Steel structure fireproof coating thickness detection method based on multi-eddy current excitation

Abstract

The invention provides a steel structure fireproof coating thickness detection method based on multi-eddy current excitation, and the method comprises the steps: 1, manufacturing a standard workpiece, and providing calibration and initial data for system detection, and 2, carrying out the multi-frequency calibration operation of a system, and correcting the high-frequency and low-frequency states of a probe, step 2, establishing a linear mapping relation between the impedance phase angle theta H and the thickness of the fireproof coating; step 3, performing dynamic detection and data fusion on a to-be-detected product to obtain product coating thickness data; 4, after the thickness value is obtained, the detection equipment is set to generate a composite excitation signal; according to the invention, through technical innovation of multi-frequency eddy current excitation, dynamic self-adaptive compensation, intelligent data fusion and the like, high-precision and high-efficiency detection of the thickness of the fireproof coating of the steel structure and material defects is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of steel structure fire retardant coating thickness detection technology, in particular to a steel structure fire retardant coating thickness detection method based on multi-eddy current excitation. Background Art

[0002] The traditional testing instruments used for thickness detection of fire retardant coatings on steel structures can only detect one thickness indicator, but cannot detect impurities and defects inside the fire retardant coating. Summary of the Invention

[0003] To this end, the present invention provides a detection method to achieve the purpose of detecting thickness and internal impurities with one device.

[0004] To achieve the above object, the present invention provides a method for detecting the thickness of a fire retardant coating on a steel structure based on multi-eddy current excitation, comprising the following steps:

[0005] Step 1: Make a standard workpiece to provide calibration and initial data for system testing:

[0006] A Q235B steel substrate was used to prepare a fire retardant coating thickness gradient test block. The thickness of the fire retardant coating ranged from 0.1 to 20 mm. The surface was sprayed with a fire retardant coating containing 0.5% tungsten powder to simulate the common metal impurity interference scenario in engineering.

[0007] The test block is treated with constant temperature and humidity: temperature 20±2℃, humidity 50%±5% for 24 hours to ensure that the coating curing state is consistent with the on-site; Step 2, high-frequency calibration (1MHz): the probe is vertically attached to the test block and a constant pressure of 0.5N is applied. It moves along the surface of the test block at a constant speed of 10mm / s and records the impedance phase angle θ in the coating thickness range of 0.1-0.5mm. H , establish θ H Linear mapping relationship with thickness:

[0008] δ H =0.12θ H -5.3μm

[0009] δ H : coating surface thickness, in μm;

[0010] θ H : Phase angle of high-frequency (1MHz) eddy current impedance, in degrees (°); reflects the electromagnetic characteristics of the coating surface (0.1-0.5mm);

[0011] 0.12: Linear coefficient of phase angle and thickness (experimental calibration value), indicating the thickness change corresponding to a 1-degree change in phase angle;

[0012] -5.3μm: Calibration offset, used to correct initial errors caused by differences in substrate material;

[0013] Step 3: Low frequency calibration (100kHz): Scan in 0.5-20mm thickness range with 0.5mm step, and use the real part of impedance Re L Logarithmic relationship with thickness: Re L =12.3·ln(δ L )+4.7Ω; establish the coating deep thickness model;

[0014] Re L : The real part of the low-frequency 100kHz eddy current impedance, expressed in ohms, and is logarithmically related to the thickness of the deep coating.

[0015] δ L : deep layer thickness calculated by low frequency;

[0016] 12.3: Coefficients of the logarithmic model (experimental calibration values), reflecting the sensitivity of the real part of the impedance to changes in thickness;

[0017] 4.7Ω: Model constant term, used to compensate for the influence of the conductivity of the matrix material;

[0018] Step 4: Perform dynamic detection and data fusion on the product to be tested to obtain product coating thickness data:

[0019] The high-frequency mode probe acquires the surface thickness (resolution ±2μm) at a scanning speed of 10mm / s, and the low-frequency mode probe simultaneously acquires deep thickness data. The weighted algorithm δ total =0.7δ H +0.3δ L Output the overall thickness value;

[0020] δ total Represents the overall thickness of the coating after fusion;

[0021] δ H : Surface thickness data detected by high frequency (1MHz);

[0022] δ L : Deep thickness data detected by low frequency (100kHz);

[0023] 0.7 and 0.3: Weight coefficients, determined through experimental verification, to optimize measurement accuracy over the full thickness range.

[0024] Step 5. After obtaining the thickness value, set up the detection equipment to generate a composite excitation signal:

[0025] A DDS chip is used to generate a composite signal of the fundamental frequency f0 (1MHz) superimposed on the second harmonic 2f0, with a peak-to-peak voltage of 5V. Orthogonal encoding technology is used to avoid signal crosstalk.

[0026] The signal is filtered through a 6th-order Butterworth bandpass filter with a center frequency of 2 MHz and a bandwidth of 200 kHz. The second harmonic component is extracted with a signal-to-noise ratio of ≥ 60 dB.

[0027] Step 6. Use the above signal to scan the product a second time and calculate the harmonic distortion (THD) at the same time:

[0028] The data is updated every 100ms. The fundamental wave and second / third harmonic amplitudes are decomposed by FFT. The calculation formula is:

[0029]

[0030] V 2nd and V 3rd are the voltage amplitudes of the second harmonic (2MHz) and third harmonic (3MHz), respectively;

[0031] V fund is the voltage amplitude of the fundamental wave (1MHz), in volts (V);

[0032] In spatial scanning mode, the probe generates a THD distribution heat map with a step size of 2mm. When THD>5% at three consecutive points and the phase mutation Δθ>15°, it is determined to be a metal impurity or pore accumulation area, and an alarm is triggered.

[0033] Step 7: Material uniformity detection abnormality verification mechanism:

[0034] After the alarm is triggered, it switches to pulsed eddy current mode (frequency 500kHz) and verifies the nature of the anomaly through the difference in eddy current penetration depth: if the distortion rate of the deep signal decreases, it is judged to be surface impurities; if the distortion rate continues to increase, it is judged to be uneven deep material.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] Simultaneous detection of thickness and material defects: Through dual-modal analysis of eddy current impedance (fundamental signal) and harmonic distortion rate (non-linear characteristics), it can not only accurately measure the coating thickness of 0.1-20mm, but also identify defects such as metal impurities and pores in the coating, solving the problem that traditional single-parameter methods (such as magnetic method and ultrasonic method) cannot take into account both thickness and material uniformity.

[0037] Depth adaptability of multi-frequency eddy current: 100kHz low frequency is used to penetrate deep coatings (1-20mm) and 1MHz high frequency is used to detect surface layers (0.1-0.5mm). A weighted fusion algorithm is used to achieve full thickness coverage, avoiding the problem of limited detection range of a single frequency.

[0038] Description of the drawings: Figure 1 This is a flowchart of the system workflow of the present invention; DETAILED DESCRIPTION

[0039] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0040] Step 1: Make a standard workpiece to provide calibration and initial data for system testing:

[0041] A Q235B steel substrate was used to prepare a fire retardant coating thickness gradient test block. The thickness of the fire retardant coating ranged from 0.1 to 20 mm. The surface was sprayed with a fire retardant coating containing 0.5% tungsten powder to simulate the common metal impurity interference scenario in engineering.

[0042] The test blocks are treated with constant temperature and humidity: temperature 20±2℃, humidity 50%±5% for 24 hours to ensure that the coating curing state is consistent with the on-site condition;

[0043] Step 2: High-frequency calibration (1MHz): Place the probe vertically against the test block and apply a constant pressure of 0.5N. Move along the surface of the test block at a constant speed of 10mm / s and record the impedance phase angle θ in the coating thickness range of 0.1-0.5mm. H , establish θ H Linear mapping relationship with thickness:

[0044] δ H =0.12θ H -5.3μm

[0045] δ H : coating surface thickness, in μm;

[0046] θ H : Phase angle of high-frequency (1MHz) eddy current impedance, in degrees (°); reflects the change in the electromagnetic characteristics of the coating surface (0.1-0.5mm); reflects that the eddy current field distribution induced by high-frequency eddy current (1MHz) in the coating is affected by the thickness of the surface layer, specifically, the thickness increases → the eddy current path lengthens → the imaginary part (reactance component) of the coil impedance increases → the impedance phase angle θ H Increase;

[0047] 0.12: Linear coefficient of phase angle and thickness (experimental calibration value), indicating the thickness change corresponding to a 1-degree change in phase angle;

[0048] -5.3μm: Calibration offset, used to correct initial errors caused by differences in substrate material;

[0049] Step 3: Low frequency calibration (100kHz): Scan in 0.5-20mm thickness range with 0.5mm step, and use the real part of impedance Re L Logarithmic relationship with thickness: Re L=12.3·ln(δ L )+4.7Ω; establish the coating deep thickness model;

[0050] Re L : The real part of the low-frequency 100kHz eddy current impedance, expressed in ohms, and is logarithmically related to the thickness of the deep coating.

[0051] δ L : deep layer thickness calculated by low frequency;

[0052] 12.3: Coefficients of the logarithmic model (experimental calibration values), reflecting the sensitivity of the real part of the impedance to changes in thickness;

[0053] 4.7Ω: Model constant term, used to compensate for the influence of the conductivity of the matrix material;

[0054] Step 4: Perform dynamic detection and data fusion on the product to be tested to obtain product coating thickness data:

[0055] The high-frequency mode probe acquires the surface thickness (resolution ±2μm) at a scanning speed of 10mm / s, and the low-frequency mode probe simultaneously acquires deep thickness data. The weighted algorithm δ total =0.7δ H +0.3δ L Output the overall thickness value;

[0056] δ total Represents the overall thickness of the coating after fusion;

[0057] δ H : Surface thickness data detected by high frequency (1MHz);

[0058] δ L : Deep thickness data detected by low frequency (100kHz);

[0059] 0.7 and 0.3: Weight coefficients, determined through experimental verification, optimize the measurement accuracy of the full thickness range. High-frequency data has a higher resolution (±2μm), so it is given a higher weight (0.7).

[0060] Step 5. After obtaining the thickness value, set up the detection equipment to generate a composite excitation signal:

[0061] A DDS chip is used to generate a composite signal of the fundamental frequency f0 (1MHz) superimposed on the second harmonic 2f0, with a peak-to-peak voltage of 5V. Orthogonal encoding technology is used to avoid signal crosstalk.

[0062] The signal is filtered through a 6th-order Butterworth bandpass filter with a center frequency of 2 MHz and a bandwidth of 200 kHz. The second harmonic component is extracted with a signal-to-noise ratio of ≥ 60 dB.

[0063] Step 6. Use the above signal to scan the product a second time and calculate the harmonic distortion (THD) at the same time:

[0064] The data is updated every 100ms. The fundamental wave and second / third harmonic amplitudes are decomposed by FFT. The calculation formula is:

[0065]

[0066] V 2nd and V 3rd are the voltage amplitudes of the second harmonic (2MHz) and third harmonic (3MHz), respectively;

[0067] V fund is the voltage amplitude of the fundamental wave (1MHz), in volts (V);

[0068] In spatial scanning mode, the probe generates a THD distribution heat map with a step size of 2mm. When THD>5% at three consecutive points and the phase mutation Δθ>15°, it is determined to be a metal impurity or pore accumulation area, and an alarm is triggered.

[0069] Step 7: Material uniformity detection abnormality verification mechanism:

[0070] After the alarm is triggered, it switches to pulsed eddy current mode (frequency 500kHz) and verifies the nature of the anomaly through the difference in eddy current penetration depth: if the distortion rate of the deep signal decreases, it is judged to be surface impurities; if the distortion rate continues to increase, it is judged to be uneven deep material.

Claims

1. A method for detecting the thickness of fire retardant coating on steel structure based on multi-eddy current excitation, characterized in that: Use the following steps: Step 1: Make a standard workpiece to provide calibration and initial data for system testing: A fire retardant coating thickness gradient test block was prepared using a steel substrate. The thickness of the fire retardant coating ranged from 0.1 to 20 mm. The surface was sprayed with a fire retardant coating containing 0.5% tungsten powder to simulate the common metal impurity interference scenario in engineering. The test blocks are treated with constant temperature and humidity: temperature 20±2℃, humidity 50%±5% for 24 hours to ensure that the coating curing state is consistent with the on-site condition; Step 2: High-frequency calibration (1MHz): Place the probe vertically against the test block and apply a constant pressure of 0.5N. Move along the surface of the test block at a constant speed of 10mm / s and record the impedance phase angle θ in the coating thickness range of 0.1-0.5mm. H , establish θ H Linear mapping relationship with thickness: d H =0.12θ H -5.3μm δ H : coating surface thickness, in μm; θ H : Phase angle of high-frequency (1MHz) eddy current impedance, in degrees (°); reflects the electromagnetic characteristics of the coating surface (0.1-0.5mm); 0.12: Linear coefficient of phase angle and thickness (experimental calibration value), indicating the thickness change corresponding to a 1-degree change in phase angle; -5.3μm: Calibration offset, used to correct initial errors caused by differences in substrate material; Step 3: Low frequency calibration (100kHz): Scan in 0.5-20mm thickness range with 0.5mm step, and use the real part of impedance Re L Logarithmic relationship with thickness: Re L =12.3·ln(δ L )+4.7Ω; establish the coating deep thickness model; Re L : The real part of the low-frequency 100kHz eddy current impedance, expressed in ohms, and is logarithmically related to the thickness of the deep coating. δ L : deep layer thickness calculated by low frequency; 12.3: Coefficients of the logarithmic model (experimental calibration values), reflecting the sensitivity of the real part of the impedance to changes in thickness; 4.7Ω: Model constant term, used to compensate for the influence of the conductivity of the matrix material; Step 4: Perform dynamic detection and data fusion on the product to be tested to obtain product coating thickness data: The high-frequency mode probe acquires the surface thickness (resolution ±2μm) at a scanning speed of 10mm / s, and the low-frequency mode probe simultaneously acquires deep thickness data. The weighted algorithm δ total =0.7δ H +0.3δ L Output the overall thickness value; δ total Represents the overall thickness of the coating after fusion; δ H : Surface thickness data detected by high frequency (1MHz); δ L : Deep thickness data detected by low frequency (100kHz); 0.7 and 0.3: Weight coefficients, determined through experimental verification, to optimize measurement accuracy over the full thickness range. Step 5. After obtaining the thickness value, set up the detection equipment to generate a composite excitation signal: A DDS chip is used to generate a composite signal of the fundamental frequency f0 (1MHz) superimposed on the second harmonic 2f0, with a peak-to-peak voltage of 5V. Orthogonal encoding technology is used to avoid signal crosstalk. The signal is filtered through a 6th-order Butterworth bandpass filter with a center frequency of 2 MHz and a bandwidth of 200 kHz. The second harmonic component is extracted with a signal-to-noise ratio of ≥ 60 dB. Step 6. Use the above signal to scan the product a second time and calculate the harmonic distortion (THD) at the same time: The data is updated every 100ms. The fundamental wave and second / third harmonic amplitudes are decomposed by FFT. The calculation formula is: V 2nd and V 3rd are the voltage amplitudes of the second harmonic (2MHz) and third harmonic (3MHz), respectively; V fund is the voltage amplitude of the fundamental wave (1MHz), in volts (V); In spatial scanning mode, the probe generates a THD distribution heat map with a step size of 2mm. When THD>5% at three consecutive points and the phase mutation Δθ>15°, it is determined to be a metal impurity or pore accumulation area, and an alarm is triggered. Step 7: Material uniformity detection abnormality verification mechanism: After the alarm is triggered, it switches to pulsed eddy current mode (frequency 500kHz) and verifies the nature of the anomaly through the difference in eddy current penetration depth: if the distortion rate of the deep signal decreases, it is judged to be surface impurities; if the distortion rate continues to increase, it is judged to be uneven deep material.

Images