Corrosion Gel for Weld Detection, Preparation Method, Corrosion Method and Weld Surface Crack Detection Method

Abstract

The present invention relates to a corrosion gel for weld detection, a preparation method, a corrosion method and a weld surface crack detection method, belonging to the technical field of weld detection. The corrosion gel for weld detection comprises the following raw materials: agar, water, 98% sulfuric acid, 10% hydroxylamine hydrochloride solution, p-tolylthiourea, stannous sulfate, thiourea, 10% Triton X-100 solution and 0.05% ethanol solution of o-phenanthroline derivative. The preparation method of the corrosion gel for weld detection comprises the following steps: weighing agar and dissolving it in water; sequentially adding 98% sulfuric acid, hydroxylamine hydrochloride solution, p-tolylthiourea, stannous sulfate, thiourea, Triton X-100 solution and ethanol solution of o-phenanthroline derivative; adding 100 mL of ethanol solution of o-phenanthroline derivative and mixing evenly to obtain a hot corrosion gel. A weld surface crack detection method comprises the following steps: making an indicating electrode; preparing a corrosion gel; treating the weld with the corrosion gel; evaluating the weld crack.

Description

Technical Field

[0001] The present invention relates to a corrosion gel for weld detection, a preparation method, a corrosion method and a weld surface crack detection method, belonging to the technical field of weld detection. Background Art

[0002] Due to advantages such as short construction period, light self-weight, beautiful appearance, strong adaptability, and convenient maintenance, steel structures have developed very rapidly in recent years. At present, building steel structures have occupied a very important position in the national economic construction. During the construction of building steel structures, Q355D steel is widely used because of its good mechanical properties, welding properties, processing properties, and corrosion resistance. Q355D steel plates with various thicknesses are spliced into target buildings and bridges by welding according to design requirements. For the butt welds of steel plates, gas shielded welding is mostly carried out with copper-plated solid wire, but the copper plating layer will enter the molten pool during the melting process of the wire, and copper elements will inevitably exist after the weld is formed. The inclusion of copper elements in the weld will reduce the mechanical properties of the weld, and even more likely to generate surface cracks when the copper element content in the weld is high.

[0003] Cracks generated in the weld during the welding process will greatly affect the overall safety of the steel structure. Therefore, it is necessary to detect potential welding cracks. Among the methods for detecting weld surface cracks, liquid penetrant testing is the most convenient and economical. Fluorescent dyes or coloring dyes are coated on the surface to be tested as markers and penetrate into the surface cracks. After removing the surface markers, a developer is coated, and the markers at the defect locations are made visible through a special light source, so as to detect the distribution state of the weld surface cracks. However, the results of liquid penetrant testing are seriously affected by personal operations, not only with low accuracy, but also only able to detect the two-dimensional surface distribution of significant cracks, and it is difficult to make a quantitative evaluation of the crack depth.

[0004] Therefore, for the liquid penetrant testing evaluation system for weld surface defects, it is crucial to improve the detection accuracy and expand the quantitative evaluation ability. Developing a precise liquid penetrant testing method with quantitative evaluation ability is not only of great significance to the field of welding flaw detection, but also can greatly eliminate the safety hazards of steel structure projects. Summary of the Invention

[0005] The first object of the present invention is to provide a corrosion gel for weld detection to solve the problem of low accuracy of current penetrant testing.

[0006] The second and third objects of the present invention are to provide a preparation method and a corrosion method for the corrosion gel for weld detection that are simple and convenient to operate.

[0007] The fourth object of the present invention is to provide a method for detecting surface cracks in welds, which can not only qualitatively and accurately detect cracks on the weld surface, but also quantitatively evaluate the crack depth according to the potential analysis results by the content of cuprous ions in the corrosion gel.

[0008] To achieve the above object, the present invention is realized by the following technical solutions:

[0009] A corrosion gel for weld detection, comprising the following raw materials: 15.0 - 20.0 g of agar, 600 mL of water, 2.0 - 5.0 mL of 98% sulfuric acid, 20.0 - 50.0 mL of 10% hydroxylamine hydrochloride solution, 0.3 - 1.5 g of p-tolylthiourea, 0.1 - 0.5 g of stannous sulfate, 50.0 - 80.0 g of thiourea, 200 mL of 10% Triton X-100 solution, and 100 mL of 0.05% ethanol solution of o-phenanthroline derivative.

[0010] Based on the above corrosion gel for weld detection, the o-phenanthroline derivative is one of cuproin or bathocuproine.

[0011] A preparation method of a corrosion gel for weld detection, comprising the following steps:

[0012] (1) Weigh 15.0 - 20.0 g of agar, dissolve it in 600 mL of boiling water and stir evenly, and maintain the temperature constant after cooling to 60 °C;

[0013] (2) Sequentially add 2.0 - 5.0 mL of 98% sulfuric acid, 20.0 - 50.0 mL of 10% hydroxylamine hydrochloride solution, 0.3 - 1.5 g of p-tolylthiourea, 0.1 - 0.5 g of stannous sulfate, 50.0 - 80.0 g of thiourea, and 200 mL of 10% Triton X-100 solution to step (1) and stir evenly;

[0014] (3) Add 100 mL of 0.05% ethanol solution of o-phenanthroline derivative to step (2), mix evenly and maintain the solution at 60 °C to obtain a hot corrosion gel.

[0015] A corrosion method for detecting surface cracks in welds, comprising the step of corroding the weld with the above corrosion agent: after cleaning the surface of the weld to be tested, pour molten solid paraffin around the area of the weld to be tested to form a small pool; pour the corrosion gel for weld detection into the small pool and make the hot corrosion gel cover all positions of the weld inside the small pool. After several minutes, remove the cooled corrosion gel and observe the bottom surface of the gel. If it shows a uniform color, there is no crack on the weld surface; if there are local stripe marks, there are cracks at the corresponding positions on the weld surface; wherein the weld surface is a single-layer single-pass butt weld and a straight bead weaving method is adopted.

[0016] A method for detecting surface cracks of welds, comprising the following steps:

[0017] S1. Fabricate an indicating electrode:

[0018] (1) Measure 1.0 - 5.0 mL of 6 mol / L concentrated hydrochloric acid, and respectively weigh 0.01 - 0.03 g of hydroquinone, 0.05 - 0.2 g of thiourea, and 0.3 - 1.0 g of carboxylated graphitized carbon nanotubes. Place them successively in a mixed solvent of 100 mL of water and ethanol and ultrasonically stir for 24 hours. Evaporate the solvent at 60 °C, then mix with 0.1 - 0.5 g of solid paraffin and heat to melt. After stirring for 12 - 48 h, obtain a thiourea-functionalized carbon nanotube paraffin paste, where the volume ratio of water to ethanol in the mixed solvent of water and ethanol is 3:1;

[0019] (2) Cut a glass capillary with an inner diameter of φ 0.3 mm and a length of 2 cm, and use the capillary phenomenon to fill it with the thiourea-functionalized carbon nanotube paraffin paste. Insert a stainless steel wire with a diameter of φ 0.2 mm and a length of 3 cm from the other end as a current collector. After the carbon nanotube paraffin paste cools and solidifies, remove the excess outside the tube. Polish the electrode on suede and immerse it in a 0.1% ethanol solution of hydroxylamine hydrochloride for activation for more than 12 hours to obtain an indicating electrode;

[0020] S2. Prepare a corrosion gel;

[0021] S3. Treatment of the weld with the corrosion gel: After cleaning the surface of the weld to be measured, pour melted solid paraffin around the area of the weld to be measured to form a small pool; pour the corrosion gel for weld detection into the small pool and make the hot corrosion gel cover all positions of the weld inside the small pool. After several minutes, remove the cooled corrosion gel and observe the bottom surface of the gel. If it shows a uniform color, there are no cracks on the weld surface; if there are local stripe marks, there are cracks at the corresponding positions on the weld surface; where the weld surface is a single-layer single-pass butt weld and a straight stringer bead welding method is adopted;

[0022] S4. Evaluation of weld cracks: Place the corrosion gel treated in step S3 in reverse, keep the temperature of the corrosion gel constant at 25 °C, and make the surface of the corrosion gel in contact with the weld face upward. Use a silver / silver chloride reference electrode as the positive electrode and the indicating electrode fabricated in step S1 as the negative electrode. Make the two electrodes contact the corrosion gel without stripe marks and connect them to a potentiometer, and record the reading a1 mV; make the indicating electrode contact the stripe marks in the corrosion gel and connect it to the potentiometer, and record the reading a2 mV; compare the difference in the battery electromotive force between the defect-free area and the defective area to judge the depth of the surface cracks of the weld.

[0023] Based on the above method for detecting surface cracks of welds, the depth of the surface cracks of the weld is not less than .

[0024] The working principle of the present invention is as follows:

[0025] 1. Hydroquinone is used as an antioxidant to ensure the stability of thiourea. By mixing carboxylated graphitized carbon nanotubes and thiourea, and utilizing the mutual attraction between carboxyl and amino groups, thiourea is fixed on the surface of carboxylated graphitized carbon nanotubes. After thiourea functionalization, the carboxylated graphitized carbon nanotubes are mixed with liquid paraffin and solidified to form a sensitive film for cuprous ions, and a cuprous ion indicating electrode is fabricated. When the indicating electrode is immersed in a solution containing cuprous ions, the complexing attraction of thiourea for cuprous ions can be utilized to attract and fix cuprous ions on the surface of the sensitive film, forming an ion double layer with positive charges on one side of the indicating electrode. Therefore, the electrode potential of the indicating electrode is related to the concentration of cuprous ions in the solution. The more cuprous ions in the solution, the more positive charges on one side of the indicating electrode, the more positive the electrode potential, and the lower the electromotive force of the primary battery formed with the reference electrode.

[0026] 2. Both thiourea and o-phenanthroline derivatives are strong complexing agents for cuprous ions. Strong complexing agents for cuprous ions can significantly enhance the activity of metallic copper. When metallic copper undergoes complexing dissolution and oxidation to cuprous ions under the action of strong complexing agents such as thiourea, the generated electrons can reduce cations such as hydrogen ions and stannous ions in the solution. Moreover, since thiourea and p-tolylthiourea are corrosion inhibitors for steel, when the hot corrosion gel contacts the weld seam, the corrosion of steel is inhibited and is less reactive than copper, and basically no dissolution and oxidation occur. Therefore, the influence of ferrous ions on subsequent measurements is very small. When the hot corrosion gel contacts the gas shielded welding seam using a copper-plated solid wire, trace amounts of copper in the weld seam generated by the copper-plated solid wire will undergo complexing dissolution under the action of thiourea and o-phenanthroline derivatives. Since the metal activity at the crack is higher than that of the normal metal, the copper at the crack will preferentially undergo complexing dissolution. As a result, after the weld seam with cracks is treated with the corrosion gel, the content of cuprous ions complexed and dissolved in the corrosion gel is relatively high, showing colored stripes, thereby enabling qualitative and quantitative observation of the surface cracks of the weld seam. By measuring the electromotive force of the battery using the potentiometric method and comparing the difference in the electromotive force of the battery between the defect-free area and the defective area (i.e., the potential of the indicating electrode), the relative content of cuprous ions in the corrosion gel in the two cases can be known, and thus the depth of the surface crack can be judged.

[0027] The advantages of the present invention are as follows:

[0028] A method for detecting surface cracks in weld seams of the present invention can not only qualitatively and accurately detect the cracks on the surface of the weld seam, but also quantitatively evaluate the crack depth based on the potential analysis results by the content of cuprous ions in the corrosion gel, overcoming the defects of traditional liquid penetration testing, and playing an important role in promoting the elimination of potential safety hazards in steel structure projects. Specific embodiments

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Embodiment 1

[0031] A method for detecting surface cracks of weld seams is carried out according to the following steps:

[0032] S1. Fabricate an indicating electrode:

[0033] (1) Measure 1.0 - 5.0 mL of 6 mol / L concentrated hydrochloric acid, and respectively weigh 0.01 - 0.03 g of hydroquinone, 0.05 - 0.2 g of thiourea, and 0.3 - 1.0 g of carboxylated graphitized carbon nanotubes. Place them in turn in a mixed solvent of 100 mL of deionized water and ethanol and ultrasonically stir for 24 hours. Use a rotary evaporator to evaporate the solvent to dryness at 60 °C, then mix with 0.1 - 0.5 g of solid paraffin and heat to melt, and stir for 12 - 48 h to obtain a thiourea-functionalized carbon nanotube paraffin paste, where the volume ratio of water to ethanol in the mixed solvent of water and ethanol is 3:1;

[0034] (2) Cut a glass capillary with an inner diameter of φ 0.3 mm and a length of 2 cm, and fill it with the thiourea-functionalized carbon nanotube paraffin paste using capillary action. Insert a stainless steel wire with a diameter of φ 0.2 mm and a length of 3 cm as a current collector from the other end. After the carbon nanotube paraffin paste cools and solidifies, remove the excess outside the tube, polish the electrode on suede, and immerse it in a 0.1% ethanol solution of hydroxylamine hydrochloride for more than 12 hours to obtain an indicating electrode;

[0035] S2. Prepare a corrosion gel: Weigh 15.0 - 20.0 g of agar and dissolve it in 600 mL of boiling deionized water and stir evenly. After cooling to 60 °C, maintain the temperature constant. Dissolve 2.0 - 5.0 mL of 98% sulfuric acid, 20.0 - 50.0 mL of 10% hydroxylamine hydrochloride solution, 0.3 - 1.5 g of p-tolylthiourea, 0.1 - 0.5 g of stannous sulfate, 50.0 - 80.0 g of thiourea, and 200 mL of 10% Triton X-100 solution in turn and stir evenly, then mix evenly with 100 mL of 0.05% ethanol solution of o-phenanthroline derivative and maintain the solution at 60 °C to obtain a hot corrosion gel;

[0036] S3. Corrosion Gel Treatment of Weld: After cleaning the surface of the weld to be tested, pour molten solid paraffin around the weld area to be tested to form a small pool with a length of 5 cm, a width of 1 cm, and a height of about 1 cm. Pour 2.5 mL of corrosion gel for weld detection into the small pool and make the hot corrosion gel cover all positions of the weld inside the small pool. After 5 minutes, remove the cooled corrosion gel and observe the bottom surface of the gel. If it shows a uniform color, there are no cracks on the weld surface; if there are local stripe marks, there are cracks at the corresponding positions on the weld surface; where the weld surface is a single-layer single-pass butt weld and a straight-line stringer bead method is adopted;

[0037] S4. Weld Crack Assessment: Place the corrosion gel treated in step S3 in reverse, keep the gel temperature constant at 25 °C, and make the gel surface in contact with the weld face up. Use a micro silver / silver chloride reference electrode as the positive electrode and the indicator electrode made in step (1) as the negative electrode. Make the two electrodes contact the gel without stripe marks and connect them to a potentiometer. After standing for 2 minutes, record the reading a1 mV; then make the indicator electrode contact the stripe marks in the corrosion gel, and after standing for 2 minutes, record the reading a2 mV; then the crack depth on the weld surface is not less than .

[0038] Hydroquinone in step S1 is used as an antioxidant to ensure the stability of thiourea. By mixing carboxylated graphitized carbon nanotubes and thiourea, and using the mutual attraction between carboxyl and amino groups, thiourea is fixed on the surface of carboxylated graphitized carbon nanotubes. After thiourea functionalization, the carboxylated graphitized carbon nanotubes are mixed with liquid paraffin and solidified to form a sensitive film for cuprous ions, and a cuprous ion indicator electrode is fabricated. When the indicator electrode is immersed in a solution containing cuprous ions, the complexing attraction of thiourea for cuprous ions can be used to attract and fix cuprous ions on the surface of the sensitive film, forming an ion double layer with a positive charge on one side of the indicator electrode. Therefore, the electrode potential of the indicator electrode is related to the concentration of cuprous ions in the solution. The more cuprous ions there are in the solution, the more positive charges there are on one side of the indicator electrode, the more positive the electrode potential is, and the lower the electromotive force of the primary battery formed with the reference electrode is.

[0039] In step S2, both thiourea and the phenanthroline derivative are strong complexing agents for cuprous ions. Strong complexing agents for cuprous ions can cause the activity of metallic copper to increase sharply. When metallic copper undergoes complexation dissolution and oxidation to cuprous ions under the action of strong complexing agents such as thiourea, the electrons generated can reduce cations such as hydrogen ions and stannous ions in the solution. Moreover, since thiourea and p-tolylthiourea are corrosion inhibitors for steel, when the hot corrosion gel contacts the weld seam, the corrosion of steel is inhibited and is less reactive than copper, and basically no dissolution oxidation occurs. Therefore, the influence of ferrous ions on subsequent measurements is very small. When the acidic hot corrosion gel in step S3 contacts the gas shielded weld seam using a copper-plated solid wire, a small amount of copper in the weld seam generated by the copper-plated solid wire will undergo complexation dissolution under the action of thiourea and the phenanthroline derivative. Since the metallic activity at the crack is higher than that of the normal metal, the copper at the crack will preferentially undergo complexation dissolution. As a result, after the weld seam with cracks is treated with the corrosion gel, the content of cuprous ions complexed and dissolved in the corrosion gel is relatively high, showing colored stripes, thereby enabling qualitative and quantitative observation of the surface cracks of the weld seam. In step S4, the potentiometric method is used to measure the electromotive force of the battery, and by comparing the difference in the electromotive force of the battery between the defect-free area and the defective area (i.e., the potential of the indicating electrode), the relative content of cuprous ions in the corrosion gel in the two cases can be known, thereby judging the depth of the surface crack.

[0040] A method for detecting surface cracks in a weld seam of the present invention can not only qualitatively and accurately detect the cracks on the surface of the weld seam, but also quantitatively evaluate the crack depth based on the analysis result of the potential, by means of the content of cuprous ions in the corrosion gel, overcoming the defects of traditional liquid penetration testing, and playing an important role in promoting the elimination of potential safety hazards in steel structure projects.

[0041] Example 2

[0042] The difference between this specific embodiment and specific embodiment 1 is that the phenanthroline derivative described in step S2 is one of cuproin or bathocuproine. Others are the same as specific embodiment 1.

[0043] The following tests are used to verify that the present invention has beneficial effects when used to detect weld seams with surface cracks that have already been discovered:

[0044] Test 1: A method for detecting surface cracks in a weld seam of this test is carried out according to the following steps:

[0045] (1) Fabrication of the indicating electrode: Measure 1.0 mL of 6 mol / L concentrated hydrochloric acid, and weigh 0.01 g of hydroquinone, 0.05 g of thiourea, and 0.3 g of carboxylated graphitized carbon nanotubes respectively. Place them successively in a mixed solvent of 100 mL of deionized water and ethanol and ultrasonically stir for 24 hours. Evaporate the solvent to dryness using a rotary evaporator at 60 °C, then mix with 0.1 g of solid paraffin and heat to melt. After stirring for 12 h, a thiourea-functionalized carbon nanotube paraffin paste is obtained, where the volume ratio of water to ethanol in the mixed solvent of water and ethanol is 3:1; Cut a glass tube with an inner diameter of φ 3 mm and a length of 6 cm and fill it with the thiourea-functionalized carbon nanotube paraffin paste. Insert a clean graphite rod with a diameter of φ 2 mm and a length of 8 cm from the other end as a current collector. After the carbon nanotube paraffin paste cools and solidifies, remove the excess outside the tube. Polish the electrode on suede and immerse it in a 0.1% hydroxylamine hydrochloride ethanol solution for activation for more than 12 hours to obtain the indicating electrode;

[0046] (2) Preparation of the corrosion gel: Weigh 15.0 g of agar and dissolve it in 600 mL of boiling deionized water and stir evenly. After cooling to 60 °C, maintain the temperature constant. Dissolve 2.0 mL of 98% sulfuric acid, 20.0 mL of 10% hydroxylamine hydrochloride solution, 1.5 g of p-tolylthiourea, 0.1 g of stannous sulfate, 50.0 g of thiourea, and 200 mL of 10% Triton X-100 solution successively and stir evenly. Then mix it evenly with 100 mL of 0.05% bathocuproine ethanol solution and maintain the solution at 60 °C to obtain the hot corrosion gel;

[0047] (3) Treatment of the weld with the corrosion gel: After cleaning the surface of the weld to be tested, use molten solid paraffin to pour a small pool with a length of 5 cm, a width of 1 cm, and a height of about 1 cm around the area of the weld to be tested. Pour 2.5 mL of the hot corrosion gel obtained in step (2) into the small pool and make the hot corrosion gel cover all positions of the weld inside the small pool. After 5 minutes, remove the cooled corrosion gel and observe the bottom surface of the gel. If it shows a uniform color, there is no crack on the weld surface; if there are local stripe marks, there are cracks at the corresponding positions on the weld surface; where the weld surface is a single-layer single-pass butt weld and a straight-line stringer bead method is adopted;

[0048] (4) Weld crack assessment: Place the corrosion gel treated in step (3) in the reverse direction, keep the gel temperature constant at 25 °C, and make the gel surface in contact with the weld face upward. Use a silver / silver chloride reference electrode as the positive electrode and the indicating electrode fabricated in step (1) as the negative electrode. Make the two electrodes contact the gel without stripe marks and connect to a potentiometer. After standing for 2 minutes, record the reading of 136 mV; then make the indicating electrode contact the stripe marks in the corrosion gel. After standing for 2 minutes, record the reading of 107 mV; then the weld surface crack depth is not less than = 0.62 mm.

[0049] Experiment 2: A method for detecting surface cracks in a weld seam of this experiment is carried out according to the following steps:

[0050] (1) Fabricate an indicating electrode: Measure 2.0 mL of 6 mol / L concentrated hydrochloric acid, and separately weigh 0.02 g of hydroquinone, 0.1 g of thiourea, and 0.5 g of carboxylated graphitized carbon nanotubes. Place them successively in a mixed solvent of 100 mL of deionized water and ethanol and ultrasonically stir for 24 hours. Use a rotary evaporator to evaporate the solvent to dryness at 60 °C, then mix with 0.2 g of solid paraffin and heat to melt. After stirring for 24 h, obtain a thiourea-functionalized carbon nanotube paraffin paste, where the volume ratio of water to ethanol in the mixed solvent of water and ethanol is 3:1; Cut a 6 cm long glass tube (inner diameter φ 3 mm) and fill it with the thiourea-functionalized carbon nanotube paraffin paste. Insert an 8 cm long clean graphite rod (φ 2 mm) from the other end as a current collector. After the carbon nanotube paraffin paste cools and solidifies, remove the excess outside the tube. Polish the electrode on suede and immerse it in a 0.1% hydroxylamine hydrochloride ethanol solution for activation for more than 12 hours to obtain an indicating electrode;

[0051] (2) Prepare a corrosion gel: Weigh 18.0 g of agar and dissolve it in 600 mL of boiling deionized water and stir evenly. After cooling to 60 °C, maintain the temperature constant. Successively dissolve 3.5 mL of 98% sulfuric acid, 30.0 mL of 10% hydroxylamine hydrochloride solution, 1.0 g of p-tolylthiourea, 0.3 g of stannous sulfate, 60.0 g of thiourea, and 200 mL of 10% Triton X-100 solution and stir evenly. Then mix it evenly with 100 mL of a 0.05% ethanol solution of bathophenanthroline and maintain the solution at 60 °C to obtain a hot corrosion gel;

[0052] (3) Treatment of the weld seam with the corrosion gel: After cleaning the surface of the weld seam to be measured, use molten solid paraffin to pour a small pool with a length of 5 cm, a width of 1 cm, and a height of about 1 cm around the area of the weld seam to be measured. Pour 2.5 mL of the hot corrosion gel obtained in step (2) into the small pool and make the hot corrosion gel cover all positions of the weld seam inside the small pool. After 5 minutes, remove the cooled corrosion gel and observe the bottom surface of the gel. If it shows a uniform color, there are no cracks on the weld seam surface; if there are local stripe marks, there are cracks at the corresponding positions on the weld seam surface; where the weld seam surface is a single-layer single-pass butt weld and a straight-line stringer bead method is adopted;

[0053] (4) Weld crack assessment: Place the corrosion gel processed in step (3) in reverse, keep the gel temperature constant at 25 °C, and make the gel surface in contact with the weld face upward. Use a silver / silver chloride reference electrode as the positive electrode and the indicator electrode made in step (1) as the negative electrode. Make the two electrodes contact the gel without stripe marks and connect them to a potentiometer. After standing for 2 minutes, record the reading of 131 mV; then make the indicator electrode contact the stripe marks in the corrosion gel, and after standing for 2 minutes, record the reading of 88 mV; then the surface crack depth of the weld is not less than = 1.07 mm.

[0054] Test three: A method for detecting surface cracks of a weld in this test is carried out according to the following steps:

[0055] (1) Making the indicator electrode: Measure 5.0 mL of 6 mol / L concentrated hydrochloric acid, and respectively weigh 0.03 g of hydroquinone, 0.2 g of thiourea, and 1.0 g of carboxylated graphitized carbon nanotubes. Place them in turn in a mixed solvent of 100 mL of deionized water and ethanol and ultrasonically stir for 24 hours. Use a rotary evaporator to evaporate the solvent to dryness at 60 °C, then mix with 0.5 g of solid paraffin and heat to melt, and stir for 48 h to obtain thiourea-functionalized carbon nanotube paraffin paste, where the volume ratio of water to ethanol in the mixed solvent of water and ethanol is 3:1; Cut a glass tube with an inner diameter of φ 3 mm and a length of 6 cm and fill it with thiourea-functionalized carbon nanotube paraffin paste. Insert a clean graphite rod with a diameter of φ 2 mm and a length of 8 cm from the other end as a current collector. After the carbon nanotube paraffin paste cools and solidifies, remove the excess outside the tube, polish the electrode on suede, and immerse it in a 0.1% ethanol solution of hydroxylamine hydrochloride for more than 12 hours to obtain the indicator electrode;

[0056] (2) Preparing the corrosion gel: Weigh 20.0 g of agar and dissolve it in 600 mL of boiling deionized water and stir evenly. After cooling to 60 °C, keep the temperature constant. Dissolve 5.0 mL of 98% sulfuric acid, 50.0 mL of 10% hydroxylamine hydrochloride solution, 0.3 g of p-tolylthiourea, 0.5 g of stannous sulfate, 80.0 g of thiourea, and 200 mL of 10% Triton X-100 solution in turn and stir evenly, then mix evenly with 100 mL of 0.05% ethanol solution of bathocuproine and keep the solution at 60 °C to obtain a hot corrosion gel;

[0057] (3) Corrosion gel treatment of the weld: After cleaning the surface of the weld to be tested, molten solid paraffin is used to pour a small pool with a length of 5 cm, a width of 1 cm, and a height of about 1 cm around the area of the weld to be tested. Pour 2.5 mL of the hot corrosion gel obtained in step (2) into the inside of the small pool and make the hot corrosion gel cover all positions of the weld inside the small pool. After 5 minutes, remove the cooled corrosion gel and observe the bottom surface of the gel. If it shows a uniform color, there are no cracks on the weld surface; if there are local stripe marks, there are cracks at the corresponding positions on the weld surface; wherein the weld surface is a single-layer single-pass butt weld and a straight-line stringer bead method is adopted;

[0058] (4) Weld crack assessment: Place the corrosion gel treated in step (3) in reverse, keep the gel temperature constant at 25 °C, and make the gel surface in contact with the weld face up. Use a silver / silver chloride reference electrode as the positive electrode and the indicating electrode made in step (1) as the negative electrode. Make the two electrodes contact the gel without stripe marks and connect them to a potentiometer. After standing for 2 minutes, record the reading of 137 mV; then make the indicating electrode contact the stripe marks in the corrosion gel, and after standing for 2 minutes, record the reading of 101 mV; then the depth of the crack on the weld surface is not less than = 0.82 mm.

[0059] For the defective welds in Tests 1 to 3, the comparison results of the surface crack depths obtained by the present invention and those obtained by a laser displacement sensor are summarized in Table 1 as follows:

[0060]

[0061] As can be seen from Table 1, the results obtained by the present invention are basically the same as those obtained by the laser displacement sensor, indicating that the detection results of the present invention for the surface cracks of the weld are accurate, and can provide the three-dimensional distribution of the surface cracks of the weld, effectively detecting the detailed information of the cracks.

[0062] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A corrosion gel for weld inspection, characterized in that, It includes the following raw materials: 15.0 - 20.0 g of agar, 600 mL of water, 2.0 - 5.0 mL of 98% sulfuric acid, 20.0 - 50.0 mL of 10% hydroxylamine hydrochloride solution, 0.3 - 1.5 g of p-tolylthiourea, 0.1 - 0.5 g of stannous sulfate, 50.0 - 80.0 g of thiourea, 200 mL of 10% Triton X-100 solution, and 100 mL of 0.05% ethanol solution of o-phenanthroline derivative.

2. The corrosion gel for weld detection according to claim 1, characterized in that: The o-phenanthroline derivative is one of cuproin or bathophenanthroline.

3. The method for preparing the corrosion gel for weld detection according to claim 1 or 2, characterized in that It includes the following steps: (1) Weigh 15.0 - 20.0 g of agar, dissolve it in 600 mL of boiling water and stir evenly. After cooling to 60 °C, maintain the temperature constant. (2) Sequentially add 2.0 - 5.0 mL of 98% sulfuric acid, 20.0 - 50.0 mL of 10% hydroxylamine hydrochloride solution, 0.3 - 1.5 g of p-tolylthiourea, 0.1 - 0.5 g of stannous sulfate, 50.0 - 80.0 g of thiourea, and 200 mL of 10% Triton X-100 solution to step (1) and stir evenly. (3) Add 100 mL of 0.05% ethanol solution of o-phenanthroline derivative to step (2), mix evenly and maintain the solution at 60 °C to obtain a hot corrosion gel.

4. A corrosion method for detecting surface cracks in welds, characterized in that It includes the step of corroding the weld with the corrosion gel for weld detection described in claim 1: After cleaning the surface of the weld to be tested, use molten solid paraffin to pour a small pool around the area of the weld to be tested; pour the corrosion gel for weld detection into the small pool and make the hot corrosion gel cover all positions of the weld inside the small pool. After several minutes, remove the cooled corrosion gel and observe the bottom surface of the gel. If it shows a uniform color, there is no crack on the weld surface; if there are local stripe marks, there are cracks at the corresponding positions on the weld surface; where the weld surface is a single-layer single-pass butt weld and a straight-line stringer bead method is adopted.

5. A method for detecting surface cracks in weld seams, characterized in that, It includes the following steps: S1. Fabricate an indicator electrode: (1) Measure 1.0 - 5.0 mL of 6 mol / L concentrated hydrochloric acid, and respectively weigh 0.01 - 0.03 g of hydroquinone, 0.05 - 0.2 g of thiourea, and 0.3 - 1.0 g of carboxylated graphitized carbon nanotubes. Place them in turn in a mixed solvent of 100 mL of water and ethanol and ultrasonically stir for 24 hours. Evaporate the solvent at 60 °C, then mix with 0.1 - 0.5 g of solid paraffin and heat to melt. After stirring for 12 - 48 h, obtain a thiourea-functionalized carbon nanotube paraffin paste, where the volume ratio of water to ethanol in the mixed solvent of water and ethanol is 3:

1. (2) Cut a glass capillary with an inner diameter of φ 0.3 mm and a length of 2 cm, and fill it with the thiourea-functionalized carbon nanotube paraffin paste using capillary action. Insert a stainless steel wire with a diameter of φ 0.2 mm and a length of 3 cm as a current collector from the other end. After the carbon nanotube paraffin paste cools and solidifies, remove the excess outside the tube. Polish the electrode on suede and immerse it in 0.1% ethanol solution of hydroxylamine hydrochloride for activation for more than 12 hours to obtain an indicator electrode. S2. Prepare the etching gel according to the preparation method described in claim 3; S3. Etching gel treatment of the weld: After cleaning the surface of the weld to be tested, pour molten solid paraffin around the area of the weld to be tested to form a small pool; pour the etching gel for weld inspection into the small pool and make the hot etching gel cover all positions of the weld inside the small pool. After several minutes, remove the cooled etching gel and observe the bottom surface of the gel. If it shows a uniform color, there are no cracks on the weld surface; if there are local stripe marks, there are cracks at the corresponding positions on the weld surface. The weld surface is a single-layer single-pass butt weld and the linear weaving method is adopted; S4. Weld crack assessment: Place the etching gel processed in step S3 in reverse, keep the temperature of the etching gel constant at 25 °C, and make the surface of the etching gel in contact with the weld face upward. Use a silver / silver chloride reference electrode as the positive electrode and the indicator electrode made in step S1 as the negative electrode. Make the two electrodes contact the etching gel without stripe marks and connect them to a potentiometer, and record the reading a1 mV; make the indicator electrode contact the stripe marks in the etching gel and connect it to the potentiometer, and record the reading a2 mV; compare the difference in the cell electromotive force between the defect-free area and the defective area to judge the depth of the crack on the weld surface.

6. The weld surface crack detection method according to claim 5, wherein: The depth of the crack on the weld surface is not less than .

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