Common Defects and Prevention of Hot-Rolled Steel Pipes

Hot-rolled steel pipes are critical to modern engineering—from high-pressure energy transmission and petrochemical piping to construction, machinery, and boilers. Yet their production—involving high-temperature deformation, piercing, rolling, sizing, and controlled cooling—renders them prone to defects if any step lacks precision. Such flaws degrade mechanical properties, risk safety hazards, leaks, and higher operational costs. Understanding common defects, their causes, and proven prevention methods is vital to ensuring product integrity and compliance with standards like ASTM A106, API 5L, EN 10210, and GB/T 8162.

1. Surface Defects

Surface issues are visually identifiable and harm both aesthetics and integrity. Rapid oxidation and high deformation in hot rolling amplify small inconsistencies.

1.1 Cracks

Longitudinal, transverse, or irregular cracks are severe—forming from pre-existing billet micro-cracks or excessive rolling tensile stress. Improper temperature control, high reduction ratios, or abrupt force changes accelerate propagation, undermining ductility and pressure resistance. Prevention: Strict billet ultrasonic testing (UT), maintain rolling temperatures, optimize pass deformation, and ensure uniform material flow.

1.2 Scabs and Laps

Scabs—raised patches from folded/detached surface layers—stem from incomplete descaling or billet defects, creating weak zones that peel during machining/welding. Prevention: Improve high-pressure descaling, stabilize rolling equipment, shorten billet oxidation time, and ensure clean billet surfaces pre-rolling.

1.3 Scale Pits

Scale pits—irregular depressions from pressed-in oxide scale—harm appearance and cause coating adhesion or corrosion. Prevention: Minimize billet air exposure post-heating, upgrade descaling systems, maintain uniform heating, and optimize furnace atmosphere to cut oxidation.

2. Geometric Defects

Geometric accuracy is key for fit, weldability, and performance. Complex deformation and uneven cooling often cause dimensional distortion.

2.1 Ovality

Ovality—deviations from roundness—hinders fitting, welding, threading, and pressurization, arising from uneven rolling forces, tool wear, mis-centered material, or uncontrolled cooling. Reduce it via regular roll groove maintenance, precise piercing centering, optimized inter-stand tension, and controlled cooling.

2.2 Wall Thickness Variation

Longitudinal/circumferential thickness deviation impairs strength and pressure ratings, stemming from piercing misalignment, uneven deformation, worn mandrels/guide shoes, or unstable reduction. Prevent with high-precision piercing alignment, calibrated mandrels, optimized passes, proper lubrication, and continuous rolling force monitoring.

3. Internal Defects

Undetectable visually, these flaws impact performance and weldability—found via UT, eddy current testing (ET), or hydrostatic inspection.

3.1 Laminations

Layered separations in the metal matrix come from improper billet metallurgy (e.g., segregation or raw material defects). Unfused weak layers risk bursting under pressure. Prevention: Strict steelmaking quality control, improved refining, high-frequency billet UT, and optimized casting to eliminate segregation.

3.2 Non-Metallic Inclusions

Inclusions (oxides, sulfides, slag) reduce toughness and trigger stress cracks, from molten steel impurities, poor slag removal, contaminated molds, or subpar refining. Prevent with stronger ladle metallurgy, better desulfurization/deoxidation, cleaner casting, and strict pre-rolling internal checks.

4. End Defects

Ends are vulnerable to damage from cutting, beveling, or calibration.

4.1 End Cracks and Burrs

End cracks form from improper cutting temperatures, excessive sawing stress, or misaligned supports; burrs hinder threading/welding. Prevention: Automated cutting with stable cooling, regular blade replacement, proper end support, and verifying cutting temperature to avoid brittleness.

5. Integrated Prevention Strategies

Systematic control across raw materials, process, equipment, and inspection is key:

· 
· Use high-quality billets with strict UT/ET.
· Apply high-pressure descaling pre-rolling for clean surfaces.
· Ensure precise piercing/mandrel alignment for stable thickness.
· Optimize rolling parameters (temperature, reduction, speed).
· Use controlled cooling to prevent deformation.
· Implement automated inline flaw detection.
· Maintain rolling mills, mandrels, and guides strictly.

Conclusion

Hot-rolled steel pipes are vital to many industries, but quality depends on rolling precision and metallurgical control. By addressing common defects—surface, geometric, internal, and end—and using robust, data-driven prevention, manufacturers boost reliability, cut costs, and ensure safe, efficient use in high-pressure pipelines, structures, and thermal equipment.

Read more : Methods for improving the surface quality of hot rolled steel platesor Hot-dip vs Cold galvanized pipe