Mild steel welds can be quite difficult to get right if you are not used to this kind of work. It can be one of the most difficult jobs to do when working with mild steel tubes. Hats off, if you can do it well, but it takes a real man to be able to do this job. You will need to wait for the mild steel tube to cool after interval passes, while making sure that you keep the tip extremely hot and shielded with argon. You also have to make sure that you snip the tip of the welding rod if it ever gets crapped up so as to keep your tungsten sharp as it should be.
Purging steel is a very tough thing to do. Mild steel tubes and all the other types of stainless steel products need to be purged with argon gas to prevent them from sugaring or granulation, which is the effect of severe oxidation.
Mild steel welds cannot be complete without an argon purge on the inside surface of common mild steel tube. And this process is done by wrapping aluminum duct tape around the ends of the mild steel tubes while argon gas is left to be trapped inside it.
To be able to determine whether the tube has been purged enough, you need to use an oxygen analyzer; and to make sure that you do a good purge, here are some tips that you can follow:
1. Check that there is no water left inside in mild steel tube. Even a single drop of water will cause damage on the purging process. This is due to the components of water which are hydrogen and oxygen. Wait until all the water will evaporate.
2. You can poke a small hole at the topmost part of the tube to allow the argon gas to flow continuously inside it. Argon should freely flow inside the tube to let all the air out of the tube, as argon is denser than air. Argon will also remove air out of the tube because it has the ability to displace it.
3. Use a diffuser and place it at both ends of your argon hose to ensure a higher flow rate of the gas. A homemade diffuser can be easily fabricated with using stainless steel wool, perforated stainless steel sheet and small piece of sheet metal.
If you are sure that a good purge was done, you can proceed with tacking. You can do this by getting the tape off to let the tack cool down, after which you should re tape it. The tacking should be done 180 degrees apart.
There are more tips that you can follow when welding stainless steel pipe.
1. Instead of using a 3/32 inch rod, you should use a 1/8 inch wire to do better welding.
2. Re welding can be done on impenetrable areas.
3. Prefer to use stainless steel wire brushes and files which are for stainless steel alone.