TPT November 2013

Article

Polysoude SAS

Figure 3: Increase in productivity between a conventional groove and a Narrow Gap groove

Figure 4: Narrow Gap V2/V3 torch module for thicknesses of 0–100mm

Several decisive factors come into play when analysing this question and the final choice must take account of the notion of relativity which may exist between the various situations. It can therefore be seen from comparative tests that, for thicknesses ranging from 12 to 15mm, the increase in productivity between a conventional groove (angle of approximately 20°) and a Narrow Gap groove optimised in relation to the materials is not significant. Profitability will then increase, reaching a factor of 3 on sections around 55 to 60mm thick. At thicknesses of 30mm and above, apart from the specific case of welding one-off parts, a Narrow Gap procedure must be used. The difficulties relating to materials or other operating restrictions are to be considered in order to choose the Narrow Gap technique that is appropriate and compatible with the application in question. Today, Polysoude has a comprehensive line of Narrow Gap welding torches for all thicknesses from 30 to 300mm. The ranges and thicknesses to be welded are to be considered on the basis of the line of torches created and constructed according to various technological constraints. Each torch has a scope which enables it to be used from maximum thickness (maximum torch insertion depth into the groove) up to completion of surface capping runs. With conventional torches from 0 to 45mm, electrode stick-out has to be adjusted over a 5 to 10mm range. So-called conventional torches remain fully versatile torches that are suited to all types of work. A category of intermediate tools called “V2 and V3 nozzles” exists for 0 to 100mm thick sections. These nozzles have the particular feature of being insulated and channelling the gas to the root better than a conventional torch but without guiding the tungsten via a true electrode lance. From an insertion thickness of approximately 45mm, these nozzles are combined with removable trailing shield

assemblies to complete the weld, oscillated capping run included. For thicknesses of 0 to 150mm, 0 to 250mm and finally 0 to 300mm, a line of torches is also available with trailing shield assemblies (removable if necessary) for all runs from root to cap. All Narrow Gap solutions (ie 0 to 100mm V2 and V3 nozzles, and 0 to 150 mm, 0 to 250mm and 0 to 300mm NG torches) exist as fixed electrode or oscillating electrode versions. The deliberate reduction in the volume of metal to be deposited, which is the main objective of Narrow Gap applications, highlights several operational difficulties including that relating to the lack of visibility for operators to track the welding.

Figure 5: Narrow Gap NG torch module for thicknesses of up to 300mm

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November 2013