Manufacturing Defects of SSAW Steel Pipe

Surface folding defects are a common quality problem in SSAW steel pipe production. These defects are often invisible to the naked eye and are difficult to detect effectively with traditional eddy current testing equipment. More problematic is that these defects sometimes trigger alarms using other testing methods, while eddy current testing fails to respond, leading to inconsistent test results and complicating quality control.

Application of Phase Analysis Eddy Current Testing: 

Since the advent of eddy current testing devices with phase analysis capabilities (such as multi-frequency eddy current or array eddy current technology), the above problems have been significantly improved. These devices can distinguish defects based on their phase characteristics, effectively improving the detection rate of surface folding defects. However, selecting appropriate instruments and probes and correctly adjusting the testing parameters remain crucial steps to ensure testing effectiveness.

Influence of Defect Orientation on Detection Sensitivity: 

The orientation of the defect relative to the optimal sensitivity direction of the testing method is another key factor. Theoretical and experimental studies show that when artificial grooves are at an angle to the normal direction of the pipe surface, defects parallel to the surface (such as layered defects) are difficult to detect effectively by magnetic flux leakage (MFL) testing. Furthermore, in some steel pipe production tests, the magnetic flux leakage method also showed limited detection capability for penetrating voids in the spiral steel pipe wall.

Advantages and Requirements of Eddy Current Testing: Eddy current testing (ET) has been widely used for quality inspection of spiral steel pipes for many years due to its fast detection speed and sensitivity to surface and near-surface defects, especially in assessing the tightness of steel pipes. Practical applications show that crack-like defects in ferromagnetic spiral steel pipes place higher demands on eddy current testing, thus requiring the use of highly sensitive probe coils and strict adherence to relevant testing standards (such as GB/T 7735, ASTM E309, etc.).

Method Comparison and Recommendations:
1. Eddy Current Testing (ET): Applicable to surface and near-surface cracks and folds.
Advantages: Fast detection speed; phase analysis can distinguish defect types.
Limitations: Limited sensitivity to ferromagnetic materials; requires a high-sensitivity probe.

2. Magnetic Flux Leakage (MFL): Suitable for volumetric defects and corrosion pits.
Advantages: Can detect internal defects.
Limitations: Insensitive to layered defects parallel to the surface and small pores.

Recommended Solution: 

For surface folds and cracks in spiral welded pipe production, eddy current testing equipment with phase analysis capabilities should be prioritized, supplemented by appropriate calibration samples and strict process parameter control. For thick-walled pipes or scenarios with high requirements for internal defects, a comprehensive inspection can be performed using magnetic flux leakage.

Conclusion: 

Eddy current testing technology plays an irreplaceable role in the surface defect detection of spiral welded pipes, but its effectiveness is highly dependent on probe selection, instrument adjustment, and the understanding of defect orientation. By introducing phase analysis capabilities, optimizing detection parameters, and combining with other detection methods (such as magnetic flux leakage), the overall quality control level of steel pipes can be significantly improved.

Read more: Seamless pipe vs Spiral pipe: What's the difference?