Hot Rolled Pipe Defects Causes and Quality Standards

Hot-rolled steel pipes, particularly hot-rolled seamless steel pipes, are widely used in critical industries such as oil & gas, construction, and boilers due to their superior strength and durability. However, certain defects may occur during the manufacturing of these hot-rolled pipes, affecting their performance and safety. This comprehensive guide explores common defects in hot-rolled seamless steel pipes, their root causes, and industry acceptance criteria.

1. Indentations (Surface Dents) in Hot-Rolled Pipes

Defect Characteristics

· Irregular or regular dents frequently observed on the longitudinal surface of hot-rolled seamless steel pipes

· Various forms including pits, strips, transverse marks, peeling, or fragmented metal chips

Primary Causes in Hot-Rolled Pipe Production

· Roll contamination: Metal debris accumulation on stretch-reducing mill rolls during hot rolling

· Process issues: Foreign materials pressed into the surface of hot-rolled steel pipes

· Handling damage: Impact marks occurring during transportation of hot-rolled pipes

Quality Standards for Hot-Rolled Seamless Pipes

For standard hot-rolled pipes with wall thickness ≤8mm, indentations must not exceed 90% of negative tolerance (max 1.0mm). Thicker hot-rolled seamless steel pipes (>8mm) allow up to 80% of negative tolerance.

2. Longitudinal Scratches in Hot-Rolled Seamless Steel Pipes

Defect Characteristics

· Continuous grooves running along hot-rolled pipes, affecting both internal and external surfaces

Manufacturing Causes

· Tooling wear: Mandrel issues during the hot-rolling process of seamless pipes

· Temperature control: Suboptimal rolling temperatures in hot-rolled pipe production

· Acceptance Criteria for Hot-Rolled Steel Pipes

External scratches on hot-rolled seamless pipes must stay within 90% of wall thickness tolerance (max 1.0mm). For demanding applications, hot-rolled boiler pipes restrict scratches to just 5% of wall thickness.

3. Out-of-Roundness in Hot-Rolled Pipes

Quality Impact

· Non-circularity in hot-rolled seamless steel pipe cross-sections

Production-Related Causes

· Improper handling during the cooling phase of hot-rolled pipe manufacturing

· Equipment misalignment in stretch-reducing mills for hot-rolled steel pipes

4. Wall Thickness Variation in Hot-Rolled Seamless Pipes

Defect Severity

· Critical quality parameter for hot-rolled pipes used in high-pressure applications

Root Causes

· Inconsistent billet quality in hot-rolled seamless steel pipe production

· Process control issues during the hot-rolling operation

5. Bending Issues in Hot-Rolled Steel Pipes

Common Problems

· Curvature defects particularly noticeable in longer hot-rolled seamless pipes

Manufacturing Solutions

· Proper cooling system design for hot-rolled pipe production

· Precision alignment of finishing stands in hot-rolling mills

Conclusion: Quality Assurance for Hot-Rolled Seamless Steel Pipes

To maintain the highest quality standards in hot-rolled steel pipe production, manufacturers must:
✔ Implement rigorous temperature monitoring throughout the hot-rolling process
✔ Conduct regular tooling inspections for seamless pipe production
✔ Adopt advanced process controls for hot-rolled pipe manufacturing

Understanding these common defects helps buyers make informed decisions when sourcing hot-rolled seamless steel pipes for industrial applications.