What is Weld Purging?
Preventing oxidation and contamination of joints during fusion welding demands that special attention be given to local protection using an inert gas.
Whilst the welding torch provides a protective cover to the top of the fusion zone, inert gas coverage is also required in the region of the weld root.
If this is not done, the weld root and local metal will at best discolour but invariably will become heavily oxidised.
The solution to the problem is to provide a weld purging technique. This is most easily done by sealing the weld region using inflatable purge bladders.
Other techniques are available - expanding plugs, tapes and membranes are often used. The sealed region can then be filled with inert gas such as argon or helium and this provides a very effective insurance against oxidation during welding.
Typical expanding plug manufactured in corrosion resistant nylon and rubber.
This is a low cost solution to sealing for tubes up to 150 mm diameter. A wide range is available from Huntingdon Fusion Techniques and these incorporate inlet/outlet holes for gas purging.
The Argweld® QuickPurge® II flagship weld purging range. Designed as a fully integrated solution to purging thatoffers the worlds fastest method of producing high integrity joints.
Is Filling or even Flushing with Inert Gas not satisfactory?
If the sealing system is perfect, yes. But note that there may be leaks where air can enter, especially at the weld seam. Try to overcome this by ensuring a leak tight seal on both sides of the weld zone whilst at the same time allowing entry and exit points for inert gas.
A slight positive pressure will give excess gas to prevent air from entering through the joint gap.
Don't try bypassing the need for proper sealing by using a high gas flow rate. This will only lead to turbulence and this in turn entraps air, leading to poor weld production.
How do I make sure that the gas in the weld zone does not contain oxygen?
By sampling the gas and testing it with an oxygen sensing system the welder can be assured about the oxygen content. Huntingdon Fusion Techniques has designed the world's leading monitors the Argweld® PurgeEye® Weld Purge Monitors® range of which the PurgeEye®100 is the first to be released.
The PurgEye® 100 Weld Purge Monitor® has been specifically designed for indicating oxygenlevels in inert gas during weld purging.
This is the world's first purpose-designed and built Weld Purge Monitor® for use during welding of critical pipe joints, the production of orbital tube and pipe welds and chamber welding. It is superbly suited to the welding of reactive materials such as titanium and nickel alloys and the entire range of stainless steel components.
This rugged instrument measures and clearly indicates actual oxygen levels down to 100 ppm [0.01%] on an alpha-numeric display.
You are not allowed to use or copy any of this material or content without the written permission of Huntingdon Fusion Techniques HFT®, copyright protected. All rights belong to Huntingdon Fusion Techniques HFT® exclusively. Not for any reproduction without consent.