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. Metal surfaces are cleaned by contacting the surface with the cleaning solvent and then passivated by contact with aqueous solutions of citric acid or sodium nitrite or a combination of the two

Alexander, George B.

Carpenter, Norman F.

NASA Technical Reports Server

United States Patent t 191 
Alexander et al. 
[ 1 1  I 3,957,529 
[ 541 METHOD FOR CLEANING AND 3,l 14,657 12/1963 Stilwell ................................. 134/28 
3,162,547 12/1964 Kendall ............................. 134/28 X 
Carpenter, both of Tulsa, Okla. 3,522,093 7/1970 Woolman .......................... 134/28 X 
3,239,467 3/1966 Lipinski 252/143 X 
[75] Inventors: George B. Alexander; Norman F. 3,330,769 7/1967 Golben et a1 ................... 252/143 X 
[73] Assignee: The Dow Chemical Company, 
Primary Examiner-S. Leon Bashore 
[22] Filed: June 3, 1974 Assistant Examiner-Marc L. Caroff 
Attorney, Agent, or Firm-Stephen R. Wright 
[21] Appl. No.: 475,704 
PASSIVATING A METAL SURFACE .......................... 
Midland, Mich. 
Related U.S. Application Data 
[62] Division of Ser. No. 324,651, Jan. 18, 1973. 
[52] U.S. Cl. ...................................... 134/3; 134/28; 
134/40; 13414 1 
[51] Int. C1.* ............................................ C23G 1/02 
IS81 Field of Search ............. 252/143, 146, 170, 87, 
252/DIG. 1; 134/3, 28, 40, 41 
1561 References Cited 
UNITED STATES PATENTS 
2,994,664 8/1961 Wachter ......................... 252/146 X 
1571 ABSTRACT 
A cleaning solvent useful in the cleaning of metal sur- 
faces, e.g. nickle-iron alloys, contains sulfamic acid, 
citric acid, a solvent for hydrocarbon residues, and a 
surfactant. Metal surfaces are cleaned by contacting 
the surface with the cleaning solvent and then passiv- 
ated by contact with aqueous solutions of citric acid 
or sodium nitrite or a combination of the two. 
10 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=20080006888 2019-08-30T03:10:02+00:00Z
3,9 57,529 
1 2 
DETAILED DESCRIPTION OF THE INVENTION 
The composition may be prepared by mixing any or 
all of the ingredients together and then adding water or 
5 by adding the ingredients one at a time to water. ,411 
percentages hereafter mentioned are to be taken as 
weight percentages unless otherwise indicated. The 
sulfamic acid should be present in an amount between 
8 to 12 percent (%) of the aqueous solution, preferably 
10 10%. The citric acid should be present in an amount 
between 4 to 6% of the aqueous solution, preferably 
The solvent for hydrocarbon residues is a substance 
tains to a composition for the dynamic cleaning 15 greases, waxes or oils, present on the metal surface or 
of such metals as Invar alloy, which is a nickel-iron created during the cleaning. Included within our use of 
the term “solvent” are those substances popularly alloy especially suited for cryogenic temperatures be- termed “degreasers,” however, the present solvents cause of its low thermal expansivity. A representative will in addition dissolve certain residual organic con- sample of this alloy contains the following elements by 
Such solvent must be soluble in and nonreactive with weight percent: 
the acid cleaning solution as well as being capable of 
lron 6 I .4 - 64.4 dissolving hydrocarbon residues. The solvent may be 
Cobalt 0.50 any nonionic material which at the concentration used 
Titanium 0.30 -0.60 25 in the present acid cleaning solution and at a tempera- 
ture of 75°F. will give a clear solution having substan- Silicon e 0.30 
Carhon S 0.05 tially no turbidity. Representative solvents include, for 
Phosphorus 60.015 example, glycol ethers such as 2-butoxyethanol, 2(  2- 
Sulfur Lcad S O.015  0  I butoxyethoxyl)ethanol, 2-(ethoxyethoxy)ethanol, 2- 
Tin SO015 3” methoxyethanol, and 2-ethoxyethanol. The solvent 
Sclcnium < 0.0 IO should be present in an amount between 4 and 6 9  of 
the aqueous cleaning solution, preferably 59. 
cleaning alloys for use in cryogenic applications, The surfactant serves as a wetting agent, Le.. it lowers 
such as piping for extremely low temperature fuel and the surface tension of the water, and emulsifies and 
oxidizer systems in rockets and spacecraft presents 35 helps to remove hydrocarbon residues. Any nonionic 
difficult problems: for the systems must be surfactant which has a cloud point in excess of about 
devoid of hydrocarbon and particulate contamina- 90°F. and which at a concentration of 0.1% in the pre- 
tion. Conventional cleaning solvents are not satisfac- sent acid cleaning solution has a surface tension of 
about 32 dynes/cm. or less is usable. Cloud point is the tory for the present purpose. 
4” temperature at which the surfactant becomes insoluble Although acids such as phosphoric, sulfuric, and in the composition. Representative substances include hydrochloric display low corrosion rates, they produce linear alcohol ethoxylates, polyoxyethylene esters. and 
alkyl aryl polyethylene oxides. An especially useful objectionable smut on the metal surface. Smut is de- 
METHOD FOR CLEANING AND PASSIVATING A 
METAL SURFACE 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject 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). 
This is a division of application Ser. No. 324,65 1 filed 
Jan. 18, 1973. 
BACKGROUND OF THE INVENTION 5%. 
The invention relates generally to the cleaning of 
metal surfaces. More specifically, the invention per- of hydrocarbon residues, 
20 taminants not properly defined as greases. 
Nickcl 34.5 - 36 5 
Manganese 0 30 -0.60 
fined as the Of amounts Of surfactant comprises a mixture of primary a~coho~s  
nonadsorbent products O n  chemically treated 45 with 10-1 2 atoms carbon chains, 60% ethoxylated, The 
surfaces, usually resulting from cleaning or etching. surfactant should be present in an amount between 
Use of oxidizing agents in conjunction with acids in- o.095 and o,159 of the aqueous mixture, preferably 
creases corrosion rates without lessening the smut for- o. 1%, 
mation. Although the nickel-iron alloys have good cor- The present composition is useful in cleaning metal 
rosion resistance to caustic solutions at ambient tem- 5 0  surfaces in general. It is particularly useful in the clean- 
perature, effective cleaning and degreasing with aka- ing of iron-nickel alloys, carbon steel, and titanium. 
line solutions requires elevated temperatures, where The compos~t~on will satisfactorily clean metal sur- 
corrosion rates become objectionable. faces at ambient temperatures. At lower temperatures 
Consequently there is a need for a excessive time is required and cleaning is less efficient. 
which satisfactorily descales, cleans, and degreases 5 5  Higher temperatures usually ease the cleaning but may 
metal surfaces, particularly iron-nickel surfaces, with- objectional corrosion rates, Operating tempera- 
out leaving smut or causing excessive corrosion. tures within the range of about 40” to 140°F. are feasi- 
SUMMARY OF THE INVENTION 
The present composition produces minimum corro- 
sive 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. 
ble for the use of the present cleaning solution; the 
preferred operating temperatures are within the range 
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 
65 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 clean- 
ing required. Higher flow rates are found to induce 
60 of about 70”-80°F. 
3,957,529 
3 
greater turbulence at the metal surface which allows 
the solvent to pick up occluded particles. Thus, re- 
moval of particulate contamination to leave only a very 
small residue will require higher flow rates. For exam- 
ple, an iron-nickel alloy pipe was satisfactorily cleaned, 
Le., the contamination was reduced from about 76 mg. 
of triolein and mineral oil per square foot of surface to 
about 0.027 mg. per square foot, by flowing a composi- 
tion comprising 10% sulfamic acid, 5% citric acid, 5 8  
2-butoxyethanol and 0.1% of a mixture of primary 
alcohols (60% ethoxylated) through the pipe at a rate 
of 5.5 feet per second. For various materials, including 
nickel-iron alloys. flow rates may be chosen by prac- 
tioners of this invention to effect the desired degree of 
cleaning based on the parameters present. A represen- 
tative range of rates is from 2 to about 30 feet per 
second; 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 ii density of from about 
0.04 to about 0.08 grams per square inch was prefer- 
ably cleaned for 2 hours at ;i 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 suscep- 
tible to oxidation. For example, a newly cleaned iron- 
nickel alloy was passivated by flowing a I %  citric acid 
solution over the surface at 5.5 ft./sec. for 10 min., 
followed by a flow of 0.1% aqueous sodium nitrite 
solution at 5.5 ft./sec. for 10 min. Thereafter, the sur- 
face wiis rinsed with a 20 min. flow of water at a rate of 
3.S ft./sec. 
In the following examples cleaning mixtures compris- 
ing various proportions of ingredients were tested in 
static and dynamic cleaning applications. 
EXAMPLE 1 
Herein iron nickel alloy coupons of size 4.6 X 2.5 X 
0.3 cm. were first contaminated with a hydrocarbon 
residue consisting of triolein and mineral oil and partic- 
ulate matter consisting of polystyrene spheres of 
20-200 micron size. The coupons were immersed in 
the cleaning solution which was maintained at ambient 
temperature (about 60"-80"F.). The solution was 
stirred with a magnetic stirrer to create a vortex and 
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 effective- 
5 
IO 
15 
20 
25 
3 0 
35 
40 
45 
50 
55 
60 
4 
ness was evaluated visually. The results of these tests 
are tabulated in Table I. 
The iron nickel alloy contained the following in 
weight percent: 
Iron 
Nickel 
Cobalt 
Titanium 
Manganese 
Silicon 
Carbon 
Phosphorus 
Sulfur 
Lead 
Tin 
Selenium 
6 I .4 - 64.4 
34.5 - 36.5 
0.50 
0.30 -0.60 
0.30 -0.60 
< 0.30 
s 0.05 
s 0.0 I5 
6 0 . 0 1 5  
G 0.015 
6 0.0 I5 
G 0.0 I0 
TABLE I 
STATIC CLEANING OF IRON-NICKEL ALLOY COUPONS 
Metal Loss Wt. Corrosion Penetration 
Test No .  Clcanliness ( mg/dm2/ hr) (rnils/yr) 
Clean 6 
17 
I 
21 
2 
3 
4 47 
Trace 6 
IO 
5 
12 
h 
7 
R Minor . Y  
9 Some I I  
2 .9 
8.2 
10.0 
23.0 
2.9 
4 3  
5.8 
4.3 
5 .1  
~~ ~~~ 
COMPOSITION 
2 -  hu [oxy  
Sulfaniic Citric ethanol S'* ~ - ~ -  
Wcieht Derccnt of aaueous solution .rest NO. 
4 15 
5 I5 
6 10 
7 - 
8 5 
Y - 
20 
5 
5 
5 
20 
5 
I 8  
- 
- 
- - 
- 0.1 
- 0. I 
- 0. I 
- 0. I 
5 0. I 
5 0.1 
5 0. I 
2 0. I 
*so= A surfwlant which is a mixture of primary alcohols of ahout 1 0  ti1 I2 mcmhcr 
carhon chains. ahout hO? cthoxylatcd. 
EXAMPLE 2 
In this example dynamic cleaning tests were per- 
formed 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 I ,  which also 
had been contaminated with the same substances used 
in Example I .  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 74°F. with initial 
contaminations of varying amounts, the parameters of 
corrosion metal loss, corrosion penetration depth, and 
residual hydrocarbon amount were measured and a 
visual evaluation of the cleaning effectiveness was 
made. The results are tabulated in Table 11. 
TABLE I1 
DYNAMIC CLEANING OF IRON-NICKEL ALLOY PIPE 
Initial 
66 
mg. (triolein Cleanliness 
+mineral oil) visual 
+ 1.0 ml. Residual obscrvation Metal Loss Corrosion 
particulatc Hydrocarbon smut wcight Penetration 
3,957,529 
5 
TABLE 11-continued 
DYNAMIC CLEANING OF IRON-NICKEL ALLOY PIPE 
Test No. solids (mg.) present (mg/dm'/ h r )  (mils/yr.) 
clean 102 49 
4s  22 
72 5.8 
69 33  
rust 20 9 7  
22 I 1  
1 5300 1.6 
2 5800 1.7 
3 4400 1.7 
4 5700 2.0 
5 3300 0.6 
6 4 100 1.9 
7 4700 2.6 dirty 44 22 
COMPOSITION 
Sulfamic Citric ethanol S '* 
Weight percent of aqueous solution 
2-hutoxy 
Test No. 
I I O  5 5 0.1 
2 10 5 5 0 .  I 
3 - 20 5 0. I 
4 IO 5 S 0.1 
5 - 20 - 0.  I 
6 - I O  S 0.1 
I IS 5 - 0. I 
*S' hcrcin is thc samc mixturc us that dcfincd hy S' in Tahlc I .  
What is claimed is: 
1. A method of cleaning a metal surface which com- 
a. contacting said surface for a sufficient period of 
time to clean said surface with a composition com- 
prising in percentages by weight the following in- 
gredients: 
i. about 8 to 12% sulfamic acid; 
ii. about 4 to 6% citric acid; 
iii. about 4 to 6% of a nonionic solvent for hydro- 
carbon residues which solvent is characterized as 
not producing turbidity at 75°F when present in 
said composition; 
iv. about 0.095 to 0.15% of a soluble nonionic 
surfactant which surfactant is characterized as 
having a cloud point of at least about 90°F and 
having a surface tension of about 32 dyneslcm. 
or less when present in an amount of 0.1 % of said 
composition; 
prises the sequence of steps: 
v. the balance, water; 
Composition; and 
and sodium nitrite. 
b. rinsing said surface with water to remove residual 
c. passivating the surface with a solution of citric acid 
2. The method of claim 1 wherein the flow rate of the 
composition applied in step ( a )  is about 2 to about 30 
feet per second. 
3. The method of claim 1 wherein the temperature of 
the composition applied in step ( a )  is about 40°F to 
about 140°F. 
4. The method of claim 1 wherein the temperature of 
the composition applied in step ( a )  is about 70°F to 
about 80°F. 
5. The method of claim 1 wherein the surface is that 
of an iron-nickel alloy. 
6. The method of claim 1 wherein the solvent is a 
glycol ether. 
7. The method of claim 1 wherein the solvent is 
chosen from the group consisting of 2-butoxyethanol, 
6 
2-( 2-butoxyethoxy)ethanol, 2-( 2-ethoxyethoxy )e- 
thanol. 2-methoxyethanol, and 2-ethoxyethanol. 
8. The method of claim 1 wherein the surfactant is 
25 chosen from the group consisting of linear alcohol 
ethoxylates, polyoxyethylene esters, and alkyl aryl pol- 
yethylene oxides. 
9. The method of claim 1 wherein the surfactant is a 
3o mixture of primary alcohols of about I O  to about 12 
10. A method of cleaning an iron-nickel alloy surface 
member carbon chains, about 6 0 8  ethoxylated. 
which comDrises in seauence: 
35 
40 
45 
50 
5 5  
60 
65 
a. contacting said surface for a sufficient period of 
time to clean said surface with a composition com- 
prising in percentages by weight the following in- 
gredients: 
i. about 8 to 12% sulfamic acid; 
ii. about 4 to 6% citric acid; 
iii. about 4 to 6% of a nonionic solvent for hydro- 
carbon residues which solvent is characterized as 
not producing turbidity at 75°F when present in 
said composition; 
iv. about 0.095 to 0.15% of a soluble nonionic 
surfactant which surfactant is characterized as 
having a cloud point of at least about 90°F and 
having a surface tension of about 32 dyneslcm. 
or less when present in an amount of 0.1% of said 
composition; 
v. the balance, water; at a rate of 4 feet per second 
for a period of about 2 hours, said composition 
being maintained at a temperature of about 70°F 
to 80"F, 
b. contacting said surface with a 1% aqueous citric 
acid solution at a rate of 5.5 ft/sec for about I O  
minutes, 
c. contacting said surface with a 0.1% aqueous so- 
dium nitrite solution at a rate of 5.5 ft/sec for about 
10 minutes to passivate said surface, and 
d. contacting said surface with water at a rate of 3.5 
ft/sec for about 20 minutes to remove residual 
substances. * * * * *  
UNITED STATES PATENT OFFICE 
CERTIFICATE OF CORRECTION 
P A T E N T  NO. 3 , 957 , 529 
D A T E D  m y  l a ,  1 9 7 6  
I N V E N T O K ( 5 )  George B. Alexander;  Norman F. Carpenter  
are hereby corrected as shown below. 
It is cer t i f ied that error appears in  the above-identif ied patent and that sald Let ters  Patent 
C o l .  2, l i n e  9 ,  a f t e r  " 8 "  change " to"  t o  --and--; 
C o l .  2 ,  l i n e  11, a f t e r  " 4 "  change " t o "  t o  --and--; 
Col. 4 ,  Table 11, f i r s t  column, change "66" t o  --concentrat ion-- ,  
Col. 4 ,  Table 11, l a s t  e n t r y ,  each column, move t o  r i g h t  under 
prev ious  e n t r y ;  
Signed and Sealed this 
Twenty-third Day o f  November 1976 
 SEAL^ 
A rresr: 
RUTH C .  MASON 
Attesting Officer 
C. MARSHALL DANN 
Commissioner o f '  Parerr i s  and Trademarks 


Method for cleaning and passivating a metal surface

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