Nondestructive testing method for solid solution state of 18Cr-8Ni series austenitic stainless steel elbow

Abstract

The invention discloses a nondestructive testing method for the solid solution state of 18Cr-8Ni series austenitic stainless steel bent pipes. The nondestructive testing method comprises the steps that S1, the 18Cr-8Ni series austenitic stainless steel bent pipes with the bending angle being theta are selected; s2, setting relative permeability detector parameters; s3, uniformly selecting a plurality of detection angles alpha in a range of 0-theta; s4, respectively testing the relative permeability of the detection points corresponding to different detection angles alpha of the 18Cr-8Ni series austenitic stainless steel elbow pipe, and simultaneously testing the relative permeability of the 18Cr-8Ni series austenitic stainless steel elbow pipe at the maximum deformation quantity theta / 2; and S5, according to the relative permeability, measured in the step S4, of the 18Cr-8Ni series austenitic stainless steel bent pipe, judging whether the bent pipe is subjected to solid solution or not. According to the nondestructive testing method for the solid solution state of the 18Cr-8Ni series austenitic stainless steel bent pipe, the problem that the austenitic stainless steel bent pipe needs to be subjected to destructive sampling in an existing detection technology is solved.

Description

Technical Field

[0001] This invention belongs to the field of austenitic stainless steel testing technology, specifically relating to a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bent pipes. Background Technology

[0002] 18Cr-8Ni series austenitic stainless steel is widely used in high-temperature pressure-bearing components such as high-temperature superheaters and high-temperature reheaters in power plant boilers due to its fine grain structure, excellent resistance to intergranular corrosion and good fatigue performance. Its maximum operating temperature can reach 700℃.

[0003] According to DL / T 438-2023 "Technical Supervision Regulations for Metals in Thermal Power Plants," austenitic heat-resistant steel requires solution treatment if the bending radius is less than 2.5D (where D is the diameter of the steel pipe) after cold bending. Furthermore, ASME BPVC I - 2015 "Rules for Construction of Power Boilers" also stipulates that when austenitic stainless steel is operated within the design temperature range of 540℃ to 675℃, if the post-cold working strain value is greater than 15% (i.e., the bending radius is less than 3.3D), solution treatment at a temperature above 1175℃ is required.

[0004] Currently, commonly used laboratory methods for detecting the solution-treated state of austenitic stainless steel bends include metallographic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical corrosion testing. However, these methods have certain limitations in practical applications: metallographic analysis, XRD, SEM, and electrochemical corrosion testing all require destructive sampling of the bend. Summary of the Invention

[0005] The purpose of this invention is to provide a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, which solves the problem that existing testing technologies require destructive sampling of austenitic stainless steel bends.

[0006] The technical solution adopted in this invention is: a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bent pipes, the specific method of which is as follows: S1. Select 18Cr-8Ni series austenitic stainless steel bends with a bending angle of θ. S2. Set the parameters of the relative permeability detector; S3. Select several detection angles α uniformly within the range of 0-θ; S4. Test the relative permeability of the test points corresponding to different test angles α of the 18Cr-8Ni series austenitic stainless steel bend, and at the same time test the relative permeability at the maximum deformation θ / 2 of the 18Cr-8Ni series austenitic stainless steel bend. S5. Determine whether the bend has been solution-treated based on the relative magnetic permeability of the 18Cr-8Ni series austenitic stainless steel bend measured in S4.

[0007] The invention is further characterized by: The 18Cr-8Ni series austenitic stainless steel bends selected in S1 include TP347HFG austenitic stainless steel, TP347H austenitic stainless steel, and SUPER 304H austenitic stainless steel.

[0008] The parameters set for the relative permeability meter in S2 are as follows: The excitation field strength was 30 kA / m, the measurement mode was relative permeability μr, and the detection error was (μr-1)×5%.

[0009] In the relative permeability testing process of S4, the probe of the relative permeability tester is set perpendicular to the outer arc surface of the 18Cr-8Ni series austenitic stainless steel bend.

[0010] The relative permeability of each detection point in S4 needs to be tested 3 to 5 times. The average value of the test results for each detection point is the relative permeability of that detection point.

[0011] The specific criteria for determining whether solution treatment has been performed in S5 are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the maximum relative permeability of the 18Cr-8Ni series austenitic stainless steel bend exceeds 1.007, it indicates that the 18Cr-8Ni series austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the 18Cr-8Ni series austenitic stainless steel bend is not greater than 1.005, it indicates that the 18Cr-8Ni series austenitic stainless steel bend has undergone solution treatment. The specific criteria for determining whether TP347HFG austenitic stainless steel has undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the TP347HFG austenitic stainless steel bend exceeds 1.009, it indicates that the TP347HFG austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the TP347HFG austenitic stainless steel bend is not greater than 1.005, it indicates that the TP347HFG austenitic stainless steel bend has undergone solution treatment.

[0012] The specific criteria for determining whether SUPER 304H austenitic stainless steel has undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the SUPER 304H austenitic stainless steel bend exceeds 1.007, it indicates that the SUPER 304H austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the SUPER 304H austenitic stainless steel bend is not greater than 1.005, it indicates that the SUPER 304H austenitic stainless steel bend has undergone solution treatment. The specific criteria for determining whether TP347H austenitic stainless steel bends have undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the TP347H austenitic stainless steel bend exceeds 1.009, it indicates that the TP347H austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the TP347H austenitic stainless steel bend is not greater than 1.005, it indicates that the TP347H austenitic stainless steel bend has undergone solution treatment. The beneficial effects of this invention are as follows: (1) The non-destructive testing method for the solid solution state of 18Cr-8Ni series austenitic stainless steel bent pipe of the present invention can determine whether the bent pipe is solid solution by detecting the relative magnetic permeability of the outer arc of the bent pipe and comparing the value distribution of the test results with the value of the maximum value with the threshold value. (2) The non-destructive testing method for the solid solution state of 18Cr-8Ni series austenitic stainless steel bends of the present invention does not require destructive sampling of the sample, can preserve the integrity of the bend, and has the characteristics of low cost, simple and quick operation, and high precision, which can significantly improve the testing efficiency. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the TP347HFG austenitic stainless steel bend in Embodiment 1 of the nondestructive testing method of the present invention; Figure 2 This is a graph showing the relative permeability test results of a TP347HFG austenitic stainless steel bend with a bending radius of 2D in Example 1 of the non-destructive testing method of the present invention. Figure 3This is a graph showing the relative permeability test results of a TP347HFG austenitic stainless steel bend with a bending radius of 3D in Example 2 of the non-destructive testing method of the present invention. Figure 4 This is a graph showing the relative permeability test results of a TP347HFG austenitic stainless steel bend with a bending radius of 4D in Example 3 of the non-destructive testing method of the present invention. Figure 5 This is a graph showing the relative permeability test results of a SUPER 304H austenitic stainless steel bend with a bending radius of 2D in Example 4 of the non-destructive testing method of the present invention. Figure 6 This is a graph showing the relative permeability test results of a SUPER 304H austenitic stainless steel bend with a bending radius of 3D in Example 5 of the non-destructive testing method of the present invention. Figure 7 This is a graph showing the relative permeability test results of a SUPER 304H austenitic stainless steel bend with a bending radius of 4D in Example 6 of the non-destructive testing method of the present invention. Figure 8 This is a graph showing the relative magnetic permeability test results of a TP347H austenitic stainless steel bend with a bending radius of 2D in Example 7 of the non-destructive testing method of the present invention. Detailed Implementation

[0014] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0015] This invention provides a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, the specific method being as follows: S1. Select 18Cr-8Ni series austenitic stainless steel bends with a bending angle of θ, such as... Figure 1 As shown; the 18Cr-8Ni series austenitic stainless steel bends selected in this invention include TP347HFG austenitic stainless steel, TP347H austenitic stainless steel, and SUPER 304H austenitic stainless steel.

[0016] Similarly, the non-destructive testing method of the present invention is also applicable to S301 austenitic stainless steel, S304 austenitic stainless steel, S316 austenitic stainless steel, S321 austenitic stainless steel, etc.

[0017] S2. Set the parameters of the relative permeability meter; the parameters for the relative permeability meter are as follows: The excitation field strength was 30 kA / m, the measurement mode was relative permeability μr, and the detection error was (μr-1)×5%.

[0018] S3. Select several detection angles α uniformly within the range of 0-θ; among them, the measurement points include the location of the maximum deformation of the 18Cr-8Ni series austenitic stainless steel bend (e.g., Figure 1 (as shown at θ=45°) and the lowest point of the bend (as shown) Figure 1 (As shown at θ=0° and θ=90°).

[0019] The greater the deformation of a stainless steel pipe, the more martensite is induced, resulting in a higher relative permeability. Therefore, the maximum relative permeability will only occur at the location of maximum deformation. In practice, the maximum deformation may occur near θ / 2. Multiple measurements can be taken near θ / 2 to find the maximum relative permeability.

[0020] S4. Test the relative permeability of the test points corresponding to different test angles α of the 18Cr-8Ni series austenitic stainless steel bend, and at the same time test the relative permeability at the maximum deformation θ / 2 of the 18Cr-8Ni series austenitic stainless steel bend. Furthermore, during the S4 detection process, the probe is set perpendicular to the outer arc surface of the 18Cr-8Ni series austenitic stainless steel bend.

[0021] The relative permeability of each detection point needs to be tested 3 to 5 times. The average value of the test results for each detection point is the relative permeability of that detection point.

[0022] S5. Determine whether the bend has been solution-treated based on the relative magnetic permeability of the 18Cr-8Ni series austenitic stainless steel bend measured in S4.

[0023] The specific criteria for determining whether 18Cr-8Ni series austenitic stainless steel bends have undergone solution treatment are as follows: On the one hand, several data obtained by measuring the bend at different detection angles α through S4 conform to a normal distribution. On the other hand, the relative permeability at the maximum deformation θ / 2 of the 18Cr-8Ni series austenitic stainless steel bend exceeds 1.007, indicating that the 18Cr-8Ni series austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the 18Cr-8Ni series austenitic stainless steel bend is not greater than 1.005, it indicates that the 18Cr-8Ni series austenitic stainless steel bend has undergone solution treatment. Furthermore, the specific criteria for determining whether TP347HFG austenitic stainless steel has undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the TP347HFG austenitic stainless steel bend exceeds 1.009, it indicates that the TP347HFG austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the TP347HFG austenitic stainless steel bend is not greater than 1.005, it indicates that the TP347HFG austenitic stainless steel bend has undergone solution treatment. The specific criteria for determining whether SUPER 304H austenitic stainless steel has undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the SUPER 304H austenitic stainless steel bend exceeds 1.007, it indicates that the SUPER 304H austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the SUPER 304H austenitic stainless steel bend is not greater than 1.005, it indicates that the SUPER 304H austenitic stainless steel bend has undergone solution treatment. The specific criteria for determining whether TP347H austenitic stainless steel bends have undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the TP347H austenitic stainless steel bend exceeds 1.80, it indicates that the TP347H austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the TP347H austenitic stainless steel bend is not greater than 1.005, it indicates that the TP347H austenitic stainless steel bend has undergone solution treatment.

[0024] In this invention, the effects of different materials and bending radii on relative permeability vary significantly. The relative permeability at point C differs for the same material with different bending radii, and the relative permeability at point C differs for different materials with the same bending radii. It is necessary to combine actual measurement results to make a judgment.

[0025] The non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends in this invention is based on the principle of weak magnetic detection. This invention proposes a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends based on weak magnetic properties. This method determines whether the bend has undergone solution treatment by detecting changes in the weak magnetic properties of the surface. Due to the instability of the austenitic structure, paramagnetic austenite is prone to ε-M (hcp) and α-M (bcc) phase transformations under bending strain conditions, resulting in weak magnetism in the stainless steel, especially at the bend core where strain is greatest and weak magnetism is strongest. During solution treatment, deformation-induced martensite, δ-ferrite, and carbide phases in the austenitic matrix redissolve, making the microstructure more homogeneous. At the bend core, the stress-induced martensite and other magnetic phases redissolve after solution treatment, restoring the austenitic state to near-original levels, and its relative permeability returns to the level of straight pipes. Specifically, the strain-induced martensite and other magnetic phases generated during cold bending enhance magnetism, while these phases redissolve after solution treatment, weakening the magnetism.

[0026] By comparing the relative permeability of the bent pipe and the straight pipe, it is possible to quickly and accurately determine whether the bent pipe has undergone solution treatment. If several data points measured at different detection angles α on the outer arc of the bent pipe conform to a normal distribution, and the maximum relative permeability exceeds 1.007, it indicates that the austenitic stainless steel bent pipe has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the maximum relative permeability is not greater than 1.005, it indicates that the austenitic stainless steel bent pipe has undergone solution treatment. By comparing the relative permeability of the bent pipe and the straight pipe, it is possible to quickly and accurately determine whether the bent pipe has undergone solution treatment. This detection method is a non-destructive testing method.

[0027] This invention's testing process does not require damage to the sample, preserving the integrity of the bend, making it particularly suitable for testing finished TP347HFG austenitic stainless steel bends. Using a FerroPro compact permeability meter with an FPC-5 probe, the testing process is simple and quick, suitable for on-site operation. The scanning function performs multi-point testing on the outer arc section of the bend, automatically recording data and generating curves, improving testing efficiency.

[0028] This invention's detection method exhibits high sensitivity to changes in the solution-treated state, accurately distinguishing the state before and after solution treatment. Precise determination is achieved by comparing the distribution characteristics of relative magnetic permeability (normal distribution or stable value). It is applicable to TP347HFG austenitic stainless steel bends with different bending radii (bending radius less than 3.3D) as specified in ASME BPCV I-2015 and DL / T 438-2023, demonstrating broad engineering applicability. It can be extended to the solution-treated state detection of other austenitic stainless steel materials. This invention's detection method provides a standardized testing process from sample pretreatment and equipment calibration to data comparison, ensuring the reliability and consistency of the test results.

[0029] Example 1 This embodiment describes a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, which is implemented according to the following steps: Step 1: Select two TP347HFG austenitic stainless steel pipe samples with a bending angle of 90°, an outer diameter of 60mm, a wall thickness of 4mm, a length of 440mm, a bending radius of 2D (120mm), a bending method of cold bending, and a bending arc length of 188.4mm for testing. One of the steel pipes has undergone solution treatment (treatment temperature of 1180℃, holding time of 10min, using oil quenching and rapid cooling method), while the other steel pipe has not undergone solution treatment.

[0030] Step 2: Use a FerroPro compact permeability meter with an FPC-5 probe to characterize the weak magnetism of the sample. Set the excitation field strength to 30 kA / m, the measurement mode to relative permeability (μr), and the detection error to (μr-1)×5%. After installing the probe, calibrate the instrument to ensure that the relative permeability of the probe is 0 in the vertical state in air. Then, use a standard test block with a relative permeability of 1.380 for calibration.

[0031] Step 3: Use the scanning function to inspect the middle section of the outer arc of the bend in both the solution-treated and untreated samples. The inspection range is arc segment AB. After starting the inspection, slowly move the probe from point A to point B, and evenly select 11 inspection points with angles of 0°, 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70°, 80°, and 90°. Use the outer arc position corresponding to the selected angle as the inspection point for relative permeability. Use the scanning function to inspect the relative permeability of the two bends. Move the probe along the outer arc of the stainless steel bend in the direction of its extension. Measure the relative permeability of each inspection point three times and take the average of the three measurements. During the inspection, ensure that the probe is perpendicular to the bend surface.

[0032] Step 4: Measure the weak magnetic properties of the solution-treated and untreated samples as follows: Figure 2 As shown, through Figure 2 It can be seen that the relative permeability of the middle section of the outer arc of the untreated bent pipe exhibits a normal curve distribution from point A to point B, first increasing and then decreasing. The relative permeability at points A and B are 1.004 and 1.003, respectively, while the relative permeability at point C (the point of maximum strain) is the highest, at 1.025. In contrast, the relative permeability of the middle section of the outer arc of the treated bent pipe remains consistently within the range of 1.003-1.005 from point A to point B, consistent with the relative permeability in air, and the curve shows no significant fluctuations.

[0033] To determine whether a TP347HFG austenitic stainless steel bend with a bending radius of 2D has undergone solution treatment: Characterization based on weak magnetic properties analysis shows that if the relative permeability of the middle section of the outer arc within a 90° range is close to the relative permeability of air (μr ≤ 1.005), it indicates that the pipe has undergone solution treatment. If the relative permeability exhibits a normal distribution and the maximum relative permeability reaches 1.02 ± 0.001, it indicates that the pipe has not undergone solution treatment.

[0034] Example 2 This embodiment describes a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, which is implemented according to the following steps: Step 1: Select two TP347HFG austenitic stainless steel pipe samples with a bending angle of 90°, a wall thickness of 4mm, a length of 540mm, a bending radius of 3D (180mm), a bending method of cold bending, and a bending arc length of 282.6mm for testing. One of the steel pipes has undergone solution treatment (treatment temperature of 1180℃, holding time of 10min, using oil quenching and rapid cooling method), while the other steel pipe has not undergone solution treatment.

[0035] Step 2: Use a FerroPro compact permeability meter with an FPC-5 probe to characterize the weak magnetism of the sample. Set the excitation field strength to 30 kA / m, the measurement mode to relative permeability (μr), and the detection error to (μr-1)×5%. After installing the probe, calibrate the instrument to ensure that the relative permeability of the probe is 0 in the vertical state in air. Then, use a standard test block with a relative permeability of 1.380 for calibration.

[0036] Step 3: Use the scanning function to inspect the middle section of the outer arc of the bend in both the solution-treated and untreated samples. The inspection range is arc segment AB. After starting the inspection, slowly move the probe from point A to point B, and evenly select 11 inspection points with angles of 0°, 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70°, 80°, and 90°. Use the outer arc position corresponding to the selected angle as the inspection point for relative permeability. Use the scanning function to inspect the relative permeability of the two bends. Move the probe along the outer arc of the stainless steel bend in the direction of its extension. Measure the relative permeability of each inspection point three times and take the average of the three measurements. During the inspection, ensure that the probe is perpendicular to the bend surface.

[0037] Step 4: Measure the weak magnetic properties of the solution-treated and untreated samples as follows: Figure 3 As shown, through Figure 3It can be seen that the relative permeability of the middle section of the outer arc of the untreated bent pipe exhibits a normal curve distribution from point A to point B, first increasing and then decreasing. The relative permeability at points A and B are 1.004 and 1.003, respectively, while the relative permeability at point C (the point of maximum strain) is the largest, at 1.010. In contrast, the relative permeability of the middle section of the outer arc of the treated bent pipe remains consistently within the range of 1.003-1.004 from point A to point B, consistent with the relative permeability in air, and the curve shows no significant fluctuations.

[0038] To determine whether a TP347HFG austenitic stainless steel bend with a bending radius of 3D has undergone solution treatment: Characterization based on weak magnetic field studies shows that if the relative permeability of the middle section of the outer arc within a 90° range is close to the relative permeability of air (μr ≤ 1.005), it indicates that the pipe has undergone solution treatment. If the relative permeability exhibits a normal distribution and the maximum relative permeability reaches 1.010 ± 0.001, it indicates that the pipe has not undergone solution treatment.

[0039] Example 3 This embodiment describes a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, which is implemented according to the following steps: Step 1: Select two TP347HFG austenitic stainless steel pipe samples with a bending angle of 90°, a wall thickness of 4mm, a length of 630mm, a bending radius of 4D (240mm), a bending method of cold bending, and a bending arc length of 376.8mm for testing. One of the steel pipes has undergone solution treatment (treatment temperature of 1180℃, holding time of 10min, using oil quenching and rapid cooling method), while the other steel pipe has not undergone solution treatment.

[0040] The operation methods for steps 2 and 3 are the same as those in Example 1.

[0041] Step 4: Measure the weak magnetic properties of the solution-treated and untreated samples as follows: Figure 4 As shown, through Figure 4 It can be seen that the relative permeability of the middle section of the outer arc of the untreated bent pipe exhibits a normal curve distribution from point A to point B, first increasing and then decreasing. The relative permeability at points A and B are 1.002 and 1.003, respectively, while the relative permeability at point C (the point of maximum strain) is the largest, at 1.009. In contrast, the relative permeability of the middle section of the outer arc of the treated bent pipe remains consistently within the range of 1.002-1.003 from point A to point B, consistent with the relative permeability in air, and the curve shows no significant fluctuations.

[0042] To determine whether a TP347HFG austenitic stainless steel bend with a bending radius of 4D has undergone solution treatment: Characterization based on weak magnetic properties analysis shows that if the relative permeability of the outer arc section within a 90° range is close to the relative permeability of air (μr ≤ 1.005), the pipe has undergone solution treatment. If the relative permeability exhibits a normal distribution and the maximum relative permeability reaches 1.009 ± 0.001, the pipe has not undergone solution treatment.

[0043] Example 4 This embodiment describes a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, which is implemented according to the following steps: Step 1: Select two SUPER 304H austenitic stainless steel pipe samples with a bending angle of 90°, a wall thickness of 4mm, a length of 440mm, a bending radius of 2D (120mm), a bending method of cold bending, and a bending arc length of 376.8mm for testing. One of the steel pipes has undergone solution treatment (treatment temperature of 1100℃, holding time of 10min, using oil quenching method), while the other steel pipe has not undergone solution treatment.

[0044] The operation methods for steps 2 and 3 are the same as those in Example 1.

[0045] Step 4: Measure the weak magnetic properties of the solution-treated and untreated samples as follows: Figure 5 As shown, through Figure 5 It can be seen that the relative permeability of the middle section of the outer arc of the untreated bent pipe exhibits a normal curve distribution from point A to point B, first increasing and then decreasing. The relative permeability at points A and B are 1.002 and 1.003, respectively, while the relative permeability at point C (the point of maximum strain) is the largest, at 1.010. In contrast, the relative permeability of the middle section of the outer arc of the treated bent pipe remains consistently within the range of 1.002-1.005 from point A to point B, consistent with the relative permeability in air, and the curve shows no significant fluctuations.

[0046] To determine whether a SUPER 304H austenitic stainless steel bend with a bending radius of 2D has undergone solution treatment: Characterization based on weak magnetic field studies shows that if the relative permeability of the middle section of the outer arc within a 90° range is close to the relative permeability of air (μr ≤ 1.005), it indicates that the pipe has undergone solution treatment. If the relative permeability exhibits a normal distribution and the maximum relative permeability reaches 1.010 ± 0.001, it indicates that the pipe has not undergone solution treatment.

[0047] Example 5 This embodiment describes a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, which is implemented according to the following steps: Step 1: Select two SUPER 304H austenitic stainless steel pipe samples with a bending angle of 90°, a wall thickness of 4mm, a length of 630mm, a bending radius of 3D (180mm), a bending method of cold bending, and a bending arc length of 282.6mm for testing. One of the steel pipes has undergone solution treatment (treatment temperature of 1100℃, holding time of 10min, using oil quenching method), while the other steel pipe has not undergone solution treatment.

[0048] The operation methods for steps 2 and 3 are the same as those in Example 1.

[0049] Step 4: Measure the weak magnetic properties of the solution-treated and untreated samples as follows: Figure 6 As shown, through Figure 6 It can be seen that the relative permeability of the middle section of the outer arc of the untreated bent pipe exhibits a normal curve distribution from point A to point B, first increasing and then decreasing. The relative permeability at points A and B are 1.002 and 1.002, respectively, while the relative permeability at point C (the point of maximum strain) is the largest, at 1.008. In contrast, the relative permeability of the middle section of the outer arc of the treated bent pipe remains consistently within the range of 1.002-1.005 from point A to point B, with a measurement error range of ±0.001, consistent with the relative permeability in air, and the curve shows no significant fluctuations.

[0050] On the one hand, the test results show that the deformation-induced magnetism of SUPER 304H austenitic stainless steel is small, and the measured value of 1.001 is normal; on the other hand, the relative permeability measurement results will have a certain error, with an error range of ±0.001. Figure 6 The minimum measured value is 1.001, which is within the error range. Austenitic stainless steel has internal stress and more or less undergoes martensitic induced transformation, so it cannot be lower than the maximum relative permeability of 1.002 in air (the relative permeability of air is 1.000-1.002). Considering the actual measurement error, the relative permeability of the middle section of the outer arc of the solution-treated bend in this embodiment remains within the range of 1.002-1.005 from point A to point B.

[0051] To determine whether a SUPER 304H austenitic stainless steel bend with a bending radius of 3D has undergone solution treatment: Characterization based on weak magnetic field studies shows that if the relative permeability of the middle section of the outer arc within a 90° range is close to the relative permeability of air (μr ≤ 1.005), it indicates that the pipe has undergone solution treatment. If the relative permeability exhibits a normal distribution and the maximum relative permeability reaches 1.008 ± 0.001, it indicates that the pipe has not undergone solution treatment.

[0052] Example 6 This embodiment describes a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, which is implemented according to the following steps: Step 1: Select two SUPER 304H austenitic stainless steel pipe samples with a bending angle of 90°, a wall thickness of 4mm, a length of 630mm, a bending radius of 4D (240mm), a bending method of cold bending, and a bending arc length of 376.8mm for testing. One of the steel pipes has undergone solution treatment (treatment temperature of 1100℃, holding time of 10min, using oil quenching method), while the other steel pipe has not undergone solution treatment.

[0053] The operation methods for steps 2 and 3 are the same as those in Example 1.

[0054] Step 4: Measure the weak magnetic properties of the solution-treated and untreated samples as follows: Figure 7 As shown, through Figure 7 It can be seen that the relative permeability of the middle section of the outer arc of the untreated bent pipe exhibits a normal curve distribution from point A to point B, first increasing and then decreasing. The relative permeability at points A and B are 1.001 and 1.002, respectively, while the relative permeability at point C (the point of maximum strain) is the largest, at 1.007. In contrast, the relative permeability of the middle section of the outer arc of the treated bent pipe remains consistently within the range of 1.001-1.003 from point A to point B, with a measurement error range of ±0.001, consistent with the relative permeability in air, and the curve shows no significant fluctuations.

[0055] To determine whether a SUPER 304H austenitic stainless steel bend with a bending radius of 4D has undergone solution treatment: Characterization based on weak magnetic field studies shows that if the relative permeability of the middle section of the outer arc within a 90° range is close to the relative permeability of air (μr ≤ 1.005), it indicates that the pipe has undergone solution treatment. If the relative permeability exhibits a normal distribution and the maximum relative permeability reaches 1.007 ± 0.001, it indicates that the pipe has not undergone solution treatment.

[0056] Example 7 This embodiment describes a non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bends, which is implemented according to the following steps: Step 1: Select two TP347H austenitic stainless steel pipe samples with a bending angle of 90°, a wall thickness of 4mm, a length of 440mm, a bending radius of 2D (120mm), a bending method of cold bending, and a bending arc length of 376.8mm for testing. One of the steel pipes has undergone solution treatment (treatment temperature of 1150℃, holding time of 10min, using oil quenching method), while the other steel pipe has not undergone solution treatment.

[0057] The operation methods for steps 2 and 3 are the same as those in Example 1.

[0058] Step 4: Measure the weak magnetic properties of the solution-treated and untreated samples as follows: Figure 8 As shown, through Figure 8 It can be seen that the relative permeability of the middle section of the outer arc of the untreated bent pipe exhibits a normal curve distribution from point A to point B, first increasing and then decreasing. The relative permeability at points A and B are 1.04 and 1.03, respectively, while the relative permeability at point C (the point of maximum strain) is the highest, at 1.86. In contrast, the relative permeability of the middle section of the outer arc of the treated bent pipe remains consistently within the range of 1.002-1.003 from point A to point B, consistent with the relative permeability in air, and the curve shows no significant fluctuations.

[0059] To determine whether a TP347H austenitic stainless steel bend with a bending radius of 2D has undergone solution treatment: Characterization based on weak magnetic properties analysis shows that if the relative permeability of the middle section of the outer arc within a 90° range is close to the relative permeability of air (μr ≤ 1.005), it indicates that the pipe has undergone solution treatment. If the relative permeability exhibits a normal distribution and the maximum relative permeability reaches 1.86 ± 0.001, it indicates that the pipe has not undergone solution treatment.

Claims

1. 18Cr-8Ni series austenitic stainless steel bends in solution-treated state non-destructive testing method, characterized in that, The specific method is as follows: S1. Select 18Cr-8Ni series austenitic stainless steel bends with a bending angle of θ. S2. Set the parameters of the relative permeability detector; S3. Select several detection angles α uniformly within the range of 0-θ; S4. Test the relative permeability of the test points corresponding to different test angles α of the 18Cr-8Ni series austenitic stainless steel bend, and at the same time test the relative permeability at the maximum deformation θ / 2 of the 18Cr-8Ni series austenitic stainless steel bend. S5. Determine whether the bend has been solution-treated based on the relative magnetic permeability of the 18Cr-8Ni series austenitic stainless steel bend measured in S4.

2. The non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bent pipes according to claim 1, characterized in that, The 18Cr-8Ni series austenitic stainless steel bends selected in S1 include TP347HFG austenitic stainless steel, TP347H austenitic stainless steel, and SUPER 304H austenitic stainless steel.

3. The non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bent pipes according to claim 1, characterized in that, The parameters set for the relative permeability detector in S2 are as follows: The excitation field strength was 30 kA / m, the measurement mode was relative permeability μr, and the detection error was (μr-1)×5%.

4. The non-destructive testing method for the solution-treated state of 18Cr-8Ni series austenitic stainless steel bent pipes according to claim 3, characterized in that, In the S4 process of relative permeability detection, the probe of the relative permeability detector is set perpendicular to the outer arc surface of the 18Cr-8Ni series austenitic stainless steel bend.

5. The non-destructive testing method for the solution-treated state of 18Cr-8Ni austenitic stainless steel bent pipe according to claim 4, characterized in that, The relative permeability of each detection point in S4 needs to be tested 3 to 5 times. The average value of the test results of each detection point is the relative permeability of that detection point.

6. The non-destructive testing method for the solution-treated state of 18Cr-8Ni austenitic stainless steel bent pipe according to claim 2, characterized in that, The specific criteria for determining whether solution treatment has been performed in S5 are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the maximum relative permeability of the 18Cr-8Ni series austenitic stainless steel bend exceeds 1.007, it indicates that the 18Cr-8Ni series austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the 18Cr-8Ni series austenitic stainless steel bend is not greater than 1.005, it indicates that the 18Cr-8Ni series austenitic stainless steel bend has undergone solution treatment.

7. The non-destructive testing method for the solution-treated state of 18Cr-8Ni austenitic stainless steel bent pipes according to claim 6, characterized in that, The specific criteria for determining whether the TP347HFG austenitic stainless steel has undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the TP347HFG austenitic stainless steel bend exceeds 1.009, it indicates that the TP347HFG austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the TP347HFG austenitic stainless steel bend is not greater than 1.005, it indicates that the TP347HFG austenitic stainless steel bend has undergone solution treatment.

8. The non-destructive testing method for the solution-treated state of 18Cr-8Ni austenitic stainless steel bent pipe according to claim 6, characterized in that, The specific criteria for determining whether the SUPER 304H austenitic stainless steel has undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the SUPER 304H austenitic stainless steel bend exceeds 1.007, it indicates that the SUPER 304H austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the SUPER 304H austenitic stainless steel bend is not greater than 1.005, it indicates that the SUPER 304H austenitic stainless steel bend has undergone solution treatment.

9. The non-destructive testing method for the solution-treated state of 18Cr-8Ni austenitic stainless steel bent pipes according to claim 6, characterized in that, The specific criteria for determining whether the TP347H austenitic stainless steel bend has undergone solution treatment are as follows: If several data obtained from different detection angles α conform to a normal distribution, and the relative permeability of the TP347H austenitic stainless steel bend exceeds 1.80, it indicates that the TP347H austenitic stainless steel bend has not undergone solution treatment. If several data points measured at different detection angles α do not conform to a normal distribution, and the relative permeability of the TP347H austenitic stainless steel bend is not greater than 1.005, it indicates that the TP347H austenitic stainless steel bend has undergone solution treatment.

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