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J-Preps and Orbital Welding
When it comes to orbital welding in general, the pipe or tube fit-up is crucially important. The reason the fit-up is so crucial is because orbital welding as we know it today is program-based, meaning that the machine does not really make real-time weld parameter adjustments to compensate for pipe misalignment. Yes, we have some orbital welding machines that can use AVC (arc voltage control) to manipulate the torch height but there are many other parameters that would need to be adjusted in real-time to compensate for fit-up misalignment such as travel speed, background and primary amps, oscillation width, oscillation dwell time, oscillation speed and so on. While we can adjust all of these parameters with our orbital welding machines, many of them are hard to adjust in real-time and so we rely heavily on a precise and clean cut, bevel and accurate fit-up before welding with our orbital welding machine. The machine plays out the same welding program with the same weld parameters on each weld. Therefore, it is crucial that we take away any variables such as bevel inconsistency, pipe ID inconsistency or other misalignment which the orbital welding machine cannot account for.
Why We Use a J-Prep
The reason we prefer to utilize a j-prep for orbital pipe welding is because the j-prep makes for a nice consistent landing so that we can lock-in a uniform welding program for the root pass. We want to reduce the pipe thickness on the landing created by the j-bevel into a uniform landing so that we can perform a fusion TIG root pass with no wire needed. We like this for orbital welding because it makes the root pass program very simple and thus easily repeatable. The j-bevel then cuts the rest of the bevel out with a radius usually 10 degrees after the radius and this allows the orbital welder to fill this in with a uniform oscillating motion. This makes the oscillation simpler to program because it is more uniform than the oscillation needed to fill say a standard 37.5 degree bevel. Again the idea is to create as few variables as possible so that the same welding parameters can make the same x-ray quality welds day in and day out.
How We Control Landing Thickness and Account for Pipe Wall Thickness Variation
Since we know that pipe is not perfectly round nor does pipe have perfect uniform wall thickness and we know it is not likely that you were able to cut the pipe perfectly square we want to account for these variables as well so that we give our orbital welding machine the least amount of variables.
How We Control for Out of Roundness and Wall Thickness Variation
The most practical way to control the pipe wall thickness variations and account for out-of-round pipe for orbital welding is to use an ID-mount pipe end prep tool (or beveler) like our American-manufactured like from Esco Millhog. These tools utilize a three-rib internal clamping system that is patented for Esco Millhog to rigidly lock the tool on the ID of the pipe or tube whilst centering itself automatically. These rugged tools are totally mechanical if utilized with an air motor or they can used with an electric or even a battery powered motor if you so choose. Millhog brand bevelers have been known to last multiple decades with regular annual maintenance. If you are beveling small-bore, heavy-wall pipe we recommend the C-Hog tool from Esco which performs the same uniform fast machine-quality bevels as the ID mounted Esco tools except the C-Hog clamps on the OD of the pipe. The reason the C-Hog is utilized for beveling small bore pipe with heavy wall is that the ID of these pipes can be quite small making it difficult to firmly lock a tool into their ID.
How We Control The Bevel Land Thickness
When beveling for orbital welding it is very important that we have a consistent landing thickness all around the ID of the pipe. This is important because our root pass will be a fusion weld with no wire or oscillation, therefore we want to present the orbital welding head with the same ID landing to weld with the same program each time. By creating an even thickness landing we will avoid any variables that can cause problems with our weld quality. Remember if we add any more variables like a changing wall thickness the machine really cannot account for this in real time and so any needed adjustments would require a new weld program which may not take that much time to make but you do risk failing a weld which is very costly. The way we do this is by inserting a flat, landing blade on one of the three tool posts of the Millhog beveling tool. This flat blade with ensure that our landing is even and perfectly square. If we fail to have a square butt-up joint, there will be gaps in the fitup which can cause our welds to blow through. The other way we control the landing thickness is by inserting a counterbore blade to machine the ID of the pipe. This counterbore blade reaches into the ID of the pipe and machines back some of the bore of the pipe to produce a perfectly round ID. This will further control not only the thickness of the landing but also help minimize high-low misalignment from the out of roundness of the pipe. By utilizing a landing blade and a counterbore blade along with our j-prep beveling blade we control the variables in pipe dimensions that can cause problems in our orbital welding process.
How We Consistently Make Accurate J-Preps
Consistently making accurate J-bevels is easy using the Esco Millhog pipe and tube beveling, counterboring and facing tools. We can not only create perfect j-bevels but we can simultaneously cut a perfect square landing and bore the ID of the pipe to a perfectly round ID measurement. Simply insert our Esco Millhog J-bevel blade into one of the tool posts on the cutterhead of the millhog. Align the tool so as to leave a slight landing and lock the blade into place. It is recommended to use a scrap piece of pipe while dialing in the blade positions as you may need to slightly adjust the blade positions to achieve the desired landing thickness. The j-bevel degree needed for the orbital welding application is pre-cut into the tooling so no adjustment is needed to achieve the perfect bevel.
Conclusion
To sum it all up, you basically just need to utilize one of our Esco Millhog ID-mounted pipe beveling machines with a landing blade, j-bevel blade and counterbore blade in order to make the perfect pipe weld preparation for orbital welding. These tools are simple to operate and learn; we train operators on this tool in a matter of hours. The Millhog pipe beveling tools make bevels in a matter of seconds and this process is easily repeatable for day-in day-out consistently perfect pipe beveling. This pipe end prep consistency makes for a reliable orbital welding process that will produce fast, beautiful x-ray quality welds everyday.
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