Welded steel pipe quality physical testing method

Welded steel pipe refers to a steel pipe with seams on the surface that is welded after bending and deforming a steel strip or steel plate into a circular, square (such as a500 rectangular tube) shape. The blanks used for welded steel pipes are steel plates or strips. The production cost of welded steel pipe is low, and it replaces seamless pipe in more and more fields

There are many kinds of quality inspection methods for welded steel pipe products, among which physical methods are common detection methods, and physical inspection refers to the method of using some physical knowledge to carry out measurement or inspection. The detection of internal defects of raw materials or steel parts generally adopts the method of non-destructive testing. The current non-destructive testing includes magnetic field flaw detection, ultrasonic flaw detector, radiographic flaw detection, penetration flaw detection and so on.

1. Magnetic field detection

Magnetic field flaw detection can only detect defects on the surface and near the surface of magnetic metals, and can only do qualitative analysis on defects, and the characteristics and depth of defects can only be estimated based on work experience. Magnetic field detection is to use the electromagnetic field to detect the fault by the magnetic flux leakage caused by the magnetized ferromagnetic metal parts. According to the different methods of measuring magnetic flux leakage, it can be divided into magnetic powder method, induction coil method and magnetic recording method, among which the magnetic powder method is widely used.

2. Penetration detection

Penetration testing uses the hydrophilicity and other physical characteristics of some liquids to detect and display information defects, including color testing and fluorescent flaw detection, which can be used to detect defects on the surface of ferromagnetic and non-ferromagnetic materials.

3. Radiographic inspection

Radiographic flaw detection is a flaw detection method that uses the characteristics that radiation can penetrate substances and have an attenuation coefficient in substances to detect defects. According to the radiation used in flaw detection, it can be divided into three types: x-ray flaw detection, gamma ray flaw detection, and source energy ray flaw detection. Due to the different methods of displaying defects, each radiographic inspection is divided into weak electrolyte method, display screen observation, photography method and industrial television method. Radiographic testing is suitable for detecting defects such as cracks, incomplete penetration, air holes, and weld spalls inside the weld.

4. Ultrasonic flaw detector

In the propagation of metal materials and other uniform substances, ultrasonic waves can be used to detect internal defects because they form reflective surfaces on the pages of different substances. Ultrasonic waves can detect defects in all weldment materials and positions, and can detect defect parts more flexibly, but it is difficult to determine the nature, shape and size of defects. Therefore, ultrasonic flaw detectors are often used in conjunction with radiation testing.

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