Large Stainless Steel pipes and vessels can be purged of air quickly and easily with reported savings of up to 90% in purge gas requirements using a British invented, developed and patented weld purging system.

The Argweld® Quick Purge from Huntingdon Fusion Techniques (HFT) will typically purge a 914-mm-diameter stainless steel pipe to below 0.1% oxygen in less than ten minutes, with faster purging for smaller pipes, says a spokesman for the Company.

Savings in time and purge gas consumption are achieved by reducing the volume purged. Two inflatable dams are positioned inside the pipe, restricting the length of the purged section to approximately 75mm on each side of the weld.

At the same time, a sleeve joining the dams occupies most of the pipe’s diameter, so that only the annulus space between the outer surface of the sleeve & the inner surface of the pipe needs to be purged. (Argweld® Quick Purge systems are available in sizes for pipes between 200mm and 1800mm in diameter.

Inert gas supply When the Argweld® Quick Purge has been positioned inside the pipe, by using pull tags, it is inflated by the inert gas supply so that each end dam forms a seal. Once the dams are fully inflated, the inert gas pressure opens a valve to allow the inert gas to enter the space between the sleeve and the pipe to displace the air, thereby creating the weld purge. An Argweld® Weld Purge Monitor is attached to one of the exhaust hoses where the air and the purge gas flows out. Welding can begin as soon as the oxygen reaches 0.1%.

The flow of inert gas is maintained throughout the welding operation, to purge any oxygen released by the increasing temperature, and is continued until the completed weld has cooled to below oxidation temperature. The purge gas supply is then cut off and the system deflates to allow its removal from the pipe. Heat-resistant material protects the Argweld® Quick Purge from high temperatures close to the weld.

Argweld Quick Purge Devices have been used successfully by Bechtel for the Sabine Pass Liquid Natural Gas 30 inch diameter Pipeline in the USA as well as by Ledwood Construction Welding a similar pipeline for the South Hook Project in Wales. Many large diameter pipeline installation companies internationally have also taken up the use of Argweld® Quick Purge Devices, represent a true success for a British patented invention and development.