CORROSION PROTECTION SYSTEM

SYSTEME DE PROTECTION CONTRE LA CORROSION

English Abstract

An electrolyte protection system has a strap extending from an electrode to the base of the vessel. The strap is non-conductive and porous to carry electrolyte into contact with the electrode. A secondary current path is thus established to inhibit electrical discharge from the electrode.

French Abstract

Un système de protection électrolytique a une sangle qui s'étend entre une électrode et la base du navire. La sangle est non conductrice et poreuse pour mettre l'électrolyte en contact avec l'électrode. Un trajet de courant secondaire est ainsi établi pour inhiber une décharge électrique de l'électrode.

Claims

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THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A corrosion protection system for a vessel
containing an electrolytic liquid comprising a first
electrode electrically connected to said vessel, a second
electrode disposed within said vessel and electrically
isolated therefrom, a current source connected between said
first electrode and said second electrode and a
non-conductive strap extending between said second
electrode and said vessel, said strap being porous to
absorb said electrolytic liquid and thereby establish an
electrolytic path between said vessel and said second
electrode whereby a current path is provided through said
strap.
2. A corrosion protection device according to claim
1 wherein said strap extends between said second electrode
and a base of said vessel.
3. A corrosion protection device according to claim
2 wherein said strap is flaccid.
4. A corrosion protection device according to claim
2 wherein said strap is a braided rope.
5. A corrosion protection device according to claim
4 wherein said rope is braided from glass fibres.

9
6. A corrosion protection device according to
claim 4 wherein a mass is secured to a distal end of said
strap to bias said strap toward said base.
7. For use with a vessel having a base and
upstanding side walls to contain a liquid electrolyte, a
corrosion protection device comprising an electrical
source connected to said vessel to provide a first
electrode and connected to a second electrode disposed
within and electrically isolated from said vessel and a
non-conductive strap connected to said second electrode
and extending to said vessel, said strap being porous to
absorb electrolyte within said vessel and carry it into
contact with said second electrode to maintain an
electrolytic current path between said vessel and said
second electrode whereby voltages induced on the second
electrode by said electrical source are mitigated.
8. A device according to claim 7 wherein said
second electrode is disposed vertically within said
vessel and said strap extends from said second electrode
to said base of said vessel.
9. A device according to claim 8 wherein said
strap is flaccid.
10. A device according to claim 9 wherein a mass is
attached to said strap at the distal end thereof to bias

10
said strap toward said base.
11. A device according to claim 9 wherein said strap
is a rope.
12. A device according to claim 11 wherein said rope
is formed of glass fibres.
13. A device according to claim 12 wherein said rope
is braided.
14. In a fluid storage system having a vessel to
store an electrolytic fluid and having a corrosion
protection system associated therewith to inhibit corrosion
of said vessel, the improvement comprising a strap
extending from an electrode of said protection system to
said vessel, said strap being non-conductive and porous to
absorb electrolyte within said vessel and thereby establish
a current path between said vessel and said electrode upon
application of a potential difference therebetween.
15. The improvement of claim 14 wherein said strap is
flaccid.
16. The improvement of claim 15 wherein said strap is
woven from glass fibres.
17. The improvement of claim 15 wherein a mass is

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attached to said strap adjacent one end thereof.
18. A method of inhibiting an electrical discharge in
a vessel having a corrosion protection system incorporated
therein to inhibit corrosion of said vessel, said system
including a current source connected between said vessel
and an electrode located in said vessel to establish an
electrical current through electrolyte stored in said
vessel, said method comprising the steps of extending a
non-conductive porous strap from said electrode to said
vessel, immersing at least a portion thereof in said
electrolyte and allowing said strap to absorb said
electrolyte to establish a current path between said
electrode and said vessel and thereby inhibit accumulation
of electrical potential at said electrode in the absence of
electrolyte around said electrode.
19. A method according to claim 18 including the step
of biasing said strap into engagement with said vessel.

Description

~14~1~'~
CORROSION PROTECTION SYSTEM
The present invention relates to a corrosion
protection system.
It is well known that the storage of certain
liquids in vessels may lead to corrosion of the vessel and
subsequent weakening of the structure. Although materials
are available that are impervious to corrosion, it may be
necessary for reasons of economy or structural strength to
utilize materials, particularly metals, that are subject to
corrosion. To inhibit the effect of corrosion, various
techniques have been developed that utilize the
electrolytic action of the liquid and the material of the
vessel.
One such technique is cathodic protection which
utilizes a sacrificial anode in electrical contact with the
metal of the vessel. Alternatively, an impressed EMF
method may be utilized, in which a direct current is
provided by an external source and is passed through the
system by the use of essentially non-sacrificial anodes
that may be buried in the ground or suspended in the
electrolyte in the case of an aqueous system.
A relatively new form of corrosion control
involves pacifating a metal used in the vessel by applying
an external current that makes it more anodic. Such a
technique is known as "anodic protection".
With anodic protection, the current is applied
from an external source between an anode formed as the
walls of the vessel and a cathode located within the

214112
2
vessel. The cathode is normally immersed in the liquid to
be stored which acts as an electrolyte and establishes a
current path between anode and cathode. The current is
maintained within predetermined limits by a control system
utilizing reference electrodes and an adjustable
potentiometer.
The current will be maintained at a level
determined by the material of the vessel and the liquid to
be stored. It has been found that by maintaining the
current within predefined limits, a potential is maintained
that generates a film at the surface of the vessel to
inhibit corrosion. This technique has been found
particularly beneficial with vessels of steel or stainless
steels and liquids with extreme Ph valves, i.e. strongly
acid or strongly alkali.
The control system associated with such anodic
systems is sensitive to the level of liquid within the
vessel and operates to cut off the current flow if the
liquid level drops below the cathode. However, situations
may arise where the cathode is intermittently covered and
uncovered by liquid in the tank. In these circumstances,
the inductance of the electrical circuit established
between the current source and the cathode may permit a
relatively large potential to be induced on the cathode as
it is uncovered, which then may result in a spark or
discharge as the liquid again approaches the cathode. As
explosive gases may be present within the vessel, it is
clearly undesirable to permit an electrical discharge

~1412~~
3
within the vessel.
It is therefore an object of the present
invention to provide a corrosion protection system in which
the above disadvantages are obviated or mitigated.
In general terms, the present invention provides
a non-conductive strap extending from an electrode to the
vessel. The strap is porous and absorbs electrolyte and,
through wicking action, carries the electrolyte into
contact with the electrode. A current path is therefore
provided through the electrolyte carried by the strap to
inhibit the generation of potential at the cathode.
More particularly, the present invention provides
a corrosion protection system for a vessel containing an
electrolytic fluid comprising a first electrode
electrically connected to said vessel, a second electrode
disposed within said vessel and electrically isolated
therefrom, a current source connected between said
electrodes and a non-conductive strap extending between
said second electrode and the vessel. The strap is porous
to absorb electrolyte and thereby through a capillary
action, establishes an electrolytic path between said
vessel and the second electrode whereby a current path is
provided through said strap.
Preferably, the strap is a braided rope and a
mass is secured to the distal end of the strap to bias the
strap towards the base of the vessel.
In a further aspect, the present invention
provides a corrosion protection device for use with a

4
vessel having a base and upstanding side walls to contain
a fluid electrolyte. The device comprises an electrical
source connected to the vessel to provide an anode and
connected to an electrode disposed within the vessel. A
non-conductive strap is connected to the electrode and
extends to the vessel. The strap is porous to absorb
electrolyte within the vessel and maintain an electrolytic
current path between the vessel and electrode with
electrolyte in the vessel. Voltages induced on the
electrode by said electrical source are therefore
mitigated.
In a further aspect, the present invention
provides a fluid storage system having a vessel to store an
electrolytic fluid and having a corrosion protection system
associated therewith to inhibit corrosion of the vessel.
The improvement comprises a strap extending from an
electrode of the protection system to the vessel. The
strap is non-conductive and porous to absorb electrolyte
within the vessel and thereby establish a current path
between the vessel and the electrode upon application of a
potential difference therebetween.
An embodiment of the invention will now be
described by way of example only, with reference to the
accompanying drawings, in which
Figure 1 is a side elevation of a storage vessel;
and
Figure 2 is a view on an enlarged scale of a
portion of the storage vessel shown in Figure 1 within the

i
CA 02141127 2003-09-25
circle II.
Referring therefore to the drawings, a storage
vessel indicated at 10 has a base 12, a cylindrical side
wall 14, and a domed roof 16. The vessel 10 is formed from
5 a material subject to corrosion by the liquid to be stored
in the vessel and is typically carbon steel or stainless
steel.
Liquid indicated at 18 is introduced into the
vessel 10 through an inlet 20 and is extracted from the
vessel through an outlet 22.
An anodic protection system generally indicated
at 24 includes an external current source 26 electrically
connected through cable 28 to the wall 14. The wall 14
defines the anode of the protection system. It will be
understood that cathodic protection systems could also be
implemented if appropriate.
The current source 26 is also connected through
a cable 30 to a cathode assembly 32 mounted on the roof 16.
Cathode assembly 32 includes a cathode 34 that extends
vertically from the roof 16 into the interior of the vessel
1o and terminates prior to the base 12. Typically it is
spaced in the order of 12"-18" from the base. Cathode 34
is electrically isolated from the vessel 10 and is located
on the longitudinal axis of the tank. The cathode 34 is
formed from a rigid rod of a suitable cathode material such
TM
as hastalloy, as is well known in the art.
Reference electrodes 36,38 are also located
within the vessel 10 and provide control signals to the

6
current source 26 to maintain the applied current within
predetermined parameters. Such control systems are again
well known in the art and will not be described in further
detail.
As can be seen in Figure 2, a strap 40 is secured
to the lower end of the cathode 34 by means of clamps 42.
The strap 40 is formed from a braided or woven fibreglass
rope which is therefore electrically non-conductive but
which is porous to the liquid 18. As such, it will absorb
the liquid 18 and carry it by capillary action into contact
with the cathode 34. The strap 40 is flaccid and has a
weight 44 secured at the opposite end to the cathode to
bias the strap 40 into contact with the base 12.
In operation, the liquid 18 is normally above the
lower limit of the cathode 34 and acts as an electrolyte.
An electrical current path is established between the walls
14 through the liquid 18 to the cathode 34. With the
current controlled within the appropriate range of
parameters, a passive film is generated at the inner
surface of vessel 10 that inhibits corrosive action on the
base 12 and walls 14. The current will depend upon the
material of the tank and the liquid. As noted above, the
parameters controlling the current are well known in the
art.
In the event that the level of liquid drops below
the end of the cathode 34, the reference electrodes will
switch off the current source 26. However, in certain
circumstances, the liquid level 18 may be adjacent to the

2~~? ~~~
lower end of the electrode 34 so that contact is
intermittently made and lost between the liquid 18 and the
cathode due to bodily movement within the liquid 18. In
this condition, the strap 40 acts as a wick to bring the
liquid 18 into contact with the cathode 34. A secondary
current path is established through the liquid within the
strap 40 to the cathode and so inhibits the accumulation of
electrical charge on the cathode 34 due to the inductance
of the electrical circuit. The strap 40 is maintained
within the liquid 18 by virtue of the mass 44 which holds
the strap 40 against the base 12.
In a practical embodiment, the strap 40 has been
formed from a ~Ys inch fibreglass braided rope such as that
available from A.R. Thompson Limited under Part No. G-38.
With a spacing between the cathode 34 and tank 12 of 18
inches, it was found that a 36-inch length of such rope was
effective to maintain contact with the base of the tank and
provide the secondary leakage. The strap 40 was effective
to inhibit the formation of sparks such as might occur with
intermittent contact between the cathode 34 and liquid 18.
It will be seen, therefore, that a very simple
but effective device is provided to inhibit the formation
of sparks and to provide a secondary current path through
the liquid between the anode and cathode.

Representative Drawing