The most common issues when using fluxes cored arc welding wire are porosity, wormholes, and worm tracks. The cause of these defects is improper storage of electrodes. Electrodes pick up moisture inside the wire and create wormholes, porosity, and worm tracks when the welder starts welding.
The way to fix this is to cut off at least 10 feet from the electrodes and then start welding. To avoid these issues, the electrodes need to be stored in a dry place or moisture-proof bag.