There are many methods for quality inspection of large-diameter longitudinally welded steel pipes, among which physical methods are also commonly used inspection methods. Physical inspection is a method of measuring or inspecting by using some physical phenomena. The inspection of the internal defects of materials or large-diameter straight seam welded steel pipes generally adopts the method of non-destructive testing. The current non-destructive testing includes magnetic testing, ultrasonic testing, radiographic testing, penetration testing, and so on.
Magnetic flaw detection can only find defects on the surface and near-surface of magnetic large-diameter longitudinally welded steel pipes, and only quantitative analysis of defects can be done, and the nature and depth of defects can only be estimated based on experience. Magnetic inspection uses the magnetic flux leakage produced by the magnetic field to magnetize ferromagnetic large-diameter straight seam welded steel pipes to find defects. The different methods of measuring magnetic flux leakage can be divided into the magnetic powder method, magnetic induction method, and magnetic recording method, among which the magnetic powder method is widely used.
Penetrant inspection uses physical properties such as the permeability of certain liquids to find and display defects, including coloring inspection and fluorescent inspection, which can be used to inspect defects on the surface of ferromagnetic and non-ferromagnetic materials.
Radiographic flaw detection is a flaw detection method that uses the properties of ray penetrating substances and attenuation in substances to find defects. The different rays used in flaw detection 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 radiographic inspection is divided into the ionization method, fluorescent screen observation method, photographic method, and industrial television method. Radiographic inspection is mainly used to inspect defects such as cracks, incomplete penetration, pores, and slag inclusions in the weld of large-diameter longitudinally welded steel pipes.
Ultrasonic flaw detection
In the propagation of ultrasonic waves in metals and other homogeneous media, due to reflection at the interface of different media, it can be used for the inspection of internal defects. Ultrasonics can inspect any weldment material, any defect in any part, and can find the defect location more sensitively, but it is difficult to determine the nature, shape, and size of the defect. Therefore, ultrasonic flaw detection of large-diameter straight seam welded steel pipes is often used in conjunction with radiographic inspection.