Raw material and piercing are the foremost critical procedures in seamless steel tube manufacturing, which directly determine the internal metallurgical quality of tube blanks. Improper billet composition control, unreasonable heating regime and unstable piercing parameter setting are major triggers for internal cracks, central laminations and non‑metallic inclusion defects. If such flaws remain undetected in subsequent processes, they will be inherited into finished tubes, resulting in pressure‑bearing failure, fatigue fracture and product rejection. Strict control over raw material quality and piercing production process helps seamless steel tube manufacturers effectively suppress internal crack and inclusion risks, improving the intrinsic quality of tubular products.

Raw material control starts from incoming inspection of steel billets. Manufacturers shall verify the mill test certificate, heat number and chemical composition of each batch of billets. Harmful impurity elements such as sulfur and phosphorus shall be kept within specified limits, while excessive non‑metallic inclusions including oxides and sulfides need to be strictly restricted. Large‑size aggregated inclusions inside the billet cannot be eliminated by piercing and rolling; they will separate the metal matrix and become potential crack sources under radial and tangential stress during hot working. Sampling inspection for billet macrostructure shall be carried out to check for central porosity, shrinkage cavity residue and segregation. Billet surface shall be thoroughly cleaned by grinding or scarfing to remove surface cracks, scabs and folded defects, preventing surface flaws from being pressed into inner walls during piercing. Unqualified billets must be isolated and prohibited from flowing into the production line.

Billet heating quality lays the foundation for stable piercing performance. Uneven heating, over‑heating or insufficient soaking time will worsen metal plasticity and raise crack risk. The heating furnace shall strictly follow segmented temperature curves, avoiding rapid temperature rise that causes excessive thermal stress inside the billet. Soaking period shall be reasonably arranged to guarantee uniform temperature distribution across billet core and surface. Over‑high heating temperature will lead to coarse grain and over‑burning, which irreversibly damage metal microstructure; too low temperature increases deformation resistance, bringing heavy load to piercing plug and piercing roll, and easily inducing internal shear cracks. Temperature monitoring and recording for each furnace batch are required to realize traceability of heating parameters.

Piercing parameter matching is the core to restrain internal crack defects. Key adjustable parameters include piercing roll angle, plug advance, plug nose shape, feed rate and piercing speed. The roll skew angle determines the helical deformation degree of the billet. Excessive skew angle will produce severe tensile stress at the billet center and cause Mannesmann effect‑related internal cavity and cracking. Too small skew angle will result in insufficient penetration and unstable hole‑forming. The piercing plug bears high‑temperature friction and cyclic mechanical load. Worn, deformed or surface‑damaged plugs will generate scratch and tearing on the inner surface of tube blank. Regular inspection and replacement cycle for piercing plugs shall be formulated, and surface lubrication coating for plugs shall be maintained to reduce friction heat and metal adhesion.

Real‑time monitoring of tube blank status after piercing is essential. Operators shall observe inner and outer surface of pierced shell. Abnormal phenomena such as inner spiral crack, inner folding and uneven wall thickness shall trigger process review. When central inclusion aggregation occurs, it is necessary to trace back to billet smelting quality instead of merely adjusting piercing parameters. Process parameters shall not be modified blindly in mass production. Any parameter adjustment should be followed by sampling inspection of tube blank metallographic structure to confirm defect improvement effect.

Supporting management measures should be put in place. Production lots shall be managed by heat number, so that defective products can be traced back to corresponding raw material batch and process records. The non‑destructive testing procedure shall be arranged after piercing to screen out tube blanks with internal cracks and large inclusions as early as possible, rather than leaving defect detection to finished‑product inspection only. Tooling such as piercing rolls and guide shoes shall be kept in good condition. Severe wear of guide shoes will cause unstable billet centering, resulting in eccentric deformation and additional internal stress.

In short, raw material and piercing process control is a systematic barrier against internal quality defects of seamless steel tubes. Strict billet incoming inspection, standardized billet heating, scientific piercing parameter matching and intermediate‑procedure quality check work together to reduce internal crack and inclusion defects from the source. This not only cuts down subsequent rejection rate, but also enhances the reliability of seamless steel tubes for pressure‑vessel, mechanical processing and pipeline transportation applications.