ASTM E709

Covers — magnetic particle examination techniques (dry/wet, continuous/residual, AC/DC, yoke/prod/coil) for detecting surface and near-surface discontinuities in ferromagnetic materials.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Non-magnetic materials (austenitic stainless, aluminium, copper) → liquid penetrant (E165).
• Deep subsurface/volumetric flaws → radiography (E94) or ultrasonics (E213).
• Acceptance criteria → the construction code (via ASME Section V).

MT works only on ferromagnetic steel; for non-magnetic materials use PT.

E709 sets guidance for magnetic particle examination:

• Magnetization — technique (yoke, prod, coil, central conductor) and adequate field strength in the correct direction.
• Particle Application — dry or wet (fluorescent/visible) particles applied during or after magnetization.
• Two-Direction Coverage — magnetization in perpendicular directions so flaws of any orientation are detected.
• Demagnetization & Evaluation — post-test demagnetization where required, interpretation, and documentation.

ASTM E709 guides magnetic particle testing (MT), which finds surface and slightly subsurface flaws in ferromagnetic steel. The part is magnetized and iron particles collect at the flux leakage caused by a discontinuity, making cracks visible.

MT is faster and more forgiving of surface condition than penetrant testing, but only works on magnetic materials. Because a flaw is detected only when the magnetic field crosses it, examinations are performed in two perpendicular directions. Acceptance comes from the referencing code via Section V.

Engineering Note: Apply MT in two directions (or use multidirectional technique) — a crack parallel to the field can be completely missed, a classic MT pitfall.