Why narrow gap welding? The whole range of benefits linked to TIG welding have not only encouraged the automation of sequences that were previously only done manually but have also been the starting point towards applications involving increasingly large workpieces.
Consequently, many variants or developments towards high-power welding power sources, or the introduction of additional functions such as the use of hot wire or double wire feed, or the creation of specific tools such as cladding and narrow groove torches have decidedly widened the scope for TIG.
Nowadays it is no longer unrealistic to consider using TIG to weld workpieces 30 to 300mm thick given the numerous relevant advantages compared with all of the processes available on the market.
The TIG welding approach on thick workpieces does however require some specific knowledge with regard, on the one hand, to the choice and use of equipment and, on the other, to workpiece preparation and the development of operating techniques.
Narrow Gap Welding
Decades of progress in TIG welding have seen it become an essential process that offers the widest scope of use and reasonable operating constraints. The hot wire TIG process is effective in producing quality welds in all welding positions and now forms the basis of many automatic applications, including those involving increasingly large workpieces.
Narrow Gap, or Narrow Groove, is just one Polysoude development of specific tools, in the form of specialised torches, which uses the hot wire TIG technology.
Now a well-established process, Narrow Gap is used to weld thick sections of metal, such as thick-walled pipes and vessels of 30 to 300mm, more economically, by substantially increasing the efficiency of the deposition rate of the hot wire TIG process.
Everything you need to know is here: free download our Free Handbook about Narrow Gap TIG- GTAW welding – 56 pages of essentials about narrow groove welding
An important gain in productivity can be achieved by reducing the groove volume. The narrow-groove technique deals with the shrinkage of the workpiece after each ﬁller pass. Using a small gap at the root and a narrow V groove, allows for the insertion of a ﬂat-proﬁle (narrow groove) torch which can weld stringer beads of ﬁller metal, deposited in one pass per layer.
With the resulting shrinkage, the gap above each layer becomes slightly narrower after the weld, thus forming the borders for the next pass. This technique, with a high ratio of depth to width, can offer economic advantages for workpieces with a wall thickness of at least 25 mm, weld seams of unchanging width can be obtained on wall thicknesses up to 250 mm.
This welding procedure is mainly used to weld the high pressure and high temperature pipes found in fossil or nuclear power plants. Only a few companies around the world can offer the required sophisticated equipment and technologies: Polysoude is one of them.
Why Choose Narrow Gap TIG Welding ?
Narrow Gap TIG welding should always be considered when welding workpieces 30 to 300mm thick, given the numerous advantages compared with other processes available on the market.
The TIG welding approach on thick workpieces requires some speciﬁc knowledge regarding choice and use of equipment, workpiece preparation and development of operating techniques. However, once certain prerequisites have been fulfilled, the technology is open to all areas of industry with examples in construction of equipment for energy plants (hydroelectric, conventional fossil fuel / nuclear power), petrochemical and metalworking sectors and the manufacture or repair of thick pipes.
Productivity gains are considerable when employing the Narrow Groove operating procedure. Furthermore, they increase in proportion to the thickness to be welded: the thicker the section, the more profitable it is to use Narrow Gap hot wire TIG welding. Tests have shown that increase in productivity between a conventional groove and narrow groove, begins at a thickness point where multiple passes per layer of filler becomes unavoidable, reaching a profitability factor of 3 times that of conventional welding on welded sections of around 55 to 60mm thick and five times higher on thicknesses over 50mm.
- Reduced degree bevel angles mean that thick sections can be welded more economically. A standard pipe bevel angle is 37.5 degrees, whereas a NG angle can be as little as 3 degrees.
- Weld shrinkage is controlled due to reduced weld layers.
- Joint volume is reduced.
- Increased rate of joint completion means reduced welding time.
- Reduced labour costs.
- Distortion of angle is reduced, due to almost parallel joint side walls.
- The low heat input reduces stress on the pipe metal.
- Metallurgical properties are more consistent.
- Reduced cost of consumables. Less filler material is required for narrow gap welding, making substantial savings considering the cost of appropriate alloys.
Narrow Gap Welding - Torches
POLYSOUDE manufactures a series of Narrow Gap torches, necessarily specialised, due to the limited access into the joint root.
Torch design is key to the development of NG “Narrow Gap” or Narrow Groove welding:
- Hot wire compatibility
- Fully Insulated
- Easy electrode replacement
- 8 to 1.2mm wire
- Light (orbital)
- All-material gas shield
- Preheating to 350°C
- 100% Duty cycle-350 to 400A
Types of welding Torch
- Each torch type has a maximum gap insertion depth, determining the thickness of material it can be used on.
Narrow Gap V2 and V3 welding torch
Used for up to 100mm thicknesses, the nozzles are insulated and specially profiled, to channel gas to the root efficiently, guaranteeing a satisfactory gas shield. From an insertion thickness of approximately 45mm, nozzles are combined with removable trailing shield assemblies to complete the weld.
For thicknesses of 0 to 150mm, 0 to 250mm and 0 to 300mm, a series of torches is also available with trailing shield assemblies (removable if necessary) for all runs from root to cap. All Narrow Gap torch solutions have ﬁxed or oscillating electrodes.
These torches are 7mm in thickness, allowing access to 8.5 - 9mm wide grooves and enable implementation of single stringer beads, in all hot wire TIG positions. The design guarantees 100% duty cycle, irrespective of depth of gap, in preheated environments up to 350°C. The electrode holder is insulated from the torch body, to prevent short circuits should the nozzle touch the groove.
NG-OSC oscillation torches
The minimum thickness for these torches is 10mm. Insulated from the groove, the electrode and wire oscillate in a circular motion, synchronised by a single drive motor. The mechanism allows a differential amplitude setting between wire movement and electrode movement. The torches can be used for welding with an oscillating electrode or simply for a stringer bead with automatic electrode prepositioning.
Who we are
Polysoude specialises in the design, development and manufacture of innovative arc welding solutions. The brand is synonymous with world-leading expertise in 3 core sectors: automatic orbital TIG welding systems, automated TIG, Narrow Gap welding and plasma welding solutions as well as TIGer™ weld overlay.
Situated in Nantes since 1961, the company manufactures a variety of power sources and orbital welding equipment, like a wide range of open and closed orbital weld heads.
Nowadays, as a smart factory-oriented company, Polysoude products are all designed to be ready for Industry 4.0.