Overview
ISO 17927-2:2020 - Welding for aerospace applications: Fusion welding of metallic components - Part 2: Acceptance criteria specifies acceptance criteria for fusion weldments used in aerospace metallic components. It applies when referenced or approved by the responsible design/engineering authority and covers specific fusion welding processes (oxyfuel, gas tungsten arc, plasma arc, electron beam, laser - see ISO 4063 process numbers) and material groups A–F (steels, titanium, aluminium/magnesium, nickel/cobalt alloys, etc., as per ISO 24394).
This standard is primarily a practical inspection and quality-control document: it defines quality levels, permissible imperfections, dimensional limits and acceptance/rejection rules for welds used in airworthiness-critical hardware.
Key topics and requirements
- Scope & conformance: Acceptance criteria apply only when mandated by the engineering/design authority. When conformance is claimed, all provisions must be met unless specifically exempted.
- Processes and materials covered: Lists fusion welding processes (ISO 4063 codes: 31, 14, 15, 51, 52) and material groups A–F.
- Quality levels: Defined A (high), B (moderate) and C (typical). The engineering authority specifies the required level.
- General rules:
- Imperfection size is the largest dimension; closely spaced defects can be treated as a single discontinuity.
- Surface imperfections removable by machining are acceptable if minimum thickness and other engineering requirements remain.
- Fillet weld minimum leg lengths: single-side = 1.5 t, double-side = 1.0 t (t = minimum nominal wall/plate thickness).
- Limits for specific imperfections (examples):
- Cracks and crater cracks: Not permitted at any quality level.
- Surface porosity (individual pore size): Quality A ≤ 0.25 t or 0.76 mm, B ≤ 0.33 t or 1.50 mm, C ≤ 0.50 t or 2.30 mm (whichever is less).
- Root porosity accumulation (in any 75 mm): A ≤ 1 t or 3.00 mm, B ≤ 1.33 t or 6.00 mm, C ≤ 2 t or 9.00 mm.
- Undercut, incomplete fusion/penetration, burn-through, insufficient throat/leg length: Many are explicitly “Not permitted” depending on quality level.
- Discolouration (titanium, stainless, Ni/Co alloys, steel): Acceptability varies by color and quality level. Black oxidation is generally rejectable; specific colors (e.g., blue, green, gray) require removal or testing to rule out embrittlement.
- Geometric tolerances: Linear misalignment limits depend on process and thickness (see Table 5), e.g., electron beam/laser have different limits than arc processes.
Applications and users
- Aerospace OEMs and suppliers implementing weld acceptance criteria for airframe, engine and structural components.
- Design/engineering authorities specifying weld requirements on drawings and certification documents.
- Welding inspectors, non‑destructive testing (NDT) personnel and QA engineers performing weld acceptance and conformity checks.
- Maintenance/repair organizations ensuring airworthiness compliance during overhaul and repair.
Related standards
- ISO 6520-1 - Classification of geometric imperfections (normative reference used by ISO 17927-2).
- ISO 4063 - Welding process codes (used to list covered processes).
- ISO 24394 - Material group classification referenced for material grouping.
Keywords: ISO 17927-2:2020, aerospace welding standard, fusion welding acceptance criteria, weld inspection, porosity limits, lack of fusion, fillet weld requirements, titanium discolouration.
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