Title:
Corrosion prevention of stainless steel
Kind Code:
A1


Abstract:
A surface of an article of stainless steel becomes to have increased corrosion resistance by treatment with a heated aqueous hydroxylamine salt solution.



Inventors:
Imai, Naoshi (Isesaki-shi, JP)
Application Number:
09/816386
Publication Date:
10/25/2001
Filing Date:
03/26/2001
Assignee:
IMAI NAOSHI
Primary Class:
Other Classes:
148/320, 134/19
International Classes:
C23F11/00; C23C22/50; C23C22/62; C23C22/68; C23C22/73; C23F11/18; C23F15/00; (IPC1-7): C23G1/00; C21D1/68
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Primary Examiner:
WYSZOMIERSKI, GEORGE P
Attorney, Agent or Firm:
NIXON PEABODY, LLP (WASHINGTON, DC, US)
Claims:

What is claimed is:



1. A method for preventing an article of stainless steel from corroding, which comprises keeping the article in contact with a heated aqueous solution of a hydroxylamine salt.

2. The method of claim 1, wherein the aqueous solution is heated to 50° C. or higher.

3. The method of claim 2, wherein the aqueous solution is heated to a temperature in the range of 60° C. to 200° C.

4. The method of claim 1, wherein the article is kept into contact with the heated solution for a period of 3 minutes or longer.

5. The method of claim 3, wherein the article is kept into contact with the heated solution for a period of one hour or longer.

6. The method of claim 1, wherein the heated solution contains the hydroxylamine salt in an amount of 0.2 to 50 weight %.

7. The method of claim 1, wherein the hydroxylamine salt is hydroxylamine sulfate or hydroxylamine phosphate.

8. The method of claim 1, wherein the article is a reaction vessel or a distilling apparatus.

9. An article of stainless steel having a corrosion resistance surface which is treated with a heated aqueous solution of a hydroxylamine salt.

Description:

FIELD OF THE INVENTION

[0001] The present invention relates to a method for pre venting an article of stainless steel from corroding.

BACKGROUND OF THE INVENTION

[0002] It is known that a surface of article made of steel can be converted to have increased corrosion resistance by treating the surface with an inorganic or organic corrosion inhibitor. A typical inhibitor is an aqueous phosphate solution. It is further known that the aqueous phosphate corrosion inhibiting solution can contain a hydroxylamine salt so as to form an improved phosphate coating on the treated metal surface.

[0003] U.S. Pat. Nos. 4,149,909, No. 4,865,653, and No. 5,597,465; Published EP Applications No. 0 695 817 A1 and No. 0 315 059 A1; WO 93/03198; and WO 93/20259 teach that a metal such as iron or zinc can be made to have improved corrosion resistance by placing the metal in contact with an aqueous iron phosphate or zinc phosphate solution, respectively, and forming on the metal surface a phosphate coat and that the formation of phosphate coat is enhanced by addition of a small amount of a hydroxylamine salt into the aqueous phosphate solution.

[0004] An article of stainless steel having 11 wt. % or more of chromium element has been known to have high corrosion resistance. Therefore, almost no studies have been made for enhancing corrosion resistance of a stainless steel article by chemical coating, though improvements of the corrosion resistance have been studied with respect to the alloy composition of stainless steel.

[0005] It has been noted by the present inventor that articles made of stainless steel may be corroded when they are placed under very severe conditions such as strong acidic conditions. Otherwise, the articles of stainless steel kept under relatively weak corrosive conditions for a long period of time can be corroded on their surfaces.

[0006] It is known that an aqueous free hydroxylamine solution (which is not in the salt form) can be concentrated from an aqueous diluted free hydroxylamine solution. The concentration is performed by distillation of the aqueous diluted free hydroxylamine solution using a vessel of stainless steel and a distilling apparatus of stainless steel. Since the aqueous free hydroxylamine solution is very corrosive, even the vessel and distilling apparatus of stainless steel is corroded.

[0007] Accordingly, it is an object of the invention to provide a method for effectively preventing an article of stainless steel from corroding.

SUMMARY OF THE INVENTION

[0008] The present invention provides a method for preventing an article of stainless steel from corroding, which comprises keeping the article in contact with a heated aqueous solution of a hydroxylamine salt.

DETAILED DESCRIPTION OF THE INVENTION

[0009] In the method, an article of stainless steel can be preventing from corrosion by keeping the article in contact with a heated aqueous solution of a hydroxylamine salt. The aqueous hydroxylamine salt solution is preferably heated to a temperature of 50° C. or higher, more preferably to a temperature of 60 to 200° C., more specifically to a temperature of 60 to 160° C. If the article of stainless steel is kept into contact with an heated hydroxylamine salt solution in an pressure resistant reaction vessel such as an autoclave, the temperature can be 100° C. or higher. The stainless steel article is kept in contact with the heated hydroxylamine salt solution, preferably for a period of 3 minutes or longer, more preferably 1 to 20 hours.

[0010] The heated hydroxylamine salt solution preferably contains a hydroxylamine salt at a concentration of 0.2 to 50 wt. %.

[0011] Examples of the hydroxylamine salts include hydroxylamine sulfate, hydroxylamine phosphate, and hydroxylamine hydrochloride. Preferred are hydroxylamine sulfate and hydroxylamine phosphate.

[0012] The method of the invention is very advantageous for keeping an article of stainless steel comprising chromium element (especially 15 wt. % or more) ad nickel element in addition to a major portion of iron, from corrosion.

[0013] The present invention is further described by the following examples.

EXAMPLE 1

[0014] In a glass-made flask equipped with a reflux condenser, an aqueous hydroxylamine phosphate solution (concentration: 20 wt. %) was placed. A specimen of stainless steel having the below-mentioned alloy composition was placed in the aqueous hydroxylamine phosphate solution.

[0015] The flask was then placed on an oil bath heated to approx. 100° C., for 8 hours or 24 hours, for performing anti-corrosive treatment.

[0016] (1) SUS 304L Stainless steel (composition: Fe approx. 73%, Ni approx. 9%, Cr approx 18%)

[0017] (2) SUS 316L Stainless steel (composition: Fe approx. 70%, Ni approx. 12%, Cr approx. 16%, Mo approx. 2%)

[0018] (3) SUS 310S Stainless steel (composition: Fe approx. 57%, Ni approx. 19%, Cr approx. 24%)

[0019] Thus treated specimen was weighed, and placed in an aqueous 10 wt. % sulfuric acid solution in a heat-resistant glass bottle. The glass bottle was placed in a thermostat heated to 80° C. and kept for certain periods Then, the glass bottle was taken out from the thermostat. The specimen was recovered from the sulfuric acid solution, washed with water, dried, and weighed.

[0020] Both weights were compared for determining weight loss which was caused by corrosion of the stainless steel specimen.

[0021] For comparison, the equivalent stainless steel specimen having no corrosion-inhibiting treatment was subjected to the abovementioned test for evaluating the resistance in the sulfuric acid solution.

[0022] The results are set forth in the following tables. 1

TABLE 1
(for SUS 304L)
SpecimenSpecimenSpecimen
Time (hr.)of 8 hrs.of 24 hrs.of no
intreatmenttreatmenttreatment
aq. H2SO4(weight g)(weight g)(weight g)
016.452617.955818.5543
118.2378
2416.452317.9557
4416.452117.9556
6816.451817.9554
11616.451717.9553
16416.451317.9548
18816.451317.9548
23616.451417.9554
28416.451617.9554
38017.9546
52917.9544

[0023] 2

TABLE 2
(for SUS 316L)
SpecimenSpecimen
Time (hr.)of 8 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
018.264118.2103
2418.124417.6733
4418.0132

[0024] 3

TABLE 3
(for SUS 310S)
SpecimenSpecimen
Time (hr.)of 8 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
017.369017.5489
117.4191
817.3690
2317.3686
4717.3687
7117.3685
9517.3688
11917.3686
16117.3684
20917.3683
28117.3685
32917.3681
45517.3679

EXAMPLE 2

[0025] The procedures of Example 1 were repeated except for replacing the aqueous hydroxylamine phosphate solution with an aqueous hydroxylamine sulfate solution (concentration: 20 wt. %)

[0026] In the corrosion resistance enhancing treatment, a treatment of 72 hours was additionally performed.

[0027] The results are set forth in the following tables. 4

TABLE 4
(for SUS 304L)
SpecimenSpecimen
Time (hr.)of 8 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
015.594318.5543
118.2378
2415.5944
4415.5940
6815.5937
11615.5935
16415.5931
18815.5931
23615.5935
28415.5937
38015.5930
52915.5929

[0028] 5

TABLE 5
(for SUS 316L)
SpecimenSpecimen
Time (hr.)of 8 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
 018.204518.2103
2418.067217.6733
4417.9577

[0029] 6

TABLE 6-1
(for SUS 310S)
SpecimenSpecimen
Time (hr.)of 8 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
017.790017.5489
117.4191
817.7901
2417.7897
4717.7897
7117.7895
9517.7898
11917.7896
16717.7892
21517.7894
28717.7895
33517.7888
45517.7889
62817.7887

[0030] 7

TABLE 6-2
(for SUS 310S)
SpecimenSpecimen
Time (hr.)of 24 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
017.978617.5489
117.4191
2417.9787
4417.9788
6817.9785
11617.9782
16417.9784
23617.9784
28417.9779
33517.9777

[0031] 8

TABLE 6-3
(for SUS 310S)
SpecimenSpecimen
Time (hr.)of 72 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
017.571217.5489
117.4191
1917.5713
6717.5710
11517.5711
18717.5711
23517.5707
35517.5707
52817.5706

EXAMPLE 3

[0032] In an autoclave, an aqueous hydroxylamine sulfate solution (concentration: 20 wt. %) was placed. A specimen of stainless steel (3) described in Example 1 was placed in the autoclave.

[0033] The autoclave was then placed on an oil bath heated to approx. 160° C., for 3 hours, for performing anti-corrosive treatment of the specimen.

[0034] The specimen was then placed in the aqueous sulfuric acid solution in the manner described in Example 1, to examine the corrosion resistance of thus treated specimen. The specimen having been subjected to no anti-corrosive treatment was also examined in the same manner.

[0035] The results are set forth in the following Table. 9

TABLE 7
(for SUS 310S)
SpecimenSpecimen
Time (hr.)of 3 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
017.104517.5489
117.4191
12417.1041

EXAMPLE 4

[0036] In an autoclave, an aqueous hydroxylamine sulfate solution (concentration: 5 wt. %) was placed. A specimen of stainless steel (1) or (3) described in Example 1 was placed in the autoclave.

[0037] The autoclave was then placed on an oil bath heated to approx. 160° C., for a hours, for performing anti-corrosive treatment of the specimen.

[0038] The specimen was then placed in the aqueous sulfuric acid solution in the manner described in Example 1, to examine the corrosion resistance of thus treated specimen. The specimen having been subjected to no anti-corrosive treatment was also examined in the same manner.

[0039] The results are set fort in the following Tables. 10

TABLE 8
(for SUS 304L)
SpecimenSpecimen
Time (hr.)of 8 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
017.958818.5543
118.2378
12417.9583

[0040] 11

TABLE 9
for SUS 310S
SpecimenSpecimen
Time (hr.)of 8 hrs.of no
intreatmenttreatment
aq. H2SO4(weight g)(weight g)
035.507417.5489
117.4191
124 35.5066

[0041] As is apparent from the results set forth in Tables 1 to 9, the specimens of stainless steel having been treated with an aqueous hydroxylamine salt solution according to the present invention keep their weights even after they are placed in a heated aqueous sulfuric acid solution for several ten hours or several hundred hours. In contrast, the equivalent specimens of stainless steel having been subjected to no anticorrosive treatment loss their weights within one to 24 hrs. In the aqueous sulfuric acid solution, the untreated specimens show blacken surface or give bubble formation within a short period of time.





 
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