Definition
Magnetic Particle Inspection — Magnetic particle inspection is a nondestructive testing method that reveals surface and near-surface cracks in ferromagnetic components by magnetizing the part and applying fine magnetic particles that gather at flux leakage from a flaw.
Also known as: MPI, magnetic particle inspection, mag particle, MT
What MPI detects
Magnetic particle inspection (MPI or MT) is used to find cracks and linear discontinuities at or just below the surface of steel drill stem components. The part is magnetized and coated with fine ferromagnetic particles, usually suspended in a fluid and often fluorescent under UV light. Where a crack interrupts the magnetic field, flux leaks at the surface and attracts the particles, forming a visible indication directly over the flaw.
MPI is the primary method for inspecting tool joints, box and pin threads, upsets, slip and elevator areas, and BHA connections, where fatigue cracks tend to initiate. It is fast, sensitive to tight surface cracks, and applicable to any ferromagnetic steel.
Where it is applied
- Tool joints and connections — thread roots, shoulders and the last-engaged thread.
- Slip and elevator recesses — high-stress areas prone to fatigue.
- BHA components — drill collars, subs and stabilizer connections.
Because MPI only works on magnetic materials, non-magnetic drill collars are inspected by other methods such as liquid penetrant or ultrasonics.
Why it matters for rentals
Connection MPI to a defined standard such as DS-1 or API RP 7G-2 is essential before rental drill stem goes back to the field. See our drill pipe and quality program, or contact us for inspection records.