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D1.1:2025 언더컷 허용 기준

D1.1:2025 Table 8.1 Item (7) defines separate undercut 한계 for statically loaded and cyclically loaded nontubular connections. The criteria are applied during 육안 검사 per Clause 8.9. Undercut is measured as depth from the 모재 surface at the weld toe — it is a groove melted into the base metal that has not been filled by 용접 금속.

정하중 비강관 연결부

정적 기준은 1 in [25 mm] 경계에서 모재 두께에 따라 나뉘며, 얇은 모재의 누적 길이에 대한 추가 예외가 있습니다.

The exceptions in (a) and (b) only apply to material less than 1 in thick. For thicker material, the flat 1/16 in limit applies with no accumulated-length allowance. In practice, the 1/16 in allowance on thicker material reflects the reduced sensitivity of heavier sections to stress concentrations at the weld toe.

반복하중 비강관 연결부

Cyclic loading imposes stricter limits because undercut creates a stress concentration that accelerates fatigue crack initiation. The criteria distinguish between primary tension members and all other members.

주 인장 부재에 대한 0.01 in 한계는 D1.1에서 가장 엄격한 언더컷 허용 오차입니다. 이 깊이에서는 언더컷이 육안으로 거의 보이지 않습니다. — 대부분의 검사관은 이 얕은 언더컷을 측정하기 위해 필릿 용접 게이지 또는 깊이 마이크로미터를 사용합니다. 보조 부재 또는 계산된 인장 응력을 받지 않는 부재의 용접의 경우, 1/32 in 한계는 정적 얇은 모재 기준과 일치합니다.

용접 언더컷의 원인

Undercut forms when the 용접 arc melts a groove into the base metal at the weld toe that is not filled by deposited 용가재. The defect appears as a narrow channel running along one or both sides of the weld bead. Three parameter errors account for the majority of undercut seen in structural fabrication.

용접 속도가 너무 빠름

When the 전극 moves too quickly, the arc melts base metal at the weld toe but advances before filler metal can flow into the groove. This is the most common cause of undercut in production welding, particularly with FCAW and GMAW where wire feed speed is constant. Slowing 용접 속도 allows the weld pool to wet the toe and fill the groove before solidification.

전류가 너무 높음

Excessive current widens the arc cone and increases the volume of base metal melted at each point along the joint. The weld pool becomes wider than the filler metal can bridge, leaving unfilled grooves at the toes. This is especially problematic on fillet welds where the horizontal leg melts into the vertical member. Reducing 전류 or switching to a smaller electrode diameter narrows the melt zone.

잘못된 전극 각도

Holding the electrode at too steep an angle — or favoring one side of the joint — concentrates arc force unevenly. One toe gets excessive heat and melts a groove while the other toe may show adequate fusion. On T-joints, angling the electrode too far toward the vertical member undercuts the horizontal plate. Maintaining a consistent 45-degree work angle on fillet welds distributes heat evenly across both legs.

부적절한 위빙 기술

On weave beads, pausing too briefly at the weld toes does not allow filler metal to fill the edges of the bead. The center of the weave gets adequate fill while the toes are left undercut. Pausing slightly longer at each toe — particularly on vertical-up welds with SMAW — allows the pool to wet and fill the base metal groove before moving across the bead width.

언더컷 수리 시기 및 방법

If undercut exceeds the applicable Table 8.1 limit, the weld does not pass 육안 검사 per Clause 8.9 and must be repaired. D1.1:2025 Clause 7.25.1.2 addresses the 보수 procedure for undercutting specifically.

For undercut that is only slightly deeper than the acceptance limit, grinding alone may bring the weld toe profile into compliance. Grinding blends the transition between weld metal and base metal, effectively reducing the measured depth of the undercut groove. This approach works when the undercut is shallow enough that removing a small amount of material still leaves the base metal above its 최소 required thickness.

For deeper undercut, the surfaces shall be prepared per Clause 7.29 (weld cleaning) and additional weld metal deposited to fill the groove. The repair weld must use a qualified WPS and meet the same acceptance criteria as the original weld. In practice, a single stringer bead along the undercut toe using a small-diameter electrode (such as 3/32 in E7018 for SMAW) at reduced amperage fills the groove without introducing new undercut on the opposite side.

The removal of weld metal or base metal during repair may be done by machining, grinding, chipping, or gouging per Clause 7.25. Oxygen gouging is permitted only on as-rolled steels. The repaired or replaced weld shall be retested by the same method originally used, and the same acceptance criteria apply.

Undercut is one of eight 불연속 categories evaluated during visual inspection. For the complete list of D1.1 Table 8.1 acceptance criteria — including 균열, 불완전 융합, and 기공 — see the weld defects overview. When a repair weld is required, it must be performed using a qualified WPS — see Procedure Qualification Records (PQR) for D1.1’s two qualification paths.