If you need a high quality weld, the preparation of the pipe is essential. Several steps have to be followed before welding and the preparation of the bevel is most important. A high quality bevel ensures a clean and perfect weld. There are two ways to prepare a bevel.
- J bevel without counterboring: perfect for pipe with wall thickness between 3 and 10 mm
- J bevel with counterboring for pipe with wall thickness of more than 10 mm.When the wall thickness exceeds 3 mm, the weld puddle will become too large for controlling its geometrical behavior. In this case a J bevel is necessary in order to obtain wall thicknesses that can be welded easily. Filler wire will be necessary in order to fill the groove.
# Bevelling without counterboring
Different machines can be used to prepare a bevel: from a traditional turning machine up to portable bevelling equipment. All of these devices will prepare a round bevel at the edge of the pipe. However, considering that no pipe is perfectly round, this preparation will lead to an important problem: the land will not be consistent due to the ovality of the pipe and the difference of its thickness on the circumference.
Technical means for compensation:
- This machining can be achieved by tracking the external profile. In this process the tool will remove the metal and will follow the external geometry of the pipe. However, the consistency of the land is subject to the consistency of the wall thickness.
- Machining while tracking the ID of the pipe: this kind of machining will not only help with the problem of the pipe being potentially out of round but also with the variation in the wall thickness. In this process you will have a consistent land at the edge of the pipe. But this solution is only possible for pipe of more than 4 inches (114.3 mm) and you will have to use mechanical equipment to track the internal profile of the tube.
This preparation without counterboring will have a good land but does not solve the problem of the oval shape of the tube, which can be of more or less importance.
As soon as you align the pipe you will notice an offset of the land (high-low). This offset must be handled with alignment tools that allow the operator to position the land correctly, without offset. Ideally, a round tool is positioned in the inner profile of the tube in order to position the workpieces correctly. These tools exist on the market, but they are very expensive and can be difficult to use.
# Bevelling with counterboring
This kind of preparation – if applicable – is the ideal process. “If applicable” is the key phrase to consider. Measurements of the ID and wall thickness must be calculated. A counterbore is allowed if all these elements are verified. When you do a counterbore the ID of the tube is milled and thus calibrated. The tube will be perfectly round. This type of tool is used with a continuous adjustment of 2 to 4° in order to prevent any breaking points.
With this process, all of the surfaces of the tubes are calibrated and the land is shaped in a perfect way (without profile control). The workpieces will be completely aligned.
In both cases, when you carry out a weld on a pipe, this will lead to multi-pass welding which will need filler wire. This will modify your welding procedure, as you will probably need and an oscillation feature and AVC (Arc Voltage Control).
Orbital welding is an automated procedure. A simple V groove with a clearance factor of 2 or 3 mm or a V groove with land or even a V groove with land and without clearance play are not possible.