GB/T 47576-2026Non-destructive testing - Coercivity testing method for static equipment in petroleum and chemical plants (English PDF)

Foreword

GB/T 47576-2026 | Non-destructive testing - Coercivity testing method for static equipments of petroleum and chemical plant

GB/T 47576-2026 English version. Non-destructive testing - Coercivity testing method for static equipments of petroleum and chemical plant National Standards of the People's Republic of China ICS 19.100CCS J

04 Nondestructive testing of coercivity of static equipment in petrochemical plants Detection methods Released on 2026-05-

25 Implemented on December 1, 2026 State Administration for Market Regulation The State Administration for Standardization issued a statement.

1.Scope This document describes the coercivity testing method for static equipment in petrochemical plants, specifying the principle, testing equipment, and test blocks for coercivity testing. Testing process specifications, pre-testing preparation, testing implementation, evaluation of test results, and testing records and reports. This document applies to static design specifications for pressure vessels, pressure pipelines, and large atmospheric pressure storage tanks made of carbon steel or low alloy steel in petrochemical plants. Coercivity testing of equipment. Coercivity testing of rotating equipment in petrochemical and chemical plants and other industries should be conducted in accordance with this procedure.

4 Principles

4.1 Coercivity Coercivity is a quantitative reflection of the pinning effect of magnetic domain walls, and the coercivity test results are closely related to the microstructure of the workpiece itself. Factors such as body-centered cubic crystal structure, doping with alloying elements, grain refinement, second-phase precipitation, and dislocation multiplication can all increase coercivity; it is also affected by... The physical properties of the workpiece being inspected also have an impact; for example, for the same material, the smaller the wall thickness, the greater the coercivity. Simultaneously, the load conditions of the workpiece will also significantly affect the coercivity. Effects include the influence of stress on coercivity; in addition, the heat treatment process and service condition of the workpiece under inspection can also indirectly affect coercivity. Effects such as quenching heat treatment, damage accumulation, and material aging can all increase coercivity. The coercivity detection principle is shown in Figure

1.An excitation coil and a detection coil are wound around a U-shaped magnetic yoke, forming a magnetic probe with a Hall sensor. The head contacts the workpiece to form a closed magnetic circuit. Under the action of a positive excitation magnetic field, the magnetization direction of the detection area of the workpiece will be unified with the positive magnetic field. When the magnetic field is applied in the direction of the magnetic field and the magnetic domains reach saturation magnetization, a reverse demagnetizing field is applied, and the magnetic domains begin to reverse magnetization until the magnetic induction intensity decreases. The voltage is zero. The Hall sensor, in conjunction with the detection coil, acquires the voltage signal generated by the change in the magnetic field of the workpiece being inspected, which is then converted into a recognizable signal by the acquisition module. The digital signal is input into the host, and the data processing software automatically calculates the corresponding coercivity value.

4.2 Relationship between coercivity and stress Based on the force-magnetic coupling effect, the magnetic domain structure and domain wall motion at stress concentration sites in materials undergo significant changes under the action of a magnetic field, leading to coercivity When the force signal changes abruptly, such as under quasi-static tensile conditions, the relationship between the coercive force in the parallel stress direction and the uniaxial stress of a low-carbon steel specimen is given by formula (1).

5 Testing equipment and test blocks

5.1 Detection System The coercivity testing system is shown in Figure 2.A suitable magnetic probe is selected based on the characteristics of the workpiece being inspected, and the excitation module is controlled by the host computer to generate... A sufficiently large current is applied to the excitation coil to generate a pulsed magnetic field, causing the inspected workpiece to reach a localized saturation magnetization state before demagnetization. Hall effect sensor The sensor and detection coil work together to collect the electrical signal generated by the change in the magnetic properties of the workpiece under inspection, and the signal acquisition module converts it into a digital signal input. The host computer, after being processed by data analysis software, yields the coercivity test results.

7 Preparations before testing

7.1 Data Inquiry The following information should be consulted to understand the relevant details of the equipment.

a) Manufacturing-related documents of the inspected workpiece. product certificate, quality certificate, and as-built drawings, with a focus on understanding its structural features and materials. feature;

b) Operation records of the inspected workpiece. operating process parameters, years of operation, and any abnormal situations that occurred during operation;

c) Inspection data of the inspected workpiece. inspection and testing records and reports from previous years;

d) Other materials. relevant documents for maintenance, repair and modification.

7.2 Site Survey On-site inspections should be conducted in the following situations.

a) Analyze the potential stress concentration points on the workpiece under inspection, identify the inspection area, and mark its location;

b) Identify and eliminate all interfering factors that may affect the test results;

c) The operating environment should be free of factors that could affect personnel safety.

7.3 Determination of Detection Method Depending on the purpose of the inspection and the structural characteristics of the workpiece being inspected, the inspection methods generally include the following.

a) Use contact or fixed-lift non-contact detection methods.

b) Magnetization should preferably proceed along two orthogonal directions. perpendicular to the stress direction and parallel to the stress direction. For tensile stress, perpendicular to the stress direction... The coercivity detection sensitivity is higher in the direction of compressive stress. For compressive stress, the coercivity detection sensitivity is higher in the direction parallel to the stress.

c) For flat surfaces, a contact inspection method can be selected; for painted surfaces, a fixed-lift non-contact inspection method can be selected, depending on the paint thickness. No more than 6 mm.

d) If poor contact of the magnetic probe is the cause, small-diameter cylindrical or tubular workpieces to be inspected can be tested using a single magnetization direction consistent with the Z-axis, as shown in Figure 4. Towards contact-based detection methods.

8 Implementation of Testing

8.1 Environmental Requirements Coercivity testing should be conducted in a location free from vibration and strong magnetic interference. The ambient temperature should be between -20°C and 50°C, and the relative humidity should be... The degree should not exceed 80%.

8.2 Testing of Equipment Base Materials The inspection process for the base material of the workpiece includes the following steps.

a) Based on the stress state of the workpiece under inspection, determine the inspection area and magnetization direction, and mark each inspection point with a grid in sequence. Note that the grid size should match the probe's detection area, and the overlap rate of the grid sides should not be less than 20%.

b) When using contact testing, the magnetic probe should be placed vertically on the surface of the base material and pressed firmly; there should be no significant vibration during the excitation process. During non-contact testing, the magnetic probe is placed vertically on the surface of the base material and the lifting height of the magnetic probe is kept stable.

c) Starting from the first test point, perform tests row by row and point by point, and record the coercivity values;

d) After all points have been tested, the coercivity data is stored.

8.3 Inspection of Equipment Welds The inspection process for the weld seam of the workpiece includes the following steps.

a) Based on the stress state of the workpiece under inspection, determine the inspection area and magnetization direction, and mark each inspection point with a grid in sequence. Note that the grid size should match the probe's detection area, and the overlap rate of the grid side lengths should not be less than 20%.

b) When using contact testing, the probe should be placed vertically on the surface of the weld inspection area and pressed firmly. There should be no significant vibration during the excitation process. When using non-contact testing, the magnetic probe is placed vertically on the surface of the base material and the lifting height of the magnetic probe is kept stable.

c) Starting from the first inspection point, inspect the weld and the heat-affected zones on both sides line by line and point by point along the direction parallel to the weld, and record the results. Coercivity value;

d) If necessary, inspect each line and point of the above-mentioned inspection area along the vertical direction of the weld and record the coercivity values;

e) After all points have been tested, the coercivity data is stored.

8.4 Sensitivity Verification The sensitivity verification should use the same control block and technical conditions as the initial setup. If the readings are compared to the calibration curve during verification, If the deviation is greater than 20%, all data since the start of the test or the last verification should be retested. Sensitivity should be verified in the following situations.

a) When replacing the magnetic probe, cable, or instrument;

10 Testing Records and Reports

10.1 Inspection Record The test record should include at least the following.

a) Information on the device under inspection, including name, model and specifications, material, heat treatment and surface condition, etc.

b) Welded joint information, including structural type, welding process, and inspection timing;

c) Information on the testing instruments, such as instrument model and serial number, probe model, calibration block and control block, etc.

d) Testing process documents, including testing standards, testing process specifications, and testing operation instruction numbers;

e) Detection process parameters, including detection method, detection area, probe layout diagram, detection system settings, detection sensitivity, and ambient temperature. Degree, etc.;

f) Test results and conclusions, including data file name, coercivity data, stress concentration assessment results, and test conclusions.

10.2 Test Report The test report should include at least the following.

a) Information about the testing organization;

b) Reference this document;

c) Information about the client;

d) Inspection record number;

e) The device under inspection, including its name, model and specifications, material, heat treatment and surface condition, etc.

f) Welded joints, including structural type, welding process, and inspection timing;