TPT May 2016

T E CHNOLOG Y Monitoring tube production to find scarfing defects By Cameron Serles, Xiris Automation Inc, Canada

Detecting if the scarf tool is properly adjusted is a difficult task to do on a continuous basis. In particular, some thick walled tube and pipe mills make precision end products with multiple scarfing tools that operate sequentially to make successive cuts to the weld bead down to the parent material. If not correctly adjusted, the tube or pipe could end up with an incorrect profile shape where the scarf occurred. A way to make sure the right amount of material is removed from the welded tube is important. If placed after the scarfing process on a tube mill, a laser- based inspection tool can measure the scarf width and bead height left behind after a scarfing process to provide quality control of the scarfing process itself. the scarf width is defined as the length of the ‘flat’ portion of the tube that appears after the weld bead has been removed. Scarf width measurement can change quickly during production as the pipe or tube moves up or down, causing the scarfing tool to cut deeper or not as deep into the weld bead. Therefore it is best to average the scarf width over a number of inspections, in order to make the measurement stable. Laser-based inspection systems typically use a sensor head incorporating a laser line and a camera whose optical axis is offset to the axis of the laser line by an ‘offset angle’. The sensor head 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 cut or out of round profile can be mathematically detected. The best laser-based inspection systems base all of their measurements on the

RECENT advancements in camera and optics technology have come together to make a new type of inspection device able to see defects related to the forming and welding area of a tube or pipe. 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. The result is improved quality assurance and process control on the production line. scarfing is a process of removing excess weld bead on a pipe or tube to create a desired shape. It is done by longitudinally planing or grinding the welded tube or pipe right after the welding process. If it is performed perfectly, the resulting profile will match the ideal shape of the parent material. However, if the scarf tool is set to plane or grind too much material, or not enough, the resulting profile could appear too deep or leave a weld bead above the parent material. In Figure 1, the scarf tool has not cut deep enough into the weld bead, creating a flat surface along the top of the weld bead, but narrower than the bead width. In Figure 2, the scarf tool has cut too deeply, removing some of the parent material as well as the top of the weld bead, producing a much wider scarf width. Typically, NDT systems are used to detect defects on a tube and pipe mill. However, some defects, such as those caused by scarfing, cannot be easily detected. In contrast, a laser inspection system can scan the surface of the tube near the weld zone. This lets operators know how well their scarfing tool has been set to match their process, allowing them to perform corrective action before significant scrap occurs. this ability is especially helpful for one of the most common defects found across all types of tube and pipe manufacturing: scarf defects.

Figure 1: Result of a scarf tool not cutting deep enough

Figure 2: Result of a scarf tool cutting too deeply

Figure 3: The scarf width, where w = the width of the scarf cut

of the actual laser profile, the ideal mathematical profile and the size of the pixels in the image, a laser inspection system can rapidly determine the scarf width – a task that is difficult to accomplish using traditional NDT quality control tools such as eddy current or ultrasonic testing techniques. Figure 4 shows an image taken from a laser-based inspection system. a laser profile is shown of a welded tube, after the scarfing operation. the area of the scarfing does not reflect the laser line as well as the area outside of the scarfing, so the scarfed area can be easily detected and measured. As the scarf cuts deeper into the material, the scarf width will increase; as it cuts shallower, the scarf width will decrease. In such a way, by measuring the width of the scarf zone, the depth of the scarf cut can be inferred. Laser-based inspection systems offer an effective way for tube and pipe producers to monitor the quality of their scarfing process on a real-time basis.

differences between the actual laser profile line seen by the camera, and the ideal mathematical profile based on the tube parameters. Using the position

Figure 4: Image of an ideal scarf zone

Xiris Automation Inc – Canada Fax: +1 905 331 6661 Email: sales@xiris.com Website: www.xiris.com

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M ay 2016