Keeping the operator involved in the act of automating pipe welding
September 1, 2009
Automation has emerged as an alternative to manual welding, but these robotic and fixed automation technologies tend to work for specific applications, rather than general pipe fabricating. Automation coupled with the flexibility of a human operator during the welding process, however, represents a new alternative for those companies looking to squeeze more productivity out of the pipe fabricating process.
Pipe welders follow "spool" drawings that map out how the fit-ups are to be joined and how they fit into the overall piping structure to be constructed in the field.
When it comes to welding pipe, a welder has to be highly skilled and prepared for many variables. No two jobs are exactly alike, even when they are somewhat similar.
The welder has to be skilled enough to perform code-quality, multiple-pass welding and be experienced enough to recognize when the weld joint will require modifications in technique and parameters to achieve success. In some instances, the welder has to be strong enough to work in unusual positions over large and awkward part configurations and be flexible enough to accommodate inconsistent fit-ups and endless varieties of fittings. It's not an easy job, and employers do not find a deep pool to fish from when they are looking for welding talent in the oil-rich economies of North America.
Automation has long been an alternative to manual welding, but these robotic and fixed automation technologies tend to work for specific applications, rather than general shop pipe fabricating. Robotic automation coupled with the flexibility of a human operator during the welding process, however, represents a new alternative for those companies looking to squeeze more productivity out of the pipe fabricating process.
Not everyone has had the chance to visit an oil refinery or a chemical processing plant to see the miles of piping that wind their way throughout the plant. Even without that personal experience, it is easy to envision all of the pipe configurations with different diameters and wall thicknesses joined to all kinds of connections (flanges, elbows, T's, etc.) needed to complete the maze of connecting pipe.
Engineers create spool drawings that provide the pipe fabricator with a 2-D representation of the pipe section that needs to be created. These drawings detail the elevations, angles, pipe characteristics, fitting sizes, and other specifications needed to create the final pipe fabrications, or "spools."
At the fabrication shop, the joining process begins at the material preparation station where spool segments are prepared. Bevels are created on the ends to lay down the multiple weld passes, and any other pipe end or surface preparation typically takes place at this time.
From there the segments go to the fit-up station where a pipe fitter connects all of the pieces with tack welds to prepare them for the welder. During this stage, inconsistencies often arise, such as larger-than-normal gaps between pipe segments, or material problems are magnified, such varying pipe roundness (or "out-of-round") or a fitting that doesn't perfectly match the adjoining pipe section.
The result is often a part that is unique to a particular spool section, unlikely to be duplicated for another job or even the next section to be fit and welded.
Because of the nearly infinite variation of weld joints, manual welders have long been the logical choice to tackle pipe welding projects. They are flexible and can work on numerous joint types. This is especially evident when it comes to huge section lengths that are difficult to move around a shop.
Manual welding also has its shortcomings. Weld quality may differ from one welder to another. Welders can get fatigued quickly when working in strenuous positions and maintaining a welding arc for extended periods of time, which could lead to more downtime or poor-quality workmanship. Probably the biggest issue is that companies couldn't find enough experienced journeyman pressure pipe welders when the energy markets jumped into full-scale development mode. The current slowdown certainly isn't encouraging more workers to enter the welding field, so this dearth of skilled labor is likely to continue, especially when the work loads increase.
As in other areas of metal fabrication, automation is an attractive alternative. Several approaches can be taken.
Basic Automated Welding. This covers 1G position welding, or flat-position groove welding, where a fixed welding torch on a manipulator is positioned at the pipe weld joint. The pipe section, which sits horizontally on pipe rolls, is then rolled in place as the weld is applied (see Figure 1). This type of welding is done in a majority of pipe welding shops.
This setup has some advantages. The 1G position allows for the use of high-deposition processes, such as submerged arc welding, and nonstop, multipass welding usually is easy to accomplish.
However, these systems are usually large in size and are fixed in their location. This often results in extra part handling and limits the amount of welding that can be accomplished when compared to using the typically more abundant manual weld stations.
Orbital GMAW/FCAW. This approach is most suitable for fixed-position weldments (see Figure 2). Orbital systems offer excellent real-time function and parameter control and some program memory.
A manual root pass may be required before engaging the equipment, and the orbital welding units do not accommodate certain spool configurations as the equipment requires some parking space on the pipe section to be welded. Also, the required setup time for 1G rotated weldments can make it hard to compete with manual welding.
Robotics With Sensing. Robots with vision-based sensing or through-the-arc sensing represent some of the most cutting-edge technology in the fabricating market. The multiaxis robotic arms can work around almost any part geometry and perform the work quickly and consistently (see Figure 3).
Each new part, however, does require programming, which might take several hours to develop depending on the software program. Most companies invest in a robotic operation with sensing for high-volume pipe applications where part tolerances can be significantly better than one-offs.
Additionally, because traditional robots have such a wide envelope of movement, safety precautions have to be taken to protect nearby workers. This usually means using light curtains and/or constructing a cage around the robotic cell.
A hybrid approach (see Figure 4), in which an operator controls the placement of a robotic welding head and the welding process, holds the promise of offering the consistency of robots, but with the flexibility to address the infinite variables involved in pipe welding.
In this setup, a small robot sits on the end of a large manipulator with a reach of about 30 feet. An operator, not necessarily a journeyman pipe welder, can move the weld torch attached to the robot onto the pipe at the joint area that needs to be welded.
As the robot is manually moved to the weld joint, the hybrid robot's programming is strictly based on the weld joint preparation. For example, a program made for mild steel pipe with a 0.5-in. wall thickness and a 60-degree bevel will work for almost any pipe diameter with the same wall thickness and joint preparation. Thus, the number of programs required for a broad range of applications is dramatically less than a traditional robot that also must account for joint location and diameter.
How long does it take to start welding once the part is in place? It takes about a minute or about as long as it takes a manual welder to strike an arc.
Real-time human interaction with the robot adds another level of quality control because, with welding helmet on and pendant control in hand, the operator can ensure the weld is tracking the way it is supposed to. If a large gap or some other problem arises during the weld, the operator can alter the weld pattern or the welding parameters to address the inconsistency immediately instead of having to wait until the end of the process and reworking the weldment.
The robot used in the hybrid process does not have a large window of movement—actually about 4 by 4 by 4 in.—so the addition of the typical robotic safety barriers is not necessary. If a large pipe section needs to be fabricated and moving it is not an option, the hybrid equipment can be moved to where the welding needs to take place.
As with other forms of automation, several monitoring capabilities are offered. For instance, a data flag can be raised if a weld is not done at a certain quality/parameter level. Remote system monitoring with a camera and remote system control also can be utilized.
The hybrid approach is one more automation choice for pipe fabricators looking for some relief in the complicated world of pressure pipe welding.