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What is narrow gap welding?


Narrow gap welding (also called narrow groove welding) was developed to weld thick sections more economically. This welding procedure uses joint preparations with small, included angles, typically in the range 2-20°, which require less weld metal and less welding time to fill. Narrow gap techniques have been applied when welding using submerged arc welding (SAW), gas shielded metal arc welding (MIG/MAG, GMAW) and tungsten inert gas welding (TIG, GTAW) processes. However, narrow gap welding does require specialised equipment, because of the limited accessibility to the root of the preparation.

The advantages of the narrow gap technique are:

  • The process offers better economy for welding of thick materials (generally over 50mm thick) because of reduced consumable requirements and shorter welding times.
  • There is low angular distortion because the joint preparation is almost parallel-sided.

The disadvantages are:

  • The weld is more prone to defects for certain welding processes - especially lack of sidewall fusion.
  • It is difficult to remove any defects when detected, because of poor joint accessibility.
  • Expensive J-preparations must be machined onto the parent material, unless a backing bar is permitted. This will affect the economics of the process.

The risk of lack of sidewall fusion can be reduced in narrow gap welding by several methods:

  1. Using two electrodes in tandem with each electrode oriented so that a weld bead is directed towards each sidewall (applicable to SAW and MIG/MAG processes)
  2. Using an electrode that has been bent into a wave form (for MIG/MAG welding). This should make the arc move from side to side across the joint
  3. Using two electrodes that are twisted around each other to oscillate the arc (applicable to MIG/MAG welding)
  4. Using an angled contact tip, which automatically aims the electrode at one sidewall and then the other (applicable to MIG/MAG welding)
  5. Arc oscillation
  6. Use of seam tracking to ensure alignment of the arc with the sidewall

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