GB/T 5248-2016 in English

1. Standard background and technical evolution

GB/T5248-2016 Eddy Current Flaw Detection Method for Copper and Copper Alloy Seamless Tubes is an important part of the national standard, replacing the original GB/T5248-2008 standard. This standard introduces the definition of "standard penetration depth" and its calculation formula, and makes a number of technical improvements to the flaw detection method, such as adding flaw detection specifications for smooth tubes and internally threaded tubes, and clarifying the online detection process.

2. Interpretation of the core content of the standard

2.1 Basic principles of eddy current flaw detection

Eddy current flaw detection is based on the principle of electromagnetic induction, and determines whether there are defects by detecting the changes in the eddy current magnetic field generated by the detection coil on the surface and near the surface of the inspected tube. Its sensitivity is closely related to the electrical conductivity, magnetic permeability and detection frequency of the material.

2.2 Key performance indicators of flaw detection system

The comprehensive performance of the flaw detection system directly affects the accuracy of the test results. Table 1 lists the performance requirements of the offline eddy current flaw detection system, including sensitivity, signal-to-noise ratio and stability.

3. Implementation suggestions and technical points

3.1 Selection of flaw detection equipment

Select appropriate detection coils and excitation frequencies according to the pipe specifications to ensure that the probe filling factor is not less than 0.56. For online detection, reliable transmission devices and saturation magnetization devices are required.

3.2 Preparation of standard artificial defect sample tubes

The corresponding relationship between the standard artificial defect aperture and wall thickness is shown in Table 4. During production, the aperture deviation should be ≤±0.02mm, and the length tolerance should be ±0.1mm.

3.3 Optimization suggestions for online detection

During online detection, the performance indicators of the flaw detection system should be tested regularly to ensure that the sensitivity fluctuation value is ≤2dB. For high-speed production lines, it is recommended to use a combined flaw detection method (through-type + rotary type) to improve the detection coverage.