ERW steel pipe welding defect inspection method:
1. Appearance inspection
The inspection usually relies on naked eye observation. The accuracy of the inspection can be greatly improved with the help of some tools. Commonly used tools include: weld inspection gauge, tape measure, steel ruler, low-power magnifying glass, etc., which are generally used to inspect external defects of the weld.
2. Air tightness inspection
Generally, air tightness inspection is required for melters, pipes, etc., and different inspections are conducted according to the requirements of the objects being tested.
① Submersion test: Place a container filled with a certain pressure in the water tank, press it to a certain depth, and then slowly rotate it to observe whether there are bubbles on the container to determine whether there is leakage.
② For soapy water inspection, apply a brush dipped in soap solution to the weld in sequence on a container filled with gas under pressure. If no bubbles appear, it is considered qualified.
③ Kerosene test, which uses the strong penetration ability of kerosene to test the tightness of the weld. Apply lime water to one side of the weld (the outside of the container). After the lime water dries, apply kerosene to the other side of the weld (the inside of the container) to check whether there are oil spots on the white lime.
3. Pressure test
Pressure test is also called pressure test, which includes water pressure test and air pressure test. The pressure test is an inspection method that pressurizes the container (water pressure or air pressure) to the test pressure to check whether there is leakage and maintain pressure. The test pressure should be higher than the working pressure, otherwise the safe operation of the container cannot be guaranteed. Pressure testing is used to evaluate the overall strength performance, deformation and leakage of welded components such as boilers, pressure vessels, and pressure pipes.
On the one hand, the pressure test tests the compactness of the structure, and on the other hand, it can also test the strength of the structure. For the hydraulic pressure test, when the water is filled with water and the air is completely drained, the water valve is closed, and then a high-pressure water pump is used to pressurize the container in stages until the test pressure is reached (generally 1.25 to 1.5 times the working pressure); check whether there are water beads on the weld ( Leakage), if there is a leak;
Check the pressure-holding condition. After stopping the pressurization, keep the pressure for 5 to 10 minutes. There should be no obvious pressure drop. In the air pressure test, a high-pressure air pump is used to gradually increase the pressure of the container. Each step is maintained for a certain period of time until it reaches the specified test pressure. Use soapy water to check for leaks and check the pressure maintenance.
4. Ray detection
During the process of penetrating the material, the intensity of the ray is weakened and attenuated due to absorption and scattering. The degree of attenuation depends on the attenuation coefficient of the penetrating material and the thickness of the penetrating material. If there are defects inside the transilluminated workpiece, and the defective medium is different from the inspected Different degrees of attenuation of rays by the workpiece will cause differences in the intensity of the rays that pass through the workpiece, resulting in different photosensitivity levels of the film. After darkroom processing, the defective parts of the film will be darker, and film reviewers can use this to judge the defect. Radiographic testing should be performed by personnel with professional qualifications.
5. Ultrasonic testing
It is a method that uses the acoustic characteristics of ultrasonic waves propagating in media to detect internal or surface defects in metal materials and their workpieces. During the propagation process of ultrasonic waves in metal, reflection occurs when encountering the interface. During detection, ultrasonic waves have reflected pulses on both surfaces of the workpiece. If there is a defect inside the workpiece, a third pulse will appear between the two pulses, and the location of the defect can be determined based on the position of this pulse. Ultrasonic flaw detection equipment is relatively lightweight, flexible and has a wide detection range.
6. Magnetic particle testing
The magnetic permeability of ferromagnetic metal materials is much greater than that of air. When it is magnetized in a magnetic field, the magnetic field lines will be concentrated in the material. If there are defects such as pores, cracks, and slag inclusions on or near the surface of the material, the magnetic field lines will be difficult to pass through. Passing through these defects, a local leakage magnetic field will be formed at the defect. At this time, magnetic powder is sprinkled on the material, and the magnetic powder will be attracted by the leakage magnetic field and gather at the defect, thus showing macroscopic traces of the defect. Workpieces that have undergone magnetic particle testing must be demagnetized.
7. Other inspections: ① Magnetic yoke method inspection; ② Penetration inspection; ③ Eddy current inspection; ④ Bending test; ⑤ Impact test; ⑥ Metallographic inspection.
Read more: ERW Pipe Manufacturing Process
