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Introduction

Longitudinal welded pipes (LWPs) are essential in industries such as oil & gas, construction, and automotive due to their high strength-to-weight ratio and cost-effectiveness. However, improper manufacturing and handling can lead to fractures, causing costly failures. This guide explores the root causes of longitudinal welded pipe breakage and provides actionable solutions to enhance durability.

Common Causes of Longitudinal Welded Pipe Fracture

1. Residual Stresses from Cold Working

Cold drawing is a common method to enhance the strength of longitudinal welded pipes, but it introduces residual stresses. If not properly relieved, these stresses lead to microcracks and eventual fractures under operational loads.

2. Excessive or Insufficient Deformation

路&苍产蝉辫;Over-Deformation: Stretching grains into a fibrous structure reduces ductility, making the pipe brittle and prone to cracking.

路&苍产蝉辫;Under-Deformation: Fails to meet required strength and dimensional precision, leading to premature failure.

3. Material Anisotropy & Weak Welds

Longitudinal welded pipes exhibit anisotropic behavior鈥攕tronger along the grain direction but weaker perpendicularly. Poor welding techniques can further weaken the seam, creating fracture initiation points.

4. Improper Heat Treatment

Skipping stress relief annealing after cold working leaves internal stresses unaddressed, accelerating crack propagation under pressure or cyclic loading.

Proven Methods to Prevent Longitudinal Welded Pipe Fracture

1. Optimized Alloy Composition

Adding elements like chromium, molybdenum, or vanadium improves:

路&苍产蝉辫;Strength & Toughness 鈥� Reduces crack susceptibility.

路&苍产蝉辫;Weldability 鈥� Minimizes defects in the heat-affected zone (HAZ).

2. Precision Cold Drawing with Controlled Deformation

路 Maintain deformation within 15-30% to balance strength and ductility.

路&苍产蝉辫;Use multi-pass drawing for uniform grain structure.

3. Mandatory Stress Relief Annealing

路&苍产蝉辫;Process: Heat to 600-650掳颁, hold, then slowly cool.

路&苍产蝉辫;Benefits: Eliminates residual stresses, restores ductility, and prevents stress corrosion cracking.

4. Advanced Welding Techniques

路&苍产蝉辫;Submerged Arc Welding (SAW): Ensures deeper penetration and fewer defects.

路&苍产蝉辫;Post-Weld Heat Treatment (PWHT): Refines grain structure near welds.

5. Non-Destructive Testing (NDT) for Quality Assurance

路&苍产蝉辫;Ultrasonic Testing (UT): Detects internal flaws.

路&苍产蝉辫;Radiographic Testing (RT): Identifies weld defects.

路&苍产蝉辫;Hydrostatic Testing: Verifies pressure resistance.

Industry Applications & Case Studies

Oil & Gas Pipelines

路&苍产蝉辫;Challenge: High-pressure environments cause longitudinal welded pipes to fail at weak seams.

路&苍产蝉辫;Solution: PWHT + SAW welding improves fracture resistance.

Structural Engineering

路&苍产蝉辫;Challenge: Cyclic loads lead to fatigue cracks.

路&苍产蝉辫;Solution: Controlled cold drawing + annealing enhances fatigue life.

Conclusion: Ensuring Longevity of Longitudinal Welded Pipes

Preventing fractures in longitudinal welded pipes requires a multi-faceted approach:
鉁�&苍产蝉辫;Material optimization with alloying elements.
鉁�&苍产蝉辫;Precision cold working within safe deformation limits.
鉁�&苍产蝉辫;Stress relief annealing to eliminate residual stresses.
鉁�&苍产蝉辫;High-quality welding & NDT to detect flaws early.

By implementing these best practices, manufacturers can produce high-performance longitudinal welded pipes that withstand extreme conditions while minimizing failure risks.