When it comes to welding titanium pipes, there is only one word at the core: "protection". Titanium, at high temperatures, is a "courtesan", extremely hungry for oxygen, nitrogen, hydrogen, once it is exposed to air during welding, the weld will become brittle, discolored, or even cracked, and its famous corrosion resistance will also plummet. Therefore, all our preparations and operations revolve around how to make it completely air-isolated from the entire process from heating, melting to cooling down to below 300 degrees Celsius.
Preparation Before Welding
The first is cleaning. This is not just a simple wipe. At least within 25 mm on both sides of the titanium pipe bevel, as well as on the surface of the welding wire, any bit of oil, moisture, dust or even a fingerprint will decompose into carbon, hydrogen, and oxygen at high temperatures, polluting the weld seam and causing porosity and cracks. The bevel must be thoroughly sanded with a stainless steel wire brush specially designed for titanium until it reveals its metallic luster. Then clean with a special solvent such as acetone, remember that you must never use a solvent containing chlorine (such as trichloroethylene), chloride ions can cause stress corrosion cracking, which is catastrophic. After cleaning, it is best to wear gloves to take it, and it must be welded within 4 hours after cleaning, otherwise it will have to be reprocessed.
The second is gas protection, which is the soul of titanium welding. The purity of argon gas must reach more than 99.999%, and there must be no moisture or impurities at all. It is not enough to protect the front weld pool with the nozzle of a welding gun. You must create an inflatable chamber for the back of the weld (inside the tube) and separate a space inside the tube with high-temperature foil tape or special "water-soluble paper" to ensure that argon gas fills and stays in it. More importantly, titanium still needs to be protected during the post-weld cooling phase. The brilliant color of the weld surface is a good look, but it is evidence of a failure to protect. Therefore, a device called a "tail tow" must be used, which follows the torch like a moving umbrella and continues to blow argon on the weld and heat-affected zone that has just solidified but is still at high temperature until the temperature drops below 300 degrees. Before welding, be sure to do a protective effect test: vent well, arc the test plate without filling the wire, and melt a solder joint. If the surface of the solder joint is silver-white as a mirror, then congratulations, the protection is in place. If it appears yellowish, blue or even gray, then you have to check your gas, flow rate and protection device quickly, and you must not start formal welding until the problem is solved.
Welding Process
Before arcing, there should be a pre-ventilation time, about 3 to 5 seconds, to completely replace the air in the welding torch, gas pipe, and gas hood. When welding, use the shortest arc (1 to 2 mm), the longer the arc is easy to stir the air, and the protection effect will be worse. When feeding wire, the welding wire head must always stay in the argon gas protection area, and must not be pulled out and sent in, as soon as it enters and exits, it brings air in. The welding wire should be pointed into the weld pool smoothly and evenly.
Controlling heat input is also very important, don't use too much current to grind the ground welding, under the premise of ensuring penetration, the speed is appropriately faster, reduce the residence time of the weld and the base metal at high temperature, and prevent the grain from growing thicker.
When welding arc retraction, the knowledge is greater. It's not like you immediately raise your gun and turn off the air as soon as you close the arc. The welding torch should stay at the arc point for a while, and at the same time lag the air supply, and continue to blow argon gas to cool the red high-temperature weld. This time can last from 15 seconds to half a minute until the weld metal completely loses its red color and is no longer hot with the back of the hand. This step is the last step to ensure the quality of the weld, and it is also the easiest to be lazy.
Post-Weld Inspection (Color)
Silver white/bright silver: perfect protection, best weld quality.
Light yellow/golden yellow: There is slight oxidation, which may be acceptable in some undemanding occasions, but for harsh working conditions, this is already a warning.
Dark blue/purple: Oxidation is more obvious, the plasticity and corrosion resistance of the weld have decreased, and it is usually necessary to cut off the re-welding.
Off-white/gray-black: Severe oxidation, brittle welds, and even powder peels off, must be completely removed and re-welded.
All in all, welding titanium pipes is not as extensive as welding carbon steel, it is more like doing a precision sterile surgery. The rigor and meticulousness of each step will ultimately be reflected in the bright, dense and strong weld. It tests not only technology, but also the welder's patience, sense of responsibility and a deep understanding of material properties.
