Undercut along the weld toe weakens the joint by removing material from the base metal, creating a notch that can concentrate stress. Codes set acceptance limits for how large this imperfection can be. For a single undercut, the maximum length allowed is 1.6 mm (about 1/16 inch). This means a single continuous undercut shorter than or equal to 1.6 mm is acceptable (assuming no other defects exceed limits). If the undercut extends longer than 1.6 mm, it would fail the inspection criteria for undercut. When inspecting, you measure along the weld toe from the edge into the undercut to determine its length; multiple shorter undercuts are evaluated individually, but the single undercut length limit applies to each continuous instance. The other options exceed typical code limits or, in the case of a shorter value, are simply not the maximum allowed.

Penetration depth describes how far weld metal fuses into the joint thickness. A fillet weld sits at the corner of the two pieces and does not weld through the thickness like a groove weld designed for complete joint penetration. When the fillet angle is less than 60 degrees, the geometry of the weld reduces the effective fusion depth relative to the joint, so the weld does not achieve full-through fusion. That situation is classified as partial joint penetration. Complete joint penetration would require a groove weld intended to fuse through the full thickness, which a fillet weld does not provide. No penetration would imply no fusion at all, which isn’t the case here, and mixed penetration isn’t the standard classification for this scenario.

When two plates are joined, the fit-up along the joint must stay nearly level to ensure the weld bead can fill a consistent, uniform gap and throat. A slope describes how much one edge rises or falls along the length of the joint. The highest allowable slope is very small, meaning only a tiny misalignment is permitted. One inch of rise per twenty-five inches of run (one in twenty-five) is the standard limit. Keeping the slope this shallow helps the weld deposit remain balanced on both sides, supports proper penetration, and avoids areas where the weld could be too thin or lack fusion. If the plates were steeper than this, the gap would vary along the joint, making it hard to weld cleanly and risking weaker joints or defects. The other options describe much steeper inclines that would not meet proper fit-up tolerances.

When a discontinuity is removed and no welding is required, the surface should be finished by grinding the depression to blend smoothly with the original plate. Create a gradual, flush contour so there isn’t a sharp change in geometry. The transition should not be steeper than 1 in 10 to minimize stress concentrations and maintain a surface suitable for inspection and coating. Leaving the depression, filling with filler, or patch-welding would introduce unnecessary features or materials when no repair welding is needed.