the external walls if the
water circulates outside the tubes.
This application of copper may be affected in three different ways, viz.
a The metal is cleaned by means of hydrochloric acid diluted with an equal
volume of water, and the clean internal surface is coated with copper by the
oxide of copper dissolved in the excess of ammonia employed as electrolytic bath,
the bath being maintained saturated.
b/ A coating of zinc or nickel is made upon the internal wall of the steel tube
and the auxiliary metallic coating is then coppered by means of the same
ammoniacal coppered liquid.
c/ Or the steel tube may be plunged in a copper vessel, in which marine salt
has been dissolved with a certain quantity of bichromate of potash, but in a
sensible proportion, or in an iron vessel containing a very liquid bath of chloride
of sodium and bichromate of potash, but in which copper nails or fragments of
sheet copper have been introduced, the operation necessarily taking place at a
high temperature.
When the wall of the tubes has been covered with copper by means of one of
the processes above described, silvering is affected in a double bath of cyanide
of potassium and silver maintained in a state of constant saturation.
These tubes are suited for the boilers of war vessels or ships of the mer-
cantile marine, for railway engine boilers, and in short to boilers of all kinds
used for industrial purposes.
These same tubes may be silvered, when required for rectangular shoulders
or elbows, by silvering them in a straight condition and then bending them to
the desired form after they have been raised to a dull red heat; but in this case
the preliminary coppering should be effected by ignition in the extremely liquid
bath of chloride of sodium and of bichromate of potash.
Dadal L
COLL
e
1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.
A Process for the Protecting of Tubes, Pipes, and Reservoirs of Steam
Generators by the Application of Silver.
I, EUGENE JULES MARIE LA COMBE, of 41, Rue de la Rampe, Brest, in the
Republic of France, Professor of Mathematics, do hereby declare the nature of
this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
My invention relates to a process for the protection of steel boiler tubes; feed
reservoirs; supply pipes and steam conduits in steam generators; and generally
speaking, of all parts traversed by steam or water.
My invention has for its object to provide means for protecting such parts
against corrosion or alteration arising either from the accidental admission
of sea water into the evaporating apparatus, or from the lubricants with which
it is necessary to supply the various parts of the engine. As is well known the
elements of such lubricants constantly enter the feed water from all sides, not-

page_text: withstanding the employment of filters, or the like and at the working tempera-
ture of the engine, either attack the walls of the tubes and necessitate frequent
renewals, or obstruct the conduit pipes and thus cause explosions.
My improved process consists in applying a layer of silver upon the steel tubes
and other parts which are in contact with the steam or with the water to be
vaporised.
I have been led to adopt this method because these tubes are now frequently
raised to a temperature of 200° C. for the purpose of producing steam at hign
pressure; at this temperature, silver is the only metal which is not altered in
any manner, and which adheres strongly to the steel to which it has been
applied, especially when such application has been made by the means which I
will now describe.
At a high temperature, such as 200° C. it is not only the heat which con-
stitutes a source of danger, but the mineral and other fats which may be con-
tained in the boiler are converted into a kind of black mud which attacks the
metals. At a temperature approximating 200° C., silver is the only metal which
resists the action of this black mud; I have in fact ascertained that silver
could not be attacked by the product resulting from the decomposition of these
fats at this high temperature, unless the formation of a double salt into which a
silicate entered took place, which latter is of course impossible under the cir-
cumstances.
It will thus be seen that the application of silver to the internal surfaces of
steel tubes reduces the risk of injury or corrosion to a minimum, as tubes so
treated resist the corrosive action of fats under the conditions which have been
explained.
I have also ascertained that from a temperature of 100° C. chloride of sodium in
solution in water renders the deposits of calcareous salts and of magnesium
salts arising from the evaporation of water easily removable from the surface of
silver, whilst, on the contrary, these deposits form a highly adherent tartar upon
tubes of steel or other metals. As a result of the silvering of boiler tubes
according to my invention, the admission of sea water is no longer a drawback,
on the contrary, it will be advantageous to a certain extent since under these
circumstances, the marine salt in combination with the coating of silver is an
auxiliary for preventing the adherence of deposits.
In order to effect this application of silver upon steel tubes, a very thin
layer of copper is first of all caused to adhere to the walls of such tubes; the
internal walls if the water circulates internally, and the external walls if the
water circulates outside the tubes.
This application of copper may be effected in three different ways namely;
(a.) The metal having been cleaned by means of hydrochloric acid diluted
with an equal volume of water, the clean internal surface is coated with copper
by means of oxide of copper dissolved in an excess of ammonia and employed as
an electrolytic bath, the bath being maintained saturated, or (b) a coating of zinc
or nickel may be made upon the internal wall of the cleansed tube, and this
auxiliary metallic coating is then coppered by means of the process above
described. The strength of the current employed in the electrolytic processes
above described (a) is as follows:
With a Daniel cell having a zinc-plate of 20 centimeters in height and 8
centimeters internal diameter, a copper plate 4 centimeters wide, 23 centimeters
high and 2m thick, a solution of half a kilo. of chloride of sodium in one kilo.
of water, and a saturated solution of sulphate of copper, the duration of the
operation of galvanizing is from 23 to 42 hours, according to whether operating
at 100 or 620, for coppering the operation takes from 3 hours 40 minutes to
7 hours, and for silvering it takes from 11 to 13 minutes.
(c) The steel may be coated by steeping it in a copper vessel, in which marine
salt has been fused with a sensible proportion of bichromate of potash, or in an
iron vessel containing the chloride of sodium and bichromate of potash, but in

page_text: which copper nails or fragments of sheet copper have been introduced, the opera-
tion necessarily taking place at a high temperature. This process is not an
electrolytic process, but a process for coppering (copper-plating) by steeping.
When the walls of the tubes have been covered with copper by means of one
of the processes above described, silvering is effected in an electrolytic bath of
cyanide of potassium and silver maintained in a state of constant saturation,
Instead of applying copper to steel by plunging the steel tube in a bath of
chloride of sodium and bichromate of potassium melted with an addition of
copper pieces, the said tubes may be silvered (silver-plated) by treating them in
the same manner, but re-placing the copper by pieces of silver. The following
proportions give good results, 500 grs. of marine salt, 200 gr. of bichromate,
1eated to a temperature varying between 480° C. to 600° C.
The silver coating thus formed is hardly more than 1/1000 of a millimeter in
thickness, and is capable of resisting a dry heat exceeding 650° C.
These tubes are suited for the boilers of war vessels or ships of the mer-
cantile marine, for railway engine boilers, and in short to boilers of all kinds
used for industrial purposes.
These same tubes may be silvered, when required for rectangular shoulders
or elbows, by silvering them in a straight condition and then bending them to
the desired form after they have been raised to a dull red heat; but in this case
the preliminary coppering should be effected by plunging them in the chloride of
sodium and of bichromate of potash and heating them as above described.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. The process for the protection of tubes, reservoirs, pipes and generally
speaking all parts of boilers or other vessels exposed to the high temperature of
water in vaporisation or of steam, this process consisting in applying a coating
of silver to the interior or to the exterior of the tubes or other surfaces.
2. For carrying this process into effect, the various methods of silvering above
described.
3. As a new product, the steel tubes and other surfaces for steam generators
and for similar purposes, provided with a protecting coating, either internal or
external according to circumstances, consisting of a layer of silver presenting
the properties and advantages above specified.
Dated this 27th day of January 1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.