When tubes and pipes of certain materials, such as stainless steel, titanium, nickel alloys and zirconium are welded together, it is desirable to purge the oxygen out of the inside of the weld zone to prevent it from reacting with the hot metal and causing oxidation, porosity and corrosion.
Some weld purging products available include Inflatable Systems (balloons), tandem units made of rubber discs and even double ended systems made of wood, foam and other unsuitable materials. Such dual ended systems require an open end to retrieve the system after the weld is finished and therefore, are not suitable for closing welds.
To overcome this limitation, Huntingdon Fusion Techniques HFT has developed and manufactured Argweld Weld Purge Film kits, with water-soluble materials that can be used for open assemblies and closing welds. The film produces an impenetrable purge barrier, which can easily be washed away when hydrostatically testing the pipe or just by normal wash out with water.
To obtain a quality purge is not easy and it has been customary to fill pipes with expensive argon gas and keep the gas running at what is thought to be a suitable flow rate for an estimated period of time. In today’s climate of ever improving quality control and increasing demands on procedures with traceability, it is inappropriate to use such hit and miss methods to guarantee a satisfactory purge.
It is not desirable to simply ‘pour’ gas into a pipe assembly in the hope that a good purge and ultimately, a good weld will be achieved. This technique rarely works very well.
Luke Keane, Distributor Support for HFT said: “It is so easy to cut a circle of water soluble film and paste it a short distance inside each pipe end, before welding those ends together. The film dams are fixed in place using the Argweld super water-soluble adhesive to ensure a leak tight barrier, keeping the purging volume to the barest minimum.
“Weld Purge Film will save operators large costs by minimising gas usage by cutting down dramatically on time taken to make a purge. Weld Purge Film has been designed and developed by HFT as a complete kit, containing all products and accessories needed.”
After welding, the water-soluble film is simply washed away during the standard hydrotest cycle or by simply washing of the pipe interior and dissolved down to molecular level, leaving no trace.