Orbital welding

Orbital welding is a mechanized arc welding process in which the arc machine uninterrupted 360 degree passing around pipes or other round object.

System components

The basic components of each orbital welding system are current source with control, welding head and, if appropriate wire feed. For plants, the welding parameters ( for example, arc length, thickness and pulse rate of the welding current, welding speed, shielding gas type), depending on the geometry of the weld, the base and filler materials and other components such as the shielding gas type, freely programmable. The welding process is either the tungsten inert gas welding (TIG) or metal inert gas welding ( MIG ). The welding process proper is effected by means of a welding gun, also called orbital welding head, which in the

• Closed version, the pipe must be completely covers and 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 addition of filler metal is not possible because of encapsulation. Therefore, the tubes blunt ( gaps and without offset ) are joined together (I -joint). This type welding gun is suitable for the complete enclosing the tube especially for the processing of stainless steels, since the pipe seam on the outside can not oxidize. This means that no tarnish. The inside of the pipe should be protected by transforming from oxidation. The dimension of the welding gun is relatively compact, so that even under conditions beengteren assembly can not be welded. The use of a closed welding gun is restricted to smaller pipe diameters from currently about 76 mm (DN 65).

• In the open design, the welding gun comprises the tube does not complete; there is not a closed inert gas chamber. The possible pipe diameters are variable in intervals - from the moment a few millimeters to about 275 mm (DN 250). Because of the rapidly increasing size and weight of the low compactness of the process is above a certain pipe diameter is not more economically applicable and manageable. It can weld filler are supplied, since the welding chamber is open. Thus, other weld preparations as the gap-free I- joint are possible. In general, the tulip-shaped U- joint is preferred.

• For larger pipe diameters, in the boiler and pipeline are particularly necessary, welding systems are used, in which the arc or the burner head is led around on a rail around the pipe. With multi-layer welds there are sometimes multiple burner heads that simultaneously bring in succession, the weld passes. A maximum pipe diameters, there is no limitation on these systems.

Application

The orbital welding process is preferably used in pipeline cases where application under controlled conditions consistently high weld quality must be achieved. Main applications are in the pipeline, the Boilers, the food and chemical industries.

The welding process

Since the welding parameters must be programmed before the welding process, a precise weld preparation and accurate offset- free Vorrichten of the workpieces is necessary because, for example, the root formation in pipe offset can not be manually balanced by the welder. Although the welding guns have become more compact in today's systems, adequate space must be available so that the welding head can turn around the pipe, which is to ensure rare in predicaments in cramped, often difficult assembly conditions. In the assembly area, the orbital welding therefore hardly applies.

Materials

Weldable are all materials that can be joined with the corresponding TIG or MIG. The weld preparation and weld is then similar to perform these procedures. In difficult and only under very controlled conditions safe sealable materials such as some high-strength, high-temperature resistant and corrosion-resistant steels - especially among the most difficult to be welded materials such as nickel alloys or titanium - unfold fully mechanized welding processes such as orbital welding its greatest strength. By means of full mechanization consistent quality can be achieved with careful welding preparation and production control.

Tube wall thickness and economy

According to the state of the art in 2009, the orbital is only economical for single-layer welds. An exception workpieces, where the weld quality is paramount. Can reproducible, consistent weld quality can be achieved, the welding speed is secondary to the welding safety. With the simultaneous use of several welding heads, for example, in pipeline, allows the Orbital welding - even in multi-pass - high welding speed and efficiency. However, this is limited to large pipe diameters because of the dimensions of such equipment. With smaller dimensions, generally, that should be used because of the higher therefore achievable welding speed with the slitless I- joint. This is possible up to about 4 mm. Otherwise, the shock tube is to be prepared as a U- joint. The preparation of this joint must Completely machine, for example, be made by turning, as with manual or partially mechanical processes sufficient quality of the weld preparation can be obtained. The welding can be carried out only with the addition of filler metal, which makes open weld heads required. These factors make the orbital then compared to manual welding - especially in orther multipass - uneconomical, and it is only used when high demands on the weld quality.