When tubes and pipes that are made of certain materials – such as stainless steel, titanium, nickel alloys and zirconium – are welded together, ideally, the oxygen is purged out of the weld zone in order to stop it from reacting with the hot metal and causing oxidation, porosity and corrosion.
Weld purging products include inflatable systems (balloons), tandem units made of rubber discs and double-ended systems made of wood, foam and other unsuitable materials. Such dual-ended systems require an open end to retrieve the system once the weld is finished. Therefore, these are not suitable for closing welds.
In order to overcome this limitation, Huntingdon Fusion Techniques (HFT®) has developed and manufactured Argweld weld purge film® kits. The company uses water-soluble materials that can be used for both open assemblies and closing welds. The film produces an impenetrable purge barrier, which can be easily washed away when hydrostatically testing the pipe or just by normal wash out with water.
Obtaining a high quality purge is not easy and it has been customary to fill pipes with expensive argon gas and keep this 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 unreliable 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 effectively.
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 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.”
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.
Adapted from press release by Anna Nicklin
Read the article online at: https://www.worldpipelines.com/equipment-and-safety/31082016/huntingdon-fusion-techniques-introcudes-weld-purge-film/