Seamless steel tubes are widely used in high-pressure, low-temperature and corrosion-resistant environment piping systems. Mechanical properties, process performance and corrosion resistance are three important indicators to measure the quality of steel pipes. Each pipe-making process complements each other, especially the quality control of raw materials and intermediate products, which is an important guarantee to ensure that the chemical composition, surface quality, mechanical properties, process performance and corrosion resistance of the finished pipe meet the specifications and standards.
The raw materials used in the production of seamless steel tubes are mainly continuous casting round pipe billets and rolled (forged) round steel. Ensuring the quality of steel billets is the first step to ensure the quality of steel pipes. It mainly includes steelmaking level, pouring and cooling processes, and forming. quality. The first is to increase the level of steelmaking. It is necessary to reduce harmful elements and gases (nitrogen, hydrogen and oxygen), improve the uniformity and purity of the composition, reduce non-metallic inclusions, and change their distribution patterns. When the composition of the steel billet is not uniform and severe segregation occurs, the rolled steel pipe will show a serious band structure, thereby reducing the mechanical properties and corrosion properties of the steel pipe, or even unqualified. Non-metallic inclusions (such as sulfides, oxides, and silicates) are pressed into thin sheets, which will not only affect the performance of the steel pipe, but may also cause cracks in the steel pipe during the production process. Secondly, perfect the pouring and cooling process to reduce subcutaneous bubbles, subcutaneous cracks, porosity and shrinkage holes. It cannot be ignored, because no matter what kind of defects, they may cause defects in the process of piercing and rolling. Some defects are amplified after use, which shortens the service life of the product; in severe cases, intermediate products are directly scrapped, such as inward folding. In addition, the shape deviation of the billet, such as straightness, diameter and ovality, will directly affect the quality of the perforation and cause the quality of the waste pipe.
Therefore, it is not only necessary to pay attention to steelmaking equipment and processes, but also to carry out tests that extend to seamless steel tubes. Through such an approval process, the inspection items, sampling quantities and acceptance criteria for the billet factory inspection are determined, especially in the specifications and guidelines. There are no clear quality items that need to be focused on, such as low power and microstructure testing.