Cutting Defects: Identification, Causes, and Corrective Action

Cutting Defects: Identification, Causes, and Corrective Action

Producing a clean, accurate cut depends on controlling several process variables at once: travel speed, standoff distance, gas pressures, tip or nozzle condition, and technique. When any variable drifts out of range, the cut surface records the mistake as a visible defect. Learning to read those defects and trace them back to their cause is a core diagnostic skill for any welder working in structural or mechanical fabrication.

Common Defects and Their Causes

Excessive Top-Edge Melting (Rollover)

The top edge of the cut washes over and rounds, sometimes leaving a bead of solidified metal. Cause: travel speed is too slow, preheat flame is too large (oxy-fuel), or standoff distance is too close. The metal surface absorbs more heat than is carried away by the cutting action, and the edge melts back. Corrective action: increase travel speed in small increments, reduce the preheat flame size to the correct neutral setting, or increase standoff to the distance shown on the manufacturer's cutting chart.

Hard Slag

Slag that sticks firmly to the bottom edge and resists chipping indicates that the metal re-solidified before it could be ejected from the kerf. Cause: oxygen pressure too low, travel speed too slow, or tip size too small for the plate thickness. On plasma, low amperage relative to thickness produces the same result. Corrective action: increase cutting oxygen pressure or plasma amperage to the chart value; verify tip or nozzle is sized for the plate being cut.

Incomplete Cut (Failure to Sever)

The torch passes along the joint line but the plate does not separate. Cause: travel speed too fast for the thickness, cutting oxygen pressure too low, or preheat insufficient. The oxygen jet does not penetrate the full plate thickness. Corrective action: slow travel speed, verify oxygen pressure at the regulator matches the chart, and allow full preheat before opening the cutting oxygen valve.

Wandering Kerf

The cut line curves or drifts from the intended layout line. Cause: inconsistent hand travel, guide or template not secured, or torch tip clogged and producing an asymmetric flame. Corrective action: use a straight-edge guide, clean or replace the tip, and practice steady controlled travel.

Excessive Drag Lines

Drag lines are the curved striations visible on the cut face. A moderate pattern is normal; severe backward curvature indicates the oxygen stream is lagging far behind the travel point. Cause: travel speed too fast or oxygen pressure too low. Corrective action: reduce travel speed or increase cutting oxygen pressure incrementally until drag lines are nearly vertical.

Gouged Face

Irregular pits or grooves cut into the face. Cause: tip or nozzle is damaged, partially blocked, or too close to the work, causing turbulence; in plasma cutting, a swirl ring that is damaged or the wrong part number produces an erratic arc. Corrective action: inspect and replace consumables, re-establish correct standoff distance per the cutting chart.

Process-Variable Reference: Oxy-Fuel vs. Plasma

| Variable | Oxy-Fuel Effect | Plasma Effect |

|---|---|---|

| Travel speed too fast | Incomplete cut, severe drag | Incomplete cut, dross on bottom |

| Travel speed too slow | Top-edge melt, hard slag | Top-edge melt, wide kerf |

| Oxygen/amperage too low | Hard slag, incomplete cut | Dross, incomplete cut |

| Standoff too close | Gouged face, spatter on tip | Arc instability, gouged face |

| Standoff too far | Loss of preheat efficiency | Loss of arc, incomplete cut |

Using a Cutting Chart

Manufacturers publish cutting charts for each tip or nozzle that specify plate thickness range, tip size, oxygen and fuel pressures, and recommended travel speed. Always locate the row matching your plate thickness before making the first cut. A chart value is a starting point; minor field adjustments are normal, but large deviations signal a problem with equipment or technique rather than the chart.

Safety Requirements for This Lab

Lockout/tagout all equipment before changing tips, nozzles, or consumables. Never use an open flame or spark to locate a gas leak; use an approved leak-detection solution. Verify cylinder valves, regulators, and hoses are in serviceable condition before lighting the oxy-fuel torch. Keep the plasma cutting unit's work-lead clamp secured to clean base metal. Wear leather gloves, a welding jacket, and shade-appropriate eye protection—a minimum shade 5 cutting lens for oxy-fuel and the shade specified by the plasma unit's documentation for the amperage used. Keep the cutting area clear of combustibles and confirm a fire extinguisher is within reach. Never point a lit torch or active plasma torch at another person or at hose connections.