JPH01316475A - Corrosion suppressing method in low hardness water and high hardness water and composition therefor - Google Patents

Abstract

A method for inhibiting corrosion in aqueous systems comprising adding to the system being treated an effective amount of a composition comprising a molybdate ion source, a carboxylic acid/sulfonic acid polymer or salt thereof and polyphosphoric acid or an ester of polyphosphoric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for inhibiting corrosion of metal surfaces that come into contact with a water system, and a composition for use in such a method, particularly when the water system contains oxygen. The present invention relates to corrosion inhibition methods and corrosion inhibitors.

More specifically, the present invention provides a composition comprising a source of molybdate ions, a water-soluble polymer containing sulfonic acid moieties and carboxylic acid moieties, or a salt thereof, and polyphosphoric acid or an ester of polyphosphoric acid, for use in metals in water distribution systems. It relates to use in inhibiting surface corrosion.

As used herein, the term "water system" refers to a system that includes water in all its physical states, including water that contains one or more substances dissolved or dispersed, such as inorganic salts. It is all-encompassing.

The term "metal" as used herein includes iron and iron-containing materials.

Corrosion of metal surfaces in water systems occurs when ferrous metals are destroyed by chemical or electrochemical reactions of the metals in the adjacent environment.

When corrosion is electrochemical in nature, transfer or exchange of electrons is required for the corrosion reaction to proceed. When corrosion of metals occurs, at least two types of electrochemical processes occur and need to occur simultaneously. One is the anodic oxidation reaction, in which metal ions go into a solution and leave behind electrons.

At least one other reaction is the cathodic reduction reaction.
This is a reaction in which the species in the solution consume the electrons generated in the anodic reaction and are reduced. When it comes to iron or iron-containing materials,
When the water contains oxygen and the pH is neutral or above, the above process can be described by the equation below.

Anodic oxidation Fe →Fe”+ 2e-cathode reaction 21
hO+ llh +4e--40H-These two reaction product ions, iron (n) ions and hydroxide ions, combine to form iron hydroxide (■), Fe(OH)z
which is then oxidized to form iron(III) hydroxide
, Fe(OH)z (rust) is formed. For iron or iron-containing materials and other metals in water systems, the essential factors that influence the corrosion process are the water flow rate, the temperature of the water system, and the relationship between dissimilar metals in the water system. Depending on the characteristics of the water in the water system including, but not limited to, contact. Variable water properties that affect corrosion are dissolved oxygen concentration, carbon dioxide content, pH, hardness, and total dissolved ion concentration.

The presence of dissolved oxygen in water in water systems is primarily due to contact between water and the atmosphere.

The solubility of oxygen in water is mainly dependent on temperature,
Solubility decreases as temperature increases.

Corrosion caused by the presence of oxygen in water in water systems is
It appears in the form of small holes or depressions and/or general metal loss. As the corrosion process continues, the depth of the holes and depressions generally increases. Corrosion is even more severe when a hole or depression occurs in the metal, as it penetrates deeper into the metal and rapidly breaks down at that location.

Many compositions are used in the art to inhibit surface corrosion in water systems where dissolved oxygen causes corrosion. Polyphosphates such as sodium tripolyphosphate are widely used for treatment of flow-through systems. US patent cylinder 2
, 742, 369. It is also said that silicic acids such as sodium silicate can be used.

U.S. Pat. No. 3,483.133 discloses amino-tris (
A corrosion inhibiting composition comprising a methylene phosphonic acid compound in combination with a water-soluble zinc salt is disclosed. US patent cylinder 3,7
No. 62,873 discloses corrosion inhibition methods using substituted succinimides. Canadian Patent Tube 854.151
No. 1 uses an organic phosphonic acid compound and a water-soluble polymer containing a carboxyl group or an amide group in combination. Corrosion and/or
Alternatively, compositions and methods for inhibiting scale formation containing calcium and magnesium are disclosed.

U.S. Pat. No. 3,810,834 discloses a method for treating water systems with hydrolyzed polymaleic anhydride having a molecular weight of 300 to 5,000 for the purpose of inhibiting scale formation. Also, U.S. Pat.
The same issue discloses the use of hydrolyzed polymaleic anhydride materials in combination with zinc salts to inhibit both corrosion and scale formation.

U.S. Pat. No. 3,965,027 discloses certain amine adducts of polymaleic anhydride for use as scale and corrosion inhibitors.

U.S. Pat. No. 4,176,059 discloses the use of compositions containing molybdates, organic cationic or nonionic surfactants, water-soluble polyphosphates and triazoles for corrosion inhibition. ing. U.S. Pat. No. 4,217,216 discloses corrosion inhibitors comprising an azole, a molybdate and at least one aminomethylenephosphonic acid or derivative thereof. U.S. Pat. Corrosion inhibiting compositions containing other inhibitors are disclosed.

U.S. Pat. No. 4,675,158 discloses mercaptobenzothiazole/tolyltriazole corrosion inhibiting compositions, and U.S. Pat. No. 4,668,474 discloses mercaptobenzothiacyl and iron ( II)
Discloses use with an ion source.

U.S. Pat. No. 4,640,793 discloses a synergistic scale and corrosion inhibiting mixture comprising a carboxylic/sulfonic acid polymer and a molybdate.

No. 4,618,448 discloses the use of carboxylic acid/sulfonic acid/polyalkylene oxide polymers as scale and corrosion inhibitors.

However, the above-mentioned prior art documents do not in any way suggest the unexpected results obtained with the novel compositions of the present invention.

The method for inhibiting corrosion in a water system according to the present invention uses a molybdate ion source, a water-soluble polymer containing a sulfonic acid moiety and a carboxylic acid moiety, or a salt thereof, and a composition containing polyphosphoric acid or an ester of polyphosphoric acid. It involves the process of treating the water system in quantity.

The corrosion inhibiting compositions of the present invention can optionally contain other known corrosion inhibitors such as triazoles. The addition of a triazole, such as tolyltriazole, makes the composition of the present invention an excellent corrosion inhibitor for copper and copper alloys.

The present invention also relates to novel compositions for use in the corrosion inhibition method of the present invention.

The compositions of the present invention are particularly effective over the pH range of about 6.5 to about 8.2, preferably about 7.0 to about 8.0, and are effective in water of various hardnesses. Approximately 8
．． At a pH higher than 2, the composition generally contains calcium carbonate and/or calcium phosphate.
It becomes unusable.

The present invention provides: (A) a molybdate ion source of about 1.0% to about 20% effective MoO4,-''; CB) a water-soluble polymer containing a carboxylic acid moiety and a sulfonic acid moiety or a water-soluble salt thereof; , about 2.0% as effective polymer.
and (c) from about 5% to about 40% by weight as an active ingredient selected from the group consisting of polyphosphoric acid, esters of polyphosphoric acid, and combinations thereof. The present invention relates to a method for inhibiting corrosion in a water system, characterized by adding an effective amount to the water system.

Any molybdate ion source can be used. Preferred ion sources are water-soluble molybdates, and the most preferred molybdates are magnesium molybdate, ammonium molybdate, and alkali metal molybdates such as lithium molybdate, sodium molybdate, and potassium molybdate.

The carboxylic acid/sulfonic acid polymer used in the present invention comprises (a) about 25 to about 95% by weight of an unsaturated monocarboxylic acid compound selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof; and (bl 2 - from about 5 to about 75% by weight of an unsaturated sulfonic acid compound selected from the group consisting of acrylamide-2-methylpropylsulfonic acid, 2-methacrylamido-2-methylpropylsulfonic acid, and combinations thereof; 25.00 as measured by scattering method
It can be any water-soluble polymer having a weight average molecular weight of zero or less. Water-soluble salts of these polymers can also be used. Examples of these polymers include TR, commercially available from Calgon Corporation.
C-233 and Acrysol Q R-1086, available from Rohm and Haas.

Additionally, other monomers can also be used.

Nonionic monomers such as acrylamide, methacrylamide and acrylonitrile may be present in the polymers.

Preferred carboxylic acid/sulfonic acid polymers of the present invention include 5
It is produced by polymerizing 0 to 95% by weight of unsaturated monocarboxylic acid and 5 to 50% by weight of unsaturated sulfonic acid. The most preferred carboxylic acid is acrylic acid and the most preferred sulfonic acid is 2-acrylamido-2-methylpropylsulfonic acid.

These polymers are described in U.S. Pat. No. 3.928.196 and U.S. Pat.
It can be prepared by mixing the monomers in the presence of a free radical initiator, as described in No.

In theory any free radical initiator can be used. Examples of preferred initiators include peroxides, azo initiators and redox systems. This polymerization can also be initiated photochemically. Preferred catalysts are sodium persulfate and sodium metabisulfite.

The preferred polyphosphoric acid for use in the present invention is an equilibrium mixture of orthophosphoric acid, birophosphoric acid and highly linear polyphosphoric acid, commercially available from FMC Corporation. Polyphosphoric acid esters can also be used as component (c). Preferred esters are glycol esters and esters of polyhydroxy alcohols such as esters of pentaerythritol. Such esters are available from Carbon Corporation as conductors (
conductor) 5712.

The composition of the present invention contains about 1 to about 20% by weight of (A) as an active ingredient and about 2 to about 25% of (B) as an active ingredient.
% by weight, and (c) as active ingredient from about 5 to about 4
It contains 0% by weight, and the remainder contains water. Preferred compositions contain from about 3 to about 1 of (A) as the active ingredient.
2% by weight, about 8 to about 15% by weight of (B), and about 8 to about 20% by weight of (c).

The compositions of the invention should be used in effective amounts. As used herein, the term "effective amount" refers to an amount that inhibits or prevents corrosion of metal surfaces in contact with the water system being treated. From about 0.1 to about 20 active ingredient weight to weight
It is necessary to add it so that the dosage becomes 0 ppm. Components (A), (B) and (c) may be added separately or in combination, and any convenient method may be used.

The composition of the present invention is effective in preventing corrosion of mild steel,
It also suppresses corrosion of aluminum. These compositions are particularly effective where excessive phosphate levels or zinc are undesirable.

The method of the present invention is effective when the pH ranges from about 6.5 to about 8.2, preferably from about 7.0 to about 8.0. Furthermore, the method of the present invention is effective for water of various hardnesses. For example, corrosion could be effectively inhibited in water systems containing a total hardness of about 50 to about 500 .mu./1, measured as CaC0. To form an effective suppression film, at least about 2 to 5I11r/1, preferably 1
It is preferable to maintain a calcium level of 0 ■/l.

Other known corrosion inhibitors such as azole or orthophosphoric acid sources can be used with the compositions of the present invention.

Implementation M The invention is further illustrated by the following examples.

However, the scope of the present invention is not limited thereby.

Corrosion experiments were performed by precleaning 1# x 2# carbon steel coupons in an ultrasonic bath with xylene, Calclean (alkaline silicate phosphate cleaner available from Calvon Corporation), water, and acetone, respectively. The coupons were then dried on house air. The coupon was weighed and suspended in 81 test solutions. The pH of this test solution was adjusted and maintained at 7.0 or 8.0, the temperature was heated and maintained at 50° C., and the solution was circulated and aerated. Three types of test solutions with different hardness were used.

Soft water is deionized water 6.601! 4x Pittsburgh (
Pittsburg) water was added.

4x Pittsburgh water contains 50.2■/l of MgC11.
6H! 0.43.2wg/l Na,SO,,13,8
w/ Il of NaHCO, and 379.5 mg/j!
This is a solution containing Ca5O, .2HzO. Medium hard water is deionized water 0.70 f to 4x Pittsburgh water 7.30
1 was added.

Hard water is 4 x Pittsburgh water 8. 50.0g/jI to Ol
It was prepared by adding 43.26 g of CaCl t .21hO solution.

The ions present in the water tested are listed below.

Inhibitor stock solutions were prepared to have an oil concentration of 8.0 g/l and were added separately to the various test solutions before immersing the coupons. The M, O, -” sources used in the test were all Na
2MoOa' 2820 was used. ptt is 8
．． In the 0 test, Ca+2/M. In order to prevent the precipitation of O4-2 and/or Ca''''/PO4-'', in addition to adding the inhibitor stock solution, the oil content of acrylic acid/acrylamide sulfonic acid/polyalkylene oxide inhibitor was 8.0 g/ 15 mf of the solution was added to each test solution.

The following inhibitors were tested: Carvone (sodium hexametaphosphate); HEDP
(Hydroxyethylidene diphosphonic acid); Orthophosphate; Conductor-5712 (manufactured by Calvone Corporation,
3% by weight of pentaerythritol ester of polyphosphoric acid,
15% by weight of active polyphosphoric acid and 3% active orthophosphate
AA-AMPSA (manufactured by Carbon Corporation, acrylic acid/2-acrylamide with a molecular weight of approximately 8,200)
60/40 copolymer of 2-methylpropylsulfonic acid)
; and AA-AMPSA/Conductor-5712/M (10-
” (AA/AMPSA active content 10% by weight, LOa-”
Active bone 5% by weight and conductor-5712 active content 43
% by weight) After 7 days, the coupons were taken out and treated with suppressed acid in an ultrasonic bath.
Washed with water and acetone respectively.

This suppressed acid has a ratio of 1:11 (1! II!
0.0 g SnC1z and 20.0 g 5bzO: +
It contains. The coupons were then dried with house air and reweighed. Corrosion rate (mpy) was calculated from the weight loss of the coupon.

The test results are shown in Table 1.

Table 1 * Comparative example Procedural amendment June 23, 1999

Claims (1)

[Claims] 1. (a) Molybdate ion source effective MoO_4^-
(b) about 25 to about 95% by weight of the carboxylic acid moiety;
a water-soluble polymer containing from about 5 to about 75% by weight of sulfonic acid moieties and having a molecular weight of about 25,000 or less, wherein the carboxylic acid moieties are selected from the group consisting of acrylic acid and methacrylic acid, and The sulfonic acid moiety is 2-acrylamido-2-methylpropylsulfonic acid and 2-acrylamido-2-methylpropylsulfonic acid.
- about 2.0 to about 25% by weight of a polymer selected from the group consisting of methacrylamide-2-methylpropylsulfonic acid or a salt of such a polymer as an active ingredient, and (c) polyphosphoric acid, an ester of polyphosphoric acid. and a combination thereof, comprising adding to the water system an effective amount of a corrosion inhibiting composition containing about 5 to about 40% by weight as an active ingredient. . 2. (a) Molybdate ion source effective MoO_4^-
(b) about 25 to about 95% by weight of the carboxylic acid moiety;
a water-soluble polymer containing from about 5 to about 75% by weight of sulfonic acid moieties and having a molecular weight of about 25,000 or less, wherein the carboxylic acid moieties are selected from the group consisting of acrylic acid and methacrylic acid, and The sulfonic acid moiety is 2-acrylamido-2-methylpropylsulfonic acid and 2-acrylamido-2-methylpropylsulfonic acid.
- about 2.0 to about 25% by weight of a polymer selected from the group consisting of methacrylamide-2-methylpropylsulfonic acid or a salt of such a polymer as an active ingredient, and (c) polyphosphoric acid, an ester of polyphosphoric acid. A composition comprising about 5 to about 40% by weight of an ingredient selected from the group consisting of and combinations thereof as an active ingredient.