Have you ever encountered a customer or welder complaining of “worm tracks”? This is the term given to describe the surface discontinuity encountered predominately with gas shielded flux-cored wires. They appear as a linear void at or near the centerline of the weld and parallel to the weld bead. What causes these things? How do we get rid of them? And are they detrimental to the weld integrity? First, the cause of these “tracks” is an “outgassing” of the weld metal during the solidification of the molten metal. The weld metal/slag covering solidifies before the gas can completely escape, whereby trapping the gas between the weld metal and the slag, creating a wormtrack. The causes can be one or more of the following.

1. Moisture from contaminates in or on the surface of the base material.
2. Contamination due to a leak in the shielding gas hoses and/or fittings.
3. Excessive shielding gas flow rates, creating a venturi at the arc, which results in atmosphere getting to the arc.
4. Moisture contamination from the welding wire itself.
5. Less likely, but still possible is the shielding gas having excessive moisture or a high dew point temperature.

Now that we understand the causes, we can systematically prescribe the cure. For contaminates on the material, such as cutting fluids, oils or lubricants from forming or machining operations, these can be remedied by simply removing them from the weld area. Remember though that some lubricants are hydrocarbons, just wiping the surface clean may alleviate the wormtracking but still be detrimental to the weld metal integrity. An anti-spatter spray could also be a potential cause, especially when used in excess.

Checking the gas delivery system can be done using a soapy water solution and brushing it on the connections and looking for bubbles. Normally, checking from the cylinder to the back end of the welding torch is sufficient but don’t rule out the possibility of a leak in the torch itself.

When excessive gas flow rates are used and a venturi occurs, atmosphere is aspirated into the arc, this can also cause gross porosity. Flow rates should normally be between 30 to 45 cubic feet per hour to avoid this as the cause of wormtracks.

Moisture contamination from the wire results when the wire is exposed for a prolonged period of time at high humidity. To avoid this, the spool should be bagged and sealed when it is known that a wire will be exposed without use for more than 1-2 days or the humidity is extreme. If this is the suspected cause, the wire can be reconditioned by baking in an oven held at a minimum temperature for a specified period of time, thereby removing the moisture on and/or in the wire. If this is the suspected cause, contact the technical department for recommended reconditioning times and temperatures as this will vary depending on the wire and packaging type. If wire moisture is suspect, an easy way to determine if this is the culprit is to either increase the arc voltage or increase the tip to work distance. The latter will increase the resistance from the point of contact to the arc, thereby increasing the heat on the wire in this area and essentially “preheating” or burning off excessive moisture prior to the wire burning off in the puddle.

Shielding gas dew points are generally kept at  –40 degrees F, so this is rarely the cause of wormtracks.

Now, the final aspect of wormtracks, when none of the aforementioned conditions are present and wormtracking is occurring is the customer welding flat or horizontal stringer beads with an all-position type wire, (EX1T-1)? Remember that these wires have a fast freezing slag system to enable them to weld in the vertical and overhead position. If the slag freezes before the gas can escape a wormtrack will result. Consider a flat and horizontal wire for these applications, (EX0T-1). More times than not, this cures the problem of wormtracking, not to mention, they generally have a more desirable bead appearance in the flat and horizontal position than do the all position types. The common theory is to use one wire for all welding so if there’s a chance that the customer may weld out of position, they choose an all position gas shielded flux-core wire. Not a bad theory but one must understand, it may not be the best when used in flat and horizontal welds. For further assistance, contact the filler metals technical assistance group at 1-800-ESAB-123.

Jay Ginder
ESAB Welding and Cutting Products