A method for determining pitting corrosion of stainless steel clad plate
By conducting a closed immersion test of stainless steel composite plates in ferric chloride solution and calculating the weight loss rate, the problem of inaccurate measurement caused by the reaction between the substrate and the solution in the existing technology was solved, and an accurate evaluation of the pitting corrosion performance of stainless steel composite plates was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANGANG STEEL CO LTD
- Filing Date
- 2026-05-09
- Publication Date
- 2026-07-24
AI Technical Summary
Existing technologies cannot accurately evaluate the pitting corrosion performance of stainless steel composite plates, especially since the reaction between the substrate and the solution leads to inaccurate measurement results.
The test results were obtained by immersing the sample in ferric chloride solution in a closed environment and calculating the weight loss rate. Direct contact between the substrate and the solution was avoided, and the substrate was sealed with acrylic glue to ensure the accuracy of the test results.
This method enables accurate evaluation of the pitting corrosion performance of stainless steel composite plates, avoids direct reaction between the substrate and the solution, and improves the reliability of the measurement results.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of corrosion detection technology, specifically relating to a method for determining pitting corrosion in stainless steel composite plates. Background Technology
[0002] Stainless steel composite plates are composite materials made by combining stainless steel with carbon steel or low alloy steel through a certain method. They are widely used because they have the excellent corrosion resistance of stainless steel and the mechanical properties and lower cost of low alloy steel.
[0003] Layered metal composite panels possess the characteristics of both cladding materials (corrosion resistance, heat resistance, and wear resistance) and base materials (strength and rigidity), making them a novel type of material. Stainless steel composite panels are the most widely used type, accounting for over 80% of all composite panels. Compared to pure stainless steel panels, stainless steel composite panels can save 70%–80% of alloying elements such as Cr and Ni, resulting in cost savings of 30%–50%. As a resource-saving product, they can be widely used in industries such as petroleum, chemical, salt, and hydropower, significantly reducing project costs and achieving a perfect combination of low cost and high performance, resulting in excellent economic benefits.
[0004] Because the production process of stainless steel composite plates can affect the performance of the stainless steel layer, it is impossible to accurately evaluate its pitting corrosion performance. Furthermore, for composite plates with a base layer of plain carbon steel, if the composite plate is completely exposed to the test solution, the base layer will react with the hydrochloric acid and ferric chloride in the solution, altering the solution composition.
[0005] [1] Chen Qingguo, Tan Chuanjiang, Tong Gen, Song Cheng, Wang Yao. Pitting corrosion of pressure vessels made of 316L + Q345R bimetallic composite plate: The development of pitting pits under typical CO2 corrosion conditions was investigated by prefabricating pits of different depths on 316 stainless steel + Q345R carbon steel bimetallic composite plates. The results showed that when the prefabricated pits were in the stainless steel layer, the corrosion was slight and no new pitting corrosion occurred; when the bottom of the pit touched the carbon steel layer, the carbon steel was preferentially corroded, forming holes, and the pitting rate reached 3.911 mm / a. A layer of uneven and thin corrosion products, mainly FeCO3, was attached to the bottom of the pit; when the pit completely penetrated to the carbon steel layer, the carbon steel layer was preferentially corroded and continued to expand to the surrounding area, forming an uneven metal loss morphology, and the pitting rate reached 4.954 mm / a. A layer of thicker and relatively dense corrosion products, mainly FeCO3, was attached to the bottom of the pit. This indicates that once pitting corrosion penetrates to the stainless steel layer on the surface of the bimetallic composite plate, it will trigger significant galvanic corrosion. The carbon steel layer will corrode preferentially and spread rapidly to the surrounding area, thereby endangering the pressure-bearing performance of the composite plate.
[0006] This document mainly introduces the pitting corrosion principle of 316 stainless steel + Q345R carbon steel bimetallic composite plate, but does not introduce how to prevent the base carbon steel from reacting with the solution.
[0007] [2] Song Xiaojun, Yang Zhongwu, Dou Lei, Zhang Xuanwei, Wei Xiyao, Tan Zhongwei, Guo Ruipeng. Experimental study on pitting corrosion behavior of S31603 composite plate pressure vessel: In order to investigate the development process of different pitting depths of the stainless steel layer of S31603 composite plate pressure vessel and the risk of galvanic corrosion after penetration into the carbon steel layer, S31603 composite plate test pieces with different pitting depths were prefabricated and corrosion tests were carried out in the laboratory and in the field of S31603 composite plate pressure vessel. Macroscopic analysis, low magnification observation, high magnification observation and corrosion product characterization analysis were performed on the test pieces. The results showed that when the pitting depth of the pre-fabricated S31603 composite plate penetrated to the carbon steel layer, significant galvanic corrosion occurred. The highest pitting rates in the laboratory corrosion test and the field test reached 4.954 and 1.023 mm / a, respectively. After the pitting depth of the pre-fabricated S31603 composite plate specimens penetrated to the carbon steel layer, galvanic corrosion preferentially occurred in the carbon steel. When the pitting depth of the pre-fabricated S31603 composite plate specimens was within the stainless steel layer, corrosion was slight, no new pitting occurred, and no significant corrosion influence was observed between adjacent pits. In Cl-containing... - In acidic and corrosive media environments, when the pitting depth of the S31603 composite plate pressure vessel is within the stainless steel layer, the corrosion is slight. However, when the pitting depth penetrates to the carbon steel layer, significant galvanic corrosion will occur. Therefore, it is necessary to shorten the opening and maintenance cycle of the S31603 composite plate pressure vessel to ensure safe use.
[0008] This paper focuses on the development process of different pitting depths of the stainless steel layer in S31603 composite plate pressure vessels and the risk of galvanic corrosion after penetrating to the carbon steel layer, but does not establish a test method for pitting corrosion of stainless steel composite plates.
[0009] Therefore, how to accurately evaluate the pitting corrosion performance of stainless steel composite plates has become an important issue that urgently needs to be addressed. Summary of the Invention
[0010] Therefore, the purpose of this invention is to provide a method for determining the pitting corrosion of stainless steel composite plates, so as to solve the technical problem that the existing technology cannot accurately evaluate the pitting corrosion performance of stainless steel composite plates.
[0011] To achieve the above objectives, the present invention provides the following technical solution:
[0012] This invention provides a method for determining pitting corrosion in stainless steel composite plates, comprising the following steps: S1: After measuring the weight, length, width and thickness of the sample, preprocessing is performed to obtain the original weight, length, width and thickness of the sample. S2: Immerse the pretreated sample in a ferric chloride solution at a specified temperature in a closed environment until the test time is reached. After cleaning the sample, the test sample is obtained. S3: Measure the weight of the sample after the test to obtain the weight of the sample after the test; S4: Calculate the weightlessness rate using the following formula: ; In the formula: W is the weight loss rate, in grams. m -2 h -1 G0 is the original weight of the sample in g; G1 is the weight of the sample after the test in g; a is the length of the sample in mm; b is the width of the sample in mm; c is the thickness of the sample in mm; t is the test time.
[0013] Among them, the weight loss rate is used to reflect the pitting corrosion resistance of stainless steel composite plate materials with severe pitting corrosion and insignificant uniform corrosion; the pitting corrosion performance of stainless steel composite plates is evaluated based on the weight loss rate.
[0014] The test lasted for 72 hours.
[0015] The ferric chloride solution is a 6% FeCl3 solution, and the preparation process is as follows: Dissolve 100g±5g of analytical grade ferric chloride (FeCl3·6H2O) conforming to HG / T 3474 in 900mL of distilled water or deionized water to prepare a 6% FeCl3 solution.
[0016] In principle, only one specimen should be tested in a single test container. For specimens of the same steel grade and under the same heat treatment regime, two or more specimens may be placed in the same container if other test conditions can be met, but the specimens must not come into contact with each other.
[0017] The weight measurement is accurate to 0.1 mg.
[0018] Based on the above technical solution, the specified temperature in S2 is further defined as 21℃-23℃.
[0019] Based on the above technical solution, further, the cross-sectional area of the sample perpendicular to the rolling or forging direction is ≤ 1 / 2 of the total area of the sample.
[0020] Based on the above technical solution, the pretreatment further includes grinding, cleaning and sealing.
[0021] Based on the above technical solution, further, when the thickness of the stainless steel cladding layer of the sample is 4.9mm-5.1mm, the grinding process is as follows: When the thickness of the sample is <5mm and the sample is a single-sided composite stainless steel layer, the sample is ground starting from the base layer of the composite plate. When the thickness of the sample is <5mm and the sample is a double-sided composite stainless steel layer, the sample is ground starting from one side of the composite plate. When the thickness of the sample is ≥5mm and the sample is a single-sided composite stainless steel layer, the sample is ground starting from the base layer of the composite plate. When the thickness of the sample is ≥5mm and the sample is a double-sided composite stainless steel layer, the sample is ground starting from one side of the composite plate. The base layer of the sample is rounded to R≥2mm.
[0022] Based on the above technical solution, the cleaning process is further described as follows: After the sample surface was polished, it was cleaned with acetone, degreased with anhydrous ethanol, and then stored in a desiccator.
[0023] Based on the above technical solution, the sealing is further specified as follows: The substrate of the cleaned sample was completely sealed with a heat-resistant, acid-resistant, and insulating coating to ensure that no substrate was exposed. The coating thickness was measured using a coating thickness gauge. The coating thickness was ≥200μm, and the curing time was not less than 24h. After the coating was fully cured, the pretreated sample was obtained.
[0024] Among them, heat resistance refers to the ability to withstand temperatures above 150℃. The coating specifically uses 302 acrylic adhesive to ensure that the substrate will not be corroded by the solution during the experiment.
[0025] Based on the above technical solution, further, in S2, a glass beaker is used as the test container, a glass support is used to keep the sample in the middle of the ferric chloride solution, a constant temperature water bath is used to maintain the specified temperature, and a watch glass is used to cover the sample to achieve a sealed environment.
[0026] Based on the above technical solution, further, the amount of ferric chloride solution required per square centimeter of surface area of the sample in S2 is ≥20 mL.
[0027] Based on the above technical solution, the cleaning process specifically involves immersing the sample after the pitting test in an organic solvent such as acetone for no less than 2 hours. After the coating becomes loose, the coating is completely peeled off, the corrosion products are removed after washing, and the sample is washed again with anhydrous ethanol and then dried.
[0028] Compared with the prior art, the present invention has the following beneficial effects: This invention pre-treats the samples before testing to prevent them from being completely exposed in the ferric chloride solution, thus avoiding the reaction between the substrate and the solution and making the measurement results more accurate. The weight loss rate is used to reflect the pitting resistance of stainless steel composite plate materials with severe pitting corrosion and inconspicuous uniform corrosion, and the pitting resistance is evaluated to achieve accurate evaluation of the pitting performance of stainless steel composite plates. Detailed Implementation
[0029] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.
[0030] Example 1 Specimens are cut from stainless steel composite plates, ensuring that the cross-sectional area perpendicular to the rolling or forging direction accounts for less than half of the total specimen area. After measuring the specimen's weight, length, width, and thickness, pretreatment is performed to obtain the original specimen weight, length, width, and thickness.
[0031] Considering that the thickness of the stainless steel layer is divided at 5 mm, this method uses 5 mm as the dividing line, giving the sample size and deviation as 5 mm ± 0.1 mm, i.e. 4.9 mm - 5.1 mm, and specifying: When the thickness of the stainless steel cladding is less than 5mm, single-sided lamination starts from the base layer of the cladding plate and double-sided lamination starts from one side of the cladding plate. When the thickness of the stainless steel cladding is not less than 5mm, single-sided cladding starts grinding from the base layer of the cladding plate, and double-sided cladding starts grinding from one side of the cladding plate. The base layer of the sample is rounded to R≥2mm.
[0032] Example 2 After cleaning the polished sample surface in Example 1 with acetone, degreased with anhydrous ethanol, and then stored in a desiccator, the entire composite board substrate was sealed with 302 acrylate adhesive to a coating thickness of 240 μm. It was ensured that the substrate would not be corroded by the solution during the experiment, and the test was conducted only after the coating had fully cured.
[0033] Example 3 Prepare a 6% FeCl3 solution by dissolving 100g of analytical grade ferric chloride (FeCl3·6H2O) conforming to HG / T3474 in 900mL of distilled or deionized water.
[0034] Example 4 Glass beakers or similar containers were used as experimental containers.
[0035] Use a glass holder of appropriate shape to keep the sample in the middle of the test solution.
[0036] A constant temperature water bath was used to maintain the test solution at a specified temperature of 22℃, and the continuous test time was 72h.
[0037] The experimental steps are as follows: Pour the prepared ferric chloride solution into the test container. The required volume of test solution per square centimeter of sample surface area is 30 mL. Place the test container in a constant temperature bath and heat it to 22°C.
[0038] After the test solution reaches the specified temperature, place the sealed composite plate sample on the support in the solution and immerse it for the corresponding test time. During the test, a watch glass or similar covering should be placed on the test container to prevent solution evaporation.
[0039] After the test, the sealed sample was removed, and the coating was completely peeled off and cleaned with organic solvents such as acetone. Then, the corrosion products were removed, and the sample was cleaned, dried, and weighed (accurate to 0.1 mg) to obtain the weight of the sample after the test.
[0040] The weightlessness rate is calculated using the following formula: ; The calculated weight loss rate of the sample was 0.3411 g / (m³). 2 ·h), and then evaluate the pitting corrosion performance of stainless steel composite plates.
[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for determining pitting corrosion in stainless steel composite plates, characterized in that, Includes the following steps: S1: After measuring the weight, length, width and thickness of the sample, preprocessing is performed to obtain the original weight, length, width and thickness of the sample. S2: Immerse the pretreated sample in a ferric chloride solution at a specified temperature in a closed environment until the test time is reached. After cleaning the sample, the test sample is obtained. S3: Measure the weight of the sample after the test to obtain the weight of the sample after the test; S4: Calculate the weightlessness rate using the following formula: ； In the formula: W is the weight loss rate, in grams. m -2 h -1 G0 is the original weight of the sample in g; G1 is the weight of the sample after the test in g; a is the length of the sample in mm; b is the width of the sample in mm; c is the thickness of the sample in mm; t is the test time.
2. The method for determining pitting corrosion in stainless steel composite plates according to claim 1, characterized in that, The specified temperature in S2 is 21℃-23℃.
3. The method for determining pitting corrosion in stainless steel composite plates according to claim 1, characterized in that, The cross-sectional area of the sample perpendicular to the rolling or forging direction is ≤ 1 / 2 of the total area of the sample.
4. The method for determining pitting corrosion in stainless steel composite plates according to claim 1, characterized in that, The pretreatment includes polishing, cleaning, and sealing.
5. The method for determining pitting corrosion in stainless steel composite plates according to claim 4, characterized in that, When the thickness of the stainless steel cladding layer of the sample is 4.9mm-5.1mm, the grinding process is as follows: When the thickness of the sample is <5mm and the sample is a single-sided composite stainless steel layer, the sample is ground starting from the base layer of the composite plate. When the thickness of the sample is <5mm and the sample is a double-sided composite stainless steel layer, the sample is ground starting from one side of the composite plate. When the thickness of the sample is ≥5mm and the sample is a single-sided composite stainless steel layer, the sample is ground starting from the base layer of the composite plate. When the thickness of the sample is ≥5mm and the sample is a double-sided composite stainless steel layer, the sample is ground starting from one side of the composite plate. The base layer of the sample is rounded to R≥2mm.
6. The method for determining pitting corrosion in stainless steel composite plates according to claim 4, characterized in that, The cleaning process is as follows: After the sample surface was polished, it was cleaned with acetone, degreased with anhydrous ethanol, and then stored in a desiccator.
7. The method for determining pitting corrosion in stainless steel composite plates according to claim 4, characterized in that, The sealing is specifically as follows: The substrate of the cleaned sample was completely sealed with a heat-resistant, acid-resistant, and insulating coating to ensure that no substrate was exposed. The coating thickness was measured using a coating thickness gauge. The curing time was not less than 24 hours and the coating thickness was ≥200μm. After the coating was fully cured, the pretreated sample was obtained.
8. The method for determining pitting corrosion in stainless steel composite plates according to claim 1, characterized in that, In S2, a glass beaker is used as the test container, a glass support is used to keep the sample in the middle of the ferric chloride solution, a constant temperature water bath is used to maintain the specified temperature, and a watch glass is used to cover the sample to achieve a sealed environment.
9. The method for determining pitting corrosion in stainless steel composite plates according to claim 1, characterized in that, The amount of ferric chloride solution required per square centimeter of surface area of the sample in S2 is ≥20 mL.
10. The method for determining pitting corrosion in stainless steel composite plates according to claim 7, characterized in that, After the pitting test, the sample is immersed in organic solvents such as acetone for no less than 2 hours. After the coating loosens, the coating is completely peeled off, cleaned, and the corrosion products are removed. The sample is then cleaned again with anhydrous ethanol and dried.