Hello Sanjay, you haven't described the joint configuration and whether or not you are using a backing bar or some other form of backing. Are the welders using a backhand or forehand progression, roughly what is the width to depth ratio of the "root pass"? All of these things can have a lot to do with the sort of issues you are describing. If the welders are using a forehand progression they might be pushing slag out in front of the puddle and running over and trapping it as the welding progresses. If they are using a backhand method and trying to fill excessively in a single pass a similar sort of thing might be occuring and trapping slag along the toes of the root pass. Please provide a bit more detail of the joint set-up, include width of opening, groove type and angles, type of backing, gun angles, forehand or backhand progression, and possibly describe width to depth ratio on the root pass. You will receive much better answers if you can provide a bit more information for the folks on the forum to process. Best regards, Allan