U.S. patent application number 14/341029 was filed with the patent office on 2014-11-13 for device for the cathodic protection of a metal wall against corrosion in a saline environment.
The applicant listed for this patent is ALSTOM Renewable Technologies. Invention is credited to Serge PRIGENT.
Application Number | 20140332373 14/341029 |
Document ID | / |
Family ID | 47748580 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140332373 |
Kind Code |
A1 |
PRIGENT; Serge |
November 13, 2014 |
DEVICE FOR THE CATHODIC PROTECTION OF A METAL WALL AGAINST
CORROSION IN A SALINE ENVIRONMENT
Abstract
A device for the cathodic protection of a metal wall against
corrosion in a saline environment, includes an anode and means for
connecting said anode to said wall. The anode has a higher
electrochemical potential than the wall, wherein the anode is
placed in a compartment delimited by a wall permeable to electrons
and, optionally, to water. The device includes a porous outer layer
made from a material selected from: polymeric materials, ceramic
materials or hydrated inorganic materials and at least one porous
layer having the ability to collect the cations emitted by the
anode during the dissolution of same. The material forming the at
least one layer is selected from osmotic membranes, active carbon,
a cation exchange resin such as a zeolite, a cation-collecting
polymer with nanofillers, cation-collecting mineral compounds such
as phyllosilicates and inosilicates, cation-retaining nanofiltering
semi-permeable organic microporous membranes.
Inventors: |
PRIGENT; Serge; (Le Sappey
en Chartreuse, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALSTOM Renewable Technologies |
Grenoble |
|
FR |
|
|
Family ID: |
47748580 |
Appl. No.: |
14/341029 |
Filed: |
July 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2013/051837 |
Jan 31, 2013 |
|
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14341029 |
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Current U.S.
Class: |
204/196.01 |
Current CPC
Class: |
C23F 2213/31 20130101;
C23F 13/08 20130101; C23F 13/06 20130101; C23F 2201/00
20130101 |
Class at
Publication: |
204/196.01 |
International
Class: |
C23F 13/08 20060101
C23F013/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2012 |
FR |
1250946 |
Claims
1. A device for the cathodic protection of a metal wall against
corrosion in a saline environment, comprising an anode and means
for connection of said anode to said wall, said anode being at a
higher electrochemical potential than said wall, wherein said anode
is placed in a compartment delimited by a wall that is permeable to
electrons and, optionally, to water, comprising: a porous outer
layer of a material selected from: polymer materials, ceramic
materials or hydrated inorganic materials; and at least one porous
layer able to capture the cations emitted by the anode during
dissolution of the latter, the material constituting said at least
one layer being selected from osmotic membranes, activated
charcoal, a cation exchange resin such as a zeolite, a cation
capture polymer with nanofillers, cation capture mineral compounds
such as phyllosilicates and inosilicates, semipermeable organic
microporous nanofiltration membranes of a type that retains
cations.
2. The device as claimed in claim 1, wherein said wall also
comprises a membrane that traps negatively charged pollutants.
3. The device as claimed in claim 1, wherein the anode is a
sacrificial anode whose electrochemical potential is naturally
higher than that of the metal wall.
4. The device as claimed in claim 1 wherein it comprises means for
applying an electrochemical potential greater than that of the
metal wall to the anode.
5. The device as claimed in claim 1, wherein the means for
connection of the anode to the metal wall are in contact with the
wall outside the compartment and in that they pass through the
porous wall of compartment hermetically.
6. The device as claimed in claim 1, wherein the means for
connection of the anode to the metal wall are in contact with the
metal wall inside compartment, and in that the porous wall of
compartment is connected hermetically to the metal wall.
7. The device as claimed in claim 1, wherein it comprises means for
keeping the anode at a distance from the metal wall.
8. The device as claimed in claim 1, wherein it comprises a
plurality of layers able to capture the cations emitted by the
anode during dissolution of the latter, each layer preferentially
capturing cations different from those captured preferentially by
the other layers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to PCT/EP2013/051837 filed
Jan. 31, 2013, which claims priority to French application 1250946
filed Feb. 1, 2012, both of which are hereby incorporated in their
entireties.
TECHNICAL FIELD
[0002] The invention relates to the cathodic protection of
installations submerged in a briny or saline environment.
Protection of the metal hulls of boats or of metal parts against
corrosion by seawater is often provided, conventionally, by a
sacrificial anode, consisting of a metal that is more
electronegative than that to be protected. When the boat and its
sacrificial anode are immersed in seawater, polarization occurs,
the hull becoming the cathode of an electrochemical cell and the
sacrificial anode becoming the anode of this same cell. As a
result, it is the metallic constituents of the sacrificial anode
that are subjected to the effects of corrosion by the seawater and
not those of the hull. These constituents M are released in the
seawater in the form of cations according to the reaction
M.fwdarw.M.sup.n++n e.sup.-.
[0003] The sacrificial anodes protecting the submerged steel parts
of a boat or of any other seagoing vessel or fixed installation are
generally of aluminum-zinc (2-6%)-indium (0.01-0.05%), or of
aluminum-gallium (0.01%) or of zinc-Al alloy (0.1-0.5%). The
drawback of this protection is that it releases the ions of the
metals constituting the sacrificial anodes into the marine
environment. Although this drawback is relatively minimal in the
case of boats at sea, it has to be taken much more seriously when
boats are berthed in a port, as the metals of the anode will
accumulate in the water and in the sea bed of the berthing zones,
where they will be absorbed by the creatures living there. The
problem also arises for fixed installations such as oil rigs and
off-shore wind turbines. It is therefore imperative to find
effective and economical solutions for avoiding this release of
harmful metals into the environment as far as possible, especially
as developments in environmental protection legislation might make
the use of solutions for controlling wastes from sacrificial anodes
obligatory in certain circumstances.
[0004] An alternative solution to the use of a sacrificial anode as
has just been described is to make this anode from a material that
is not necessarily more electropositive than the material to be
protected (which may be steel, cast iron, graphite, metal oxides,
etc.), but apply an electric potential to it, constantly or
cyclically, by means of a generator of direct or rectified current.
This potential makes the anode more corrodible than the wall to be
protected. This technique is onerous to apply, especially in zones
of the installation with difficult access, but it is effective
mainly for large installations. This technique is known as
"impressed current cathodic protection" (abbreviated to ICCP).
SUMMARY
[0005] The aim of the invention is to propose a solution for
avoiding release of the cations resulting from the dissolution of
an anode of a device for cathodic protection into the
environment.
[0006] For this purpose, the invention relates to a device for the
cathodic protection of a metal wall against corrosion in a saline
environment, comprising an anode and means for connecting said
anode to said wall, said anode being at a higher electrochemical
potential than said wall, characterized in that said anode is
placed in a compartment delimited by a wall that is permeable to
electrons and, optionally, to water, comprising: [0007] a porous
outer layer of a material selected from: polymer materials, ceramic
materials or hydrated inorganic materials; [0008] and at least one
porous layer able to capture the cations emitted by the anode
during dissolution thereof, the material constituting said at least
one layer being selected from osmotic membranes, activated
charcoal, a cation exchange resin such as a zeolite, a cation
capture polymer with nanofillers, cation capture mineral compounds
such as phyllosilicates and inosilicates, semipermeable organic
microporous nanofiltration membranes of a type that retains
cations.
[0009] Said wall may also comprise a membrane that traps negatively
charged pollutants.
[0010] The anode may be a sacrificial anode whose electrochemical
potential is naturally higher than that of the metal wall.
[0011] Otherwise, the device may comprise means by which an
electrochemical potential higher than that of the metal wall can be
applied to the anode.
[0012] The means for connecting the anode to the metal wall may be
in contact with the wall outside the compartment and may pass
through the porous wall of the compartment hermetically.
[0013] The means for connecting the anode to the metal wall may be
in contact with the metal wall inside the compartment, and the
porous wall of the compartment is connected hermetically to the
metal wall.
[0014] The device may comprise means for keeping the anode at a
distance from the metal wall.
[0015] It may comprise a plurality of layers able to capture the
cations emitted by the anode during dissolution of the latter, each
layer preferentially capturing cations different from those
captured preferentially by the other layers.
[0016] As will have been understood, the invention consists of
placing the anode in a compartment delimited by a series of porous
membranes permeable at least to electrons, or even also to water,
arranged in layers. The outer layer consists of a nonmetallic
porous membrane, intended to reduce the hydraulic flow in the
vicinity of the anode. The other porous layer or layers play(s) the
role of cation barrier or trap, which prevents the cations
resulting from dissolution of the anode to escape from the
compartment into the environment.
[0017] If the membranes are all permeable to water, the space
separating the anode from the wall of the compartment becomes
filled with water naturally. If at least one of the membranes is
not permeable to water but only to electrons, it is necessary,
during installation of the device, to fill the compartment with
water, preferably seawater to obtain good electrical conductivity,
in order to bathe the anode in an electron-conducting medium and to
endow the compartment with its operational form, with internal and
external pressures that are balanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention will be better understood on reading the
description given below, referring to the following appended
figures:
[0019] FIG. 1, which shows schematically, in longitudinal section,
a first example of carrying out the invention;
[0020] FIG. 2, which shows schematically, in longitudinal section,
a second example of carrying out the invention.
DETAILED DESCRIPTION
[0021] FIG. 1 shows a metal wall 1 belonging to equipment installed
in a marine environment 2, such as an oil rig or a wind turbine.
However, this wall 1 could also be the hull of a boat, or of some
other seagoing vessel. In a known manner, a sacrificial anode 3 is
arranged in the vicinity of the wall 1, to which it is connected by
electrical connectors 4, 5. In general, as in the prior art, the
sacrificial anode 3 is constructed around a single steel connector,
and in this case the connectors 4, 5 shown are in fact the two ends
of this single connector. The material constituting the sacrificial
anode 3 is conventional for this purpose (Al--In, Al--Ga or Zn
alloy for example), and selection thereof is not a characteristic
feature of the invention.
[0022] According to the invention, the sacrificial anode 3 is
enclosed in a compartment 6 that is delimited by a set of membranes
forming layers, and surrounds the anode 3 at a distance, for
example of the order of 1 cm.
[0023] The outermost layer 7 is a porous layer permeable to
electrons, and preferably also to water, intended to reduce the
hydraulic flow between the external environment and the internal
space 8 of the compartment. The material of which it is constituted
is selected from polymer materials, ceramic materials or hydrated
inorganic materials.
[0024] As examples of such materials, we may mention,
nonexhaustively, thermoplastic polymers of the polyethylene or
high-density polyethylene type, or porcelains of the industrial
mullite or alumina type.
[0025] If this material is electrically insulating, it must be
porous. In fact, polarization of the anode corresponds to
establishment of a small electrochemical circuit, which can only
function if electrons are circulating. The open porosity allows the
electrons to pass into the liquid even if layer 7 is
insulating.
[0026] This outermost layer 7, whose thickness is generally of the
order of a millimeter, has the function of protecting the anode and
the other membranes of compartment 6 against hydraulic abrasion. It
must have suitable properties of wear resistance and impact
strength, and resistance to deformation in the presence of a moving
fluid.
[0027] The permeability of layer 7 is for example of the order of
10 ml/min per 1 cm.sup.2 of anode surface.
[0028] The other layer or layers of the wall of compartment 6
(there are two of them, 9, 10, in the example shown) consist(s) of
one or more materials serving as cation trap, which trap the
cations emitted by the sacrificial anode 3 to prevent them entering
the marine environment 2. Various types of materials may be
suitable for this purpose: osmotic membranes, activated carbon in
the form of powder or granules, a cation exchange resin such as a
zeolite, a cation capture polymer with negative nanofillers
attracting the cations, cation capture mineral compounds such as
phyllosilicates and inosilicates. Such materials are included among
those commonly used in water treatment and softening for cation
capture or exchange. They may be supplemented with a membrane of
activated alumina or of a functionally equivalent compound, which
for its part traps the negatively charged pollutants, such as As
and fluorides, which could reduce the efficacy of the membranes
trapping the cations.
[0029] Semipermeable membranes employed in electrolytic processes
of ion exchange may also be used.
[0030] Semipermeable organic microporous nanofiltration membranes
of a type that retains cations may also be suitable.
[0031] The number of layers of cation capture materials is
arbitrary, to be chosen by the user. These layers may
advantageously be of multiple kinds, and each species of layer may,
for example, preferentially absorb one or more of the chemical
species that the sacrificial anode 3 is likely to release.
[0032] For example, we may envisage: [0033] an outer layer 9
permeable to the chemical elements with radius below 1.5 .ANG. and
impermeable to the chemical elements with radius above 1.5 .ANG.
such as Ca, K, Mg, Na; [0034] and an inner layer 10 permeable to
the chemical elements with radius below 1.1 .ANG. such as O, Cl, N
(which will therefore be able to penetrate into the internal space
8 of compartment 6 or leave it, which does not have drawbacks), and
impermeable to the chemical elements with radius above 1.1 .ANG.
such as Al, Zn, Ga, In, thus the principal elements that the anode
3 may emit in the form of cations, and whose release into the
environment is undesirable; the thickness of the layers, and
notably of layer 10, may vary from about 1 mm to some cm, as a
function of the size of the anode 3 and therefore of the quantity
of cations to be trapped.
[0035] In the case when the whole of the wall delimiting
compartment 6 is permeable to water, water penetrates into
compartment 6 and a balance of pressures is attained between the
interior and the exterior of compartment 6. Compartment 6 therefore
assumes its nominal shape permanently and its wall is not subjected
to crushing, which could lead to rupture thereof.
[0036] As has been mentioned, it is not obligatory for the whole of
the wall defining compartment 6 to be permeable to water. It may
only be permeable to electrons, but then prefilling of compartment
6 with water, preferably seawater, is necessary when installing the
device according to the invention.
[0037] Owing to the invention, gradual dissolution of the
sacrificial anode 3 takes place without pollution of the
environment by the cations resulting from said dissolution, as they
are captured by the layer or layers 9, 10. The latter must
advantageously have a total capacity for absorption of the various
cations and an absorption volume that are sufficient so that
saturation does not occur before the end of the life of the
sacrificial anode 3.
[0038] In the example shown in FIG. 1, the electrical conductors 4,
5 are in contact with the metal wall 1 in zones located outside of
compartment 6. It is therefore necessary to ensure hermeticity of
the wall of compartment 6 in the zones where the conductors 4, 5
pass through. However, as a variant, as shown in FIG. 2, the
contacts between conductors 5, 6 and the metal wall 1 may be
located within compartment 6. The wall of compartment 6 is then in
hermetic contact with the metal wall 1 to be protected.
[0039] As shown in the figures, it is preferable that the
sacrificial anode 3 is not in direct contact with the wall 1 to be
protected. This avoids the creation of short-circuits between anode
3 and at least the zone of wall 1 that is opposite it. In this way,
a larger part of the surface of wall 1 can be protected in the best
conditions by one and the same anode 3. Means for keeping the anode
3 at a distance from wall 1 are therefore preferably provided (not
shown in the figures). In practice, however, they can often consist
of the connectors 4, 5, which are generally made of steel and have,
owing to their material and their dimensions, sufficient rigidity
to keep anode 3 at a distance from wall 1.
[0040] As a variant, the invention is also applicable to the case
when the anode is not a sacrificial anode in the sense that it
naturally has an electrochemical potential higher than that of the
wall 1 to be protected, but is placed at this potential by a
generator of direct or rectified current to which it is connected
by conductors that pass through the wall of compartment 6
hermetically.
* * * * *