There are many methods for quality inspection of large-diameter straight seam welded 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 internal defects of materials or large-diameter straight seam welded 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 defects on the surface and near the surface of magnetic large-diameter straight seam welded 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 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 discover 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 discover 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 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 testing of large-diameter straight seam welded pipes is often used in conjunction with radiographic testing.