The production process of welded steel pipes involves forming steel sheets or strips into the desired cross-sectional shape using straight press rolls or helical methods, and then welding them together using heat, pressure, or other methods. As a result, defects in welded steel pipes can be categorized into two main types: base material defects and weld defects.
1. Base Material Defects
Base material defects originate from the steel sheet or strip used in production. These defects are typically planar and parallel to the surface. The most common base material defects include:
- Delamination: Layered internal defects that can lead to various cracks when subjected to tensile stress perpendicular to the surface, severely affecting the strength of the steel pipe.
- Inclusions: Non-metallic materials trapped within the steel, compromising its structural integrity.
- Cracks: Fractures within the steel that can propagate and weaken the pipe.
- Folds: Overlapping material that can create weak spots.
2. Weld Defects
Weld defects occur during or after the welding process and can significantly impact the quality and safety of the steel pipe. These defects include:
- Cracks: Fractures in the weld that can compromise the pipe's integrity.
- Pores: Small cavities within the weld caused by trapped gas.
- Slag Inclusions: Non-metallic solid material trapped in the weld.
- Incomplete Penetration: When the weld metal does not fully penetrate the joint thickness.
- Incomplete Fusion: When the weld metal fails to fuse properly with the base metal.
- Undercut: A groove melted into the base metal adjacent to the weld, reducing the pipe's thickness.
Weld defects such as porosity, slag inclusions, cracks, lack of fusion, and incomplete penetration can significantly affect the strength, plasticity, and overall quality of the steel pipe. These defects can directly impact the safe operation and service life of pipelines, especially in critical applications like oil and gas transportation. Therefore, thorough inspection and detection of these dangerous defects are crucial to ensure the quality and safety of welded steel pipes.
