Recent advancements in machine vision technology have made a new type of inspection able to see defects related to the forming and welding area of a tube or pipe. The result is improved quality assurance and process control on the production line. The new type of inspection device is a laser-based triangulation system that measures the outside contour of a tube or pipe in the vicinity of its weld.
Typically NDT systems are placed at the end of a production as a final check. However, the laser inspection system can be placed directly after the weld box. This system can let operators know what is changing in their welding process, allowing them to perform corrective action before significant scrap occurs. This capacity is especially helpful for one of the most common defects found across all types of Tube manufacturing: Tube Forming Defects, otherwise known as Deflection.
The Deflection Defect
Defection is defined as the overall variance of the tube parent material from an ideal circle. This defect moves the starting point of all other defects that the Xiris WI2000p measures, up or down. The deflection measurement detects the overall deflection from the ideal circle to the closest tube side within the bead area. The deflection metric is determined by measuring the distance between the sections of the parent material outside of the weld bead width and the ideal profile line. The deflection usually represents the overall offset of the tube walls before welding and is indicative of forming set up or variances in the parent material’s metallurgy.
The drawing below illustrates the defect:
The Defection Defect, where “h” = the height of the defect.
How the WI2000p System Measures the Deflection Defect
Xiris Automation Inc. has developed a non-destructive inspection system called the WI2000p Weld Inspection System. The WI2000p includes a laser line and a camera whose optical axis is offset to the axis of the laser line by an “offset angle”. The WI2000p creates a visible cross-section of the tube by projecting the laser line on to the tube and capturing an image of the line using the camera. The resulting image shows a profile of the tube surface as if it were cut in cross section. If a tube is ideally round, the laser image will represent a section of an ellipse and any anomaly such as a tube deflection can be mathematically detected.
The WI2000p bases all of its measurements on the differences between the actual laser profile line seen by the camera, and the ideal mathematical profile based on the tube parameters. By knowing the position of the actual laser profile, the ideal profile, and the size of the pixels in the image, the WI2000p can detect Deflection profile defects that often escape detection by other quality tools such as Eddy Current testing, or Ultrasonic Testing techniques
Conclusion
A new technique for detecting Deflection on welded Tube and Pipe has been developed by Xiris and is known as the WI2000p weld inspection system. The WI2000p system is a laser based inspection system that is capable of detecting Deflection defects immediately after welding to alert the operator of a defect in time to minimize rejects. The result is improved quality, fewer field defects and a more reliable method for the operator to optimize the welding process.
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