Improvement of seamless pipe quality
Date:2025-07-18
As the core "blood" of energy transportation, high-end equipment manufacturing, engineering machinery and other fields, the quality of seamless steel pipes is directly related to the life of equipment and operational safety. Against the background of accelerated industrial upgrading, promoting the quality of seamless pipes from "qualified" to "excellent" has become the only way for the industry to develop with high quality. The following analyzes the key path to quality improvement from the perspective of the whole process:
1. Quality defects: key pain points in the production process
Surface defects: folding, cracking, scarring, pitting, etc., mostly due to poor quality of pipe billets or out-of-control parameters of the rolling process.
Insufficient dimensional accuracy: Uneven wall thickness and excessive ovality are mainly determined by the precision of the rolling mill, the state of the mandrel and the stability of the process.
Internal defects: Central looseness, non-metallic inclusions, and internal folds are closely related to the purity of molten steel, continuous casting process and perforation parameters.
Fluctuation of mechanical properties: Strength and toughness are not up to standard or unstable, which is controlled by the composition design, heat treatment process and cooling uniformity.
Excessive residual stress: Affects subsequent processing and service performance, due to uneven deformation and improper heat treatment process.
2. Core technology path for improving quality throughout the entire process
Source control: high-purity billet manufacturing
Ultra-low impurity smelting: Use molten iron pretreatment, top and bottom combined blowing converter/arc furnace smelting, LF/VD/VOD refining outside the furnace, strictly control the S and P content (≤0.010%), and reduce the total amount of O, N, H gas and inclusions (such as Class B ≤ 1.5).
Continuous casting optimization: Electromagnetic stirring technology (improves center segregation), light pressure technology (compensates for solidification shrinkage), protective pouring (prevents secondary oxidation), improves the density and uniformity of the billet. Apply large round billet continuous casting technology (such as Ø450mm) to significantly reduce the defects caused by insufficient rolling compression ratio.
Precision rolling: dimensional accuracy and surface quality assurance
Application of advanced rolling mills: Promote high-precision limited mandrel continuous rolling mill (PQF), three-roll continuous rolling mill (Assel), precision tension reducing mill, etc., combined with hydraulic AGC thickness automatic control system, the wall thickness tolerance can be stably controlled within ±5%.
Online monitoring and closed-loop control: Integrate laser diameter gauge, thickness gauge, surface defect automatic detection system (such as machine vision, eddy current flaw detection), real-time feedback to adjust rolling parameters, and realize the "perception-analysis-decision-execution" closed loop.
Tool and mold management: High wear-resistant material mandrel/plug, application of CVD/PVD coating technology to improve life; establish a strict tool wear monitoring and replacement system.
Precise heat treatment: performance control core
Temperature control and cooling technology: Use step-type/roller bottom heat treatment furnace to achieve ±5°C precise temperature control; combine water quenching, air cooling, mist cooling and other graded cooling methods (such as ACC accelerated cooling system) to accurately control the metallographic structure.
Mathematical model and simulation: Establish a process simulation system based on CCT/TTT curve and heat transfer model to predict the microstructure transformation and stress distribution of steel pipes of different specifications during heat treatment, and guide process optimization.
Residual stress reduction: Promote thermal tension reduction (TSR) technology and online/offline thermal straightening to significantly reduce the residual stress of finished pipes.
Intelligent detection and big data analysis
Full coverage of non-destructive testing: Integrate ultrasonic flaw detection (UT - detection of internal defects), eddy current flaw detection (ET - surface and near-surface defects), magnetic flux leakage detection (MFL), industrial endoscope (inner surface detection) to achieve 100% online automatic flaw detection.
Quality data platform: Establish an MES/QMS system covering the entire process of "smelting-rolling-heat treatment-detection", associate process parameters with quality results, and use AI to trace the causes of defects, predict quality, and intelligently recommend process parameters.
Build a closed-loop quality management system
Standardization and SOP: Formulate internal control standards that are stricter than national standards/industry standards, and refine the standardized operating procedures (SOPs) of each process.
Traceability mechanism: Establish a unique identification system for the entire process from finished pipes to smelting furnace numbers to achieve accurate positioning of quality problems and definition of responsibilities.
Continuous improvement (PDCA): Based on quality data and customer feedback, continue to conduct process reviews, failure analysis (FMEA) and optimization improvements.
