Inspection of thick welded joints using laser-ultrasonic SAFT.

Area of Science:

• Materials Science and Engineering
• Non-Destructive Testing
• Welding Technology

Background:

• Early detection of defects in thick butt joints is crucial for reducing costs and rework in multi-pass arc welding.
• Non-contact methods like laser-ultrasonic technique (LUT) offer potential for automated, online inspection of welds during manufacturing.

Purpose of the Study:

• To evaluate the effectiveness of LUT combined with synthetic aperture focusing technique (SAFT) for detecting defects in thick steel butt welds.
• To demonstrate the capability of this technique for inspecting welds during different stages of the multi-pass welding process.

Main Methods:

• Laser-ultrasonic technique (LUT) was employed for non-contact defect detection.
• Synthetic aperture focusing technique (SAFT) was utilized for image reconstruction and defect localization.
• Artificial defects (EDM slits) were introduced at various depths in 25mm and 50mm thick steel butt welds.
• Line scans were performed with superimposed laser generation and detection spots on the weld surface.
• A CCD line camera captured surface profiles for SAFT processing correction.

Main Results:

• LUT combined with SAFT successfully visualized both artificial and real defects in completed and partially welded thick butt joints.
• The technique demonstrated effectiveness in detecting simulated lack of fusion defects at different depths.
• Surface profile data acquisition aided in accurate defect visualization through SAFT processing.

Conclusions:

• The laser-ultrasonic technique coupled with SAFT shows significant potential for automated inspection of thick arc welds and hybrid laser-arc welds.
• This non-contact approach can be integrated into manufacturing processes for real-time quality control and defect identification.
• Early defect detection using LUT-SAFT can lead to substantial cost and time savings by minimizing rework.