GB2072648A

GB2072648A - Method of inhibiting corrosion and composition therefor

Info

Publication number: GB2072648A
Application number: GB8108520A
Authority: GB
Original assignee: NL Industries Inc
Current assignee: NL Industries Inc
Priority date: 1980-03-25
Filing date: 1981-03-18
Publication date: 1981-10-07
Also published as: GB2072648B; NO159943C; NO810970L; NO159943B; CA1145924A

Abstract

Corrosion of metallic surfaces exposed to an aqueous system is inhibited by a composition comprised of (a) an inorganic, water soluble sulphite or bisulphite, (b) a water soluble zinc salt and (c) a water soluble organic polyphosphonate containing at least two phosphoric acid groups per molecule.

Description

SPECIFICATION Method of inhibiting corrosion and composition therefor The present invention relates to inhibiting the corrosion of metals by oxygen-bearing aqueous systems and, more particularly, to inhibiting the corrosion of ferrous metals in contact with such aqueous systems.

Oxygen corrosion is a serious problem in any water system employing metal structures exposed to the water. The corrosive attack is usually in the form of pitting which causes accelerated damage and premature failure of the metal structures. The problem can be especially severe in the case of oil and gas well drilling where the drill pipe, already under severe stresses, can rapidly deteriorate due to corrosion.

It is well known to use water-soluble sulphites and/or bisulphites, e.g. sodium sulphite, as corrosion inhibitors in oxygen-bearing, aqueous systems. The sulphite reacts with the oxygen to eliminate the latter from the system, thus preventing its reaction with the ferrous metal. Such aqueous sulphite solutions can be stabilized by including certain polyphosphonates, as described in U.S. Patents Nos. 3,899,293 and 3,971,734.

Likewise, it is well known, as exemplified in U.S. Patents 3,714,067; Re. 28,553;4,033,896 and 3,803,048 to provide corrosion-inhibiting compositions which employ water soluble zinc salts. However, in heretofore known prior art corrosion-inhibiting compositions, such as those disclosed in the patents discussed above, or in so-called chromate systems, it has been necessary to use relatively large amounts of the inhibiting composition in the aqueous systems for it to be effective. This poses a problem inasmuch as the aqueous systems containing the corrosion-inhibiting composition must frequently be discharged into rivers and other streams and the relatively large amount of the active ingredients in the corrosion inhibiting composition can create environmental problems. Additionally, chromate-based compositions are expensive.

It is therefore, an object of the present invention to provide an improved composition and method for inhibiting the corrosion of metal surfaces, particularly ferrous metals, in contact with aqueous systems..

Another object of the present invention is to provide a non-chromatecorrosion inhibiting composition employing relatively small amounts of corrosion inhibitors.

The above and other objects of the present invention will become apparent from the description given herein and the appended claims.

In one aspect, the above objects of the present invention are accomplished by a composition comprising an effective amount of a water soluble organic phosphonate containing at least two phosphonic acid groups per molecule, an effective amount of a water soluble zinc salt and an effective amount of a water soluble, inorganic sulphite.

In another aspect the above objects are accomplished by a method of inhibiting the corrosion of metals in a water system which comprises adding to said system a composition comprising an effective amount of a water soluble organic polyphosphonate containing at least two phosphonic acid groups per molecule, an effective amount of a water soluble inorganic sulphite, and an effective amount of a water soluble zinc salt.

The water soluble organic phosphonates useful in the compositions and method of the present invention are those containing at least two phosphonic acid groups per molecule.

Preferred phosphonates are selected from the group consisting of the free acids and water soluble salts of:

where each R is independently selected from the group consisting of hydrogen, -CH2PO(OH)2, and -tCnH2nO)cH wherein n is 2 to 4 and c is 1 to 3; R1 is

wherein X and Y are independently selected from the group consisting of hydrogen and lower alkyl radicals having 1 to 4 carbon atoms; a is 2 to 6 and b isO to 6; provided that at least 1/2 of the radicals represented by R are -CH2PO(OH)2;

where R is -CH2PO(OH)2, R1 is selected from the group consisting hydrogen, hydroxyl, and -(CnH2nO)CH wherein n is an integer from 2 to 4 and c is an integer from 1 to 3, and where R2 is selected from the group consisting of lower alkyl radicals containing 1 to 5 carbon atoms and

wherein a is an integer from 0 to 8; and

where R is -CH2PO(OH)2, each R1 is independently selected from the group consisting of hydrogen, -CH2PO(OH)2, and -(CnH2nO)cH wherein n is an integer from 2 to 4 and c is an integer from 1 to 3, and where R2 is selected from the group consisting of lower alkyl radicals containing 1 to 5 carbon atoms and

wherein a is an integer from 0 to 8.

Most particularly preferred polyphosphonate compounds are

where R is -CH2PO(OH)2, R is -CH2PO(OH)2, a is either 2 or 6 and b is 0 to 4, especially those compounds wherein b is or wherein a is 6 and b is 1 to 4.

Compounds represented by formula (1),

where each R is independently selected from the group consisting of hydrogen, -CH2PO(OH)2, and -(CnH2nO)cH wherein n is 2 to 4 and c is 1 to 3; R1 is

wherein X and Y are independently selected from the group consisting of hydrogen and lower alkyl radicals having 1 to 4 carbon atoms; a is 2 to 6 and b is 0 to 6, are well known polyphosphonates as described in the following United States patents, incorporated herein by reference: U. S. Patent Nos. 3,234,124; 3,288,846; 3,383,323; 3,434,969; 3,532,167; 3,613,788; 3,738,937.

Compounds represented by formula (2),

where R is -CH2PO(OH)2, R1 is selected from the group consisting of hydrogen and hydroxyl, and where R2 is selected from the group consisting of lower alkyl radicals containing 1 to 5 carbon atoms and

wherein a is an integer from 0 to 8, are well known polyphosphonates as disclosed in the following United States patents, incorporated herein by reference: U. S. Patents Nos. 3,214,454; 3,483,925; 3,496,223; 3,532,639. Compounds wherein R1 is -(CnH2nO)CH wherein n is an integer from 2 to 4 and c is an integer from 1 to 3 may be prepared from the compounds described in these patents by reaction of these compounds with either ethylene oxide (n=2), propylene oxide (n=3), or butylene oxide (n=4) in the required molar ratio.

Compounds represented by formula (3), (R)2-C-R2

wherein R is -CH2PO(OH)2, R1 is hydrogen, and R2 is selected from the group consisting of lower alkyl radicals containing 1 to 5 carbon atoms and (CH2)aC(R)2

wherein a is an integer from 0 to 8, are well known polyphosphonates as disclosed in U. S. Patent No.

3,303,139, incorporated herein by reference, and Belgium Patent No.781,462. Compounds wherein R1 is (CnH2nO)CH wherein n is an integer from 2 to 4 and c is an integer from 1 to 3 may be prepared from the compounds described in U. S. Patent No. 3,303,139 by reaction of these compounds with either ethylene oxide (n=2), propylene oxide (n=3), or butylene oxide (n=4) in the required molar ratio. Compounds wherein R1 is -CH2PO(OH)2 may be prepared from the compounds described in U. S. Patent No.3,303,139 by reaction of these compounds with formaldehyde and phosphorous acid as disclosed in U. S. Patent No.

3,288,846.

Other water soluble polyphosphonates that contain at least two phosphonic acid groups per molecule which may be used in the practice of this invention are disclosed in the following United States patents, incorporated herein by reference: U. S. Patents Nos. 3,400,148; 3,400,176; 3,497,313; 3,549,728; 3,551,339; 3,556,762; 3,576,783; 3,674,804; 3,733,270.

The polyphosphonate compound must be water soluble and is preferably an alkali metal salt, more particularly a sodium salt, of the polyphosphonic acids. Other salts which are useful in this invention are ammonium, lower alkyl ammonium containing from 1-5 carbon atoms; monethylolammonium, diethylolammonium, triethylolammonium, and partial divalent cation salts wherein the divalent cation replaces no more than 1/3 of the acidic hydrogen in the phosphonic acid groups. The preferred divalent cation is zinc.

The free acids may also be used and are intended herein to be included in the term polyphosphonates as well as in the term polyphosphonic acids.

Representative non-limiting compounds of formula (1) which are useful in this invention are the free acids and water soluble salts of nitrilo trimethylenephosphonic acid, nitrilo dimethylenephosphonic acid, nitrilo-N-hydroxyethyl-N, N-dimethylenephosphonic acid, nitrilo-N-dithoxyethanol-N, Ndimethylenephosphonic acid, ethylenediamine tetramethylenephosphonic acid, ethylenediamine-Nhydroxyethyl-N, N', N'-trimethylenephosphonic acid, tetraehylenepentamine heptamethylenephosphonic acid, hexamethylenediamine tetramethylenephosphonic acid, and trihexamethylenetetramine hexamethylenephosphonic acid.

In addition to the polyphosphonates, the compositions of the present invention contain a water soluble, inorganic sulphite. The term sulphite, as used herein, refers to sulphites as well as bisulphites. Useful sulphite compounds include the alkali metal sulphites, alkali metal bisulphites, ammonium sulphite, ammonium bisulphite, and mixtures thereof. The preferred sulphite compound is sodium sulphite.

In addition to the polyphosphonates and the sulphite compound, the compositions of the present invention contain water soluble zinc salts. Although both organic and inorganic, water soluble zinc salts may be used, preferably, the zinc salt is inorganic in nature, for example, zinc sulphate, zinc nitrate and mixtures thereof.

In preparing the compositions of the present invention, the components are admixed such that the polyphosphonate is present in an amount of from about 1 to about 30% by weight, preferably from about 1 to about 10% by weight, the zinc salt is present in an amount of from about 1 to about 40% by weight, preferably from about 15 to about 20% by weight, and the sulphite compound is present in an amount of from about 30 to about 98% by weight, preferably from about 70 to about 84% by weight, the amounts being based on the combined total weight of the polyphosphonate, the zinc salt and the sulphite compound.

As an aqueous solution, the composition will contain water and from about 10 to about 45% by weight of the mixture of the polyphosphonate, the zinc salt and the sulphite compound wherein those three components are present in the compositional ranges discussed in the preceding paragraph.

The corrosion inhibiting compositions of the present invention have been found to be effective in retarding or inhibiting corrosion when the combined amount of the polyphosphonate, the zinc salt and the sulphite compound, in the ranges discussed above, are added to the aqueous system in an amount sufficient to maintain a concentration of the mixture in the range of from about 1 to about 150 milligrams per liter, preferably from about 10 to about 50 milligrams per liter.

Although virtually any aqueous system which contacts metals subject to corrosion can be effectively treated with the compositions of the present invention, the corrosion inhibiting compositions find particular application in low solids, water based drilling fluids, flood waters used in treating subterranean formations and waste affluents pumped into disposal wells. Low solids drilling fluids contain less than about 6% undissolved solids, and generally contain one or more polymers which function as viscosifiers, suspending agents, bentonite beneficients and shale flocculants. Representative low solids drilling fluids are disclosed in the following United States Patents, incorporated herein reference: U. S. Patents Nos. 3,070,543; 3,323,603; 3,338,320; 3,360,461.The use of sulphites to reduce the corrosion of well drilling tools, drill pipe and other ferrous surfaces during drilling operations is disclosed in U. S. Patent No.3,301,323, incorporated herein by reference.

Flood waters used in treating subterranean formations in secondary recovery operations to increase the yield of petroleum from such formations are generally either fresh ground waters as obtained from lakes, rivers, wells, and the like, and brine waters obtained from producing wells. The use of sulphites and flood waters is described in the following United States Patents, incorporated herein by reference: U. S. Patents Nos. 3,119,447; 3,258,072. A particular feature of the compositions of the present invention is that the spent water from aqueous systems which employ the corrosion inhibiting compositions herein can be disposed of without adverse environmental impact.Since a relatively small amount of the corrosion inhibiting composition is necessary in order to be effective, there are correspondingly smaller amounts of sulphites, zinc salts and polyphosphonates which are discharged into waters, streams or other surface bodies of water with the spent water from the aqueous system. Moreover, since the concentration of the corrosion inhibitor is relatively low, there is less danger of harmful contamination to aquifiers used for producing drinking water should leaks or seepage occur in subterranean flooding operations.

To more fully illustrate the present invention, the following non-limiting examples are presented.

Example 1 A fresh water sample was purged with air for 3 hours. Alioquits of 100 milliliters of this fresh water were placed into bottles and treated with various combinations and concentrations of the three basic components of the inhibitor composition. The air space in the bottles was purged with nitrogen for 10 seconds, and a previously weighed coupon was added to the test solution just prior to capping. The bottles were then rolled for 16 hours at 180"F. The coupons were then removed from the bottles, cleaned, and reweighed. The corrosion rate was calculated from the measured weight loss as shown in Table 1 below.

TABLE I Dequest*2000, Zinc Sulfate, Sodium Sulfite, mg/l mg/l mg/l Corrosion Rate, mpv Protection (%) 0 0 0 49.03 0 5.55 0 0 31.94 34.9 11.10 0 0 44.08 10.1 16.65 0 0 33.74 31.1 0 5.33 0 44.98 8.3 0 10.66 0 47.23 3.7 0 16.00 0 46.33 5.5 0 0 39.07 32.39 33.9 0 0 78.14 19.34 60.6 0 0 117.21 25.64 47.7 5.55 5.33 0 24.74 49.4 11.10 10.66 0 20.24 58.7 16.65 16.00 0 10.80 78.0 5.55 0 39.07 23.39 52.3 11.10 0 78.14 19.79 59.6 16.65 0 117.21 21.59 56.0 5.55 5.33 39.07 17.99 63.3 11.10 10.66 78.14 9.90 79.8 16.65 16.00 117.21 5.85 88.1 * Sodium salt of nitrilo (trimethylene phosphinic acid) As can be seen from Table 1, there is a synergistic effect achieved by the combination of the three components.For a given amount of each of the components in a test solution, there is a greater reduction in the corrosion rate when the three components are mixed than would be expected from an analysis of the reduced corrosion rates brought on by each of the components individually.

Example 2 In this example, corrosion rate data was obtained from a 8,650 foot well drilled in Sweetwater County, Wyoming by Loffland Brothers Company, Rig No. 29. The inhibitor composition employed contained 80.75% by weight sodium sulphite, 18% zinc sulphate and 1.25% DEQUEST 2000, the weights being based on the total combined weight of the sulphite, the sulphate and the DEQUEST. The corrosion rate measurements were made with drill pipe corrosion ring coupon tests as described in API RP 13,6th Edition, 1976. The test data covered a period of 73 drilling days. The data obtained are given in Table 2 below.

TABLE NO. 2 Average Sulfite Coupon Coupon Depth Daily Residual Weight Hours Location Type Of Number Run Treatment,kg. Range,ppm Loss,g Exposed In String By-Pruducts Corrosion C/R** 305 0-1464 1.70 154.75 KSS Magnetite General 4.39 83 7328 1464-2241 15-93 0.310 76 KSS Magnetite General 3.66 9201 1464-2004 1.410 61.25 XOS Magnetite General 5.18 356 2242-3125 0.750 56.75 KSS Magnetite General 4.74 83 7242 2004-3125 8-74 0.896 75 XOS Magnetite General 3.22 9230 3125-4489 0.885 118.5 KSS Magnetite General 2.69 302 3125-3993 1.281 96 XOS Magnetite General 3.61 83 328 4489-5179 8-84 0.298 59.5 KSS Magnetite General 4.49 7314 5211-5700 0.184 39.75 KSS Magnetite General 4.15 314 5700-5846 0.279 72 KSS Magnetite General 3.47 83 7381 5846-6593 13-49 0.462 117 KSS Magnetite General 3.56 Siderite 7376 6593-6888 0.172 57 KSS Magnetite General 2.69 7386 6449-6888 0.632 104 XOS Magnetite Moderate 3.27 27.7 Iron Sulfite Pitting 7352 6888-7851 12-77 1.279 156.5 XOS Magnetite Moderate 7.32 Iron Sulfite Pitting 7199 6888-7851 0.705 184 KSS Magnetite Moderate 2.39 Iron Sulfide 6160 7851-8343 1.014 97 KSS Magnetite Moderate 6.10 55.34 Iron Sulfide 6208 6263-8650 40-59 1.531 126 XOS Magnetite Moderate 8.74 Iron Sulfide 6145 8312-8650 0.521 96 KSS Magnetite General 4.88 Iron Sulfide NOTE: Kelly Saver Sub=KSS; Crossover Sub=XOS *The treatment composition was 80.75% Sodium Sulfite, 18% zinc sulfate, and 1.25% Dequest **Corrosion Rate expressed in kg/m/yr.

As can be seen from Table 2, corrosion rates are below the designated two pounds per square foot per year (9.766 kg/sq. metre/year) (50 mpy, mils per year) criteria, the criteria which is generally accepted as an industry standard.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.

Claims

1. A composition for inhibiting the corrosion of metals exposed to an aqueous system which comprises (al, a water soluble, organic polyphosphonate containing at least two phosphonic acid groups per molecule, (b) a water soluble zinc salt, and (c) a water soluble inorganic suiphite compound.

2. A composition as claimed in Claim 1 which comprises (a) from 1 to 30% by weight of the organic polyphosphonate, (b) from 1 to 40% by weight of the zinc salt, and (c) from 30 to 98% by weight, of the sulphite compound, the percentages being based on the total weight of (a), (b) and (c).

3. A composition as claimed in Claim 2 which comprises (a) from 1 to 10% by weight of the organic polyphosphonate, (b) from 15 to 20% by weight of the zinc salt and (c) from 70 to 84% by weight of the sulphite compound.

4. A composition as claimed in any preceding Claim which comprises an aqueous solution containing from 10 to 45% by weight of (a), (b) and (c).

5. A composition as claimed in any of Claims 1 to 4 wherein the polyphosphonate has the formula:

where each R is independently hydrogen, -CH2PO(OH)2, or (CnH2nO)0H wherein n is 2 to 4 and c is 1 to 3; R1 is

wherein X and Y are independently hydrogen or alkyl having 1 to 4 carbon atoms; a is 2 to 6 and b isO to 6; provided that at least 1/2 of the radicals represented by R are -CH2PO(OH)2.

6. A composition as claimed in Claim 5 wherein R is -CH2PO(OH)2, R1 is -CH2PO(OH)2, a is 2 or 6 and b is Oto4.

7. A composition as claimed in Claim 6 wherein b is zero.

8. A composition as claimed in Claim 6 wherein a is 6 and b is 1 to 4.

9. A composition as claimed in any of Claims 1 to 4 wherein the polyphosphonate has the formula

where R is -CH2PO(OH)2, R1 is hydrogen, hydroxyl, or -(CnH2nO)CH wherein n is 2 to 4 and c is 1 to 3, and where R2 is alkyl containing 1 to 5 carbon atoms or

wherein a is 0 to 8.

10. A composition as claimed in any of Claims 1 to 4 wherein the polyphosphonate has the formula

where R is -CH2PO(OH)2, each R1 is independently hydrogen, -CH2PO(OH)2, or -(CnH2nO)CH wherein n is 2 to 4 and c is 1 to 3, and where R2 is alkyl containing 1 to 5 carbon atoms or

wherein a is0 to 8.

11. A composition as claimed in any preceding Claim wherein the zinc compound is zinc sulfate, zinc nitrate or a mixture thereof.

12. A composition as claimed in any preceding Claim wherein the inorganic sulphite compound is an alkali metal sulphite, alkali metal bisulphite, ammonium sulphite, ammonium bisulphite, or a mixture thereof.

13. A composition as claimed in Claim 1 and substantially as hereinbefore described with reference to Example 1 or 2.

14. A method of inhibiting the corrosion of metals exposed to a water system comprising adding to said system a composition as claimed in any of the preceding Claims.

15. A method as claimed in Claim 14 wherein the composition is added to said water system in an amount of from 1 to 150 milligrams per liter.

16. A method as claimed in Claim 15 wherein the amount of the composition is from 10 to 50 milligrams per liter.

17. A method as claimed in Claim 14 and substantially as hereinbefore described with reference to either of the Examples.