According to the material science point of view, the chemical composition, physical properties, and geometry of a good metal material should be continuous, pure, and uniform. If these three aspects are insufficient or damaged, the metal material is considered to be defective. If the metal material is discontinuous in geometry (ie, not tight or uncompact or not dense), such as cracks, shrinkage, peeling, pits, delamination, pinholes, slag inclusion, etc. The metal material is considered to be a scar (abbreviated as an injury), which does not include discontinuities in chemical composition or discontinuities in physical properties. It can be seen from this that the defect contains injuries.
Boiler steel pipes usually use seamless steel pipes
, which may also have defects and injuries during smelting and rolling. According to the introduction of the steel pipe plant, the defects of the boiler steel pipe (here mainly referred to as the injury) are mainly on the surface, and the outer surface is more than the inner surface. About 70% of these defects come from raw materials (steel billets), slag inclusions, shrinkage cavities, etc., which are insufficient in oxygen blowing in the billet. Rolling steel tubes with them may cause defects such as transverse cracks, interlayers, folds, and heavy skin. Longitudinal cracks are mostly caused by strains during rolling.
If these defects or scratches appear in the boiler steel pipe, it is considered that there is discontinuity in the material, the internal compactness of the material is damaged, and water leakage may occur during the hydraulic pressure test. Leaks or squibs may occur. Because of this, in order to ensure the quality of boiler steel tubes, both domestic and foreign standards for boiler tubes are clearly stipulated. As a guarantee of process performance, steel pipes should be tested hydraulic pressure one by one.