7.3 Weld Profiles, Undercut Tolerances, Porosity Limits & Crack Rejection
Key Takeaways
- For static members < 1 in. [25 mm] thick, undercut is limited to 1/32 in. [1 mm], with an exception allowing up to 1/16 in. [2 mm] for an accumulated length of 2 in. [50 mm] in any 12 in. [300 mm].
- For cyclically loaded primary members in transverse tension, undercut cannot exceed 0.01 in. [0.25 mm]; all other cyclic members allow up to 1/32 in. [1 mm].
- CJP groove welds in butt joints transverse to tensile stresses prohibit all visible piping porosity; general static welds limit porosity to <= 3/8 in. per inch and <= 3/4 in. per 12 in.
- Cyclic welds restrict general piping porosity frequency to 1 in 4 in. [100 mm] with a maximum single pore diameter of 3/32 in. [2.5 mm].
- Fillet weld convexity is capped by Clause 7.23.1 and Figure 7.4 (max 1/16 in. for face width <= 5/16 in., 1/8 in. for width < 1 in., 3/16 in. for width >= 1 in.), and overlap (cold lap) is strictly prohibited.
Weld Profiles, Undercut Tolerances & Porosity Limits
Dimensional verification and profile conformity under AWS D1.1/D1.1M:2025 bridge the gap between structural drawing specifications and physical weldments. Discontinuities such as excessive convexity, overlap, severe undercut, and clustered piping porosity degrade fatigue life and reduce static load-carrying capacity.
Certified Welding Inspectors (CWIs) must master the quantitative tolerances codified in Table 8.1 (Visual Inspection Acceptance Criteria) and Clause 7.23 and Figure 7.4 (Requirements for Weld Profiles).
Undercut Acceptance Criteria (Table 8.1 Item 7)
Undercut is a groove melted into the base metal adjacent to the weld toe or root that is left unfilled by weld metal. It reduces base metal thickness and introduces a sharp stress concentration notch.
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| AWS D1.1 UNDERCUT ACCEPTANCE RULES |
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| |
| 1. STATICALLY LOADED NONTUBULAR CONNECTIONS: |
| • Thickness t < 1 in. [25 mm]: |
| - Undercut SHALL NOT exceed 1/32 in. [1.0 mm] |
| - EXCEPTION: Undercut up to 1/16 in. [2.0 mm] is permitted for an |
| accumulated length of 2 in. [50 mm] in any 12 in. [300 mm] |
| • Thickness t >= 1 in. [25 mm]: |
| - Undercut SHALL NOT exceed 1/16 in. [2.0 mm] for any length |
| |
| 2. CYCLICALLY LOADED NONTUBULAR CONNECTIONS: |
| • Primary Members Subject to Transverse Tensile Stress: |
| - Undercut SHALL NOT exceed 0.01 in. [0.25 mm] |
| • All Other Cyclic Members (Longitudinal / Compression / Shear): |
| - Undercut SHALL NOT exceed 1/32 in. [1.0 mm] |
| |
| 3. TUBULAR CONNECTIONS: |
| • Wall thickness t <= 5/8 in. [16 mm] --> Undercut <= 1/32 in. [1 mm]|
| • Wall thickness t > 5/8 in. [16 mm] --> Undercut <= 1/16 in. [2 mm]|
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The Static "2 in. in 12 in." Rule Explained
For static steel plates thinner than $1\text{ in.}$ [$25\text{ mm}$], standard undercut must not exceed $1/32\text{ in.}$ [$1\text{ mm}$]. However, AWS D1.1 recognizes minor localized deviations:
- An undercut depth between $1/32\text{ in.}$ and $1/16\text{ in.}$ ($0.031\text{ in.}$ to $0.063\text{ in.}$) is acceptable provided the sum of all such localized undercut segments does not exceed 2 in. [50 mm] within any continuous 12 in. [300 mm] segment of weld.
- Any undercut exceeding $1/16\text{ in.}$ [2 mm] on plate $< 1\text{ in.}$ thick is immediately rejectable.
Piping Porosity Acceptance Criteria (Table 8.1 Item 8)
2025 edition change: Table 8.1 Item 8 now states the piping-porosity limits explicitly as a function of loading (static vs. cyclic), stress direction, weld type, and weld length. For welds less than 12 in. long, the sum of visible piping porosity 1/32 in. or larger shall not exceed the weld length multiplied by 0.06; welds 12 in. or longer keep the 3/4 in. per 12 in. limit. Item 7 adds a parallel rule for undercut: for welds under 12 in. long, the accumulated length of undercut deeper than 1/16 in. shall not exceed the weld length multiplied by 0.16.
Piping porosity (wormhole porosity) refers to elongated gas pores extending from the root or interior of the weld toward the outer weld face.
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| PIPING POROSITY ACCEPTANCE LIMITS (TABLE 8.1) |
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| A. TRANSVERSE TENSION CJP GROOVE WELDS (Static & Cyclic): |
| --> ZERO TOLERANCE: NO visible piping porosity permitted. |
| |
| B. OTHER STATIC GROOVE & FILLET WELDS: |
| --> Sum of visible piping porosity (>= 1/32 in. [1 mm] diameter) |
| SHALL NOT exceed: |
| • 3/8 in. [10 mm] in any linear inch [25 mm] of weld, AND |
| • 3/4 in. [20 mm] in any 12 in. [300 mm] length of weld |
| |
| C. OTHER CYCLIC GROOVE & FILLET WELDS: |
| --> Frequency: Max 1 pore in any 4 in. [100 mm] of weld length |
| --> Diameter: Max single pore diameter <= 3/32 in. [2.5 mm] |
| |
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Quantitative Porosity Calculations
When evaluating piping porosity in general static welds:
- Ignore porosity pores smaller than $1/32\text{ in.}$ [$1.0\text{ mm}$] in diameter.
- In any $1\text{ in.}$ [$25\text{ mm}$] window, sum the major diameters: $\sum d_i \le 3/8\text{ in.}$ [$9.5\text{ mm}$].
- In any $12\text{ in.}$ [$300\text{ mm}$] window, sum the major diameters: $\sum d_i \le 3/4\text{ in.}$ [$19.0\text{ mm}$].
Weld Profile Requirements & Convexity Limits (Clause 7.23 & Figure 7.4)
Welds must maintain uniform profiles without excessive convexity, undersize throat, underfill, or overlap.
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| WELD DEFECT PROFILE SCHEMATICS |
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| (A) ACCEPTABLE FILLET (B) EXCESSIVE CONVEXITY (C) OVERLAP |
| (COLD LAP) |
| | | | |
| | /| | /\ | /| |
| | / | | / \ | / | |
| |/ | |/ ) |/ (_ |
| +---+ +---+ +---+ (NOT |
| FUSED)
| |
| (D) UNDERFILL / INSUFF. (E) UNDERCUT (F) BUTT REIN- |
| THROAT FORCEMENT |
| | | | ___ |
| | (| |( / \ |
| |/ | |/| +-------+ |
| +---+ +---+ | BASE | |
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1. Fillet Weld Convexity Limits (Clause 7.23.1 & Figure 7.4)
Fillet weld convexity ($C$) is the maximum perpendicular distance from the face of a convex fillet weld to a straight line joining the weld toes. Clause 7.23.1 and Figure 7.4 set the following limits, which the 2025 edition clarifies apply to the entire weld face and to the face of each individual weld bead:
| Measured Width of Weld Face ($W$) | Maximum Permissible Convexity ($C$) |
|---|---|
| $W \le 5/16\text{ in.}$ [$8\text{ mm}$] | $1/16\text{ in.}$ [$1.6\text{ mm}$] |
| $W > 5/16\text{ in.}$ to $< 1\text{ in.}$ [$25\text{ mm}$] | $1/8\text{ in.}$ [$3.2\text{ mm}$] |
| $W \ge 1\text{ in.}$ [$25\text{ mm}$] | $3/16\text{ in.}$ [$5.0\text{ mm}$] |
2. Overlap (Cold Lap) - Strictly Prohibited (Clause 7.23.1)
Overlap occurs when molten weld metal spills over the base metal surface without fusing. Table 8.1 and Figure 7.4 mandate zero overlap because the unfused interface creates a mechanical notch that triggers fatigue failure.
3. Groove Weld Reinforcement (Clause 7.23.2)
Groove weld face reinforcement ($R$) provides positive margin but must not be excessive:
- For plate thickness $t \le 1\text{ in.}$ [$25\text{ mm}$]: $R \le 1/8\text{ in.}$ [$3.2\text{ mm}$].
- For plate thickness $t > 1\text{ in.}$ [$25\text{ mm}$]: $R \le 3/16\text{ in.}$ [$5.0\text{ mm}$].
- Weld reinforcement shall blend smoothly into the plate surface with a toe angle no steeper than $45^\circ$.
Worked Examples: Table 8.1 & Figure 7.4 Visual Inspections
Scenario 1: Static Fillet Weld Inspection & Porosity Math
A CWI inspects a 12 in. long, 3/8 in. fillet weld on a 1/2 in. thick static gusset plate. The inspector measures:
- A weld face width $W = 9/16\text{ in.}$ [$14\text{ mm}$] with a measured convexity $C = 3/16\text{ in.}$ [$5\text{ mm}$].
- Three piping porosity pores located in a 1-inch span measuring 1/16 in., 1/8 in., and 1/16 in. in diameter.
Evaluate both conditions:
- Convexity Evaluation: Face width $W = 9/16\text{ in.}$ falls in the range $> 5/16\text{ in.}$ to $< 1\text{ in.}$
- Under Clause 7.23.1 and Figure 7.4, maximum allowable convexity is $1/8\text{ in.}$ [$3.2\text{ mm}$] ($0.125\text{ in.}$). Measured $C = 3/16\text{ in.}$ ($0.1875\text{ in.}$) $\rightarrow$ REJECTED for excessive convexity.
- Porosity Evaluation: All three pores are $\ge 1/32\text{ in.}$
- Sum in 1 linear inch $= 1/16 + 1/8 + 1/16 = 1/16 + 2/16 + 1/16 = 4/16 = 1/4\text{ in.}$ ($0.250\text{ in.}$).
- Under Table 8.1 Item 8(A), allowable sum in 1 linear inch is $3/8\text{ in.}$ ($0.375\text{ in.}$). Since $1/4 < 3/8$, Porosity is ACCEPTABLE.
Scenario 2: Crane Runway Girder Undercut Evaluation
A CWI evaluates a CJP groove weld connecting the top flange of a crane runway girder subjected to transverse cyclic tensile fatigue. The inspector measures an undercut of 0.025 in. [0.64 mm] along a 3-inch length at the weld toe.
- Evaluation: The girder is a primary cyclically loaded member subject to transverse tension.
- Under Table 8.1 Item 7(B)(1), undercut must not exceed 0.01 in. [0.25 mm].
- Since $0.025\text{ in.} > 0.010\text{ in.}$, the weld is REJECTED and requires repair by blend grinding or weld build-up.
A CWI is inspecting a 12 in. [300 mm] segment of fillet weld on a 3/4 in. [19 mm] thick statically loaded plate. The inspector records a localized undercut depth of 3/64 in. [1.2 mm] over a total continuous length of 1.5 in. [38 mm]. Is this weld acceptable under AWS D1.1 Table 8.1?
Under AWS D1.1 Table 8.1, what is the maximum allowable visible piping porosity in a Complete Joint Penetration (CJP) groove weld in a butt joint subjected to transverse tensile stress in a cyclically loaded bridge member?
A fillet weld has a measured weld face width (W) of 3/4 in. [19 mm]. According to Clause 7.23.1 and Figure 7.4, what is the maximum permissible convexity (C) allowed for this weld?