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Table 8.1Weld Porosity Causes — D1.1:2025 Penerimaan Criteria
This porosity Panduan focuses on why gas becomes trapped in Logam Las and how the likely cause changes the next corrective action. Use it to separate shielding, moisture, contamination, speed, and arc-stability issues before comparing the condition with project Inspeksi Persyaratan.
Per D1.1:2025 Table 8.1 item (8), visible piping porosity 1/32 in or greater shall not exceed 3/8 in per linear inch of fillet or Las Alur on statically dimuat connections. CJP butt joints transverse to tensile stress require zero visible piping porosity.
Apa Penyebab Porositas Las?
Porosity forms when gas becomes trapped in the solidifying weld pool. The arc generates extremely high temperatures that cause chemical reactions in the Logam Induk, Logam Pengisi, and surrounding atmosphere. When the weld pool solidifies faster than trapped gas bubbles can escape to the surface, those bubbles freeze in place as pores — either visible on the surface (piping porosity) or hidden within the weld cross-section (subsurface porosity).
Enam penyebab utama adalah:
Moisture — Water in any form is the most common cause. Moisture on base metal surfaces, in filler metal flux coatings, or absorbed into Kawat inti fluks introduces hydrogen into the arc. The hydrogen dissolves into the weld pool at high Suhu and is released as the pool cools, forming hydrogen porosity. This is why E7018 and other Hidrogen Rendah electrodes require controlled storage and redrying after exposure.
Kontaminasi permukaan — Minyak, gemuk, cat, karat, kerak pabrik, dan seng (lapisan galvanis) semuanya melepaskan gas ketika masuk ke zona busur. Bahkan lapisan kontaminasi tipis pada permukaan sambungan dapat menghasilkan gas yang cukup untuk menyebabkan porositas yang terlihat. Permukaan sambungan harus bersih dan kering untuk Minimum 1 inci setiap sisi sebelum Pengelasan.
Shielding gas loss — GMAW, FCAW-G, and GTAW processes depend on an inert or semi-inert gas shield to exclude atmospheric nitrogen and oxygen from the arc. Drafts, insufficient flow rate, damaged nozzles, or excessive contact-tip-to-work distance all allow atmospheric contamination. Nitrogen porosity is particularly difficult to eliminate once the shield is compromised.
Kelembaban Elektroda (SMAW) — Elektroda Hidrogen Rendah (E7016, E7018) diproduksi dengan lapisan fluks yang dirancang untuk mempertahankan Hidrogen Difusibel di bawah 4–16 mL/100g Logam Las yang diendapkan. Paparan udara lembab dengan cepat memasukkan kembali kelembaban. Elektroda yang terpapar udara terbuka selama lebih dari 4 jam biasanya memerlukan pengeringan ulang pada 500–800°F sesuai instruksi pabrik.
Excessive travel speed — When the welder moves too fast, the weld pool does not have time to degas before solidification. Bubbles that would otherwise float to the surface become trapped. Reducing Kecepatan Lintasan allows more time for outgassing and typically reduces porosity frequency.
Arc instability — Incorrect polarity, excessive arc length, or improper Tegangan settings can destabilize the arc and disrupt the gas shield. An unstable arc also produces inconsistent Masukan Panas, leading to areas where the weld pool solidifies before degassing is complete.
D1.1:2025 Table 8.1 Item (8) — Piping Porosity Acceptance Criteria
D1.1:2025 Table 8.1 governs Inspeksi Visual of all production welds under Clause 8.9. Item (8) applies specifically to piping porosity — porosity visible on the weld surface. Subsurface porosity is evaluated by Radiografi or Ultrasonik Pengujian when specified in the contract documents.
| Connection Type | Weld Type | Porosity Limit |
|---|---|---|
| Statically loaded (A) | CJP butt joint transverse to tensile stress | No visible piping porosity |
| Statically loaded (A) | Fillet welds and other groove welds | Sum of pores ≥1/32 in dia: ≤3/8 in per linear inch; ≤3/4 in per 12 in (for welds ≥12 in); ≤weld length × 0.06 (for welds <12 in) |
| Cyclically loaded (B) | Fillet welds (except Pengaku-to-web) | Frequency: ≤1 pore per 4 in; max diameter: ≤3/32 in |
| Cyclically loaded (B) | Fillet welds connecting stiffeners to webs | Sum of pores ≥1/32 in dia: ≤3/8 in per linear inch; ≤3/4 in per 12 in; ≤weld length × 0.06 |
| Cyclically loaded (C) | CJP butt joint transverse to tensile stress | No piping porosity |
| Cyclically loaded (C) | All other groove welds | Frequency: ≤1 pore per 4 in; max diameter: ≤3/32 in |
Inspector note: The distinction between “piping porosity” and general “porosity” matters for Table 8.1. Item (8) applies only to piping porosity visible at the weld surface. The Tabel counts individual pore diameters 1/32 in or greater — pores smaller than 1/32 in are not counted toward the limit. When measuring, use a calibrated weld gauge or magnifier and count only pores meeting the minimum diameter threshold.
Pencegahan dan Panduan Lapangan
Effective porosity Pencegahan starts with the WPS. The procedure should specify Preheat requirements (which reduce moisture and hydrogen uptake), filler metal storage conditions, joint preparation requirements, and shielding gas flow rates. A WPS that does not address these parameters leaves prevention entirely to the welder.
In the field, the most reliable controls are: (1) inspect joint faces for contamination before Pengelasan and clean as needed; (2) Verifikasi shielding gas flow rate at the start of each shift and after any equipment changes; (3) check Elektroda storage — low-hydrogen electrodes should be in a rod oven at manufacturer-specified temperature, not sitting on the deck; (4) for FCAW, inspect wire spools for moisture or damage, especially after rain or overnight exposure.
When porosity is found during VT, identify the probable cause before resuming production. Continuing to weld with an unaddressed cause will produce more rejectable welds. Common cause-to-fix mappings: clustered surface porosity → check electrode storage; uniform scattered porosity → check shielding gas; porosity concentrated at weld start/stop → adjust crater fill technique and preheat.
Pertanyaan yang Sering Diajukan
The six main causes of weld porosity are: (1) moisture — in the base metal, filler metal, or atmosphere, which decomposes in the arc and releases hydrogen or oxygen; (2) surface contamination — oil, rust, paint, mill scale, or zinc coating on the joint faces that release gases as they burn off; (3) shielding gas loss — insufficient flow rate, drafts, or damaged gas lines that allow atmospheric nitrogen and oxygen into the weld pool; (4) electrode moisture — undried SMAW electrodes (especially E7018 low-hydrogen) that introduce hydrogen into the arc; (5) excessive travel speed — the weld pool solidifies before trapped gases can escape; and (6) wrong polarity or voltage — arc instability that disrupts the gas shield and allows atmospheric contamination.
Per D1.1:2025 Table 8.1 item (8)(A), for fillet welds and groove welds (except CJP butt joints transverse to computed tensile stress) on statically loaded connections, the sum of visible piping porosity 1/32 in or greater in diameter shall not exceed 3/8 in in any linear inch of weld. For welds 12 in or greater in length, the sum shall not exceed 3/4 in in any 12 in of weld length. For welds less than 12 in in length, the sum shall not exceed the weld length multiplied by 0.06.
No. Per D1.1:2025 Table 8.1 item (8)(A)(1), CJP groove welds in butt joints transverse to the direction of computed tensile stress shall have no visible piping porosity. This is a zero-tolerance criterion for that specific joint and loading condition. For other groove welds and fillet welds on statically loaded connections, limited porosity is acceptable per the frequency and size limits in Table 8.1 item (8)(A)(2).
Porosity reduces the effective cross-sectional area of the weld, lowering its load-carrying capacity in proportion to the volume of voids. Scattered porosity in small amounts has minimal effect on static strength, which is why D1.1 permits limited porosity in fillet welds under static loading. However, porosity under cyclic loading is more damaging because each pore acts as a stress concentration that can initiate fatigue cracks. D1.1:2025 Table 8.1 item (8)(B) and (C) apply tighter porosity limits to cyclically loaded connections for exactly this reason.
Referensi Terkait
■ Weld Defects HubTable 8.1 all 8 categories
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Weld PorosityTable 8.1 criteria overview
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Visual Weld InspectionClause 8.9 VT procedure
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Weld DiscontinuityDiscontinuity vs defect
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Weld CracksZero tolerance under D1.1
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Preheat CalculatorReduce hydrogen cracking risk