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Reasons for magnetic properties of large diameter seamless steel pipe

Compared with solid steel materials such as round steel, large-diameter seamless steel pipes are lighter in weight when the bending and torsional strength is the same. They are an economical cross-section steel and are widely used in the manufacture of structural parts and mechanical parts. The editor below will introduce to you the reasons why large-diameter seamless steel pipes are magnetic.

In large-diameter seamless steel pipe manufacturing plants, there are many reasons that make steel pipes magnetic. The main reasons for the residual magnetism of large-diameter seamless steel pipes are: process magnetism and induced magnetism. Induced magnetism often occurs in the pipe-making process of the factory: for example, electromagnetic cranes are often used for loading and unloading in metal smelting. The stainless steel pipes are parked in a strong magnetic field, and the magnetization method is used to complete the non-destructive inspection (before using the magnetic anomalies of the steel pipes for non-destructive testing, first conduct non-destructive testing. Magnetization of steel pipes), steel pipes placed close to strong power supply lines, etc.
 large-diameter seamless steel pipes
Among them, the magnetization method non-destructive inspection mainly refers to eddy current flaw detection. The eddy current flaw detection equipment is simple to operate and easy to master. If used properly, it can detect some defects in the steel pipe. The eddy current flaw detection method is used to detect defects such as longitudinal and transverse cracks on the metal surface. lossless method. Depending on the type of flaw, inspection is performed using either a penetrating coil or a rotating scanning probe. Inspection methods can be optimally integrated into the production process. During magnetic flux leakage inspection, the surface of the component or semi-finished product is temporarily magnetized, and then the magnetic field leaking into the space at the defect location is scanned non-contactly or in contact with the probe. Eddy current flaw detection is an indispensable non-destructive testing method in several steel pipe flaw detection tests such as visual inspection, ultrasonic testing, and hydraulic testing. Process magnetism often occurs during assembly and welding operations, the use of magnetic holders, fixtures, and vertical current welding of pipelines, such as long-term contact with wires connected to DC power supplies, exposed sections of wires, or short circuits between welding clamps and pipes, etc. .

In order to eliminate the magnetism of seamless pipes caused by the above reasons, the stable austenite arrangement can be opened through high-temperature solution treatment, thereby eliminating the magnetism. In particular, the magnetism of seamless pipes formed due to the above reasons is always very weak compared with stainless steel made of other raw materials, that is, the magnetism of seamless pipes. In addition, seamless pipes will transform into martensite through cold working. The greater the cold working deformation, the more martensitic phase transformation of the seamless pipe, and the greater the magnetic properties. Like the same batch of steel strips, φ 76 tubes are produced, and φ 9.5 tubes are produced, without obvious magnetic induction. Due to the larger bending deformation, the magnetic induction is more obvious. Since the deformation of rectangular tubes is greater than that of round tubes, especially at the corners, the deformation of seamless tubes is more severe and the magnetism is more significant.

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