Analysis of SMLS pipeline defects

　　The hot rolled Smls pipe is defined as a spiral, half spiral or irregular toothed fold in the inner surface of the steel tube, and some of them are linear Alice skins. The head of the steel pipe has internal fracture, some of which exist in the whole steel pipe, or regular or irregular. Defective steel pipes can be grinded and broken down after being broken. Internal defects have always been one of the main reasons that affect the production and output indexes of steel pipes. There are two main reasons for internal defects: continuous casting billet quality (internal) and perforating process system (external factors).

　　Analysis of the causes of internal folding

　　When the steel pipe is pierced by inclined rolling, the continuous casting of the core is subjected to tensile stress, so it is easy to break the metal center and form holes. The metal surface of the cavity is rough and quickly oxidizes the head of the cooling water and air, forming a crease attached to the inner surface of the pipe during the subsequent rolling process. Therefore, to eliminate internal defects, we must avoid loopholes.

　　The relationship between the quality of continuous casting billet and the defect of steel tube

　　In the case of continuous casting tube, if there is no folding, no internal and external surface cracks and capillary delamination, a qualified product tube can be produced in general. Therefore, smelting process is the key to producing qualified steel pipe. In recent years, experts and scholars have produced defects through experimental analysis, including central loosening, core shrinkage and columnar crystals in the depth of continuous casting.

　　The relationship between the perforation process system and the internal defects

　　The deformation of cross rolling piercing includes basic deformation and additional deformation. The matrix deformation means that when the solid CCM blank enters the capillary, the geometric size and size of the rolling are visual deformation, and the geometric size, shape and material of the deformation have nothing to do with the rolling.

　　The additional deformation is due to the uneven deformation of the metal produced in the body, mainly including torsional deformation, longitudinal shear deformation and tangential shear deformation. This deformation will reduce product quality and increase energy consumption, so this harmful deformation should be minimized in production. Any factors that reduce the plastic and brittle fracture strength of the continuous casting tube or increase the lateral tensile force of the continuous casting tube will result in the formation of internal fracture, and the internal fracture is mainly produced in the process of perforation, but the specific reasons are varied.