Use of excessive current or too high amperage is the likely cause. If your job requires amperage in the higher ranges, you can choose a bigger size of the tungsten or get a different type that handles high temperatures well. Check the polarity settings too. Higher electrode-positive current brings better cleaning action, and at the same time, the tungsten gets more current, thereby rendering faster consumption. You should set your power source to electrode negative. Thus, you can reduce the time and amount of current on your electrode. Next, you want to check if the shielding gas in use is the right one or clean. Finally, check for any leak or crack in the fittings.