Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHODS FOR INHIBITING METAL CORROSION IN AQUEOUS SYSTEMS
FIELD OF THE INVENTION
The present invention pertains to methods for inhibiting
the corrosion of metals in aqueous systems. The present invention
more particularly pertains to simultaneously inhibiting the
corrosion of iron-containing and copper-containing metals in
cooling water systems that are contaminated by sour leaks.
BACKGROUND OF THE INVENTION
In many refining operations, cooling water systems are
often used. Heat exchangers and refrigeration units are commonly
used during petrochemical and refining operations. Water is used
as the heat exchange fluid.
Iron and/or copper-bearing alloys are commonly the metals
of fabrication of heat exchangers, as well as other parts in
contact with cooling water, such as pump impellers, stators, and
valve parts.
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The cooling water systems most often used are of the
recirculating type so that the water is used repetitively and
remains in contact with the metals of the cooling system. In
refinery operations, these cooling waters are often contaminated
by "sour" leaks which contain hydrocarbons~ oryanic sulfides and
hydrogen sulfide.
These contaminants can be very deleterious if they are
left untreated. They will quickly overwhelm any standard oper-
ating treatment. The hydrocarbons can coat the metal surfaces of
the cooling system and prevent corrosion inhibitors from working
correctly. Sulfide ions can cause severe corrosion of metals,
which can eventually result in catastrophic failure of metal
- components.
Sour leaks and the attendant corrosion and scale problems
have been problematic in refineries for years, despite various
attempts to inhibit their effects. When these leaks have
overwhelmed standard treatments, remedial additive treatments
were introduced which typically addressed a specific metallurgy,
and at best offered limited improvement. The inventors of the
present invention have surprisingly found that the methods
described herein provide simultaneously effective inhibition for
both iron-containing and copper-containing metals exposed to sour
leaks.
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SUMMARY OF THE INVENTION
The present invention provides for methods for inhibiting
the corrosion of metal in aqueous systems. Alkyl benzotriazole
compounds such as butyl benzotriazole have been found to effect-
ive1y inhibit the corrosion of iron-containing and copper-con-
taining metals in contact with cooling water systems that contain
sulfides and hydrocarbons as a result of a sour leak.
DESCRIPTION OF THE RELATED ART
U.S. Patent No. 3,029,202, Brown et a1., Apri1 1962
describes methods of treating water containing sulfur impurities
using oxidation catalysts.
U.S. Patent No. 4,6809127, Edmondson, July 1987 discloses
a method for reducing the amount of hydrogen sulfide in an aqueous
system. The methods provide for adding a combination of glyoxal
and formaldehyde or glutaraldehyde or glyoxal a10ne to the aqueous
medium.
U.S. Patent No. 4,867,944, Bucher et al., September 1989
discloses a method for inhibiting the corrosion of carbon steel
in cooling tower systems. The corrosion inhibiting composition
comprises a water soluble zinc compound, a water-soluble molyb-
date compound, a water-soluble orthophosphate, a water-soluble
polyphosphate and a dispersant.
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Rogers, M.E., et al., National Association of Corrosion
Engineers, Corrosion 87, Conference Paper No. 151 (1987),
discloses treating sour leaks in heat exchanger systems. The
methods employ triazoles such as benzotriazole in combination
with sequestrants to inhibit corrosion in cooling systems. The
use of azoles alone yielded inadequate inhibition.
Schreifels, J.A., et al., Corrosion, Vol. ~5(1989)~ pp.
84-91, discloses experimental results for benzotriazole and
2-mercaptothiazole as copper corrosion inhibitors in kerosene.
These compounds did not inhibit copper sulfide formation.
Japanese Patent 51-139,162 discloses making an anti-
fouling composition useful in suppressing pitting of a copper
alloy by the action of a sulfide comprising treating a water
insoluble compound with an organic solvent, a surfactant and a
benzotriazole compound.
British Patent No. 1,065,995 teaches that 5-alkyl sub-
stituted benzotriazoles are effective in reducing corrosion or
tarn;sh of copper items in glycolic solvents or in lubricants, or
to resist tarnishin~ in the presence of atmospheric sulfides.
United States No. 4,744,950, Hollander, May 1988
discloses a method of providing a corrosion inhibiting film on
copper-containing metals in contact with an open cooling water
system. The films,are provided by C3 to C6 substituted alkyl
benzotriazoles.
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DETAILED DESCRIPTION OF THE INVENTION
Methods for inhibiting the corrosion of iron-containing
and copper-containing metals in contact with cooling water are
described. These methods comprise adding to said cooling water
containing sulfides, hydrocarbons and mixtures thereof an effec-
tive amount for the purpose of an alkyl benzotriazole compound.
The methods of the present invention are particularly
useful when the aqueous system is contaminated by a sour leak.
These aqueous systems are mostly cooling water systems associated
with refinery operations. These leaks contain sulfides and hydro-
carbons such as crude oil, diesel fuel, naphthas, kerosene and
gasoline cut hydrocarbons. In a typical refinery operation, both
sulfides and hydrocarbons will be present in a cooling system
that is experiencing a sour leak. The introduction of these
contaminants will rapidly cause corrosive attack of the iron-
containing and copper-containing metals in the cool;ng water
system.
The methods of the present invention can be applied to
cooling water systems that are not suffering from sour leaks but
merely to treat for residual sulfide ions. These methods can
also be applied with other corrosion inhibiting agents, as well
as microbiological control species such as oxidi7ing and
nonoxidizing biocides.
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A particular advantage of the present invention is that it
maintains low corrosion rates for both iron and copper metal-
lurgies simultaneously under the extremely aggressive conditions
that occur when both an oxidizing biocide, such as chlorine, and
sulfide are present in the system at the same time. In fact, the
addition of chlorine is often increased in response to sour leaks.
The preferred alkyl benzotriazole compound is butyl
benzotriazole. The compounds may be applied in any conventional
manner and can be fed to the cooling water neat or by any suitable
carrier means. Water, glycol and polyglycols can be used as the
solvent. However, aqueous solutions are preferred.
The addition of the compounds to the cooling water can be
either intermittent or continuous, continuous being preferred.
The treatment dosages of the alkyl benzotria701e compounds are
dependent upon the severity of the sour leak. Accordingly, a
range from about O.l parts per million to about lO0 parts per
million alkyl benzotriazole compound should be added. Preferably,
the compound should be added from about l part per million to
about 15 parts per million.
The data set forth below demonstrate the unexpected
results occasioned by use of this invention. The following
example is included as being an illustration of the invention and
should not be construed as limiting the scope thereof.
.
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EXAMPLE
Chlorinated recirculator testing was performed using the
treated water as described in Table A. The sour leak was simulated
by the continual feed of the equivalent of 2 parts per million
(as H2S) of aqueous sodium sulfide to the recirculator. The
temperature was kept at 120F and the pH was actively controlled
at 7.2. The condition of chlorination was simulated by the
continual fe~d of 0.9% solution of sodium hypochlorite at the rate
of 1 ml per hour into the 11 liter system. Butyl benzotriazole was
added to the treated water as an additionai inhibitor at a level of
6 parts per million. Both low carbon steel and Admiralty brass
coupons were exposed to the water for 7 days. The test results
appear in Table I.
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TABLE A
Ca+2(ppm as CaCD3) 600
Mg+2(ppm as CaCO3 264
Cl- (ppm as Cl~) 555
S04~2(ppm as S04-2) 40Q
Silicate (ppm as SiO2) 50
Orthophosphate (ppm as PO4~3) 12
Pyrophosphate (ppm as PO4~3) 3
Tolyltriazole (ppm) 4
HEDP1 (ppm) 1.6
Active Polymer (ppm) 12
HEDP = 1-hydroxyethylidene-1,1-diphosphonic acid
TABLE I
Steel Brass
Corrosion Corrosion
Additional Rate Rate
Leak Condition Inhibitor (mil/vr? ~mil/yr~
Sour leak none 7.4 2.6
Sour leak Butyl-BZT 1.4 0.7
Butyl-BZT = Butyl Benzotriazole
Table I indicates the ability to protect both steel and
copper containing metals in the presence of sulfides and chlori-
nation. The visuàl appearance of the coupons and the heated
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steel tube present in the experimenti showed less corrosion when
butyl benzotriazole was present. These resultâ are totally
unexpected considering the seYerity of the laboratory test
conditions and actual field experience.
While this invention has been described with respect to
particular embodiments thereof, it is apparent that numerous other
forms and modifications will be obvious to those skilled in the
art. The appended claims generally should be construed to co~er
all such Obviouâ forms and modifications which are within the true
spirit and scope of the present invention.
