1. Scope
This procedure covers magnetic-particle examination (MT) of weldments on carbon-steel and low-alloy-steel structural members fabricated to AWS D1.1 Structural Welding Code — Steel. It applies to complete-joint-penetration (CJP) and partial-joint-penetration (PJP) groove welds and fillet welds in primary and secondary structural members, base-metal thicknesses 3 mm (1/8 in) and greater. Applicable to shop and field examination.
2. References
- AWS D1.1 — Structural Welding Code — Steel, current edition, Clauses 6 and 8
- ASTM E709 — Standard Guide for Magnetic Particle Examination
- ASTM E1444 / E1444M — Standard Practice for MT
- ASNT SNT-TC-1A or AWS QC1 for personnel
- Customer Written Practice
3. Personnel Qualification
MT examination shall be performed by personnel certified to ASNT NDT Level II in MT per the employer's Written Practice. Interpretation of indications and Level III approval per AWS D1.1 Clause 8.14 shall be by an ASNT Level III in MT.
4. Equipment
- AC-yoke electromagnetic prod (e.g., Magnaflux Y-7 / Parker B310S) certified to lift 4.5 kg (10 lb) at the maximum pole spacing to be used (typically 75-200 mm / 3-8 in). Lift test performed before first use each shift; recorded.
- DC or half-wave-DC yoke for subsurface indication detection when specified — certified to lift 18 kg (40 lb) at maximum pole spacing.
- Visible (color-contrast) magnetic particle bath or dry powder.
- Fluorescent (UV) particle bath where Type II inspection is required — UV-A intensity ≥ 1000 µW/cm² at 38 cm (15 in) per ASTM E1444.
- White-light meter (visible MT) — minimum 1000 lux illumination at the examination surface.
- UV-A radiometer (fluorescent MT) — calibrated within 12 months.
- Pie gauge (raised-cross indicator) or Magnetic Field Indicator strips for field-direction verification.
5. Surface Preparation
Examination surface shall be cleaned of slag, weld spatter, oil, grease, rust, scale, paint, and other contamination that may interfere with particle mobility. Wire brushing or light grinding is acceptable; mechanical removal is not permitted to obliterate weld profile.
For painted or coated surfaces, maximum coating thickness 0.05 mm (0.002 in) is permissible only when the contractor demonstrates by a calibration trial that the coating does not impair test sensitivity per AWS D1.1 Section 8.14.4.
6. Magnetization Technique
6.1 Yoke Method (Standard)
Yoke prods placed across the area of interest with pole spacing between 75 mm (3 in) and 200 mm (8 in). Magnetization shall be applied in two perpendicular directions at each examination area to ensure detection of indications in all orientations.
6.2 Continuous Method
Particles applied while current is on and field is established. Visible (dry or wet) particles applied with gentle uniform coverage — heavy application masks indications.
6.3 Field-Strength Verification
Field strength shall be verified using a pie gauge or magnetic-field indicator placed on the examination surface at the most-distant point from the prods. The indicator shall produce a clear pattern of magnetic flux. Lift-test (4.5 kg AC; 18 kg DC) performed before each shift and documented.
7. Examination
- Examination shall cover the weld and a minimum of 25 mm (1 in) of adjacent base metal on each side of the weld toe.
- Two examinations at perpendicular directions per area.
- Maximum scan speed: such that the examiner can observe the indication formation — typically continuous.
- Overlap between adjacent examination areas: 10% minimum.
8. Indication Classification
Indications shall be classified per AWS D1.1 Clause 8.13 and 8.14:
- Relevant indications: linear or rounded indications associated with discontinuities in the weld or HAZ.
- Non-relevant indications: geometric, magnetic writing, or those caused by surface conditions.
- False indications: caused by contamination or insufficient cleaning.
Linear indication: length ≥ 3× the width.
9. Acceptance Criteria (AWS D1.1 Clause 8.14.6)
For statically loaded structures (Clause 8.14.6.1):
- Any crack — rejectable regardless of size.
- Linear indication greater than 5 mm (3/16 in) — rejectable.
- Rounded indications greater than 5 mm (3/16 in) — rejectable.
- Cluster of four or more rounded indications in a line, separated by 1.5 mm or less edge-to-edge — rejectable.
For cyclically loaded (fatigue) structures (Clause 8.14.6.2): all linear indications and rounded indications larger than half the limit above are rejectable. Designer-specified additional limits may apply.
10. Repair and Re-Examination
Defects shall be removed by grinding, machining, or weld repair per AWS D1.1 Clause 5.26. Repaired areas shall be re-examined by the same MT procedure plus any additional NDT specified by the Engineer of Record.
11. Reporting
Each examination shall be documented with: customer and project; member ID; weld number; weld type (groove / fillet, CJP / PJP); base-metal grade and thickness; weld procedure; surface condition; equipment serial numbers; particle type and batch; field-verification method; date and time of examination; ambient light level (visible MT) or UV intensity (fluorescent MT); examiner name and certification; Level III approval; sketch with location, length, and orientation of every recordable indication.
12. Safety
PPE per project — minimum eye protection, gloves, and where dry-powder MT is performed, a NIOSH-approved dust-particulate respirator for confined-area work. UV-A operations require approved UV-blocking eyewear and skin coverage.
This procedure is a published reference. Production use requires Engineer-of-Record approval against the current AWS D1.1 edition. Generate a custom procedure for your weld geometry, loading class, and inspection environment at the free AI Procedure Generator.