Burn-Through Weld — 원인, 예방 & D1.1:2025 Repair

What Is Burn-Through

Burn-through is a weld defect where excessive heat input melts completely through the base metal, creating a hole or severe depression in the weld zone. Unlike 기공 or 언더컷 which affect the weld cross-section, burn-through penetrates through the base material itself.

Under D1.1:2025, burn-through is classified as a weld profile defect under Clause 7.23, not separately named in 표 8.1 as a 불연속 범주. It is evaluated as a weld profile nonconformance. When burn-through creates a hole or severe profile violation, it fails 육안 검사 under Clause 8.9 and requires repair.

D1.1:2025 Clause 7.23 — Weld Profile Requirements

Clause 7.23 governs the 육안 appearance and profile of completed welds. 필릿 용접 profiles must meet Figure 7.4 요구사항. 그루브 용접 faces shall be flush or have reinforcement within specified 한계.

Burn-through creates a profile defect that fails visual 검사 under Clause 8.9 when it results in an incomplete weld profile or penetration through the base metal. The defect may also create stress concentrations detrimental to structural performance. Because the base metal itself is compromised, burn-through cannot be corrected by simply adding more 용접 금속 — the repair procedure under Clause 7.25.1 must be followed.

Causes of Burn-Through

Four primary causes drive burn-through failures:

Excessive heat input — 전류 set too high for the material 두께 generates more heat than the base metal can conduct away. The weld pool grows beyond the joint geometry and melts through.

Wrong travel speed — Moving the 전극 too slowly concentrates heat in one location. Even at correct amperage, insufficient 용접 속도 can cause cumulative heat buildup that results in burn-through, particularly on thinner sections.

Thin base metal — Material that is too thin for the 용접 공정 parameters cannot dissipate heat fast enough. The same parameters that weld heavier plate without issue will burn through thin material.

Incorrect electrode diameter — An oversized electrode deposits more heat than the joint requires. Matching electrode diameter to the material thickness and joint configuration is a fundamental WPS parameter that directly controls burn-through risk.

Prevention

Effective prevention requires matching all heat input parameters to the material thickness as specified in the WPS. 확인 amperage, 전압, and travel speed settings before production 용접. Use the smallest electrode diameter appropriate for the joint configuration. On thin material, stay at the low end of the WPS amperage range.

For thin base metal, intermittent welding technique — depositing short weld segments and allowing each to cool — limits cumulative heat accumulation. A copper backing bar behind the joint provides a heat sink and reduces burn-through risk when the joint configuration permits its use.

Repair per Clause 7.25.1

D1.1:2025 Clause 7.25.1 governs repair of defective welds. Burn-through repair requires three steps:

Step 1 — Remove to sound metal. All defective weld metal and affected base metal must be removed back to sound material. Gouging, grinding, or machining may be used. The removed area must expose clean, unaffected base metal before re-welding begins.

Step 2 — Re-weld per approved WPS. Re-weld the area using an approved WPS appropriate for the base metal type, thickness, and joint configuration. The repair WPS must address the root cause — typically by specifying lower amperage or smaller electrode diameter than the original WPS that produced the burn-through.

Step 3 — Re-inspect. Re-inspect the repaired area using the same visual 합격 기준 criteria from Table 8.1 and Clause 8.9 that identified the original defect. For CJP groove welds, complete joint penetration must be re-established and verified in the repaired area.

Related Reference

■ Weld Defects HubTable 8.1 all 8 categories ■ Incomplete FusionClause 5.22 complete fusion required ■ Visual Weld InspectionClause 8.9 VT procedure ■ Preheat CalculatorReduce hydrogen and heat input risk