Weld Porosity — D1.1:2025 Acceptance Criteria & Causes
Porosity acceptance limits under D1.1:2025 depend on weld type, joint orientation, loading, and weld length. CJP groove welds transverse to tensile stress have zero tolerance for visible piping porosity. Fillet welds and other groove welds have specific diameter and frequency limits that changed in 2025 for short welds.
Table 8.1 Item (8) — Piping Porosity Limits
Item (8) is the most conditional acceptance criterion in Table 8.1. The limits depend on: (A) statically or (B/C) cyclically loaded, the weld type (CJP groove butt joint vs. fillet vs. other groove), and whether the weld is transverse to computed tensile stress.
| Condition | Loading | Limit |
|---|---|---|
| CJP groove weld, butt joint, transverse to tensile stress | Static (A) | No visible piping porosity |
| Fillet welds & other groove welds (standard) | Static (A) | Sum of pore diameters ≥1/32 in: ≤3/8 in per linear inch |
| Fillet & other groove welds, ≥12 in length | Static (A) | ≤3/4 in per any 12 in of weld length |
| Fillet & other groove welds, <12 in length | Static (A) | Sum of pore diameters ≤ weld length × 0.06 |
| Fillet welds (general) | Cyclic (B) | Max 1 pore per 4 in of length; max diameter 3/32 in |
| Fillet welds connecting stiffeners to webs | Cyclic (B) | Sum ≥1/32 in dia: ≤3/8 in per linear inch; ≤3/4 in per 12 in; <12 in: ≤length × 0.06 |
| CJP groove weld, butt joint, transverse to tensile stress | Cyclic (C) | No piping porosity |
| All other groove welds | Cyclic (C) | Max 1 pore per 4 in of length; max diameter 3/32 in |
Why CJP Butt Joints in Tension Have Zero Tolerance
A CJP groove weld in a butt joint transverse to tensile stress is the highest-stress weld configuration in structural steel. The full load passes through the weld cross-section at 90 degrees. A pore in this location is a void in the load path — it reduces the effective throat area and, under cyclic loading, creates a stress concentration that initiates fatigue cracking.
The zero-tolerance rule is not just conservative — it reflects the structural function. A fillet weld is a connection element; a CJP butt weld in tension is the structural member at that cross-section. Any material deficit matters.
The Short-Weld Formula for Porosity
For statically loaded connections on welds less than 12 inches in length, the porosity limit uses a proportional formula: the sum of all visible piping porosity diameters (of pores 1/32 inch or larger) shall not exceed the weld length multiplied by 0.06.
Example: a 6-inch fillet weld may have a maximum total pore diameter sum of 6 × 0.06 = 0.36 inches. The inspector measures each visible pore 1/32 inch or larger and sums the diameters. Three pores each measuring 1/16 inch = 3/16 inch total — well within the 0.36 inch limit. Six pores each at 3/32 inch = 18/32 = 9/16 inch total — over limit.
What Causes Weld Porosity
Moisture and hydrogen. Water in electrode coatings, on the base metal surface (condensation, rain, dew), or in shielding gas introduces hydrogen into the weld pool. As the weld solidifies, hydrogen tries to escape as gas bubbles. Those that do not escape become pores. Using low-hydrogen electrodes stored per manufacturer requirements (E7018 kept in a rod oven at 250–300°F) is the primary control.
Surface contamination. Oil, grease, paint, and thick mill scale on the base metal surface or electrode decompose in the arc and produce gas. Cleaning the joint area per D1.1 Clause 7.14 before welding removes these sources.
Shielding gas disruption. For GMAW and FCAW-G, wind or drafts blow away the shielding gas envelope, allowing atmospheric nitrogen and oxygen to enter the weld pool. The remedy is windshields in outdoor work environments, and checking nozzle-to-work distance and gas flow rate (typically 35–50 CFH for GMAW). A clogged nozzle with heavy spatter buildup reduces effective gas coverage to near zero.
Contaminated shielding gas. Moisture in the gas supply line (particularly after long shutdowns), wrong gas mixture, or an incorrect regulator setting can introduce contaminants. Purging the line before production welding on critical joints is good practice.
Many porosity issues trace back to incorrect WPS requirements — particularly travel speed, gas flow rate, and electrode stickout settings that fall outside the validated parameter range.
Inspector scenario: You are inspecting a 20-inch CJP butt weld connecting two beam flanges. The joint is transverse to the primary tensile stress in the bottom flange of a cyclically loaded girder. VT reveals three small pores along the weld face, each approximately 1/16 inch in diameter. Under D1.1:2025 Table 8.1 item (8)(C)(1): CJP groove welds in butt joints transverse to tensile stress on cyclically loaded connections shall have no piping porosity. All three pores are rejectable defects. The weld requires repair per Clause 7.25 before acceptance.
Frequently Asked Questions
It depends on the joint and loading. For CJP groove welds in butt joints transverse to the direction of computed tensile stress, D1.1:2025 Table 8.1 item (8)(A)(1) states the weld shall have no visible piping porosity — zero tolerance for statically loaded connections. For cyclically loaded connections, item (8)(C)(1) applies the same zero-porosity rule to CJP groove welds in butt joints transverse to tensile stress. Fillet welds and other groove welds not in that category have quantitative limits based on pore diameter, frequency, and weld length.
For statically loaded connections, D1.1:2025 Table 8.1 item (8)(A)(2) limits visible piping porosity in fillet welds and groove welds (except CJP butt joints in tension) as follows: the sum of visible piping porosity 1/32 inch or greater in diameter shall not exceed 3/8 inch in any linear inch of weld. For welds 12 inches or longer, the sum shall not exceed 3/4 inch in any 12-inch length. For welds less than 12 inches, the sum shall not exceed the weld length multiplied by 0.06.
Porosity is caused by gas trapped in the solidifying weld metal. The three main sources of gas are: moisture (hydrogen from water in electrode coatings, base metal surface condensation, or shielding gas), contamination (oil, paint, mill scale, or organic material on the base metal surface or electrode), and shielding gas disruption (wind blowing away gas coverage, excessive spatter blocking the nozzle, or insufficient gas flow rate). Using low-hydrogen electrodes, properly dried and stored; cleaning the base metal before welding; and maintaining adequate shielding gas coverage are the primary prevention controls.
Per D1.1:2025 Clause 7.25.1.3, porosity that exceeds the acceptance criteria of Table 8.1 shall be removed and rewelded. Removal methods include grinding, gouging, or chipping to sound metal. The repair weld shall meet all the requirements of the original WPS, including preheat and interpass temperature. Porous areas must be fully removed — the repair extends until no visible porosity remains in the prepared cavity. After repair, the weld is subject to the same inspection requirements as the original weld.