Open welding heads are characterized by their flexibility to weld different diameters and wall thicknesses of tubes and pipes.
However, apart from the financial aspect, it must be taken into account some specific applications simply cannot be welded with closed welding heads due to the geometry of the parts.
Why should you use an open welding head?
Tube and pipe with large wall thicknesses require special attention.
Unlike thin-walled stainless steel tubes that can be fused by butt welding, stainless steel and black steel pipe with thicker wall need to be beveled before they can be welded. In orbital welding, welders usually opt for a J-bevel. During the welding process, this bevel needs to be filled in with filler material. However, with the use of an open welding head this task can be carried out with additional functions such as oscillation of the torch or AVC (Arc Voltage Control).
This is an open heads primary application. After a first so-called "root" pass, the electrode of the open head makes several passes around the tube, filling the bevel with the filler metal. This would be impossible to do with a closed head.
The weld pool and the weld bead are protected with shielding gas. Since you are working with an open head, the gas can escape into the air. As a result, you’ll have a higher gas consumption which makes the welding more expensive. Perfect control of pre- and post-gas is therefore particularly interesting for these applications.
Be sure to pay attention to your surroundings! When welding with open heads, it is important to avoid any kind of exterior interference such as draughts for example. They may deflect the shielding gas.
Below we listed 4 applications for which you should opt for open welding heads.
1) Welding geometry
In many cases, an open head cannot be attached because a straight section of the workpiece of 116 to 219 mm is required (depending on the head model) in order to be able to fasten it. The advantage of the open head is that it only needs to be clamped on one side of the tube. This advantage outweighs the fact that its rotating dimensions are larger than those of a closed welding head.
Welders face this challenge in complex and very dense piping systems, which are increasingly common in manufacturing sites for reasons of space efficiency.
These tubular systems do not only consist of tubes. Numerous accessories such as valves, elbows, fittings etc. complete the installations. An open head allows for easier clamping in many configurations such as tube-flange, tube-elbow or tube-fittings.
Moreover, these heads are more versatile by design. For example: when welding angles, the welder can change the inclination of the electrode to obtain a weld pool under perfect conditions. In the same way, tracking the out-of-roundness of tubes is easier with an open head and thus presents a gain in quality.
2) Welding of pipelines
In the specific case of pipe repair, the available space for the welder to work in is extremely limited. Therefore an open welding head is more suited since it is easier to attach to the pipe and can be operated via remote control. This is not only beneficial for the welder's comfort, but also for his personal safety.
3) Welding tubular heat exchangers
This list would not be complete without mentioning the very specific case of tubular heat exchangers. Specific open welding heads – with or without filler wire – are used to weld thousands of pipes onto a tube sheet. The welder uses multiple welding heads at the same time to increase efficiency. Identical welds with an impeccable repeatability and the possibility to trace the production are vitally important.
The "cladding" of tubes and pipes with large diameters refers to the layering of a high value alloy such as black steel, for example. Thanks to this technology, abrasion on the inside of tubes and pipes is reduced, allowing for example the extraction of oil that is carrying along sand particles. Here as well, welders make use of open welding heads.