Overview
EN ISO 4761:2022 specifies acceptance levels for phased array ultrasonic testing (UT‑PA) of full‑penetration welds in thin‑walled low‑alloy or fine‑grained steels (wall thickness 3.2 mm to 8 mm). Adopted by CEN as EN ISO 4761:2022, this document defines how to evaluate indications found using automated phased‑array UT in accordance with ISO 20601, aligning acceptance with ISO 5817 quality levels.
Key topics and requirements
- Scope: Applies to full‑penetration welds in thin‑walled steel components (3.2–8 mm) using UT‑PA.
- Sensitivity setting: Calibration on a 1.0 mm side‑drilled hole per ISO 20601; this becomes the reference level for subsequent testing.
- Signal levels: Uses three levels (reference, acceptance, evaluation). The evaluation level is defined as reference −12 dB.
- Acceptance levels: Three testing/acceptance levels map to ISO 5817 quality grades:
- ISO 5817 B → Testing level C → Acceptance level 1 (C1)
- ISO 5817 C → Testing level C → Acceptance level 2 (C2)
- ISO 5817 D → Testing level C → Acceptance level 3 (C3)
- Indication measurement:
- Indication length is measured along the weld using the 6 dB drop method.
- A length correction for unfocused lateral beams is permitted (formula specified in the standard).
- Amplitude vs. length criteria (examples from the standard):
- For all acceptance levels, indications ≤ 4 mm: maximum allowable amplitude +6 dB (relative to reference).
- For C1: 4–6 mm → +2 dB; > 6 mm → −10 dB.
- For C2: 4–7 mm → +3.5 dB; > 7 mm → −10 dB.
- For C3: 4–8 mm → +5 dB; > 8 mm → −10 dB.
- Testing modes: Separate acceptance criteria are given for two‑sided and single‑sided testing; cumulative lengths of acceptable indications over a weld section are also addressed.
Applications and who uses it
EN ISO 4761:2022 is used by:
- NDT technicians and inspection engineers implementing automated UT‑PA on thin‑walled steel welds
- Quality assurance / QC teams responsible for weld acceptance to ISO 5817 quality grades
- Fabricators and OEMs in industries with thin‑walled steel components (e.g., automotive, pressure equipment, shipbuilding, pipelines and general fabrication) requiring objective acceptance criteria
- Certification bodies and inspectors specifying test levels and reporting criteria
Related standards
- ISO 20601 - Use of automated phased array technology for thin‑walled steel components (normative reference)
- ISO 5817 - Quality levels for imperfections in fusion welded joints
- ISO 5577, ISO 23243 - Terminology and array‑UT vocabulary
This standard helps standardize UT‑PA acceptance decisions, improve reproducibility of weld inspections, and align phased‑array testing with established ISO quality grades for thin‑walled steel welds.