Orbital welding
Orbital welding is a fully mechanical inert gas welding process in which the arc is automatically guided 360 degrees around pipes or other round bodies without interruption.
Plant components
The basic components of every orbital welding system are a power source with control, welding head and, if necessary, wire feed. In the systems, the welding parameters (e.g. arc length, strength and pulse frequency of the welding current, welding speed, type of shielding gas) are freely programmable depending on the weld seam geometry, the base and filler material and other components such as the type of shielding gas. The welding process is either tungsten inert gas welding (TIG) or metal shielding gas welding (MSG). The actual welding process is carried out using welding tongs, also known as an orbital welding head, which are in the
- The closed version completely encompasses the pipe and must be matched to the pipe diameter. In the chamber, which is completely filled with the protective gas, the welding head is guided around the pipe. The supply of filler metal is not possible due to the encapsulation. This is why the pipes are butt-jointed (free of gaps and offsets) (I-joint). Because the pipe is completely enclosed, this type of welding gun is particularly suitable for processing stainless steels , as the pipe seam cannot oxidize on the outside. So there are no tarnishing colors . The inside of the pipe must also be protected from oxidation by forming . The dimensions of the welding gun are comparatively compact, so that welding can still be carried out even in confined spaces. The use of closed welding guns is limited to smaller pipe diameters of currently around 76 mm (DN 65).
- In the open version, the welding gun does not completely encircle the pipe; there is no closed protective gas chamber. The possible pipe diameters are variable in intervals - from currently a few millimeters to around 275 mm (DN 250). Because of the rapidly increasing weight with the size and the low compactness, the process is no longer economically applicable and manageable above a certain pipe diameter. Welding filler material can be added because the welding chamber is open. This means that other seam preparations than the gap-free I-joint are also possible. In general, the tulip-shaped U-joint is preferred.
- For larger pipe diameters, which are particularly necessary in boiler and pipeline construction, welding systems are used in which the arc or the torch head is guided around the pipe on a rail. In the case of multi-layer welds, there are sometimes several torch heads that simultaneously insert the weld layers one behind the other. There is no maximum pipe diameter limitation with these systems.
application
The orbital welding process is preferably used in pipeline construction, where consistently high seam quality must be achieved under controllable conditions. The main areas of application are pipeline construction, boiler construction, the food and chemical industries.
The welding process
Since the welding parameters have to be programmed before the welding process, exact weld seam preparation and precise offset-free pre-setting of the workpieces is necessary, since, for example, the root detection in the event of a pipe offset can no longer be compensated manually by the welder. Even if the welding guns have become more compact in today's systems, there must be enough space available so that the welding head can move around the pipe, which is seldom guaranteed in constrained situations in cramped, often difficult assembly conditions. Orbital welding is therefore rarely used in the assembly area.
materials
All materials can be welded that can also be joined using the corresponding TIG or MSG processes. The weld seam preparation and welding is then to be carried out analogously to this procedure. In the case of materials that are difficult to weld safely and only under particularly controlled conditions, such as some high-strength, high-temperature and corrosion-resistant steels - but especially in the case of particularly difficult-to-weld materials such as nickel alloys or titanium - fully mechanical welding processes such as orbital welding develop their greatest strengths. Through full mechanization, consistent quality can be achieved with careful welding preparation and production control.
Pipe wall thicknesses and economy
According to the state of the art in 2009, orbital welding is only economical for single-layer welds. An exception are workpieces in which the weld seam quality is paramount. If reproducible, constant seam quality can be achieved, the welding speed is less than the welding reliability. If several welding heads are used at the same time, for example in pipeline construction, orbital welding allows high welding speeds and economic efficiency - even with multi-layer welding. However, because of the dimensions of such systems, this is limited to large pipe diameters. In the case of smaller dimensions, the general rule is that the gapless I-joint should be used because of the higher achievable welding speed. This is possible up to about 4 mm. Otherwise, the pipe joint must be prepared as a U-joint. The preparation of this joint must be done fully automatically, for example by turning , since manual or partially mechanical methods cannot achieve a sufficient quality of the seam preparation. The welding can only be carried out with the addition of welding filler material, which makes open welding guns necessary. These factors then make orbital welding uneconomical compared to manual welding - especially when multi-layer welding is necessary - and it is only used when there are high demands on the seam quality.
Individual evidence
- ↑ Enclosed orbital weld heads | orbital welding, ORBIWELD. Retrieved July 25, 2017 .
- ↑ Open-arc orbital weld heads | ORBIWELD TP, orbital welding. Retrieved July 25, 2017 .
- ↑ Rail-guided orbital carriage. Retrieved July 25, 2017 .
- ↑ Possibilities and limits of orbital welding technology ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
Web links
- SLV Munich : TIG orbital welding of aluminum pipes using the alternating current method, study as the result of a publicly funded research project, PDF file