Purging in Gas Tungsten Arc Welding (GTAW) is a critical process that involves removing oxygen, water vapor, and other gases or vapors from the vicinity of the welding joint to prevent oxidation or contamination during the welding process. This is particularly important when welding materials like stainless steel, duplex steel, titanium, nickel, and zirconium alloys, which are sensitive to the presence of air, oxygen, hydrogen, water vapor, and other vapors and gases that may combine with the hot metal as it is being joined.
Importance of Purging in GTAW Welding
The primary objective of purging is to protect the weld from oxidation, which can lead to discoloration, reduced corrosion resistance, and even structural failure. Purging is typically carried out using inert gases like argon or helium, which are introduced into the welding joint to displace the unwanted gases. The pressure and flow rate of the purging gas may vary throughout the welding job, and constant monitoring is vital to ensure that the quality of the gas remains consistent and free from impurities like oxygen or moisture.
Purging Gases and Their Applications
Purging is an essential step in GTAW welding, and different metals require different kinds of purging gases. For example, argon is the most commonly used purging gas, but helium can also be used. Nitrogen, however, should not be used on stainless steel, as it can lead to cracking or brittleness once the material cools down. Inert gases like argon or helium are introduced into the welding joint through the welding torch, which covers the top of the weld zone and pushes away the unwanted gases.
Gas Quality and Monitoring
The quality of the gas used for purging is crucial, as impurities like oxygen or moisture can damage the molten weld and lead to cracking or brittleness once the material cools down. Therefore, welding engineers typically specify the correct gas quality in their welding procedures, and welding training students need to be familiar with purging to ensure that their welds are smooth, clean, and free from any particles.
Purging in High-Precision Welding Industries
Purging is especially important in industries that require high-precision welding, such as the semiconductor, biopharmaceutical, and food equipment industries. In these industries, spotless and even contact surfaces are crucial, and full-penetration welds are important for thoroughly cleaning piping systems. Therefore, if you seek a welding career in a field that requires high-precision welding, you should be familiar with weld purging and different metals’ purging requirements.
Purging Process: Step-by-Step Guide
To purge a weld, welders typically follow these steps:
- Preparation: Clean the welding joint and remove any contaminants that may interfere with the purging process.
- Setup: Set up the welding torch and the purging system, ensuring that the gas flow rate and pressure are set correctly.
- Purging: Introduce the purging gas into the welding joint, ensuring that the gas flow rate and pressure are consistent throughout the welding process.
- Monitoring: Monitor the purging process, checking for any impurities or inconsistencies in the gas quality.
- Welding: Once the welding joint is purged, welders can begin the welding process, ensuring that the weld is smooth, clean, and free from any particles.
Technical Specifications for Purging in GTAW Welding
The technical specifications for purging in GTAW welding include:
| Specification | Details |
|---|---|
| Gas type | Inert gases like argon or helium are typically used for purging. |
| Gas flow rate | The gas flow rate should be sufficient to displace the unwanted gases and maintain a consistent gas quality throughout the welding process. |
| Gas pressure | The gas pressure should be consistent throughout the welding process and should be monitored to ensure that it remains within the recommended range. |
| Purging time | The purging time should be sufficient to displace the unwanted gases and maintain a consistent gas quality throughout the welding process. |
| Monitoring equipment | Monitoring equipment, such as oxygen sensors, can be used to ensure that the gas quality remains consistent and free from impurities. |
Values and Measurements in Purging
The values and measurements associated with purging in GTAW welding include:
- Gas flow rate: The gas flow rate is typically measured in liters per minute (LPM) or cubic feet per hour (CFH).
- Gas pressure: The gas pressure is typically measured in pounds per square inch (psi) or kilopascals (kPa).
- Purging time: The purging time is typically measured in minutes or hours.
- Oxygen levels: Oxygen levels are typically measured in parts per million (ppm) or percentages.
Critical Details in Purging
The critical details associated with purging in GTAW welding include:
- Gas quality: The quality of the gas used for purging is crucial, as impurities like oxygen or moisture can damage the molten weld and lead to cracking or brittleness once the material cools down.
- Monitoring: Constant monitoring is necessary to ensure that the quality of the gas remains consistent and free from impurities throughout the welding process.
- Purging time: The purging time should be sufficient to displace the unwanted gases and maintain a consistent gas quality throughout the welding process.
References
- American Welding Society Forum – GTAW Purge: https://app.aws.org/forum/topic_show.pl?tid=12739
- Wikipedia – Weld purging: https://en.wikipedia.org/wiki/Weld_purging
- High Performance Academy – Purging TIG Welds, Here’s Why & How: https://www.hpacademy.com/blog/purging-tig-welds-heres-why-and-how/
The lambdageeks.com Core SME Team is a group of experienced subject matter experts from diverse scientific and technical fields including Physics, Chemistry, Technology,Electronics & Electrical Engineering, Automotive, Mechanical Engineering. Our team collaborates to create high-quality, well-researched articles on a wide range of science and technology topics for the lambdageeks.com website.
All Our Senior SME are having more than 7 Years of experience in the respective fields . They are either Working Industry Professionals or assocaited With different Universities. Refer Our Authors Page to get to know About our Core SMEs.