US 3909437 A
A cleaning solvent useful in the cleaning of metal surfaces, e.g. nickle-iron alloys, contains sulfamic acid, citric acid, a solvent for hydrocarbon residues, and a surfactant.
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Description (OCR text may contain errors)
AU 165 FX United States Patent [1 1 Alexander et al.
[ NONCORROSWE ACID, SOLVENT AND NoNioNlc SURFACTANT COMPOSITION  Inventors: George B. Alexander; Norman F.
Carpenter, both of Tulsa, Okla.
 Assignee: The Dow Chemical Company,
221 Filed: Jan. 18,1973
[2i] Appl. No.: 324.651
 US. Cl. 252/143; 252/146; 252/DIG. l:
252/87  Int. Cl. Clld 7/50; Cl id 7/08  Field of Search 292/143. 146, X70, DIG. l. 292/87 1 Sept. 30, 1975 Primary E.\'aminerBenjamin R. Padgett Assistant Examiner-E. A. Miller Attorney, Agent, or Firm-Bruce M. Kanuch 5 7 ABSTRACT A cleaning solvent useful in the cleaning of metal surfaces, e.g. nickle-iron alloys, contains sulfamic acid, citric acid, a solvent for hydrocarbon residues, and a surfactant.
6 Claims, No Drawings NONCORROSIVE ACID, SOLVENT AND" NONIONIC SURFACTANT COMPOSITION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of section 305 of the National Aeronautics and Space Act of 1958, Public law 85-568 (72 Stat. 435; 42 U. S. C. 2457).
BACKGROUND OF THE INVENTION I The invention relates generally to the cleaning of metal surfaces. More specifically, the invention pertains to a composition useful for the dynamic cleaning of such metals as lnvar alloy, which is a nickel-iron alloy especially suited for cryogenic temperatures because of its low thermal expansivity. A representative sample of this alloy contains the following elements by weight percent:
Iron 61 .4 64.4 Nickel 34.5 36.5 Cobalt 0.50 Titanium 0.30 0.60 Manganese 0.30 0.60 Silicon $0.30 Carbon $0.05 Phosphorus 50.015 Sulfur $0.015
Lead 5 0.0l5
Tin $0.015 Selenium $0.010
Cleaning. alloys for use in cryogenic applications, such as piping for extremely low temperature fuel and oxidizer systems in rockets and spacecraft presents difficult problems: for example, the systems must be devoid of all hydrocarbon and particulate contamination. Conventional cleaning solvents are not satisfactory for the present purpose.
Although acids such as phosphoric, sulfuric, and hydrochloric display low corrosion rates, they produce objectionable smut on the metal surface. Smut is de- SUMMARY OF THE INVENTION The present composition produces minimum corrosive effect while effectively removing hydrocarbon residue and particulate matter from a metal surface. The composition is an aqueous solution of sulfamic acid, citric acid, a solvent for hydrocarbon residues, e.g., 2- butoxyethanol. and a surfactant. A dynamic cleaning procedure involves flowing this composition over a metal surface to be cleaned at a flow rate and in an amount sufficient to clean the metal surface.
DETAILED DESCRIPTION OF THE INVENTION The composition may be prepared by mixing any or all of the ingredients together and then adding water or by adding the ingredients one at a time to water. All percentages hereafter mentioned are to be taken as weight percentages unless otherwise indicated. The sulfamic acid should be present in an amount between 8 and 12 percent of the aqueous solution, preferably 10%. The citric acid should be present in an amount between 4 and 6% of the aqueous solution, preferably 5%.
The solvent for hydrocarbon residues is a substance capable of dissolving hydrocarbon residues, e.g., greases, waxes or oils, present on the metal surface or created during the cleaning. Included within our use of the term solvent are those substances popularly termed degreasers, however, the present solvents will in addition dissolve certain residual organic con-- taminants not properly defined as greases.
Such solvent must be soluble in and nonreactive with the acid cleaning solution as well as being capable of ethers such as 2-butoxyethanol.-'
2-methoxyethanol, and Z-ethoxyethanol. The solvent should be present in an amount between 4 and 6% of the aqueous cleaning solution, preferably 5%. l
The surfactant serves as a wetting agent, i.e., it lowers the surface tension of the water, and emulsifics and helps to remove hydrocarbon residues. Any nonionic surfactant which has a cloud point in excess of about F. and which at a concentration of O. 1% in the present acid cleaning solution has a surface tension of about 32 dynes/cm. or less is usable. Cloudpoint is the temperature at which the surfactant becomes insoluble in the composition. Representative substances include linear alcohol ethoxylates, polyoxyethylene esters, and alkyl aryl polyethylene oxides. An especially useful surfactant comprises a mixture of primary alcohols with. 10-12 atoms carbon chains, 60% ethoxylated. The surfactant should be present in an amount between 0.095 and 0.15% of the aqueous mixture, preferably 0.1%.
The present composition is useful in cleaning metal surfaces in general. It is particularly useful in the cleaning of iron-nickel alloys, carbon steel. and titanium.
The composition will satisfactorily clean metal surfaces at ambient temperatures. At lower temperatures excessive time is required and cleaning is less efficient. Higher temperatures usually ease the cleaning but may cause objectional corrosion rates. Operating temperatures within the range of about 50 to F. are feasible for the use of the present cleaning solution; the preferred operating temperatures are within the range of.
It is found that although the present composition is useful in cleaning metal surfaces in static applications, it is particularly useful in dynamic cleaning techniques.
such as cleansing the interior of a pipe by passing the cleaning solvent through the pipe. In such applications,
it is important to choose an appropriate flow rate. This rate depends on the pipe size and the degree of cleaning required. Higher flow rates are found to induce greater turbulence at the metal surface which allows the solvent to pick up occluded particles. Thus, removal of particulate contamination to leave only a very small residue will require higher flow rates. For exam- -tioners of this invention to effect the desired degree of cleaning based on the parameters present. A representative range of rates is from 2 to about 30 feet per secend; on iron-nickel alloys the preferred rate is 4 feet per second.
The length of time over which the flow is continued depends on the amount of contaminant desired to be removed and the amount of corrosion of the metal surface which is tolerable. Corrosion incurred in turn depends, inter alia, on flow rate. Thus, more complete cleaning and higher flow rates cause greater corrosion of the-surfaces. An iron-nickel alloy pipe contaminated with triolein and mineral oil in a density of from about .04 to about .08 grams per square inch was preferably cleaned for 2 hours at a cleaning solvent flow rate of 4 ft./sec., for 6 hours at 2 ft./sec., and for 0.5 hour at 30 ft./sec.
It is desirable to follow the cleaning flow with a water flush to remove residual cleaning solution. With some surfaces it is also desirable to use a passivation flush,
utilizing, for example, aqueous solutions of citric acid or sodium nitrite or a combination of the two. The passivation flush renders the metal surface less susceptible to oxidation thus forming an oxide on the coating alloy exposed metal surface. For example, a newly cleaned iron-nickel alloy was passivated by flowing a 1% citric acid solution over the surface at 5.5 ft./sec. for 10 min., followed by a flow ofO. 1% aqueous sodium nitrite solution at 5.5 ft./sec. for 10 min. Thereafter, the surface was rinsed with a 20 min. flow of water at a rate of 3.5
1n the following examples cleaning mixtures comprising various proportions of ingredients were tested in static and dynamic cleaning applications.
EXAMPLE l .thus to introduce air into the liquid. The amount of metal lost by corrosion and the depth of corrosion penetration were measured, and the cleaning effectiveness was evaluated visually. The results of these tests are tabulated in Table l.
The iron nickel alloy contained the following in weight percent:
lron 61.4 64.4 Nickel 34.5 36.5 Cobalt 0.50 Titanium 0.30 0.60 Manganese 0.30 0.60 Silicon S 0.30 Carbon 0.05 Phosphorus 5 0.015 Sulfur 5 0.015
Lead 5 0.015
Tin 5 0.015 Selenium 5 0.010
TABLE I STATIC CLEANING OF IRON-NICKEL ALLOY COUPONS Metal Loss Wt. 'Corrosion Penetration Test No. Cleanliness (mg/dmlhr) (mils/yr) 1 Clean 6 2.9 2 17 8.2 3 21 10.0 4 47 23.0 5 Trace 6 2.9 6 4.8 7 12 5.8 8 Minor 9 4.3 9 Some 5.1
COMPOSITION Z-butoxy Sulfamic Citric ethanol S" Test No. Weight percent of aqueous solution 1 20 2 20 5 0.1 3 0.1 4 l5 5 0.1 5 l5 0.1 6 10 5 5 0.1 7 5 0.1 8 5 5 5 0.1 9 l8 2 0.1
'S=A surfactant which is a mixture of primary alcohols of about 10m 12 memher carbon chains. about 6054 cthoxylated.
EXAMPLE 2 In this example dynamic cleaning tests were performed on the interior surface of an iron-nickel alloy pipe. The tests in this example were performed on the same iron-nickel alloy used in Example 1,' which also had been contaminated with the same substances used in Example l. A 12 inch length of 2 inch diameter pipe was subjected to a flow of the present cleaning solution. In each test the cleaning solution was conducted through the pipe at a rate of 5.5 ft./sec. for a period of 2 hours. This flow as flowed by a water flush for 0.17 hours at a rate of 3.5 ft./sec. The cleaning solution was at a temperature of between 66 and 74F. with initial contaminations of varying amounts, the parameters of corrosion metal loss, corrosion penetration depth, and residual hydrocarbon amount were measured and 2 visual evaluation of the cleaning effectiveness was made. The results are tabulated in Table 11.
TABLE ll DYNAMIC CLEANING OF lRON-NlCKEl. ALLOY PIPE lnitial Concentration mg. (triolein Cleanliness +mineral oil) visual +1.0 m1. Residual observation Metal Loss Corrosion particulate Hydrocarbon smut Weight Penetration Test No. solids (mg) present (mg/dmlhr) (mils/yr.)
l 5300 1.6 Clean 102 49 2 5800 1.7 22 3 4400 1.7 72 5.8
5 TABLE II-Continued DYNAMIC CLEANING OF IRON-NICKEL ALLOY PIPE Initial Concentration mg. (triolein Cleanliness +mineral oil) visual +l .0 ml. Residual observation Metal Loss Corrosion particulate Hydrocarbon smut Weight Penetration Test N0. solids (mg.) present (mg/dmlhr) (mils/yr.)
4 5700 2.0 69 33 5 3300 0.6 rust 20 9.7 6 4 I I .9 22 l l 7 4700 2.6 dirty 44 22 COM POSITION Z-hutoxy Sulfamic Citric ethanol Test No. Weight percent of aqueous solution I I0 5 5 ().l
2 l0 5 5 ()fl '5' herein is the same mixture as that defined by S in Table I.
What is claimed is:
l. A composition comprising in percentages by weight the following ingredients:
a. about 8 to 12% sulfamic acid,
b. about 4 to 6% citric acid;
0. about 4 to 6% of a nonionic solvent for hydrocarbon residues which solvent is characterized as not producing turbidity at 75F. when present in said composition,
d. about 0.095 to 0.15% ofa soluble nonionic surfactant which surfactant is characterized as having a cloud point of at least about 90F. and having a surface tension of about 32 dynes/cm. or less when present in an amount of 0.1% of said composition, and
e. the balance, water.
2. The composition of claim 1 wherein the nonionic solvent for hydrocarbon residues is a glycol ether.
3. The composition of claim 1 wherein the solvent is chosen from the group consisting of 2-butoxyethanol,
2-( 2-butoxyethoxy)ethanol, thanol, Z-methoxyethanol, and 2-ethoxyethanol.
4. The composition of claim 1 wherein the soluble nonionic surfactant is chosen from the group consisting of linear alcohol ethoxylates, polyoxyethylene esters,.
and allyl aryl polyethylene oxides.
s. The composition of claim 1 wherein the soluble to about 12 member carbon chains, about 60% ethoxylated, e. 79.9% water.