Note: Descriptions are shown in the official language in which they were submitted.
WATER STORAGE CONTAINERS EXHIBITING REDUCED CORROSION, AND
DEVICES AND METHODS FOR REDUCING RATE OF CORROSION IN WATER
STORAGE CONTAINERS
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of United States Provisional
Application No.
62/384,074, filed September 6, 2016, which is incorporated herein by reference
in its entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention is directed to water storage containers that
provide reduced
corrosion rates, and devices and methods of reducing corrosion rates in
storage containers.
Description of Related Art
[0003] Elevated storage containers and other large water storage containers
are an integral part
of many municipal water distribution systems. These containers are intended to
ensure adequate
hydrostatic pressure to enable effective water delivery and to store water
hygienically. Water
storage tanks also provide relief from water surges and provide emergency
supplies for fire and
other emergencies. As components of municipal water systems, these containers
are expected to
have long, useful lives, often from 15 to 25 years, or 50 years or greater.
[0004] Achievement of the expected long lifespans of water storage tanks is
made difficult by
the very nature of their structure and function. For example, water storage
tanks are often made
of steel, which is subject to corrosion that will eventually cause failure of
the storage tanks. Water
storage tanks may be particularly susceptible to corrosion because interior
tank temperatures are
often in excess of exterior air temperatures in that the steel (or concrete)
structure absorbs heat
from the sun and re-radiates the heat into the interior of the tank and, with
a volume that holds
large amounts of water, the interior humidity ("RH") inside a water storage
tank is almost always
100%. Furthermore, the drinking water (and water held for other processes) is
often treated with
disinfectant chemicals, such as chlorine, that produces vapors which can also
accelerate corrosion
rates.
[0005]
Forced air ventilation is a process of controlling the interior humidity of
enclosed
structures (buildings, storage vessels). However, when controlling interior
conditions to lower
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rates of corrosion, it has commonly been assumed that ventilating exterior
atmosphere into an
enclosed structure is counter-productive. For example, corrosion-susceptible
equipment is
commonly stored in an enclosure that prevents the ingress of outside air. In
extreme cases (e.g.
the storage of military equipment in tropical climates), structures are built
that include active de-
humidification.
[0006] Typically, water storage tanks are designed to minimize the exchange of
air with the
outside. However, it is appreciated that at least some air must be exchanged
as water levels rise
or fall within the tank (for example in order to prevent de-pressurization of
the tank during draining
and buckling of the tank structure). Beyond permitting the minimum amount of
air required to
equilibrate air pressure inside the tank, no further ventilation is desired.
In fact, excess
ventilation/air access/air exchange is viewed as a liability because
additional air vents are: (i)
potential sources of sanitary defects and can increase the risk of
contamination of the interior of
the tank by the outside (e.g. bird droppings, insects, dust); and (ii) allow
greater air exchange inside
the tank and accelerate interior corrosion.
[0007] A common approach to controlling corrosion of water storage tanks is to
coat the interior
surfaces of the water storage tanks with epoxy paints to prevent direct
exposure of the steel to
corrosion-inducing conditions. However, 100% coverage with no gaps is
essentially impossible
to achieve. Even if a complete epoxy coating is achieved, the coating will be
subject to stresses
due to thermal cycling of the structure which will produce cracks in the
coating, thereby allowing
the underlying steel to become exposed to air or water that causes corrosion.
Similarly, VOC-
compliant coatings are not as resilient and must be reapplied more frequently.
Coating
performance has also been reduced by the requirements to remove toxic
materials, such as lead,
from the coatings. Thus, coating failure is a common problem in water storage
containers and
reapplication on a regular basis of these coatings is necessary.
[0008] Further, reapplication of a coating during tank interior refurbishment
is prone to even
greater potential for gaps. For example, tight corners and areas where roof
panels rest atop beams,
but which are not seal-welded, are not accessible for recoating and are
susceptible to corrosion.
Moreover, the ideal time to reapply the coating materials is in the summer
months such that routine
maintenance is necessary just at the time the water storage tanks are needed
most.
[0009] It is
also appreciated that not all surfaces are subjected to the same conditions.
Most
facilities focus on protection of water storage tank interiors where liquid
water is in contact with
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the surface. The coatings best to protect water container interior surfaces
from corrosion where
liquid water is in contact are not necessarily the same as those best to
protect surfaces from vapors
that comprise corrosive chemicals. The areas exposed to chemical vapors is
often referred to as
headspace. Further, headspace volume will fluctuate according to the amount of
water stored in
the tank at various times. Thus, it is difficult, if not impossible, to apply
different coatings to the
various portions of the interior of the water storage tank and achieve
satisfactory corrosion
proofing.
[0010] Thus, it is desirable to provide water storage tanks having a headspace
region with a
reduced propensity to corrode and which do not require additional maintenance
and costs to reduce
such corrosion overtime.
SUMMARY OF THE INVENTION
[0011] In certain non-limiting and preferred embodiments, the present
invention is directed to a
water storage tank comprising: a tank containing water; a roof positioned over
the tank; a
headspace region formed between the roof and a surface of the water contained
in the tank; and a
corrosion reduction system comprising: (i) a port that enables air to flow out
of the water storage
tank; and (ii) an active air ventilation system comprising at least one device
configured to facilitate
movement of air exterior of the water storage tank into the headspace region,
in which the
corrosion reduction system reduces a rate of corrosion of the water storage
tank.
[0012] In some non-limiting and preferred embodiments, the device of the
active air ventilation
system is configured to facilitate the movement of air exterior of the water
storage tank into the
headspace region in a direction that is non-perpendicular to the water
surface. The device of the
active air ventilation system can also be configured to facilitate the
movement of air exterior of
the water storage tank into the headspace region substantially laterally
across an interior surface of
the roof.
[0013] In
certain non-limiting and preferred embodiments, the device of the active air
ventilation system comprises air vent openings that fluidly connect the air
exterior of the water
storage tank to the headspace region. The device of the active air ventilation
system can further
comprise at least one screen that is positioned over at least one of the air
vent openings.
[0014] In some non-limiting and preferred embodiments, the active air
ventilation system
further comprises an air-moving device that facilitates an exchange of air
between an interior and
exterior of the water storage tank. The active air ventilation system can also
comprise a deflector
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that directs air exterior of the water storage tank into the headspace region
in a direction that is: (i)
non-perpendicular to the water surface; or (ii) substantially laterally across
an interior surface of the
roof. In some non-limiting and preferred embodiments, the active air
ventilation system includes
both an air-moving device and a deflector. In such embodiments, the deflector
is in fluid
communication with the air-moving device, and the deflector directs air
exterior of the water
storage tank into the headspace region in a direction that is: (i) non-
perpendicular to the water
surface; or (ii) substantially laterally across an interior surface of the
roof.
[0015] In certain non-limiting and preferred embodiments, the water storage
tank further
comprises a mixing device configured to bring cooler water to a top portion of
the tank. Further, at
least a portion of the water storage tank and/or at least a portion of an
interior of the roof can be
formed from a material that is prone to corrosion. The material that is prone
to corrosion can
comprise a metal.
[0016] In some non-limiting and preferred embodiments, the corrosion reduction
system of the
present invention reduces the rate of corrosion of the water storage tank by
at least about 10% to
at least about 90% as measured by ASTM G50-10(2015).
[0017] In
certain non-limiting and preferred embodiments, the present invention is also
directed
to a method of reducing a rate of corrosion of a water storage tank comprising
actively exchanging
air outside of the water storage tank with air inside the water storage tank
with a corrosion reduction
system to reduce the rate of corrosion of the water storage tank, in which the
corrosion reduction
system comprises: (i) a port that enables air to flow out of the water storage
tank; and (ii) an active
air ventilation system comprising at least one device configured to facilitate
movement of air
exterior of the water storage tank into a headspace region formed between a
roof positioned over
the water storage tank and a surface of water contained in the tank.
[0018] In some non-limiting and preferred embodiments, the corrosion reduction
system is
retrofitted into the water storage tank. In certain non-limiting and preferred
embodiments, the
water storage tank comprises a mixing device, and the method further comprises
actively mixing
with the mixing device such that cooler water is brought to a top of the water
storage tank. It is
appreciated that the water storage tank used in the method of the present
invention can also comprise
any of the previously described features.
[0019] In
certain non-limiting and preferred embodiments, the corrosion reduction system
reduces air temperature, humidity, and levels of oxidizing vapors in the
headspace region of the
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tank. In addition, the method of the present invention reduces the rate of
corrosion of the water
storage tank by at least about 10% to at least about 90% as measured by ASTM
G50-10(2015).
[0020] The present invention is also directed to the following clauses.
[0021] Clause 1: A water storage tank comprising: a tank containing water; a
roof positioned
over the tank; a headspace region formed between the roof and a surface of the
water contained in
the tank; and a corrosion reduction system comprising: (i) a port that enables
air to flow out of the
water storage tank; and (ii) an active air ventilation system comprising at
least one device
configured to facilitate movement of air exterior of the water storage tank
into the headspace
region, wherein the corrosion reduction system reduces a rate of corrosion of
the water storage
tank.
[0022] Clause 2: The water storage tank of clause 1, wherein the device of the
active air
ventilation system is configured to facilitate the movement of air exterior of
the water storage tank
into the headspace region in a direction that is non-perpendicular to the
water surface.
[0023] Clause 3: The water storage tank of clauses 1 or 2, wherein the device
of the active air
ventilation system is configured to facilitate the movement of air exterior of
the water storage tank
into the headspace region substantially laterally across an interior surface
of the roof.
[0024] Clause 4: The water storage tank of any of clauses 1 to 3, wherein the
device of the active
air ventilation system comprises air vent openings that fluidly connect the
air exterior of the water
storage tank to the headspace region.
[0025] Clause 5: The water storage tank of clause 4, wherein the device of the
active air
ventilation system comprises at least one screen that is positioned over at
least one of the air vent
openings.
[0026] Clause 6: The water storage tank of any of clauses 1 to 5, wherein the
active air
ventilation system further comprises an air-moving device that facilitates an
exchange of air
between an interior and exterior of the water storage tank.
[0027] Clause 7: The water storage tank of any of clauses 1 to 6, wherein the
active air
ventilation system comprises a deflector that directs air exterior of the
water storage tank into the
headspace region in a direction that is: (i) non-perpendicular to the water
surface; or (ii) substantially
laterally across an interior surface of the roof.
[0028] Clause 8: The water storage tank of clause 6, wherein the active air
ventilation system
comprises a deflector that is in fluid communication with the air-moving
device, and wherein the
CA 2978297 2017-09-06
deflector directs air exterior of the water storage tank into the headspace
region in a direction that
is: (i) non-perpendicular to the water surface; or (ii) substantially
laterally across an interior surface
of the roof.
[0029] Clause 9: The water storage tank of any of clauses 1 to 8, further
comprising a mixing
device configured to bring cooler water to a top portion of the tank.
[0030] Clause 10: The water storage tank of any of clauses 1 to 9, wherein at
least a portion of
the water storage tank and/or at least a portion of an interior of the roof is
formed from a material
that is prone to corrosion.
[0031] Clause 11: The water storage tank of clause 10, wherein the material
that is prone to
corrosion comprises a metal.
[0032] Clause 12: The water storage tank of any of clauses 1 to 11, wherein
the corrosion
reduction system reduces the rate of corrosion of the water storage tank by at
least about 10% to
at least about 90% as measured by ASTM G50-10(2015).
[0033] Clause 13: A method of reducing a rate of corrosion of a water storage
tank comprising
actively exchanging air outside of the water storage tank with air inside the
water storage tank with
a corrosion reduction system to reduce the rate of corrosion of the water
storage tank, wherein the
corrosion reduction system comprises: (i) a port that enables air to flow out
of the water storage
tank; and (ii) an active air ventilation system comprising at least one device
configured to facilitate
movement of air exterior of the water storage tank into a headspace region
formed between a roof
positioned over the water storage tank and a surface of water contained in the
tank.
[0034] Clause 14: The method of clause 13, wherein the corrosion reduction
system is retrofitted
into the water storage tank.
[0035] Clause 15: The method of clauses 13 or 14, wherein the device of the
active air
ventilation system is configured to facilitate the movement of air exterior of
the water storage tank
into the headspace region in a direction that is non-perpendicular to the
water surface.
[0036] Clause 16: The method of any of clauses 13 to 15, wherein the device of
the active air
ventilation system is configured to facilitate the movement of air exterior of
the water storage tank
into the headspace region substantially laterally across an interior surface
of the roof.
[0037] Clause 17: The method of any of clauses 13 to 16, wherein the active
air ventilation
system further comprises an air-moving device that facilitates an exchange of
air between an
interior and exterior of the water storage tank.
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[0038] Clause 18: The method of clause 17, wherein the active air ventilation
system comprises
a deflector that is in fluid communication with the air-moving device, and
wherein the deflector
directs air exterior of the water storage tank into the headspace region in a
direction that is: (i) non-
perpendicular to the water surface; or (ii) substantially laterally across an
interior surface of the roof.
[0039] Clause 19: The method of any of clauses 13 to 18, wherein the water
storage tank
comprises a mixing device, and wherein the method further comprises actively
mixing with the
mixing device such that cooler water is brought to a top of the water storage
tank.
[0040] Clause 20: The method of any of clauses 13 to 19, wherein the corrosion
reduction system
reduces air temperature, humidity, and levels of oxidizing vapors in the
headspace region of the
tank.
[0041] Clause 21: The method of any of clauses 13 to 20, wherein the method
reduces the rate
of corrosion of the water storage tank by at least about 10% to at least about
90% as measured by
ASTM G50-10(2015).
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG.
1 is a partial front view of a roof portion of a water storage tank having a
corrosion-
reduction system according to a non-limiting embodiment of the invention; and
[0043] FIG. 2 is a cross-sectional front view of the anti-corrosion device
shown in FIG. 1.
DESCRIPTION OF THE INVENTION
[0044] For purposes of the following detailed description, it is to be
understood that the
invention may assume various alternative variations and step sequences, except
where expressly
specified to the contrary. Moreover, other than in any operating examples, or
where otherwise
indicated, all numbers expressing, for example, quantities of ingredients used
in the specification
and claims are to be understood as being modified in all instances by the term
"about".
Accordingly, unless indicated to the contrary, the numerical parameters set
forth in the following
specification and attached claims are approximations that may vary depending
upon the desired
properties to be obtained by the present invention. At the very least, and not
as an attempt to limit
the application of the doctrine of equivalents to the scope of the claims,
each numerical parameter
should at least be construed in light of the number of reported significant
digits and by applying
ordinary rounding techniques.
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[0045] Notwithstanding that the numerical ranges and parameters setting forth
the broad scope
of the invention are approximations, the numerical values set forth in the
specific examples are
reported as precisely as possible. Any numerical value, however, inherently
contains certain errors
necessarily resulting from the standard variation found in their respective
testing measurements.
[0046] Also, it should be understood that any numerical range recited herein
is intended to
include all sub-ranges subsumed therein. For example, a range of "1 to 10" is
intended to include
all sub-ranges between (and including) the recited minimum value of 1 and the
recited maximum
value of 10, that is, having a minimum value equal to or greater than 1 and a
maximum value of
equal to or less than 10.
[0047] Further, the terms "upper," "lower," "right," "left," "vertical,"
"horizontal," "top,"
"bottom," "lateral," "longitudinal," and derivatives thereof shall relate to
the invention as it is
oriented in the drawing figures. However, it is to be understood that the
invention may assume
alternative variations and step sequences, except where expressly specified to
the contrary. It is
also to be understood that the specific devices and processes illustrated in
the attached drawings,
and described in the specification, are simply exemplary embodiments of the
invention. Hence,
specific dimensions and other physical characteristics related to the
embodiments disclosed herein
are not to be considered as limiting.
[0048] In this application, the use of the singular includes the plural and
plural encompasses
singular, unless specifically stated otherwise. In addition, in this
application, the use of "or" means
"and/or" unless specifically stated otherwise, even though "and/or" may be
explicitly used in
certain instances.
[0049] The phrases "water storage tanks", "water storage containers", "water-
containing storage
tanks" and the like are used interchangeable and mean the same thing. In
addition the term "water"
when used to describe "water storage tanks/containers" encompasses both water
and compositions
comprising water, in which water is the majority of the composition.
[0050] The present invention relates to systems and methods for reducing the
rate of corrosion
in the headspace region of water-containing storage tanks, such as municipal
water storage tanks
for example. Although the systems and methods are non-coating based, the
systems and methods
of the present invention may be used together with coating-based approaches
for reducing the rate
of corrosion. As such, the systems and methods of the present invention may be
used with coating-
based water storage tanks or non-coating based water storage tanks. In
general, the systems and
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methods of the present invention are designed to reduce at least one of the
temperature, humidity,
and levels of oxidizing vapors in the interior of the water storage tanks, for
example by actively
exchanging air from outside the tank with air inside the tank. In some non-
limiting and preferred
embodiments, the system reduces temperature and humidity levels in the
interior of the water
storage tank. In some other non-limiting and preferred embodiments, the system
reduces
temperature, humidity and oxidizing vapor levels in the interior of the water
storage tank.
[0051] The present invention also relates to water-storage tanks, including
municipal water-
storage tanks, fitted or retrofitted with non-coating based corrosion-
reduction systems that provide
a reduced rate of corrosion. The corrosion-reduction system is an active
ventilation system adapted
for use with a water storage tank. In certain non-limiting and preferred
embodiments, the active
ventilation system is configured to move air in a direction that is non-
perpendicular to the surface
of the water in the storage tank, which surface defines a boundary of the
headspace region. In
certain further non-limiting and preferred embodiments, the active ventilation
system is configured
to move air laterally (substantially laterally) across the roof of the water
storage tank.
[0052] In some non-limiting and preferred embodiments, the water-containing
storage tank 100
of the present invention is a municipal water storage tank. Municipal water
storage tanks typically
have a capacity of about 500 gallons of water or greater, or about 1000
gallons of water or greater,
or about 100,000 gallons of water or greater, or about 1,000,000 gallons of
water or greater.
Smaller water storage tanks (for example, having a capacity of 500 gallons or
less) may be made
from non-corrosive materials such as plastic. Larger storage tanks, on the
other hand, typically
comprise materials that are susceptible to corrosion such as metal (for
example steel). The systems
and devices of the present invention can be used with water-containing storage
tanks 100 that are
made of various materials including, but not limited to, the previously
described materials. The
systems and devices of the present invention are particularly useful when used
with water-
containing storage tanks comprising interior surfaces made at least partially
from materials
susceptible to corrosion such as a metal, regardless of whether the surface is
protected by a
corrosion-resistant coating.
[0053] In certain non-limiting and preferred embodiments, referring to FIG. 1,
the water-
containing storage tank 100 comprises a headspace region 5 formed between a
roof portion 3 and
the surface of the water contained in the water-containing storage tank 100.
As used herein, the
term "headspace region" refers to a region in a water-containing storage tank
100 that does not
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contain water. It is appreciated that the volume of headspace region 5
fluctuates with respect to
the amount of water stored in the water-containing storage tank 100.
[0054] The headspace region 5 is particularly vulnerable to corrosion since
the interior
conditions inside a water storage tank 100 are often worse (in terms of
corrosion rates) than
conditions outside the tank. For example, interior air temperatures are often
greater than exterior
air temperatures because the tank 100 materials (e.g. steel or concrete)
absorb heat from the sun
and re-radiate the heat into the interior of the tank 100. Furthermore, with a
volume that holds
large amounts of water, the interior humidity ("RH") inside a water storage
tank 100 is almost
always 100%. That is, air in the headspace region 5 generally exhibits a
higher relative humidity
than air on the exterior of the tank 100. The drier exterior air induces vapor
flow from the water
surface into the headspace region 5. Because drinking water (and water held
for other processes)
is often treated with disinfectant chemicals such as chlorine (a powerful
oxidizer), the vapors will
include such disinfectant chemicals that further accelerate corrosion rates.
In locations with low
relative humidity and high daytime temperatures, such as in the U.S.
Southwest, it can be expected
that corrosion-inducing vapors will be more prevalent because more evaporation
will occur under
these conditions. However, it is appreciated that corrosion from water vapors
occurs in water-
containing storage tanks 100 located in other geographic regions because,
under most
environmental conditions, evaporation of water stored in the tank 100 will
occur.
[0055] In accordance with the present invention, and as shown in FIGS. 1 and
2, the water
storage tank 100 is fitted with a corrosion reduction system 50 comprising a
port 1 and an active
air ventilation system 2. As used herein, a "corrosion reduction system"
refers to a system that
reduces the rate of corrosion of a target water storage tank 100. As such,
water-containing storage
tanks 100 comprising the corrosion-reduction systems 50 of the present
invention exhibit a reduced
rate of corrosion as compared to similar water-containing storage tanks 100
without the corrosion-
reduction systems 50. The water storage tanks 100 may be originally
manufactured with the
corrosion-reduction system 50, or may be retrofitted to include corrosion-
reduction systems 50.
[0056]
Further, the port 1 and an active air ventilation system 2 enter or are in
fluid
communication with the headspace region 5. For example, and as shown in FIGS.
1 and 2, the
port 1 and an active air ventilation system 2 are positioned through the roof
3 of the water
containing storage tank 100 such that the port 1 and the active air
ventilation system 2 are in fluid
communication with the headspace region 5.
CA 2978297 2017-09-06
[0057] In general, current water-containing storage tanks 100 are designed to
minimize
exchange of air to only that which is necessary to equilibrate the air
pressure. By contrast, the
active air ventilation system 2 of the corrosion reduction system 50 of the
present invention is
configured to increase ventilation/air access/air exchange beyond that
required to equilibrate air
pressure in the tank 100, for example by lowering the temperature, humidity,
and/or levels of
oxidizing vapors in the interior of the water storage tank 100.
[0058] In some non-limiting and preferred embodiments, the corrosion reduction
system 50
permits powered introduction of exterior air 6 into the headspace region 5 of
the water storage tank
100. In certain embodiments, the water-storage tanks 100 may exist with
installed volatile organic
chemical ("VOC") reduction devices such as described in U.S. Patent
Application Publication No.
2015-0167993, which is hereby incorporated by reference in its entirety, and
which may serve the
function of the air ventilation system 2 for the present corrosion-reduction
system 50. In some non-
limiting and preferred embodiments, the corrosion reduction system includes at
least the port 1,
the active ventilation system 2, and a (re)-configuration of the active
ventilation system 2 to reduce
the rate of corrosion as compared to a water storage tank having only the VOC
device installed.
For example, the rate of corrosion may be reduced by modifying the angle at
which the VOC
device is installed and/or including a deflector 4 as shown in FIG. 2 with the
corrosion reduction
system 50 to direct airflow from the exterior of the tank 100 into the
headspace region 5 in a
direction that is non-perpendicular to the surface of the water in the tank
100. In some non-limiting
embodiments, air is directed from the exterior laterally along the interior
surface 12 of the roof of
the tank 100.
[0059] In certain non-limiting and preferred embodiments, and referring to
FIG. 2, the corrosion
reduction system 50 includes an active ventilation system 2. The active
ventilation system 2 is
configured to control one or more parameters influencing air exchange
including airflow rate,
airflow direction, and frequency of active exchange (e.g. constant or
intermittent) and, contrary to
current teachings and understandings, the active ventilation system 2 is
configured to increase
ventilation/air access/air exchange beyond that required to equilibrate air
pressure in the tank, for
example by lowering the temperature, humidity, and/or levels of oxidizing
vapors in the interior
of the water storage tank. In some non-limiting embodiments, the active
ventilation system 2 is
configured to accomplish at least approximately 5 to 10 air exchanges/day. For
example, for a
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1MG tank with approximately 15 feet of headspace, a minimum of 5 to 10 air
exchanges per day
would correspond to 250 to 500 cfm.
[0060]
Referring to FIG. 2, the active ventilation system 2 comprises a ventilation
device 8,
which impacts airflow rate and frequency, and optionally a deflector 4, which
impacts airflow
direction. The ventilation device 8 is configured to facilitate exchange of
air exterior 6 to the water
storage tank 100 with air interior to the water storage tank 100 by fluidly
connecting the interior
headspace region 5 with the exterior environment by way of air vent openings
9. To alleviate
and/or prevent contamination of water stored within the tank 100, for example
to alleviate or
prevent ingress of animals, leaves and/or other debris into the tank 100,
screens 10 may be provided
to cover the vent openings 9. In addition, the active ventilation system 2 is
an "active" system, and
accordingly provides input energy (e.g. mechanical or electrical) to assist
the air exchange process.
In certain non-limiting and preferred embodiments, the input energy is
provided by an air-moving
device 11 such as a fan. In some non-limiting embodiments, for example where
there may be a
desire to achieve additional energy savings, a humidity switch may be included
which
automatically shuts off the air-moving device 11 if the interior humidity
falls below a pre-
determined amount such as below 100%.
[0061] The air-moving device 11 specifications and the dimensions of the air
ventilation device
8, including the relative dimensions of the air ventilation device 8 as
compared to the air-moving
device 11, determine the airflow rate (or range of airflow rates). It is
appreciated that the angle of
the device 8 connected to the water storage tank 100 relative to the surface
of water defining the
lower boundary of the headspace region 5 will impact airflow direction.
Although the air-moving
device 11, in this example a fan, is shown in FIG. 2 mounted within the
ventilation device 8 formed
on the roof 3 of the water storage tank 100, it need not be mounted on the
roof 3 or in the device
8, but, for example, could be ducted from the ground.
[0062] In certain non-limiting and preferred embodiments, a deflector 4 may be
used in
connection with the air ventilation device 8 to control the airflow direction.
The use of a deflector
4 may be desirable where the airflow direction is otherwise perpendicular to
the water surface 12.
Generally, the rate of corrosion is reduced as the direction of airflow is
closer to lateral movement
across the interior surface 12 of the roof 3 of the water storage tank 100.
[0063] In use, and without wishing to be bound by theory, the corrosion-
reduction systems 50
according to the present invention lowers the temperature, humidity, and/or
oxidizing vapor levels
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by active ventilation alone (exchanging tank air with the outside air), or by
combining active
ventilation with active mixing (not shown) (which brings cooler water to the
top of the tank 100,
lowering air temperature and humidity levels), or by active mixing alone
(which lowers the
headspace region 5 temperature by bringing cooler water to the surface). That
is, the corrosion-
reduction systems 50 according to the present invention, reduce the propensity
of the interior
surface of the water storage tank 100 at the headspace region 5 to corrode,
for example by engaging
an air-moving device 11 that is in fluid communication with the interior and
the exterior of the
tank 100 to circulate air within the headspace region 5, thereby reducing the
relative humidity of
the headspace region 5 and/or enabling at least some of the corrosion-inducing
vapors to exit
through one or more ports 1 positioned in the headspace region 5 (for example
the upper portion
of the headspace region 5), where the one or more ports 1 serve to vent vapors
from the headspace
region 5 to the exterior of the water storage tank 100 and/or to charge the
headspace region 5 with
exterior air, which may serve to reduce the concentration of corrosion-
inducing vapors in the
headspace region 5. Such lower concentration of vapors (and lower temperature)
results in a
reduced rate of corrosion of the exposed corrosion-susceptible materials in
the headspace region
5.
[0064]
Consequently, the present invention provides water storage tanks 100 that
exhibit
reduced corrosion rates as compared to those not configured as described
herein. In some non-
limiting embodiments, the water storage tanks 100 exhibit a rate of corrosion
in the headspace
region 5 that is markedly less than that seen in water storage tanks 100 that
do not include the
features of the present invention. As such, the present invention can reduce
the rate of corrosion
by at least 10%, or at least 15%, or at least 20%, or at least 25%, or at
least 30%, or at least 40%,
or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at
least 90% as compared to
water storage tanks 100 that do not include the features of the present
invention. As used herein,
the rate of corrosion is measured by AST G50-10(2015), Standard Practice for
Conducting
Atmospheric Corrosion Tests on Metals, ASTM international, West Conshohocken,
PA,
www.astm.org (retrieved March 26, 2016), the disclosure of which is hereby
incorporated in its
entirety herein by reference.
[0065] Whereas particular embodiments of this invention have been described
above for
purposes of illustration, it will be evident to those skilled in the art that
numerous variations of the
13
CA 2978297 2017-09-06
details of the present invention may be made without departing from the
invention as defined in
the appended claims.
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