Inspection methods for large-diameter straight-seam welded steel pipes

There are many methods for quality inspection of large-diameter straight-seam welded steel pipes, among which physical methods are also commonly used inspection methods. Physical inspection is a method of measuring or inspecting using some physical phenomena. Inspection of materials or internal defects of large-diameter straight-seam welded steel pipes generally adopts non-destructive testing methods. Current non-destructive testing includes magnetic testing, ultrasonic testing, radiographic testing, and penetrant testing.

First, magnetic inspection

Magnetic testing can only detect surface and near-surface defects of magnetic large-diameter straight-seam welded steel pipes, and can only make quantitative analysis of defects. The nature and depth of defects can only be estimated based on experience. Magnetic inspection uses the leakage magnetic field generated by the magnetic field magnetizing the ferromagnetic large-diameter straight-seam welded steel pipe to detect defects. The different methods of measuring leakage magnetic field can be divided into the magnetic powder method, magnetic induction method, and magnetic recording method, among which the magnetic powder method is the most widely used.

Second, penetrant testing

Penetrating testing uses the physical properties of certain liquids such as permeability to find and display defects, including color testing and fluorescent testing, which can be used to check defects on the surface of ferromagnetic and non-ferromagnetic materials.

Third, radiographic testing

Radiographic testing is a method of flaw detection that uses the characteristics of radiation-penetrating materials and attenuating materials to find defects. According to the different rays used for flaw detection, it can be divided into three types: X-ray flaw detection, gamma-ray flaw detection, and high-energy ray flaw detection. Due to the different methods of displaying defects, each type of radiographic flaw detection is divided into the ionization method, fluorescent screen observation method, photography method, and industrial television method. Radiographic testing is mainly used to detect cracks, incomplete penetration, pores, slag inclusions, and other defects inside the weld of large-diameter straight seam welded steel pipes.

Fourth, ultrasonic testing

Ultrasonic waves can be used to detect internal defects in metals and other uniform media because they will be reflected at the interface of different media. Ultrasonic waves can detect defects in any weld material and any part, and can more sensitively detect the location of defects, but it is difficult to determine the nature, shape, and size of defects. Therefore, ultrasonic flaw detection of large-diameter straight-seam welded steel pipes is often used in conjunction with radiographic inspection.