The final part of Dr. Fletcher's series emphasises the importance of maintaining low oxygen levels in the purge gas during welding to ensure defect-free welds, especially for sensitive materials like titanium and certain stainless steels.
The Importance of Low Oxygen Levels:
Maintaining a low-oxygen environment is essential to prevent weld contamination. The tolerable oxygen level varies depending on the material, with titanium requiring levels as low as 50 ppm and some stainless steels tolerating up to 150 ppm. Effective sealing around the weld zone is vital to prevent air intrusion and maintain the integrity of the low-oxygen environment.
Effective Sealing Solutions:
To ensure a secure low-oxygen environment, the study highlights several sealing solutions:
These solutions are critical for maintaining a stable weld environment and preventing oxidation.
Monitoring Oxygen Content:
Monitoring the oxygen content in the purge gas is crucial to avoiding weld defects. As industry standards have tightened, and modern requirements often demand oxygen levels below 10 ppm, advanced monitoring equipment has become essential.
Advances in Monitoring Equipment:
Modern oxygen monitors, such as those in the PurgEye® series, offer state-of-the-art technology, including auto-calibration, rugged design for on-site use, and the ability to measure oxygen levels down to 10 ppm. These monitors ensure that welds maintain their mechanical and metallurgical integrity.
Remote Monitoring Capabilities:
For complex or large-scale welding projects, remote sensing heads allow for monitoring oxygen levels from up to 1 km away, ensuring continuous and accurate readings even when direct access is impractical.
Conclusion:
Maintaining low oxygen levels in the purge gas is essential for high-quality welds, particularly with sensitive materials. The evolution of advanced monitoring equipment, such as the PurgEye® series, enables welders to meet stringent industry requirements, ensuring defect-free and durable welds.
Products Mentioned:
Eliminating Oxygen from the Purge Gas and the Use of Monitoring Equipment
In this final part of the series on shielding gas and purging techniques during welding, the focus is on maintaining a low oxygen level in the purge gas to ensure defect-free welds. While specialised weld purging equipment plays a vital role, controlling the oxygen content in the purge gas is crucial to achieving success.
The Importance of Low Oxygen Levels
The amount of oxygen that can be tolerated in the purge gas largely depends on the welded material. Sensitive alloys like titanium may require oxygen levels to be limited to as low as 50 ppm, while some stainless steels can tolerate up to 150 ppm without noticeable surface discoloration.
A key aspect often overlooked is the necessity of effective sealing around the weld zone. Poor sealing can allow air to enter, defeating the purpose of creating a low-oxygen environment. Therefore, attention must be given to sealing all contiguous surfaces, including services providing gas and other accessories, especially when using pipe purging and trailing shields or when working within enclosures.
Effective Sealing Solutions
Effective sealing solutions are essential for maintaining a low-oxygen environment. Examples include:
These solutions help to ensure that the weld zone remains free from air intrusion, thereby preventing oxidation and ensuring high-quality welds.
Monitoring Oxygen Content
Monitoring the oxygen content of the purge gas during the welding process is crucial to avoid weld contamination. While weld discolouration caused by oxygen may be acceptable in some cases, it can compromise the joint's mechanical and metallurgical properties, potentially leading to weld failures.
Traditional oxygen measuring devices, often based on outdated technology, are inadequate for weld purge gas monitoring, especially given the increasingly stringent requirements across various industries. While a decade ago, an oxygen content below 0.1% (1000 ppm) in purge gas was considered sufficient, today’s standards often require levels well below 0.001% (10 ppm).
Advances in Monitoring Equipment
Modern monitoring equipment has evolved significantly to meet these demands. Early devices relied on wet cell’ technology, which was unsuitable for the required low oxygen levels. Modern instruments, such as those using zirconia sensors, provide the necessary sensitivity, reliability, and robustness for effective weld purge gas monitoring.
State-of-the-Art Technology
The purge gas should contain less than 0.01% oxygen for most stainless steel welding. More sensitive materials, like titanium alloys, may require even lower levels. The PurgEye® range from Huntingdon Fusion Techniques is a prime example of advanced monitors capable of meeting these stringent requirements. These instruments offer a range of features, including:
Remote Monitoring Capabilities
Remote sensing heads have been developed for situations where physical access is impractical, such as in long tube and pipe fabrications. These can be fitted onto the purging system and transmit oxygen level data to a monitor up to 1 km away. This feature is handy in scenarios involving complex or large-scale welding projects.
Conclusion
Maintaining a low oxygen level in the purge gas is essential for achieving high-quality welds, mainly when working with sensitive materials like titanium and certain stainless steels. The evolution of monitoring equipment, such as the PurgEye® series, has made it possible to meet these stringent requirements with more excellent reliability and accuracy, ensuring that welds are free from defects and maintain their mechanical and metallurgical integrity.
