Maintaining welds' integrity through effective gas purging is crucial in petrochemical, pharmaceutical, cryogenics, food and beverage, and semiconductor manufacturing. Oxygen contamination during welding can lead to discolouration and, more critically, the formation of oxide deposits that jeopardise product quality and safety. Ensuring oxygen levels are precisely controlled during welding is essential for achieving high-quality, corrosion-resistant welds.
Recent advancements by Huntingdon Fusion Techniques (HFT®) have addressed a significant challenge in oxygen monitoring—accurately measuring oxygen levels at greater distances from the weld site. Traditional Weld Purge Monitors®, effective at close range, lose accuracy as the distance increases. To overcome this, HFT® has developed the Argweld® PurgEye® 1000 Remote Weld Purge Monitor®, a state-of-the-art instrument capable of delivering precise oxygen readings from up to one kilometre away.
The Argweld® PurgEye® 1000 is based on advanced zirconium oxide sensor technology, capable of measuring oxygen levels as low as ten ppm. This breakthrough allows for continuous, accurate monitoring even in complex industrial environments with extensive pipework, ensuring weld quality and minimising delays.
Field studies have demonstrated that traditional oxygen monitoring systems experience significant delays when measuring longer distances, leading to extended welding times and potential quality control issues. The Argweld® PurgEye® 1000 eliminates these delays, providing real-time data that can be integrated into quality control systems, enhancing the overall efficiency and reliability of the welding process.
These advancements in weld purge gas oxygen monitoring are critical for industries where even the slightest deviation in oxygen levels can lead to catastrophic failures. By ensuring precise control over the welding environment, the Argweld® PurgEye® series sets a new standard in welding quality and safety.
The Importance of Gas Purging in Welding
Gas purging during the welding of stainless steels has long been recognised as essential, particularly in sensitive sectors such as petrochemical, pharmaceutical, cryogenics, food and beverage, and semiconductor industries. Oxygen during welding can cause unsightly discolouration and, more critically, lead to oxide deposits on the joints that may become detached, resulting in severe product contamination.
Recent research conducted by technologists at Huntingdon Fusion Techniques, HFT®, has revealed some critical insights. While existing Weld Purge Monitors® have proven effective when measuring oxygen levels close to the weld source—within a meter—their accuracy diminishes significantly beyond this distance.
To address the need for precise remote monitoring, HFT® has developed a unique purge gas measuring instrument capable of providing accurate and rapid readings up to one kilometre from the weld. These instruments can be integrated into recording and data processing systems for enhanced quality control.
Measuring Oxygen Content in Purge Gas
Historically, electrochemical or aerometric principles have been used for oxygen measurement, but these 'wet cell' technologies are unsuitable for continuous industrial use. Modern Weld Purge Monitors® are based on zirconium oxide sensors, which form the foundation for contemporary oxygen monitoring in weld purging.
Recent studies have shown that even lower oxygen levels than previously deemed necessary are required to achieve optimal welding results. While a maximum of 100 ppm oxygen in purge gas was once considered acceptable, new findings suggest that levels as low as 20 ppm, or even less, are essential to maintain corrosion resistance.
These findings have led to the development of advanced Weld Purge Monitors® that can accurately measure oxygen levels down to 10 ppm. These monitors are robust and precise and offer extended sensor life.
Challenges in Remote Oxygen Monitoring
Basic oxygen monitoring instruments typically rely on gas flow through a tube connecting the purge volume to the analyser (Fig. 1). While these instruments are reliable when positioned close to the weld joint (within one meter), challenges arise when measurements need to be taken over longer distances, especially in industries such as petrochemical, food, cryogenics, and pharmaceuticals.
In cases where long pipework runs require monitoring, a tube is often dragged from the purge gas exhaust to the monitor, which may be several meters away. This setup can delay oxygen level readings, causing potential misjudgements and unnecessarily extending the welding process.
To address these issues, HFT® developed the Argweld® PurgEye® 1000 Remote Weld Purge Monitor® (Fig. 2), a cutting-edge instrument that eliminates delays in oxygen level measurement even at distances of up to 1000 meters from the weld site.
Recording and Processing Oxygen Levels
Field observations have confirmed that oxygen level readings can be erratic when measured over distances greater than five meters. Delays in reaching accurate oxygen levels can significantly extend welding times. For example, at a five-meter distance, a monitor may take up to 15 minutes to register an oxygen level of 0.1%, even when the actual level is as low as 0.0025%.
These delays were attributed to several factors, including gas flow velocity, sampling tube friction, and the material and diameter of the sampling tube. Despite these challenges, HFT®'s Weld Purge Systems have proven effective, achieving oxygen levels below 0.01% (100 ppm) within 15 minutes at short distances. However, at 30 meters, this oxygen level may not be recorded even after an hour, and at 10 meters, it can take over 30 minutes to reach 0.01% oxygen.
Conclusion
The development of advanced Weld Purge Monitors®, such as the Argweld® PurgEye® 1000 Remote Weld Purge Monitor®, represents a significant leap forward in ensuring accurate and reliable oxygen level measurements during welding. These instruments are essential for maintaining the integrity of welds, particularly in sensitive industries where corrosion resistance is paramount.
