Non-obstructive measurement technique for inner wall defects in small-diameter pipes

Area of Science:

• Optical Engineering
• Non-Destructive Testing
• Petroleum Engineering

Background:

• High-pressure flexible hoses in oil and gas drilling present challenges for inner wall defect detection due to small diameters and long lengths.
• Existing structured light methods are hindered by supporting structures, preventing complete scanning and measurement of the inner pipeline surfaces.

Purpose of the Study:

• To develop a novel conical structured light scanning measurement system for unobstructed inner wall inspection of pipelines.
• To address limitations of existing methods by enabling complete scanning and accurate defect detection in challenging geometries.

Main Methods:

• Developed a system with dual cameras and lasers on the same side, incorporating a vertical measurement camera to supplement horizontal imaging.
• Utilized pinhole imaging models and spatial conical surface properties to analyze system performance and overcome pixel-to-world coordinate mapping issues.
• Calibrated the system for conversion between pixel distance and 3D spatial distance for accurate measurements.

Main Results:

• Achieved blind-spot-free scanning and detection of pipeline inner walls by integrating a vertical camera.
• Tested on pipes (51 and 64 mm inner diameter) with known defects, yielding a root mean square error of defect size ≤0.076 mm.
• Demonstrated robustness within a certain pipe bending range and analyzed system errors like tilt and laser strip irregularity.

Conclusions:

• The developed conical structured light system effectively measures inner wall defects in small-diameter, long pipelines.
• The system demonstrates high application value and meets practical engineering requirements for oil and gas industry inspections.
• The dual-camera approach successfully overcomes previous scanning limitations, ensuring comprehensive defect assessment.