Polysoude (France) has released the first ever reference document for TIG narrow gap welding.
The importance of progress in welding
The quality and productivity requirements relating to welded pipe joints are inexorably driving industrial companies towards the implementation of automatic processes. These primary objectives are however supplemented by more subtle notions such as heat input, weld seam regularity or even aesthetic criteria for sectors affecting the general public. Several decades of progress in TIG welding have seen it become an essential process that offers not only the widest scope of use, but also reasonable operating constraints compared with more recent developments (laser or electron beam welding).
The effectiveness achieved in producing quality weldments using the TIG process, both in terms of productivity and control in all positions, is at the origin of a large number of automatic applications including orbital welding.
The TIG welding process
This technique has now been popularised with the creation of numerous machines, which have boosted recognition of the TIG process as a real alternative for the automated welding of a wide variety of materials. Efforts made in tool design (miniaturisation, robustness, increased duty cycles, etc.) have made it easier to optimise the designs and service performance of the equipment to be built.
The whole range of benefits linked to TIG welding have not only encouraged the automation of sequences that were previously only performed 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 gap torches have decidedly widened the scope for TIG. Nowadays it is no longer unrealistic to consider using TIG to weld workpieces from 0.5 to 300 mm thick given the numerous relevant advantages.
TIG welding on thick materials: narrow gap
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.
Productivity is a question that is invariably posed on developing a narrow gap operating procedure. However, in order to choose an operating technique, the strengths and weaknesses of that technique must be known beforehand to avoid ending up in an impasse.
Productivity gains are considerable and increase in proportion to the thickness to be welded. It is vital nonetheless to assess the thresholds below which the restrictions involved in narrow gap welding outweigh the substantial gains.
Several decisive factors come into play when analysing this question and the final choice must take account of the notion of relativity that may exist between the various situations. It can therefore be seen from comparative tests that, for thicknesses ranging from 12 - 15 mm, 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 three on sections around 55 - 60 mm thick.
At thicknesses of 30 mm 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.
Narrow gap welding torches
Today, Polysoude has a comprehensive line of narrow gap welding torches for all thicknesses from 30 - 300 mm. 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 that 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 - 45 mm, electrode stick-out has to be adjusted every 5 - 10 mm, when filling up the weld groove.
Narrow gap welding: choosing a technique
Narrow gap TIG welding is no longer a solution for exceptional circumstances. It is important to consider it whenever the thickness to be welded exceeds 30 mm. An initial analysis is imperative to ascertain the potential benefit, verify the absence of notable contraindications and above all to choose the methodology and equipment best suited to the context. There are a multitude of solutions with a significant level of industrial maturity confirmed by numerous concrete examples. The difficulties involved in implementing the welding procedures vary according to the chosen technique. The temptation to take a simplistic approach and skip a case-by-case assessment must however be avoided as there is no universal solution. Moreover, in terms of tools, the entire 30 – 300 mm thickness range is covered with numerous variants and adaptation possibilities for special cases.
For the welding process, knowledge and mastery of TIG are highly important and enable the technique to be popularised, with recourse in the event of difficulties. From the point of view of industrial companies, the implementation of a narrow gap application calls for a structured approach with marked steps. In parallel, corresponding approaches for machining facilities, tracking and traceability of materials and inspection techniques may need to be undertaken requiring validation steps close to those used in welding. All of these anticipatory measures are justified by the prospect of substantial gains compared with the use of more conventional techniques.
For further information on TIG welding, please visit www.polysoude.com
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Read the article online at: https://www.oilfieldtechnology.com/special-reports/22102013/first_tig_narrow_gap_welding_handbook_available/