Burn-Through — What It Is and Why It Matters
Burn-through occurs when excessive heat melts completely through the base metal, leaving a hole or severely thinned area in the workpiece. It is the most common defect when welding thin-gauge material and is caused by too much amperage, too slow travel speed, or excessive heat buildup from inadequate tack spacing.
Burn-through is most problematic on sheet metal (18-gauge and thinner), root passes on thin-wall pipe, and any situation where the heat-to-mass ratio is high. Once a burn-through occurs, the surrounding area is overheated and distorted, making repair more difficult than preventing the problem in the first place.
Prevention strategies include reducing amperage, increasing travel speed, using skip welding or backstep sequences to manage heat buildup, increasing tack frequency to resist distortion, using heat sinks (copper backing bars), and choosing a lower-heat process (TIG with foot pedal control is the gold standard for thin material where burn-through risk is high).
Frequently Asked Questions
How do I weld thin metal without burning through?
Reduce amperage, increase travel speed, use a tight arc, tack frequently to prevent gap opening, and consider a copper backing bar as a heat sink. TIG welding with foot pedal control gives the best heat management for thin material. For MIG, short-circuit transfer mode at low voltage and wire feed speed is the appropriate setting.
Can burn-through be repaired?
Small burn-throughs can be repaired by grinding the edges clean and carefully rewelding with reduced heat input. Larger holes may require cutting out the damaged area and welding in a patch. The surrounding heat-affected area will be distorted and may need to be straightened.