Indian success with weld purging of titanium alloy pipe
PUBLISHED: 10 Nov 16
Close up of typical titanium root weld, free of discolouration from oxidation
A new facility for the production of 1.25 million tonnes of terepthalic acid (PTA) has been built at the port of Mangalore in the Indian state of Karnataka.
The project involved factory fabrication of specialised equipment followed by integration on site. A range of stainless steels were used in manufacture along with titanium and tantalum alloys. The bulk of the fabrication involved welding of tubes and pipes.
A significant part of the project was awarded to a Chennai based customer of Weldwell Speciality Pvt Ltd in Mumbai, a major supplier to the Indian welding industry for over two decades. The customer has a long tradition of specialist fabrication of titanium, tantalum, zirconium and nickel alloys and stainless steels.
To avoid internal contamination of the pipes during welding and to prevent oxidation of the weld root, advanced purging systems from Huntingdon Fusion Techniques (HFT) in the UK were employed. The HFT Quick Purge® concept, now used successfully throughout the world, was chosen and purge systems to accommodate pipe sizes between 800 and 1500 mm ordered. HFT also supplied its unique Purge Gate ancillaries, to control and maintain the inflated state of these large diameter inflatable devices even when the purge gas flow was interrupted or stopped. This was particularly important when welding was not required but the effective gas sealing was maintained. This could be during a shift change or when work was discontinued overnight.
Using the Purge Gate feature only the dams inflate and effect good sealing when the inert gas pressure is set at 0.45 bar. After inflation the gas flow from the supply will stop and no further consumption will take place and can be kept for lengthy periods without any gas loss. Only when gas pressure was increased to 0.5 bar will purging begin. This resulted in a significant saving in expensive inert gas.
All welds in stainless steel were made successfully using the standard Quick Purge I systems, but some surface discolouration was observed when welding titanium alloys.
Contact was made with HFT and it was agreed that additional gas purging was required. This was accomplished by using QuickPurge II, since this incorporated additional gas purging and gas outlet ports. The change resulted in the production of clean and oxide-free welds, even in such sensitive materials as titanium alloys.
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