Keeping welding costs from spiraling out of control

The camera technology used for seam tracking and weld inspection is based on the principle of laser triangulation. A low-power laser beam is projected onto the surface of the part, and the reflected scattered light is delivered back in the form of an image onto a complementary metal-oxide semiconductor sensor. The controller then extracts signals from the image that can be used for either tracking or weld inspection purposes (Figure 3).

Before seam tracking of the pipe's outside-diameter groove weld can take place, the inside weld is made first. The outside diameter tracker is mounted about 4 inches to 6 in. in front of the welding torch and tracks the joint. Via a delayed shift, the tracker tells the two axis—cross-seam and up/down—slides to apply the correct trajectory shift when the wire reaches the point where the variation was measured. In this way, the wire is kept exactly in the correct position in the joint for maximum weld penetration. Figures 4a and 4bshow the equipment at work.

Before Skyline Steel could embark on its weld improvement project, it needed to select the right technology partner for its laser vision seam tracker.

The primary criteria used for this selection included technical support from purchase through production; the system's ease of use and robust design; a record of successful installations; a commitment to work on future enhancements; and a fair price.

After reviewing technology suppliers recommended by industry contacts or found on the Internet, company management selected three companies, which were then invited to the plant to learn more about Skyline Steel and the spiral welding process.

Based on the budgetary quotes received, the Skyline Steel team eliminated one of the three finalists. They then traveled to the facilities of the final two technology suppliers to evaluate their capabilities in engineering, production, quality control, and service. They also followed up with references to discover how successful those pipe fabricators had been with similarly installed equipment.

With the due diligence complete and formal quotes in hand after the three-month process, Skyline Steel selected Servo-Robot Inc. as its partner on the project. A purchase order for two laser vision seam tracking systems was issued with plans to place the units on two existing manipulators for outside-diameter welding.

Installation Preparation

Preparation for installation took place during the eight-week time period Servo-Robot required to build the systems. Skyline Steel prepared in the following ways:

• Designing and building the mounting structure to hold the AUTO-TRAC™ system equipment, which included motors, slides, controllers, and cameras (Figure 5).
• Getting the right people prepared for the new technology. This step included formal training for the maintenance and engineering people to be involved, as well as discussions with the affected welding operators.
• Scheduling production so a window of at least one week was available to do the retrofit without adversely affecting deliveries.

Once the physical installation was complete, the AUTO-TRAC system was programmed, and trial pipe was tracked to verify proper results were attained. During this time, a couple of issues had to be addressed.

The location of the camera needed to be configured so that it was far enough in front of where the submerged flux would flow. If the camera position were not optimized, the flux could fall down in front of the camera's field of view and confuse things. If the camera were too far out in front, the orientation with respect to the torch could be unwieldy.

The tracking parameters needed to be fine-tuned and a couple different programs created to handle subtle differences in the joint between different pipe diameters, joint preparations, and inside weld penetration into the top side grooves.

Real production welding then began with the operator still monitoring the process, but no longer steering the torch to keep the wire in the joint. After a very short time, the operator was redeployed to another area of the plant. Over time a few different seam tracking programs were made to accommodate further variations in pipe diameters and joint preparations.

The Results Reveal...

Skyline Steel management was pleased with the addition of the seam tracker and believes it achieved a payback on the equipment in less than one year. The company reduced welding defects, such as lack of full penetration, by approximately 50 percent to 60 percent; increased the rate of travel speed by 25 percent to 30 percent; reduced rework and re-inspection caused by welding defects; and eliminated labor cost because a person was no longer needed to watch the welding torches and constantly steer the manipulators. Additionally, Skyline Steel began chasing after new business in the area of high-quality, full-penetration pipe.

The success at the Cartersville, Ga., plant led to the installation of several more units for both outside- and inside-diameter welding over the next few years at other U.S. plants. The big difference with the inside-diameter welding is that there is an opportunity (in addition to tracking) to use the mismatch/gap data to drive the bridge control, which changes the angle that the steel (skelp) is oriented to the weld joint. Figure 6 shows the concept of how the steel is fed. Traditionally, this was manually controlled, which led to overadjustments or changes that weren't made in a timely fashion. Now the exact measurement data is fed back in a timely manner, so the equipment adjusts the skelp entry angle in small increments, improving the weld integrity.

The pipe producer has additional opportunities to use the laser vision technology to improve the overall welding and dimensional quality of the finished pipe:

• Track weld and inspect coil ends during cross splicing
• Measure plate width and edge contour
• Measure pipe OD
• Establish adaptive control of welding parameters
• Automatically inspect inside welds for appropriate geometry or defects
• Automatically provide visual weld inspection of outside welds
• Track weld for ultrasonic testing inspection
• Track outside splice weld joint on finished pipe section
• Guide robotic machining of weld at pipe end
• Track splicing of short pipe
• Measure pipe end preparation for land and angle