Weld Purge Monitor for Welding Applications
To help aid in limiting oxygen in weld points, GasLab offers the TecSense TecWeld Weld Purge Monitor, which is an oxygen analyzer specifically for welding. The TecWeld is an oxygen detector designed to provide accurate measurements down to 0% oxygen for back purging of oxygen during welding. As a trace oxygen analyzer, the TecWeld Weld Purge Monitor is most commonly used to verify argon flooding during welding of stainless steel or titanium pipe in the aerospace, automotive, nuclear, medical and food-grade industries where x-ray verification of welds is required or the backside of welds cannot be inspected.
The TecWeld features measurements in less than three seconds to ensure you can get measurements while working quickly, which is imperative in TIG welding. The large display is easy to read during the welding process, and the TecWeld comes pre-calibrated from the factory and is ready to use right out of the box. As an added benefit, the TecWeld offers data logging capabilities, which is important when needing to form a paper trial for inspection or verification.
You can count on a long lifespan with the optochemical sensing technology. Optochemical oxygen sensors are preferable over other types of oxygen sensors such as electrochemical sensors, because they are longer lasting and have a faster reaction time, as the oxygen does not have to diffuse through a membrane. Optochemical sensors also are a non-consumptive way of measurement, as opposed to zirconia sensors which require high power consumption.
The TecWeld Weld Purge Monitor also features a is the built-in 10,000-hour gas sampling micro-pump and is an ideal choice for TIG welding of stainless steel or titanium.
What is Weld Purging?
Weld purging is used in MIG and TIG welding, also known as Gas Tungsten Arc Welding. TIG welding is a welding process that joins metals by heating them with an arc between a tungsten electrode and the piece that is being worked on. One hand is used for holding the TIG torch, and the other is used to add the filler to the weld joint. TIG welding can be difficult to learn as it requires the use of two hands, but when done correctly offers one of the highest quality welds, especially when tested for oxygen levels with the TecWeld.
Weld purging is the act of removing oxygen, water vapor and any other gases or vapors that might be harmful to a welding joint as it is being welded. The oxygen, water vapor or other gases are replaced with inert gases such as argon from a welding joint as it is being welded. Stainless steel, titanium, nickel and zirconium alloys are sensitive to the presence oxygen, and water vapor and will combine with the hot metal as it is being joined. While the cup surrounding the welding tip creates a pocket of inert gas at the weld, purging surrounds the backside of the weld with the same gas. It is most commonly used when welding pipe or other hollow metal objects. Poor gas coverage can lead to contamination due to the lack of a shield gas.
What is Gas Plume Measurement?
Another factor to keep in mind during welding is the weld plume. The dimension of the plumes are important. The plume needs to be large enough to cover the entire area of the weld, and be at or very near the eutectic point where the metal loses its hardness and becomes receptive to oxidation and other undesirable processes.
The probe nature of the TecWeld allows the dimension of the plume to be measured. Too much flow will be indicated by an oversize plume, which can in turn cause inappropriate cooling at the weld point and cause the weld to become brittle. Brittleness can occur when the heavy element of the filler metal and the base alloy are joined and cooled at different times. This is sometimes referred to as the passivation of the weld, because it does not allow the stratification of the weld component from uncontrolled atmospheric or thermal conditions.
Oxidation in Welding
Oxidation is a form of metal corrosion that forms during the welding process. Oxidation prevents a good weld from forming because too much oxygen enters the area where the weld is being created. Electrons move from the metal that is being welded to the oxygen molecules during the process. Too much oxygen in the welding environment leads to corrosion, which then in turns causes a weak and unreliable weld. Corrosion can be dangerous if it affects an integral inner structure such as buildings and bridges, pipes, and ships. A weakened infrastructure can put lives at risk, so reduce oxidation in welding is essential for safety.
An example of oxidation in welding is carbide precipitation, also called sugaring, which occurs on stainless steel. Sugaring is the result of the back side of the weld being exposed to oxygen in the atmosphere during the welding process. Even though the weld looks good from the front, it is weak at the backside and over time can display stress cracks. The best way to avoid sugaring is to purge the weld with a shielding gas such as argon. The TecWeld Weld Purge Monitor can verify back-purging when you cannot view the backside of your weld and makes a valuable addition your welding equipment.