U.S. patent application number 11/612901 was filed with the patent office on 2008-06-19 for method of using sulfur-based corrosion inhibitors for galvanized metal surfaces.
Invention is credited to Srikanth S. Kidambi.
Application Number | 20080145271 11/612901 |
Document ID | / |
Family ID | 39562898 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080145271 |
Kind Code |
A1 |
Kidambi; Srikanth S. |
June 19, 2008 |
METHOD OF USING SULFUR-BASED CORROSION INHIBITORS FOR GALVANIZED
METAL SURFACES
Abstract
A composition and method for inhibiting white rust formation on
galvanized surfaces. The composition includes thiols, polymeric
dithiocarbamates, and xanthates. The composition may be introduced
onto the galvanized surface, especially in an industrial water
system, using a variety of different methods or programs including
integrating with current programs or developing a new program.
Inventors: |
Kidambi; Srikanth S.;
(Naperville, IL) |
Correspondence
Address: |
Edward O. Yonter;Patent and Licensing Department
Nalco Company, 1601 West Diehl Road
Naperville
IL
60563-1198
US
|
Family ID: |
39562898 |
Appl. No.: |
11/612901 |
Filed: |
December 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11612702 |
Dec 19, 2006 |
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11612901 |
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Current U.S.
Class: |
422/14 |
Current CPC
Class: |
C23F 11/16 20130101;
C02F 1/68 20130101; C02F 2303/08 20130101; C23C 2/26 20130101; C23F
11/173 20130101; C23F 11/161 20130101; C02F 2303/14 20130101; C23F
11/08 20130101; C23F 14/02 20130101; C23F 11/165 20130101 |
Class at
Publication: |
422/14 |
International
Class: |
C23F 11/16 20060101
C23F011/16 |
Claims
1. A method of inhibiting corrosion on a galvanized metal surface,
said method comprising: (a) introducing an effective amount of a
corrosion-inhibiting composition onto the galvanized metal surface
to form a barrier on said surface, said composition including a
sulfide-based white rust corrosion-inhibiting compound; and (b)
after one or more time intervals, optionally overlaying the barrier
by reintroducing an effective amount of the composition onto the
galvanized metal surface.
2. The method of claim 1, wherein the sulfide-based white rust
corrosion-inhibiting compound is selected from the group consisting
of: thiols; bismuthiols; dimerized bismuthiols; polymeric
dithiocarbamates; xanthates; and combinations thereof.
3. The method of claim 1, wherein the galvanized metal surface is
part of an industrial water system.
4. The method of claim 1, including preparing a solution of the
corrosion-inhibiting composition including from about 0.001 weight
percent to about 100 weight percent of the sulfide-based white rust
corrosion-inhibiting compound.
5. The method of claim 1, including spraying or physically applying
an effective amount of said composition directly onto the
galvanized metal surface.
6. The method of claim 1, including dipping the galvanized metal
surface into a solution containing the corrosion-inhibiting
composition.
7. The method of claim 1, including mixing a foaming agent with the
corrosion-inhibiting composition to form a mixture and spraying an
effective amount of the mixture onto the galvanized metal surface
to form the barrier.
8. The method of claim 1, including a plurality of different
compositions and repeating step (b) after one or more of the time
intervals by introducing a different one of the compositions onto
the galvanized surface.
9. A method of inhibiting corrosion in an industrial water system
that is at least partially full of water and has one or more
galvanized metal surfaces, said method comprising: (a) adjusting
the water in the industrial water system to have a pH from about
6.5 to about 8.2; (b) introducing an effective amount of a
corrosion-inhibiting composition that includes one or more
sulfide-based white rust corrosion-inhibiting compounds into the
water of the industrial water system when said system is either
under load or not under load; (c) circulating the water of the
industrial water system for a time interval to contact the
sulfide-based white rust corrosion-inhibiting compound with the
galvanized metal surface to form a barrier on the galvanized metal
surface, if the system was not under load; (d) operating the system
for the time interval to contact the sulfide-based white rust
corrosion-inhibiting compound with the galvanized metal surface to
form the barrier on the galvanized metal surface, if the system was
under load; (e) optionally overlaying the barrier by: i) unloading
the system, readjusting the pH of the water in the system to be
from about 6.5 to about 8.2, reintroducing an effective amount of
the corrosion-inhibiting composition into the water of said system,
and circulating the water of the system, or ii) keeping the system
under load, readjusting the pH of the water in the system to be
from about 6.5 to about 8.2 and reintroducing an effective amount
of the corrosion-inhibiting composition into the water of said
system; and (f) operating the industrial water system under load
for one or more additional time intervals and optionally repeating
step (e) after one or more of the additional time intervals.
10. The method of claim 9, wherein the industrial water system
includes a cooling water circulation system.
11. The method of claim 9, including adjusting the pH of the water
in the industrial water system to be from about 6.8 to about
7.8.
12. The method of claim 9, wherein the corrosion-inhibiting
composition includes one or more polyalkoxy compounds.
13. The method of claim 9, including adding another composition
including one or more polyalkoxy compounds to the water of the
industrial water system either simultaneously or sequentially with
the corrosion-inhibiting composition.
14. The method of claim 9, wherein the corrosion-inhibiting
composition includes from about 1 ppm to about 10,000 ppm of the
sulfide-based white rust corrosion-inhibiting compound.
15. The method of claim 9, wherein the corrosion-inhibiting
composition includes one or more compounds selected from the group
consisting of: other corrosion inhibitors, scale inhibitors,
fluorescent tracers, and water treatment polymers.
16. The method of claim 9, including adding one or more other
corrosion or scale inhibiting compositions that include one or more
corrosion or scale inhibiting compounds with or without one or more
fluorescent tracer compounds either simultaneously or sequentially
with the corrosion-inhibiting composition.
17. The method of claim 9, wherein the corrosion-inhibiting
composition includes one or more other corrosion inhibitors
selected from the group consisting of: phosphates; phosphonates;
phosphinates; silicates; molybdate; tungstate; borate; zinc and its
salts; vanadate; chromate; polycarboxylates; and combinations
thereof.
18. The method of claim 9, including adding one or more water
treatment polymers either simultaneously or sequentially with the
corrosion-inhibiting composition, said polymer selected from the
group consisting of: polyacrylic acid; polymaleic acid; copolymers
and terpolymers of acrylic acid, maleic acid, acrylamide, and
acrylamidopropyl sulfonate; prism polymers; sulfonate-based
polymers; and terpolymers or copolymers of acrylic acid,
acrylamide, and sulfomethylated acrylamide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part of application Ser. No.
11/612,702 entitled "FUNCTIONALIZED AMINE-BASED CORROSION
INHIBITORS FOR GALVANIZED METAL SURFACES AND METHOD OF USING SAME,"
filed Dec. 19, 2006, now pending.
TECHNICAL FIELD
[0002] This invention relates generally to inhibiting corrosion on
galvanized metal surfaces. More specifically, the invention relates
to a method for inhibiting white rust corrosion on galvanized
surfaces. The invention has particular relevance for inhibiting
white rust corrosion by using sulfide-based compounds on galvanized
metal surfaces in industrial water systems.
BACKGROUND
[0003] Galvanization is a protective zinc coating that is
chemically bonded to a metal (usually iron or steel) surface. Zinc
coating is used in a variety of applications and offers a certain
degree of corrosion protection for the underlying metal by
providing a mechanical barrier to the elements and environment as
well as electrochemical resistance to corrosion. Several
galvanizing methods exist, such as electroplating, continuous
galvanization, and hot-dip galvanization. Many industrial water
systems, such as cooling water circulation systems (sometimes
referred to herein as "cooling towers"), have such galvanized
surfaces.
[0004] A common problem with galvanized coatings of all kinds is
"white rust," which manifests itself as a white, waxy, fluffy, or
powdery non-protective and porous deposit that rapidly forms on
galvanized surfaces when the surface is exposed to humid and/or wet
conditions. White rust can cause considerable damage to the zinc
coating and is also detrimental to the coating's appearance. If
left unchecked, white rust will continually corrode affected
galvanized surfaces and eventually lead to early failure of the
coating. With such a non-protective, porous deposit on the
galvanized surface, the surface is not "passive" to future white
rust formation and may rapidly continue to corrode.
[0005] Increased popularity of high alkalinity, no pH control water
treatment programs have resulted in more frequent and severe white
rust corrosion issues, especially in cooling tower applications.
White rust typically forms if a new cooling tower is operated with
water at a pH greater than 8.0 for an extended period before a
"basic zinc carbonate" protective barrier forms. To ensure long
service life, the galvanized surfaces in cooling towers typically
must be allowed to "passivate" or form a protective barrier prior
to initial operation or start-up. Proper water treatment and
start-up procedures are also essential. One way to passivate the
surfaces is to allow the zinc coating to develop a natural
nonporous surface of basic zinc carbonate during initial start-up
of the cooling tower. This natural chemical barrier helps prevent
or slow further rapid corrosion of the zinc coating from the
environment as well as from normal cooling tower operation.
[0006] This basic zinc carbonate barrier, believed to be a zinc
carbonate/zinc hydroxide compound (as discussed in "Guidelines for
Treatment of Galvanized Cooling Towers to Prevent White Rust,"
published by the Cooling Tower Institute in June 1994) typically
forms within eight weeks of initial cooling tower operation with
water of neutral pH (i.e., pH 6.5 to 8.0) and moderately hard water
environment. A typical solute content range would be calcium
(CaCO.sub.3) content of 100 ppm to 300 ppm as bicarbonate
alkalinity and about 100 ppm CaCO.sub.3 hardness. Formation of the
protective zinc carbonate barrier is important for the cooling
tower to resist further corrosion. Barrier absence could result in
severe white rust formation and have a significant negative impact
on the cooling tower's service life.
[0007] White rust is also a form of zinc carbonate that has a
different porous structure, rate of formation, and density than the
protective zinc carbonate barrier described above. If the water
hardness levels, measured by CaCO.sub.3 hardness, reach levels
below 50 ppm (i.e., soft water), accelerated zinc corrosion
generally results. Certain ionic content in the water, such as
sulfates, chlorides, and nitrates at levels greater than about 250
ppm may also contribute to accelerated zinc corrosion. Thus,
routine inspection of the cooling tower coupled with adequate
control of the water chemistry aids in the prevention of white rust
formation.
[0008] Current white rust corrosion prevention programs include a
combination of pre-passivating the cooling tower combined with
ongoing water chemistry management to support the viability of the
passivation layer. In addition to the basic zinc carbonate
protective layers, as described above, white rust preventatives
include pretreatment with inorganic phosphate and chromate
passivation. Such inorganic solutions have limited effectiveness
and are steadfastly becoming the object of federal and local
regulations due to environmental concerns.
[0009] Other solutions for white rust prevention include using
selective thiocarbamates, organo-phosphorous compounds, and tannins
to passivate the surface. For example, U.S. Pat. No. 5,407,597
provides a formulation including a mixture of an organophosphorous
compound, a thiocarbamate compound, and soluble metal salt
compound. The components of this formulation are used as a
combination and the ingredients tested alone typically do not
control white rust formation. The formulation in U.S. Pat. No.
6,468,470 B1 includes a multi-component system of an
organophosphorous compound, a tannin compound, and a soluble salt
of a metal.
[0010] Moreover, under normal operating conditions, cooling towers
have substantial evaporative water loss. As a result, large
quantities of "make-up" water are introduced into the system that
commonly contains ionic species, such as calcium, magnesium,
sulphate, and chloride. Increased alkalinity (e.g., carbonate,
bicarbonate, and hydroxide ions) may also cause white rust
corrosion. Particularly, accumulation of carbonate alkalinity, with
a concomitant pH increase, creates an ideal white rust-forming
environment. This accumulation is one of the major causes of white
rust. The presence of excess anions and/or soft water can aggravate
the degree of white rust formation by, for example, reacting with
the zinc coating to produce zinc hydroxide.
[0011] As an integral component of cooling water circulation
systems biocides are essential is preventing algal, bacterial, and
fungal contamination of the systems. Some of these biocides
sometimes promote white rust formation as a byproduct because they
chemically react with certain white rust inhibitors and/or with the
zinc coating. For example, sodium hypochlorite (i.e., bleach) is a
common biocide and is highly reactive.
[0012] Because high pH levels are also contributing factor to white
rust formation, the addition of a sufficient quantity of free acid,
commonly sulfuric acid, to the cooling water helps preclude the
formation of white rust. Such free acid addition creates concerns
for those handling the free acid and also creates potential for
metal corrosion from the acid itself due to overfeed or spillage.
None of these passivation or maintenance procedures described above
provides a complete solution to the white rust problem. There thus
exists a need to provide efficient and improved compositions and
methods of inhibiting white rust corrosion.
SUMMARY
[0013] Accordingly, this invention provides a method of preventing
corrosion on galvanized metal surfaces. The method includes
introducing an effective amount of a corrosion-inhibiting
composition having a sulfur-based, preferably sulfide-based, white
rust corrosion-inhibiting compound onto a galvanized metal surface
to form a barrier on the surface. In one embodiment, the method
further includes overlaying the barrier by reintroducing an
effective amount of the composition onto the galvanized metal
surface after one or more time intervals.
[0014] In an embodiment, the invention provides a method of
inhibiting corrosion in an industrial water system that is at least
partially full of water and has one or more galvanized metal
surfaces. The method includes adjusting the water in the industrial
water system to have a pH from about 6.5 to about 8.2 and
introducing an effective amount of a corrosion-inhibiting
composition that includes one or more sulfur-based or sulfide-based
white rust corrosion-inhibiting compounds into the water of the
industrial water system.
[0015] Implementing the method may be accomplished when the system
is either under load or not under load. If the system is not under
load when introducing the corrosion-inhibiting composition, the
water in the system is circulated after such introduction for a
time interval to contact the sulfur-based white rust
corrosion-inhibiting compound with the galvanized metal surfaces of
the system to form the barrier on those surfaces. After a
sufficient interval, the unloaded system may be turned on or
brought under load at any suitable time. If the system is under
load when introducing the corrosion-inhibiting composition, the
system is operated under load after such introduction for a time
interval to contact the white rust corrosion-inhibiting compound
with the galvanized metal surfaces of the system and form the
barrier on those surfaces.
[0016] In an aspect, the invention provides a method for overlaying
the barrier formed by the sulfide-based white rust-inhibiting
compound. This aspect includes overlaying the barrier while the
system is under load or not under load. If the barrier is overlaid
while the system is under load, the method includes readjusting the
pH of the system to be from about 6.5 to about 8.2 and
reintroducing an effective amount of the corrosion-inhibiting
composition into the water of the system. The system is then
operated under load for one or more additional time intervals and
the barrier optionally is re-overlaid after one or more of the
additional time intervals.
[0017] If the barrier is overlaid while the system is not under
load, the method includes readjusting the pH of the system to be
from about 6.5 to about 8.2, reintroducing an effective amount of
the corrosion-inhibiting composition into the water of the system,
and circulating the water of the system for a sufficient interval
to contact the sulfide-based compound with the surfaces. After the
sufficient interval, the unloaded system may be turned on or
brought under load at any suitable time.
[0018] Though the invention is particularly relevant to
applications such as basins and heat transfer coils of cooling
towers, it should be appreciated that the implementation of the
method is not limited to such cooling tower applications.
Contemplated applications include any system having galvanized
metal surfaces. The invention may also be combined with one or more
other corrosion or scale inhibiting compositions, such as
silicates, borates, molybdates, tungstates, chromate, zinc salts,
orthophosphates, polyphosphates, phosphonate/phosphinate,
combinations thereof, or any other suitable corrosion or scale
inhibiting compound or composition, with or without one or more
fluorescent tracer compounds. Such combinations would form a
comprehensive corrosion and scale inhibition program, discussed in
more detail below.
[0019] An advantage of the invention is to provide a method of
inhibiting corrosion, especially white rust corrosion, on
galvanized metal surfaces.
[0020] Another advantage of the invention is to extend the lifespan
of galvanized metal surfaces in various applications including
industrial water systems.
[0021] Yet another advantage of the invention is to provide a
one-step passivation method for inhibiting white rust corrosion on
galvanized surfaces of industrial water systems.
[0022] An additional advantage of the invention is to provide a
method for initially pre-passivating with a sulfur-based white rust
corrosion-inhibiting composition and post-treating by overlaying
the sulfur-based white rust corrosion-inhibiting composition on
galvanized surfaces.
[0023] It is another advantage of the invention to provide an
approach to inhibiting white rust corrosion on galvanized surfaces
in industrial water systems that is effective under a range of pH
conditions.
[0024] It is a further advantage of the invention to provide an
approach to inhibiting white rust corrosion on galvanized surfaces
in industrial water systems that is effective with water having low
ionic content, such as soft water.
[0025] It is yet another advantage of the invention to provide a
method for inhibiting white rust corrosion on galvanized surfaces
in industrial water systems that is effective under elevated
carbonate alkalinity.
[0026] It is still another advantage of the invention to provide a
composition and method for inhibiting white rust corrosion on
galvanized surfaces in industrial water systems, which includes one
or more sulfur-based or sulfide-based compounds that adsorb and/or
bind to the surfaces and which are effective under a range of pH
conditions, a range of alkalinity levels, and a range of water
hardness levels.
DETAILED DESCRIPTION
[0027] The invention provides a method of inhibiting corrosion on a
galvanized metal surface. The method includes introducing an
effective amount of a corrosion-inhibiting composition onto the
galvanized metal surface to form a barrier on the surface. The term
"barrier" as used herein includes surface modification of the
galvanized surface, change of morphology of the galvanized surface,
chemical interaction of any of the white rust corrosion-inhibiting
compounds with the galvanized surface, or any other similar
modification of or interaction with the surface. In one embodiment,
an effective amount of the corrosion-inhibiting composition
includes from about 0.001 weight percent to about 100 weight
percent of the white rust corrosion-inhibiting compound. In a
preferred embodiment, an effective amount of the composition
includes from about 0.001 weight percent to about 50 weight percent
of the compound. In a more preferred embodiment, from about 0.1
weight percent of to about 30 weight percent of the compound of the
composition is introduced to the galvanized surface.
[0028] It should be appreciated that the white rust-inhibiting
compounds described herein can each be used independently,
simultaneously, sequentially, alternating between different
compounds, or by implementing in any suitable order or fashion.
Representative sulfur-based white rust-inhibiting compounds include
thiols, bismuthiols, dimerized bismuthiols, polymeric
dithiocarbamates, xanthates, and combinations thereof.
[0029] In one aspect, introducing the corrosion-inhibiting
composition onto the galvanized surface includes incorporating the
method into a hot dip manufacturing process. For example, the metal
would first be dipped in melted zinc at 450.degree. C. (temperature
at which iron/steel and zinc share great affinity) where the metal
would be protected with a zinc coating. The next step in the
manufacturing process would be to dip the zinc-coated metal into
the corrosion-inhibiting composition including the sulfur-based or
sulfide-based white rust corrosion-inhibiting compound.
[0030] In another aspect, such introduction includes spraying a
solution of the corrosion-inhibiting composition directly onto the
surface, including surfaces in industrial water systems. In one
embodiment, the composition is mixed with a foaming agent to form a
mixture and the mixture is subsequently sprayed onto the galvanized
metal surface using any suitable spraying device. Foaming agents
may include surfactants, such as alkoxylated alcohols, polyethylene
glycol, or any other suitable surfactant. In alternative
embodiments, the composition may be physically applied onto the
surface by rolling using a paint roller or the like, brushing using
a paintbrush or the like, swabbing using a mop or the like, or by
using any other suitable method or technique.
[0031] In another aspect, the corrosion-inhibiting composition is
reintroduced onto the surface one or more times after one or more
time intervals to "overlay" the barrier or "re-passivate" the
surface. Ongoing overlaying steps to renew the corrosion-inhibitory
barrier and/or to re-passivate the galvanized surfaces are also
contemplated. As determined on a case-by-case basis, the method may
include a plurality of different corrosion-inhibiting compositions
and overlaying the barrier may include introducing a different one
or more of the corrosion-inhibiting compositions onto the
galvanized metal surface(s).
[0032] In one embodiment, an effective amount of the
corrosion-inhibiting composition is introduced into the water of a
cooling water circulation system (sometimes referred to herein as
"cooling tower") to form a barrier on (or passivate) any galvanized
metal surfaces of the system. It should be appreciated that such
introduction may be into a new, unused system prior to initial
operation of the system or into a running, operational system. The
corrosion-inhibiting composition of the invention may be introduced
into any industrial water system as either an adjunct treatment in
combination with other compositions or programs, such as scale
and/or corrosion-inhibiting programs, or as a stand-alone treatment
program, as described in more detail herein.
[0033] The industrial water system is at least partially full of
water and has one or more galvanized metal surfaces. The method
includes adjusting the water in the system to have a pH from about
6.5 to about 8.2. In a preferred embodiment, the pH of the water in
the system is adjusted to be from about 6.8 to about 7.8. The
method further includes introducing an effective amount of a
corrosion-inhibiting composition that includes one or more white
rust corrosion-inhibiting compounds into the water of the
industrial water system.
[0034] The corrosion-inhibiting composition typically includes from
about 1 ppm to about 10,000 ppm of the white rust
corrosion-inhibiting compound. In a preferred embodiment, the
composition includes from about 1 ppm to about 1000 ppm of the
compound. In a more preferred embodiment, the composition includes
from about 1 ppm to about 100 ppm of the compound.
[0035] In one embodiment, an effective amount of the
corrosion-inhibiting composition is introduced into the water of
the industrial water system when the system is operating and under
load. In this embodiment, during and after introducing the
composition into the system, the system is operated under load
(i.e., turned on) for a time interval to contact the white rust
corrosion-inhibiting compound with the galvanized surface(s) in the
system to form a barrier on the surface(s).
[0036] Certain cases may require overlaying the barrier. Such
overlaying may be implemented when the industrial water system is
operating and under load or when the system has been turned off and
thus not under load. In one embodiment, overlaying the barrier
includes unloading (i.e., turning off) the system, readjusting the
pH of the system, reintroducing an effective amount of the
corrosion-inhibiting composition into the water of the system, and
circulating the water of the system. In another embodiment,
overlaying the barrier includes keeping the system under load,
readjusting the pH of the system (as described above) and
reintroducing an effective amount of the corrosion-inhibiting
composition into the water of the system.
[0037] In an embodiment, the method includes a plurality of
different corrosion-inhibiting compositions and overlaying the
barrier includes introducing a different one or more of the
corrosion-inhibiting compositions into the industrial water
system.
[0038] It should be appreciated that the corrosion-inhibiting
composition of the invention is preferably introduced in a
pre-passivation process prior to initially starting up the
industrial water system. This method is preferred because such
application typically provides the highest degree of passivation
and protection for the galvanized surfaces in the system.
Alternatively, the corrosion-inhibiting composition may be
introduced to a currently operating or running system. As described
above, such an application may be implemented without turning off
the system by leaving the system under load during the passivation
process or by turning off and unloading the system.
[0039] Although not required to implement this invention, it is
contemplated that the corrosion-inhibiting composition may be
combined with one or more other corrosion inhibitors, one or more
scale inhibitors, one or more fluorescent tracers, one or more
water treatment polymers, one or more polyalkoxy compounds, or any
other suitable adjunct or additional component. Any such adjuncts
may be part of an existing corrosion-inhibitive program to which
the invention becomes an additional component or program. Adjuncts
may be part of the corrosion-inhibiting composition or may be
another separate composition or compositions. In alternative
embodiments, such adjuncts may be added simultaneously or
sequentially with the corrosion-inhibiting composition of the
invention.
[0040] Exemplary other corrosion and scale inhibitors include
tungstate; molybdate; vanadate; phosphate; phosphonate;
phosphinate; silicate; borate; zinc and its salts;
polycarboxylates; benzoic acid; the like; combinations thereof, or
any other suitable corrosion or scale inhibitors. Exemplary water
treatment polymers include polyacrylic acid; polymaleic acid;
copolymers and terpolymers of acrylic acid, mateic acid,
acrylamide, and acrylamidopropyl sulfonate; prism polymers;
sulfonate-based polymers; and terpolymers or copolymers of acrylic
acid, acrylamide, sulfomethylated acrylamide, the like, and
combinations thereof.
EXAMPLES
[0041] The foregoing may be better understood by reference to the
following examples, which are intended to be illustrative and are
not intended to limit the scope of the invention.
Example I
[0042] Galvanized mild steel metal coupons were tested based on
weight after exposure to "Standard 13" make-up water (Ca: 440 ppm
(CaCO.sub.3); Mg: 220 ppm (CaCO.sub.3); M-alkalinity: 340 ppm;
Cl.sup.-: 312 ppm (CaCO.sub.3); (SO.sub.4).sup.2-: 211 ppm
(CaCO.sub.3); pH controlled using NaHCO.sub.3/Na.sub.2CO.sub.3
buffer at pH 8.9). Controls and samples included a
phosphonate-based scale inhibitor program. The Controls had no
additional corrosion inhibitor. Both Samples 1 and 2 included about
10 ppm bismuthiol. Corrosion rates were based on coupon weight
after 7 days of exposure and measured in mils per year ("mpy"), as
shown in Table I.
TABLE-US-00001 TABLE I Treatment mpy Control - A 11.7 Control - B
8.4 Sample - A 2.7 Sample - B 1.5
Example II
[0043] Linear polarization electrochemical experiments were
performed in a 10 liter cell using galvanized metal surfaces of
hot-dipped galvanized ("HDG") rotating electrodes (H-controlled at
pH 7.5). The control and sample included a passivation step with
100 ppm of a phosphonate, phosphate, and polymer-based
multi-functional water treatment program. The following synthetic
water chemistry including calcium chloride dihydrate, magnesium
sulfate heptahydrate, and sodium bicarbonate (based on calculated
values) was used: Ca.sup.2+: 150 to 170 ppm (as CaCO.sub.3);
Mg.sup.2+: 75 to 85 ppm (as CaCO.sub.3); M-Alkalinity: 85 to 105
ppm (as CaCO.sub.3); Cl.sup.-: 105 to 120 ppm (as Cl.sup.-); and
(SO.sub.4).sup.2-: 72 to 82 ppm (as (SO.sub.4).sup.2-). The control
and sample also included a second step, where the passivated
electrodes were exposed to a more extreme corrosive environment, as
in Example I above. Initial corrosion rate (from 0 to 24 hours)
followed by a longer duration corrosion rate (24 to 72 hours) were
measured in mpy. Table II describes the initial and longer duration
corrosion rates.
TABLE-US-00002 TABLE II Treatment 0 to 24 hour mpy 24 to 72 hour
mpy Control 3 to 8 3 to 4 No white rust inhibitor Post-treatment
with 100 ppm treatment program as above Sample ~0.5 to ~0.9 ~0.3 to
0.5 Post-treatment in 100 ppm treatment program as above combined
with 10 ppm white rust inhibitor (bismuthiol)
[0044] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the invention and without diminishing its intended
advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *