Cap Pass — What It Is and Why It Matters
The cap pass (also called the cover pass or final pass) is the last weld bead deposited on a groove weld — the visible surface that represents the finished weld. The cap pass must meet visual acceptance criteria for profile, width, reinforcement height, and freedom from surface defects.
The cap should be slightly convex or flat, extend slightly beyond the edges of the groove onto the base metal (providing adequate tie-in), and show a consistent, uniform ripple pattern. Excessive reinforcement (too tall) wastes filler metal and creates stress concentration; insufficient reinforcement (concave cap) reduces the weld's effective throat.
On code work, the cap pass is subject to visual inspection for undercut, porosity, cracks, incomplete fusion at the toes, and profile compliance. A well-executed cap pass is the welder's signature — it demonstrates consistent technique, proper heat management, and professional craftsmanship that speaks to the quality of the underlying root and fill passes.
Frequently Asked Questions
How tall should the cap reinforcement be?
Most codes limit cap reinforcement to 1/8" maximum above the base metal surface. Excessive reinforcement wastes material and creates stress concentration at the weld toes. The ideal cap is slightly convex, uniform in width, and blends smoothly into the base metal on both sides.
Should I weave or stringer the cap pass?
Both techniques work depending on groove width and position. For narrow grooves, straight stringer beads provide the most consistent profile. For wider grooves, a controlled weave filling the full width is efficient. Some codes restrict weave width; check the WPS for the specific weave limits allowed.