When tubes and pipes of certain materials, such as stainless steel, titanium, copper-nickel 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, discolouration and loss of corrosion resistance. Some high integrity products available for purging the insides of pipes, include Inflatable Tube and Pipe Purging Systems: PurgElite®, QuickPurge® and HotPurge®. It is not always practical however to use such systems for one off, never to be repeated work on just a few joints of one particular size, for closing welds, for ‘T’ piece joints or for a number of other branch type joints.
To overcome this difficulty, Huntingdon Fusion Techniques HFT® provides 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 that can easily be washed away when hydrostatically testing the pipe or just by flushing out. It is not easy to obtain a quality purge 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 and it is unnecessarily expensive.
Luke Keane, Distributor Support for HFT® said: “It is so easy to cut a circle of water soluble film and place it a short distance away from the root gap before welding, pasting in place with the Argweld® Water Soluble Super Adhesive™ to ensure a tough leak tight barrier, keeping the purging volume to the barest minimum”. Argweld® Weld Purge Film™ may save operators large costs by minimising gas usage and cutting down dramatically on time taken to make a purge, whilst at the same time, achieving a desirably low oxygen level.”
After welding, the water soluble film is simply washed away during the standard hydrotest cycle or by simply flushing of the pipe interior. The film is dissolved down to molecular level leaving no trace. Previously, pipe welders might have used water soluble paper, but as paper contains a high percentage of water which undesirable to have near a weld, the Argweld® Weld Purge Film™ is a tremendous new benefit for weld purging.