Surface CTS anti-corrosion treatment method for stainless steel part

Abstract

Disclosed is a surface anti-corrosion treatment method for stainless steel. The method comprises the following steps: (1) performing chemical de-oiling and alkaline corrosion treatments on the surface of stainless steel by using a sodium hydroxide solution and a solution containing an alkaline corrosion active agent, and then washing with water; (2) performing, by using an oxidation solution, an oxidation treatment on the surface of the stainless steel treated in step (1), and then washing with water; (3) using the surface of the stainless steel treated in step (2) as a cathode and soaking same in an electrolyte for electrolysis, and then washing with water; and (4) placing the surface of the stainless steel treated in step (3) at a temperature of 50° C.-60° C. under a humidity of 60%-70%, and performing a hardening treatment. Also disclosed are the use of the treatment method in the treatment of a stainless steel part and a stainless steel part obtained after the treatment by means of the treatment method.

Claims

1. An anti-corrosion method of a stainless steel surface, comprising the following steps: (1) chemically degreasing and etching with alkali the stainless steel surface using a sodium hydroxide solution and a solution containing an alkali etching active agent, followed by washing with water; (2) oxidizing the stainless steel surface treated in the step (1) by an oxidizing solution, followed by washing with water; (3) immersing the stainless steel surface treated in the step (2) as a cathode in an electrolyte to electrolyze, followed by washing with water; and (4) placing the stainless steel surface treated in the step (3) at a temperature of 50-60° C. and a humidity of 60-70% for hardening, wherein in the step (3), the electrolyte contains 100-150 g/L of CrO.sub.3, 100-150 g/L of Na.sub.2MoO.sub.4, 200-250 g/L of H.sub.3PO.sub.4 and 50-60 g/L of Na.sub.2SiO.sub.3; a current intensity is 40 to 5 A/m.sup.2 with an initial current intensity of 40 A/m.sup.2, and then the current intensity is gradually reduced to 5 A/m.sup.2 according to formula i=3+A/t, wherein i is the current intensity, t is time, and A is a parameter of 20-30.

2. The method of claim 1, which characterized in that, in the step (1), the sodium hydroxide solution and the solution containing the alkali etching active agent is 80-85° C.

3. The method of claim 1, which characterized in that, in the step (2), the oxidizing solution contains 200-300 g/L of CrO.sub.3 and 100-150 g/L of Na.sub.2MoO.sub.4.

4. The method of claim 1, which characterized in that, in the step (3), a temperature of the electrolyte is 40-52° C.

5. The method of claim 1, which characterized in that, in the step (4), a time for hardening treatment by placing is 3-4 hours.

6. The method of claim 1, which characterized in that, the stainless steel surface treated by the method is at least one surface selected from surfaces of: stainless steel plate corrugated filler, stainless steel wire mesh filler, stainless steel loose filler, tray plate, stainless steel float valves, various fasteners and connectors.

7. The method of claim 1, which characterized in that, in the step (1), a concentration of the sodium hydroxide solution is 6.5-8%.

8. The method of claim 1, which characterized in that, in the step (1), a concentration of the solution containing the alkali etching active agent is 0.3-0.5%.

9. The method of claim 1, which characterized in that, in the step (1), the alkali etching active agent is ethoxy modified polytrisiloxane.

10. The method of claim 1, which characterized in that, in the step (1), the chemically degreasing and etching with alkali treatment is performed for 10-15 minutes.

11. The method of claim 1, which characterized in that, in the step (1), the washing with water is performed by using water with a temperature of 80-85° C. for 3-5 min.

12. The method of claim 1, which characterized in that, in the step (2), a temperature of the oxidizing solution is 75-90° C.

13. The method of claim 1, which characterized in that, in the step (2), a pH of the oxidizing solution is 0.4-1.5; the pH of the oxidizing solution is adjusted to 0.4-1.5 by adding a H.sub.2SO.sub.4 solution into the oxidizing solution; and a concentration of the H.sub.2SO.sub.4 solution is 98%.

14. The method of claim 1, which characterized in that, in the step (2), the oxidizing is performed for 15-35 minutes.

15. The method of claim 1, which characterized in that, in the step (2), the washing with water in the step (2) is performed cyclically by using water at 25-40° C. for 3-5 minutes; and a pH of the water is >3.

16. The method of claim 1, which characterized in that, in the step (3), a pH of the electrolyte is adjusted to 0.5-1.5 by adding a H.sub.2SO.sub.4 solution into the electrolyte; and a concentration of the H.sub.2SO.sub.4 solution is 98%.

17. The method of claim 1, which characterized in that, in the step (3), a time for electrolyzing is 25-55 minutes.

18. The method of claim 1, which characterized in that, in the step (3), the electrolysis comprises electrolyzing for 10-25 minutes at an initial current intensity of 40 A/m.sup.2, and then electrolyzing at a current intensity gradually reduced to 5 A/m.sup.2 during 15-30 minutes.

19. The method of claim 1, which characterized in that, in the step (3), the washing with water is performed cyclically by using water 25-40° C. for 3-5 minutes; and a pH of the water is >3.

Description

DESCRIPTION OF FIGURES

(1) Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which:

(2) FIG. 1: the left side of the figure is a 304 stainless steel substrate, the right side of the figure is a 304 stainless steel substrate treated by the method according to the present invention;

(3) FIG. 2: a stainless steel surface treated by the method according to the present invention;

(4) FIG. 3: an element distribution diagram of the stainless steel treated by the method according to the present invention and 304 stainless steel substrate;

(5) FIG. 4: a trend chart of material composition layer of the stainless steel treated by the method according to the present invention analyzed by X-ray photoelectron spectroscopy;

(6) FIG. 5: a stainless steel filter hanger made of 304 stainless steel substrate treated by the method according to the present invention;

(7) FIG. 6: a 304 stainless steel filter hanger (after being placed for 40 days);

(8) FIG. 7: a stainless steel filter hanger made of 304 stainless steel treated by the method according to the present invention (after being placed for 40 days);

(9) FIG. 8: a stainless steel filter hanger made of 304 stainless steel treated by the method according to the present invention (after being placed in an acid water stripper reflux pump for 3 months);

(10) FIG. 9: an ordinary 304 stainless steel filter hanger (after being placed in an acid water stripper reflux pump for 40 days);

(11) FIG. 10: an ordinary 304 stainless steel filler (after being operated for 1247 days);

(12) FIG. 11: a 304 stainless steel filler treated by the method according to the present invention (after being operated for 1247 days);

(13) FIG. 12: a 317L stainless steel filler (after being operated for 3 years);

(14) FIG. 13: adjacent area of a 317L stainless steel filler and a 317L stainless steel filler treated by the method according to the present invention (after being operated for 3 years);

(15) FIG. 14: a 317L stainless steel filler treated by the method according to the present invention (after being operated for 3 years);

(16) FIG. 15: a current-time profile according to the formula i=40−2.33t (wherein, i is current intensity, t is dense duration time (min)) after electrolyzing for 15 min;

(17) FIG. 16: a current-time profile after electrolyzing for 15 min, wherein at 0-5 min, the current is 40 A/m.sup.2; at 5-10 min, the current is 20 A/m.sup.2; at 10-15 min, the current is 15 A/m.sup.2;

(18) FIG. 17: a current-time profile according to the formula i=30+30/t (wherein, i is current intensity, t is dense duration time (min)) after electrolyzing for 15 min.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(19) Further described the present invention in detail in conjunction with specific embodiments below, the examples are given only for illustrating the present invention and are not intended to limit the scope of the invention.

(20) The experimental methods in the following examples are conventional methods unless otherwise specified. The raw materials, reagent materials and the like used in the following examples are commercially available products unless otherwise specified.

Example 1: The Test on Current Control of the Method According to the Present Invention

(21) In the method of the present invention, the change in current during electrolysis has a large influence on the atomic packing factor of the treated stainless steel surface. It can be found from the standard ferric chloride corrosion test that the atomic packing factor of the treated stainless steel surface has a great influence on the corrosion results. The change in the coefficient of friction and the change in the corrosion resistance of the treated stainless steel surface were observed by various changes in the electrolysis current, and the results shown that the smaller the coefficient of friction was, the better the corrosion resistance was.

(22) As shown in FIGS. 15-17, X axis (horizontal axis) is time (min), Y axis (longitudinal axis) is current intensity (A/m.sup.2):

(23) Scheme 1: As shown in FIG. 15, the current intensity of the method according to the present invention was i=40−2.33t (i is current intensity, t is duration time);

(24) Scheme 2: As shown in FIG. 16, the current intensity of the method according to the present invention was: at 0-5 min, the current was 40 A/m.sup.2; at 5-10 min, the current was 20 A/m.sup.2; at 10-15 min, the current was 5 A/m.sup.2;

(25) Scheme 3 (the current was controlled according to the method of the present invention): As shown in FIG. 17, the current intensity of the method according to the present invention is: i=3+A/t (i is current intensity A/m.sup.2, t is duration time, A (parameter) is 20-30);

(26) The result was shown in Table 3.

(27) TABLE-US-00003 TABLE 4 friction coefficients of a 304 stainless steel substrate treated by the treating method of the present invention Corrosion Friction rate of standard Schemes coefficient μ ferric chloride g/m.sup.2h 304 stainless steel 0.131 17.68 substrate (untreated) Scheme 1 0.102 2.09 Scheme 2 0.113 4.36 Scheme 3 0.092 1.12 (the current was controlled according to the method of the present invention)

(28) Conclusion: Different ways of changing the current lead to different atomic packing factor of stainless steel nano-surfaces. As can be seen from the table, the smaller the friction coefficient g was, the smoother the nano-surface film layer was, and the higher the atomic packing factor of the nano-crystal surface was, this will result in good corrosion resistance.

Example 2: Surface Hardening Test of the Method According to the Present Invention

(29) The hardening on the stainless steel surface has a great influence on the corrosion resistance. At present, the hardening of the stainless steel surface is usually dried at room temperature.

(30) In the present invention, the inventors evaluated the corrosion resistance effect of the treated stainless steel surface by anti-flowing corrosion effect under different temperature, humidity and time, to screen the most suitable surface hardening conditions.

(31) The standard ferric chloride corrosion test was carried out under constant temperature and humidity conditions in a flowing corrosive environment. The surface corrosion resistance environment of the 304 substrate treated by the method of the present invention was shown in Tables 4-6.

(32) TABLE-US-00004 TABLE 4 Effect of the temperature for hardening on surface corrosion resistance Effect of the temperature for hardening on surface corrosion resistance (the humidity was controlled at 60%, the time for hardening was 4 h) Corrosion rate of flowing Temperature for (the flowing rate was 1 m/s) ferric Nos. hardening□ chloride g/m.sup.2h 1 Room temperature- 8.68-2.35 Humidity is uncertain 2 30 4.09 3 40 2.87 4 50 1.55 5 60 2.41 6 70 6.22 7 80 10.84

(33) A conclusion is drawn from Table 4 that the temperature for hardening has an effect on the hardness of the nano-film layer. When the temperature for hardening was low, the nano-film layer was easy to fall off, while the temperature for hardening was high, the surface of the nano-film layer had cracks. It could be seen from the results of the flowing ferric chloride corrosion test that a suitable temperature for hardening could greatly improve the resistance to corrosion under flowing condition. The suitable temperature was 50˜60□.

(34) TABLE-US-00005 TABLE 5 Effect of the humidity for hardening on corrosion resistance of surface treated by the method of the present invention Effect of the humidity for hardening on corrosion resistance of surface treated by the method of the present invention (the temperature was controlled at 50° C., the time for hardening was 4 h) Corrosion rate of flowing Humidity for (the flowing rate was 1 m/s) ferric Nos. hardening % chloride g/m.sup.2h 1 <2 11.27 2 20 6.58 3 30 4.61 4 40 2.23 5 50 1.78 6 60 1.55 7 70 1.62 8 80 1.76 9 95 1.82

(35) A conclusion is drawn from Table 5 that the humidity for hardening has an effect on the hardness of the nano-film layer, which similar to that of the temperature. The humidity for hardening was low, the surface of the nano-film layer had cracks, the humidity was high, and the nano-film layer was soft and easy to fall off. It could be seen from the results of the flowing ferric chloride corrosion test that a suitable humidity for hardening could improve the resistance to corrosion under flowing condition. The suitable humidity was 60˜70%.

(36) TABLE-US-00006 TABLE 6 Effect of the time for hardening on corrosion resistance of surface treated by the method of the present invention Effect of the time for hardening on corrosion resistance of surface treated by the method of the present invention (the temperature was controlled at 50□, the humidity was 60%) Time for Corrosion rate of flowing (Flow rate 1 m/s) Nos. hardening h ferric chloride g/m.sup.2h 1 0.5 3.51 2 1 2.42 3 2 1.88 4 3 1.56 5 4 1.55 6 6 1.53 7 12 1.49 8 24 1.45

(37) A conclusion is drawn from Table 6 that from comparative data, the longer the time for hardening was, the better the hardening effect was. The longer the time was, the higher the stability of the nano-film layer was. However, considering the processing time, the suitable time was 3˜4 h.

Example 3: Treating a Stainless Steel Surface (304 Substrate) by the Method According to the Present Invention

(38) (1) A sodium hydroxide solution with a concentration of 7% and a solution containing a HDW-1050 alkali etching additive with a concentration of 0.5% were used to chemically degrease and etch with alkali the stainless steel surface (304 substrate). The total amount of the whole solution was subjected to immerse the whole stainless steel surface. The temperature of the solution was controlled at 80° C., the time was 15 min; and then water with a temperature of 80° C. was used for washing for 3 min;

(39) (2) the oxidizing solution contained 300 g/L of CrO.sub.3, 140 g/L of Na.sub.2MoO.sub.4. At 78° C., the pH of the oxidizing solution is adjusted to 1.3 by adding a 98% H.sub.2SO.sub.4. The time for oxidizing was 15 min, water was used for washing at room temperature for 3 min after oxidation.

(40) (3) the composition of the electrolyte contained 100 g/L of CrO.sub.3, 100 g/L of Na.sub.2MoO.sub.4, 200 g/L of H.sub.3PO.sub.4, 55 g/L of Na.sub.2SiO.sub.3. The pH of the oxidizing solution is adjusted to 1.3 by adding a 98% H.sub.2SO.sub.4, the temperature was controlled at 40° C. The stainless steel piece (304 substrate) was taken as cathode, based on the surface area of the stainless steel, the electrolysis was performed at the current intensity of 40 A/m.sup.2 for 10 min, then was performed at a gradually reduced current intensity according to the formula i=3+30/t (i is current intensity A/m.sup.2, t is duration time) for 15 min, and then the electrolyte on the surface of the stainless steel piece was washed water at room temperature.

(41) (4) placing the stainless steel piece (304 substrate) into an environment with a temperature of 55□ and a humidity of 60% for hardening for 3 hours, and then a nanocrystalline material based on the stainless steel surface (304 substrate) was obtained.

(42) After being treated by the method according to the present invention, the stainless steel surface (304 substrate) contained 0.83% of carbon, 32.81% of oxygen, 44.28% of chromium, 14.17% of iron, 1.0% of molybdenum, 3.06% of nickel, 2.73% of silicon, 1.11% of calcium and with the balance being impurity elements.

Example 4

(43) An acid water stripping unit reflux system from Ningxia Coal Industry Group Co., Ltd. was seriously corroded, especially, the top reflux pipe, the return pump, the return tank and the condenser at the top of the tower had severe corrosion and serious leakage. The replacement of the equipment in the reflux system was short, which affected the acid water treatment of the equipment.

(44) TABLE-US-00007 TABLE 7 Water analysis data after washing acids Items Acid water stripping unit Ammonia nitrogen in incoming water 3900 (mg/L) Sulfide in incoming water (mg/L) 72 Petroleum in incoming water (mg/L) Not detected COD in outer delivery water (mg/L) did not cause excessive COD Ammonia nitrogen in outer delivery 5-30 water (mg/L) Sulfide in outer delivery water (mg/L) Not detected Petroleum in outer delivery water Not detected (mg/L) PH in reflux 8.6-10   Iron ion in reflux (mg/L) Total iron 39.6 Cl− in reflux (mg/L) Detected maximum was 11000 Non-condensable gas H.sub.2S content (%) <2 Non-condensable gas NH.sub.4.sup.+ content Total nitrogen 50 (%) Non-condensable gas CO.sub.2(%) 50

(45) Due to high content and fast flow rate of Cl.sup.− in the reflux of the acid water stripping unit reflux system and the caused washing and corrosion on the filter hanger piece was fast. When the filter hanger made of 304 stainless steel was tested, the result showed that there was visible corrosion to the naked eye after being placed for one week. The 304 stainless steel filter mesh is corroded out and the whole skeleton structure is also corroded out after being placed for 40 days.

(46) After treating the 304 stainless steel by the method according to the present invention, the filter hanger was tested. The result showed that there was no any corrosion after being placed for one week. After being placed for 40 days, the stainless steel filter hanger embrittle, and the filter mesh can be broken by hand, but the overall skeleton structure and the filter mesh were kept intact. The overall skeleton structure was still kept intact after being placed for 3 months.

Example 5

(47) A branch company of China Petroleum & Chemical Corporation designed high-sulfur and high-acid crude oil as the crude oil in an atmospheric and vacuum distillation device of a crude oil deterioration reconstruction project. A 304 filter and a 304 filter containing a nano surface layer were placed at the bottom of the third section of a packed vacuum tower. Specific temperature was shown as Table 8:

(48) TABLE-US-00008 TABLE 8 Minus three lines Carbon residue temperature (□) Sulfur content Acid value content 213~331.2 0.77m % 1.06 2.26%

(49) After being operated for 1247 days, it can be seen from the scene that the 304 substrate was corroded, become thin, and severely embrittled. While after being treated by the method according to the present invention, the stainless steel 304 showed no significant corrosion.

Example 6

(50) A branch company of China National Offshore Oil Corporation designed low-sulfur and high-acid crude oil as the crude oil in an atmospheric and vacuum distillation device. The temperature of the fifth section of the vacuum tower was 400° C., the sulfur content was 0.35%, the acid value was 2.65-3.09 and the filter substrate was 317L. After being operated for 3 years, it was seen from the scene that the 317L substrate had obvious corrosion, while the 317L substrate treated by the method according to the present invention had no obvious corrosion with an intact surface film and visible gloss.