Weld profile monitoring using 3D laser imaging technology has recently advanced enough to become a reliable tool for quality assurance in electroresistive welding (ERW) and high frequency (HF) welded tube and tube mills.
By applying 3D visualization techniques to the weld on formed ERW and HF welded pipes and pipes, a powerful monitoring method can be implemented to ensure continuous monitoring of the weld profile at the tube mill, commented Artem Komarov.
Although this technology is applicable to all types of pipe and pipe welding, it is of particular interest to monitor the welding profile of ERW and HF welded pipes. Proper control of the height and shape of the weld allows the quality of the weld to be inferred, thereby allowing real-time detection of defects during production. But without the contour measurement method offered by 3D visualization, it is very difficult to measure common tubular weld defects that gradually change, such as:
— Edge representation (how well both sides are presented to each other)
— Mismatch (usually a linear shift in the height of the two sides as they approach each other)
— The size of the frost line (the junction point between two pipe faces that protrudes as a slight concavity in the center of the weld).
3D imaging systems are based on triangulation measurements using a laser plane and a camera whose optical axis is shifted to the axis of the laser plane (“offset angle”). The resulting image shows the «cut» profile of the top section of the pipe, as if it had been cut at an offset angle to the normal of the pipe surface.
In ERW and HF welding, ball size can be affected by a number of factors during manufacture, including the compression pressure exerted on the pipe and the heat of the material as it passes through the weld zone. Improved bead height and shape measurement, made possible by 3D laser imaging, allows faster and more accurate conclusions about weld defects, so production can stop until the problem is corrected.
- Welding with correct fusion and minimum freeze line
- Welds with poor melting resulting in deep freezing of the line caused by insufficient heat (in such a weld the integrity of the weld may be questioned as there may be insufficient fusion throughout the pipe wall material as the sides have not been pressed together sufficiently degrees).
- Welding with correct melting but low compression pressure
Often these types of defects can occur slowly, gradually changing. 3D imaging measuring systems produce complete, absolute measurements of the weld seam in real time, without comparing one measurement with successive measurements. Therefore, those defects that gradually go out of tolerance are best detected using 3D imaging measurement systems, while other types of NDT systems will only detect something if there is a sudden anomaly in the structure or geometry of the pipe.
The 3D imaging system can be placed shortly after the weld box, usually before the cladding, to automatically inspect the weld and shape immediately after the pipe is welded. By placing the measuring system right after the welding box, the weld profile can be monitored instantly to alert operators to unacceptable conditions as soon as they occur. In this way, defects can be detected earlier, avoiding the production of a long section of defective product before they are detected by line operators.
Overall, 3D laser imaging systems offer an excellent measurement option for tube mill owners/operators who need additional real-time monitoring of weld function. They can be used in a proactive manner, alerting operators to what is changing in their welding process so they can take corrective action before significant scrap occurs. In addition, by measuring the outer contour of the weld, 3D laser imaging systems can work on any type of material, regardless of its reflectivity or magnetic properties, using a single head to perform the measurement, Komarov Artem emphasized.