Purge Welding
There are many processes that can be used when welding, one of which is purge welding.
One (of many things) a welder has to watch out for while performing a weld is defects. This could be: porosity, undercut, cracks, distortion, etc. The reason I mention defects is that purge welding helps prevent those. Failure to prevent defects can result in your welds breaking, leading to whatever you put your welds on failing. This process essentially cleans the weld of any other oxides or gasses while welding and, after which, greatly decreases your chances of having porosity and discoloration.
Another big defect to watch out for is sugaring. This is something that happens on stainless steel and mainly in pipe. You will want to keep the weld from sugaring on the inside of the pipe. According to Miller Welding “Sugaring (oxidation) occurs around the weld when it is exposed to oxygen in the air. The best way to prevent sugaring is to back purge the weld with argon shielding gas or reduce welding amperage.” Sugaring is not only dirty but will eventually cause the weld to break. You can prevent this by filling the piece with shielding gas before you weld. Essentially, you need to put a cap on one end of the pipe to hold your shielding gas in, and then on the other insert the gas.
Controlling gas flow is another element of purge welding. This is also a contributing factor in keeping your weld clean and free of different defects that could result in an unsatisfactory weld. Your gas flow is important because it keeps the oxygen from reaching your weld and contaminating it. It’s also worth mentioning that you can also have too much shielding gas which can be just as harmful to the weld. A good range to set your CFH (Cubic Feet per Hour) would be anywhere from 20-30. 25 CFH is always a good starting point and you can adjust up or down from there if need be. The type of gas that you want to use has to be inert gas. Argon is mainly used, but helium can also be used in certain circumstances. The purge welding process is very commonly used in the food industry where welds are required to be very sanitary and clean. This ties back to the importance of keeping the sugaring defects out of the pipe because a drink that travels through the pipe will pick up the sugary gray material left over from the weld, sugaring also leaves minuscule holes that can trap and hold bacteria. In conclusion, depending on what material you are working with, purge welding is a great process as it can help people who aren't familiar with welding get to learn more about it without worrying about too many defects resulting in the weld.
Sources
Garrett’s Brain (welding school grad)
https://www.millerwelds.com/resources/article-library/ten-common-tig-problems-a-visual-guide
