Titanium, stainless steel and other corrosion resistant materials are used for tubing and pipework especially where there are highly corrosive materials flowing through them.
When such pipework is welded for joining or repairs, it is necessary to protect the material in and close to the weld joint, carried out by a technique called Weld Purging. Oxygen and nitrogen can be harmful to the weld joint in particular as they will combine very easily with the hot material, forming oxides and nitrides, until the temperature falls below its oxidation point.
One inexpensive accessory called a Weld Trailing Shield® can be added to a GTAW/TIG welding torch before beginning a pipe weld. This lightweight tool, available in the USA from COB Industries, is easily manoeuvred around the pipe joint as it is being welded, with no inconvenience to the welder.
The Trailing Shield® is connected to an argon gas source and when the weld is started, it has extra argon flooding to the sides of the weld and covering the heat affected zone adjacent to the weld. As the welding torch is moved forward, because of the length of the Trailing Shield®, the weld remains under an argon gas shield until the welded metal has cooled below its oxidation temperature.
For manual welding, the welder finds that with this lightweight and low cost tool, there is no difficulty in dragging it along the surface being welded. One further benefit is that it carries the welding torch at 90º to the weld.
With automatic welding machines it is possible to raise the welding speed dramatically and enjoy the major benefits of automatic welding. Each Trailing Shield® is delivered with a variable diameter connector so that it can fit any size of TIG/GTAW/PAW welding torch for manual or mechanised welding.
Savings on expensive cleaning and pickling costs to remove oxidation and discolouration on these corrosion resistant materials pay for these shields in the first weld and the shields can be used for years without replacement.
Trailing Shields® are available immediately for any diameter of tube and pipe from 17 mm upwards. They are also manufactured in flat format for sheet metal welding.
COB Industries said: “The Trailing Shield® is connected to the argon gas supply and it diffuses gas out evenly without turbulence through the multi layers of stainless steel mesh built into the body of the shield. At each side, removable silicone rubber side shields provide a barrier to prevent the argon escaping sideways and remaining over the weld metal. These silicon shields are a consumable and are replaceable as they become worn.”
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