When welding stainless steel, titanium or zirconium pipes, or pipework, the oxygen level within the pipe must be reduced to a level of 50 ppm, or lower in certain cases. The most cost-effective solution is to restrict the volume around the joint with a Tandem Weld Purging System.
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 Weld Purge Dams.
Ron Sewell, Chairman at HFT® said: “As well as the standard range of Dams, we have introduced custom made special Weld Purging 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.”
“Companies continue to allow their welders to spend many hours fabricating dams made of foam, sponge, cardboard, adhesive tape, wood, paper and so on. These materials contain a high percentage of water, which is very undesirable to have in the presence of a weld.”
“As these old fashioned, poor quality dams and materials are warmed by the welding operation, they start to outgas their water as a vapour, which starts to circulate around the weld joint and combine with the weld pool to cause porosity and oxidation, leading to metallurgical defects.”
Available for pipe diameters from 6 to 88 inches (150 mm up to 2,235 mm), the HFT® Single Ended Inflatable Weld Purge Dams are made of low vapour pressure materials specially selected for optimum weld purging results to provide the lowest oxygen reading in the fastest possible time with the minimum use of expensive argon gas.
The Weld Purge Dams are fitted with a dual inflation and purge hose, an additional purge gas hose and an exhaust 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.
Once the Dam is inflated using the purge gas and seals all around the internal circumference of the pipe, the excess inert purge gas spills out and purges the space around the weld joint. The air (oxygen) is then released out and into the open through a series of venting exhausts on the dam.
Four pull tags are located around the circumference of the Weld Purge Dam, so rope or pull wires can be attached for retrieval of the deflated system, as required. By producing bright shiny welds, there will be no porosity and there will be no loss of corrosion resistance caused by oxidation.
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!
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