Weld Purging is essential when welding tubes and pipes made of reactive metals such as stainless steels, titanium and zirconium.
Usually weld zones are confined with purge dams so that the use of argon purge gas is limited and waiting times are reduced. Homemade dams fabricated from paper, sponge foam, wood etc. all contain water as a liquid or a vapour. Water vapour will outgas into the purge volume during the weld process, forming oxides with the metal being welded and create the imperfections that the dams were intended to stop.
Oxidised welds will lead to rework of some kind and in bad cases cause welds to be rejected and having to be cut out and re-welded. Displacing the oxygen with an inert gas before, during and after welding helps to create welds that are free from oxidation, however the weld purge dams should be made of materials that do not outgas water vapour or any other undesirable gases.
For pipe and tube lines, the most cost-effective solution is to restrict the volume around the joint with an inflatable Tandem Weld Purging System that is available off the shelf and designed especially for the task.
For the purging of short pipe pieces and dished end or dome end welds however, the tandem devices are unsuitable. To overcome these challenges, experts in Weld Purging Technology Huntingdon Fusion Techniques HFT® have designed and manufactured a Range of Inflatable Weld Purge Dams.
Luke Keane, Technical Sales Manager for HFT® said: “Weld Purge Dams are available for pipe diameters from 6 to 88” (150 mm up to 2,235 mm). We have also introduced custom made Dams for a variety of applications. We recently designed a ‘donut like' Weld Purge Dam to purge a pipework fabrication, where one pipe was inside the other. The Special Dam fit on the inside of the larger pipe and purged the space between the two pipes.”
Once the Dam is positioned and inflated using the purge gas, sealing all around the internal circumference of the pipe, the excess inert purge gas spills out and purges the space around the weld joint. The oxygen is then expelled through an integral vent on the dam.
Four pull tags are located around the circumference of the inflatable Weld Purge Dams for positioning and easy retrieval of the deflated dam once the joint has cooled below its oxidation temperature. By producing bright shiny welds, there will be no porosity and there will be no loss of corrosion resistance caused by oxidation.
The Weld Purge Dams are fitted with a dual inflation and purge hose, an additional purge gas hose and an exhaust vent which can be connected to one of the HFT® Weld Purge Monitors®.
The additional purge gas hose is suitable for introducing extra purge gas into the weld zone at any time to cool welds to meet interpass temperature specifications, or to provide more inert gas in the event of titanium, zirconium or special stainless applications needing a guaranteed zero colour weld.
Apart from the benefit of having a metallurgically sound weld, the difficulties of cleaning an oxidised weld are eliminated, saving vast amounts of money in labour and material costs as well as the disposal costs where acids are concerned. Now there is no more reason to put welds at risk by using apparently cheaper materials, when for a very low cost, Argweld® Inflatable Weld Purge Dams can be purchased instead!
Ron Sewell, Chairman for HFT® said: “All of Huntingdon Fusion Techniques HFT®'s Weld Purge Monitors® and Inflatable Tube, Pipe and Pipeline Weld Purging Systems are manufactured in the UK. We do not sacrifice on quality. We guarantee to help you achieve zero colour welds, time and time again.”
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