Cold Lap and Weld Overlap: CWI Inspection Under AWS D1.1
Cold lap and weld overlap are distinct but related discontinuities in structural welds. Learn how a CWI identifies, documents, and dispositions each under AWS D1.1:2025.
Cold lap and weld overlap are among the most frequently cited discontinuities during CWI visual surveys of structural fillet and groove welds. They are also among the most misunderstood. Inspectors sometimes use the terms interchangeably, contract documents occasionally mix the definitions, and some welders treat a light rollover at the toe as cosmetic. AWS D1.1:2025 draws a clear line: overlap is not permitted, regardless of size, in any weld subject to the code.
Understanding why overlap forms, how to find it, and what AWS D1.1:2025 requires for disposition separates the CWI who catches it early from the one who signs off on a weld that needs to come back out.
Defining the Discontinuity
Weld overlap is weld metal that has flowed beyond the weld toe onto the base metal surface without fusing to it. The result is a crevice or notch along the toe—sharp at the root of the overlap, hidden under solid metal. AWS defines it explicitly as an unacceptable condition.
Cold lap is sometimes used as a synonym for toe overlap, and that usage is common in shops. In a stricter metallurgical sense, cold lap can also describe incomplete fusion between passes in a multi-pass weld—a cold interface where the arc did not fully re-melt and merge the previously deposited bead. The practical distinction matters to the CWI because the two manifestations look different on visual exam and respond to NDE differently.
Both discontinuities share the same root problem: insufficient heat at the fusion zone boundary. Metal was deposited but the arc did not provide enough energy—or did not dwell long enough in the right place—to fully fuse the metal being laid with the substrate beneath it.
AWS D1.1:2025 Acceptance Criteria
The visual acceptance criteria in AWS D1.1:2025 make no accommodation for overlap based on size or length. Where the standard applies, any observable overlap at the weld toe in a structural weld is rejectable on visual examination alone. This zero-tolerance position reflects the notch geometry of overlap: the crevice at the toe acts as a stress concentrator, and under cyclic loading it becomes a fatigue crack initiation site.
For fillet welds, additional profile requirements govern convexity and concavity. A weld that is significantly convex (rounded crown rather than flat face) is more prone to toe overlap because the arc energy is concentrated at the crown rather than driven into the fusion line. AWS D1.1:2025 sets maximum convexity limits tied to weld size; a CWI who finds the crown profile outside the allowed range should also look carefully along both toes for overlap before calling the weld acceptable on all other counts.
The edition disclaimer applies here: Rule library based on AWS D1.1:2025; verify against your governing edition. Earlier editions carry the same zero-tolerance position, but CWIs working under a contract that specifies the 2020 edition should confirm the relevant acceptance table there rather than assuming all rules transferred verbatim.
What the CWI Looks For During Visual Examination
Cold lap and overlap are, in many cases, visible to the naked eye under adequate lighting. Effective visual technique requires:
Angle of observation. A CWI looking straight down at a fillet weld rarely sees the toe of the vertical leg clearly. Walk the joint, crouch to look at the horizontal-to-vertical transition, and rake a flashlight across the toe at a low angle. Overlap projects a shadow under oblique light that is invisible in overhead flood lighting.
Toe condition. The base metal adjacent to an acceptable weld toe should show a smooth, clearly fused transition. A line or groove paralleling the weld, a slight ridge of metal sitting on top of the plate surface, or any visible crevice at the junction of weld metal and base metal warrants rejection. Use a 5× to 10× magnifier when the condition is marginal.
Weld profile gauge. Measuring devices confirm whether convexity or concavity is within limits, but they do not substitute for visual judgment at the toe. A gauge read at midspan of a long fillet can miss localized overlap at an end or corner.
Adjacent passes in multi-pass welds. Between passes, look at the exposed face of the last bead before depositing the next. A line of poor fusion visible in the valley between beads, or a bright-metal zone that did not re-melt completely during the subsequent pass, indicates inter-pass cold lap. Catching this during welding—not after final visual—prevents a repair excavation that may require removing multiple layers.
Root Causes in the WPS and How to Prevent Them
Overlap and cold lap trace back to a handful of controllable welding parameters, all of which should appear in the applicable WPS.
Travel speed too high. Fast travel deposits less heat per inch. The leading edge of the puddle freezes before it can wet out the base metal at the toe. GMAW and FCAW-G are the most common culprits because wire feed speed (and therefore deposition rate) can stay high while the operator unconsciously increases travel speed trying to chase a large puddle.
Incorrect work angle. On a horizontal fillet weld (flat position on the vertical leg), the electrode should be positioned at approximately 45° between the two members, bisecting the joint angle. Pointing the electrode toward the vertical plate pulls the puddle away from the horizontal plate toe. Pointing it downward rolls metal over the horizontal toe without adequate fusion.
Insufficient preheat. Cold base metal draws heat away from the fusion boundary rapidly. Low preheat means the arc energy goes toward heating the substrate rather than achieving full fusion at the edges of the puddle. This is especially relevant on thick plate (Group II and above under AWS D1.1:2025 Table 5.6) and in cold ambient conditions where the preheat temperature drops between passes.
Electrode or wire condition. Moisture-contaminated SMAW electrodes and degraded FCAW wire (absorbed moisture, kinked wire) produce an unstable arc with poor wet-out behavior. The puddle stiffens and does not flow into the base metal the way clean, dry consumables do.
Current/voltage out of range. Both amperage and voltage must stay within the WPS-qualified range per Table 6.6 essential variables. Low voltage on a GMAW or FCAW process tends to produce a narrow, convex bead; combined with marginal travel speed, the result is overlap along both toes.
When UT or MT Is Required
Visual inspection alone may miss inter-pass cold lap buried beneath subsequent passes. AWS D1.1:2025 NDE requirements for CJP groove welds in tension applications typically mandate UT (or RT) after welding is complete. When UT is performed on a multi-pass groove weld and a planar indication appears at a pass interface—especially parallel to the fusion line—inter-pass cold lap is the most likely cause.
Toe cold lap that is technically surface-breaking or very near-surface is better detected by MT (wet fluorescent magnetic particle) or PT (liquid penetrant) than by conventional UT. MT with a yoke placed to magnetize across the weld toe will pull a clear linear indication from a cold lap that UT might classify as a geometry response and dismiss. FCAW-G welds on thick A572 Gr.50 primary connections are an appropriate application for supplemental MT precisely because the process and position combination (horizontal fillet on heavy plate) is prone to this mode of discontinuity.
When overlap or cold lap is found, the disposition path under AWS D1.1:2025 is straightforward but must be documented:
Mark and record the location and extent of the discontinuity on the inspection report.
Remove the affected area by grinding or arc gouging back to visually sound metal. The CWI should examine the excavation—a straight groove with clean bright metal at the bottom confirms full removal; any remaining dark or oxidized material at depth means go deeper.
Pre-weld the repair zone to the same or higher preheat temperature required by the original WPS.
Weld to the applicable WPS. If the shop has a qualified repair WPS with the same process, position, and base metal combination, use it. If the repair joint geometry differs materially from the original, the WPS must cover it. See weld repair procedure qualification under AWS D1.1 for the requalification path.
Re-inspect. Visual, and UT/MT if the original joint was subject to NDE requirements.
The number of repair attempts at the same location is not unlimited. AWS D1.1:2025 restricts repeat repairs and requires engineering approval for third and subsequent attempts on the same area, both to prevent metallurgical damage from repeated thermal cycles and to trigger a root-cause evaluation.
Connecting WPS Controls to Prevention
The best time to prevent overlap is during WPS review and welder qualification testing, not during production inspection. A CWI reviewing a WPS for horizontal fillet application should verify:
Travel speed range is specified and the upper end is not so high that deposition rate falls below what the joint requires.
Preheat and interpass temperature minimums are correct for the base metal and thickness per AWS D1.1:2025, and the WPS includes a minimum interpass temperature to prevent the weld pool from approaching a cold base before the next pass.
Wire and electrode classifications are appropriate for the position (not all FCAW-G wires are qualified for horizontal and overhead without WPS testing for that position).
During WPQ testing, the bend test specimen cut through the weld section shows inter-pass cold lap as a delamination or open gap on the tensile fiber side. If a candidate's WPQ bend fails and the specimen shows this mode, it is a technique problem, not a consumable problem—and it warrants a coaching session on work angle and travel speed before the retest.
For shops evaluating software to track discontinuity rates by weld type and welder, consider reviewing WPS software ROI for fab shops — built-in NDE logs tied to WPS and welder records make the root-cause chase much shorter when overlap starts showing up in production.
FAQ
Frequently asked.
Is cold lap the same as lack of fusion under AWS D1.1?
They are closely related. Cold lap typically refers to overlap at the weld toe where metal flows over the base without fusing, while lack of fusion (incomplete fusion) is a broader term covering any un-fused interface between passes or between weld metal and base metal. Both are unacceptable under AWS D1.1:2025 visual acceptance criteria.
Can cold lap be repaired, or does the weld have to be removed entirely?
Repair is possible in most cases. The affected area must be removed by grinding or gouging back to sound metal. A CWI must verify complete removal of the discontinuity before re-welding to the applicable WPS. Clause 8 of AWS D1.1:2025 governs repair procedures.
Will UT reliably detect cold lap at the weld toe?
Toe cold lap is a near-surface planar reflector and can be difficult to detect with conventional straight-beam UT. Phased array UT (PAUT) with a properly angled beam offers better sensitivity. MT (wet fluorescent) is generally more reliable for toe cold lap open to or very near the surface.
What WPS parameter most often causes weld overlap in fillet welds?
Excessive travel speed combined with a low wire feed rate (low deposition) is the leading cause in FCAW and GMAW. An incorrect work angle—pointing toward the vertical plate on a horizontal fillet—also deposits metal that rolls over the toe without fusing. Both are controllable WPS parameters.