TPT May 2008

T ube & P ipe W elding: T rends & P rogress

shielding and the argon is being dispersed evenly over the part, a uniform colour will be seen. Protective gas flow is still needed until the metal has cooled below about 250°C, to prevent discolouration. All work areas must be thoroughly cleaned according to recommended procedures that are widely available. All work components should be considered for cleaning, depending upon the welding method. For example, any titanium filler rod material should be checked for cleanliness. The welding tungsten should be clean and new, and not be contaminated by the welding of other materials on previous work. Welding torches will occasionally have leaks that will draw in atmospheric gases to the shielding gas, so should be leak tested prior to use. The welded joint must be allowed to cool before gas coverage is removed. Speciality products are now available to provide quality gas coverage, particularly low cost flexible enclosures for smaller components, weld purge monitors and trailing shields. In addition, there are ‘clean’ expandable stoppers available for use in sealing tubular components during purging. Flexible welding enclosures are lower cost than the more traditional solid metal versions. Additional benefits include the flexibility of minimal weight and the relatively fast times to achieve a weld purge. Flexible enclosures are sometimes not robust enough for welding operations. However, they are made of tough PVC plastic, and the cold purging gas helps to quickly dissipate the welding heat. Early flexible enclosures were circular in section, but are now available in square and rectangular shapes. Coupled with the ability to produce lengths to order, rectangular cross sections have made the new additions attractive to a wider range of end-users. Such enclosures are available up to 2m long and 1m x 1m in section.

There are now low cost instruments designed specifically for weld purging, measuring oxygen levels in any purge gas during the welding of titanium and its alloys. They show oxygen levels down to 10ppm using an alphanumeric display. Features include automatic fault finding diagnostics and data acquisition software. Devices called ‘trailing shields’ are available, and will fit any make of GTAW (TIG) or PAW (plasma) welding torch. They are available in flat format for sheet metal welding and in radiused format to match any diameter of pipe or vessel. The radiused versions are manufactured for welding on inside radii as well as outside. For mechanised welding machines, where weight and size considerations are less constraining, the trailing shields are larger, giving greater gas coverage and faster welding.

In recognition of the cleanliness required for reactive metal welding, clinically prepared expandable plugs are also available and widely used to seal pipes so that good gas coverage is maintained. Such plugs are available from 12 to 160mm (0.5 to 6″) diameter. This article was prepared by Dr Mike Fletcher and 1. Recommended practices for gas tungsten arc welding of titanium pipe and tubing (American Welding Society – NSI/AWS D10.6/D10.6M:2000) 2. Specification for fusion welding for aerospace applications (American Welding Society – ANSI/AWS D17.1:2001) 3. Guide for the fusion welding of titanium and titanium alloys (American Welding Society – ANSI/AWS G2.4/ G2.4M:2007) Huntingdon Fusion Techniques Ltd – UK Fax : +44 1554 836837 Email : rasewell@huntingdonfusion.com Website : www.huntingdonfusion.com Ron Sewell References:

Outstanding Tube Mill Cutoff Systems and Tooling

New-Variable Speed Shear Improves Performance

 Trailing shields for Tig/GTAW welding of titanium

Nick ‘N’ Shear ® Dimple Free Tooling Single Cut Die Sets Die Jaws Blades

Outstanding Tube Mill Cutoff Systems P.O. Box 334 • Troy, Michigan 48099 USA

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M ay 2008

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