ASNT NDT Level III MT flashcards
ASNT NDT Level III MT · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Magnetic flux density formula
- B = μH, where B is flux density in tesla, H is magnetic field strength in amperes per meter, and μ is the permeability of the material.
- Flux leakage
- Leakage of magnetic flux at a discontinuity where flux lines exit and re-enter the surface; magnetic particles collect there to form an indication.
- Ferromagnetic materials
- Materials such as iron, cobalt, and nickel that are strongly attracted to magnets and can be highly magnetized; only these are suitable for magnetic particle testing.
- Longitudinal magnetization
- Magnetization along the part's length using a coil or yoke; it produces flux lines parallel to the axis and detects circumferential defects.
- Circular magnetization
- Magnetization produced by current through the part along its axis; flux lines form circles around the axis and detect longitudinal defects.
- Retentivity
- The amount of magnetic flux density remaining in a material after the magnetizing force is removed; higher retentivity helps residual magnetic particle testing.
- Gauss to tesla
- One tesla equals 10,000 gauss; to convert gauss to tesla, divide the gauss value by 10,000.
- AC yoke lift test
- A common performance check requiring an AC electromagnetic yoke to lift a 10 lb (4.5 kg) steel weight at its poles; confirms adequate magnetizing strength.
- Continuous method
- Magnetic particles are applied while the magnetizing current flows; it is more sensitive than the residual method and preferred for critical examinations.
- Residual method
- Particles are applied after the magnetizing current is removed; it relies on the part retaining enough magnetism to produce leakage fields.
- Wet fluorescent particles
- Fine fluorescent particles suspended in a liquid vehicle, viewed under UV-A light; they give high sensitivity for small surface discontinuities.
- Dry magnetic particles
- Powdered particles applied by spray or dusting, often used with portable yokes and for rough surfaces or higher-temperature applications.
- Prod magnetization
- Current is passed through the part between two contact prods, producing circular magnetization; contact pads help prevent arc burning.
- AC demagnetization
- AC demagnetization reverses and reduces magnetization, effectively removing surface residual fields; DC demagnetization penetrates more deeply.
- Circular current rule
- A typical rule is 1,000 A per inch of part diameter for circular magnetization with head shot or central conductor; verify against the governing standard.
- Coil ampere-turn rule
- For longitudinal magnetization with a coil, use NI = 45,000/(L/D) for parts with length-to-diameter ratios between 3 and 15.
- Wet particle concentration
- Fluorescent wet bath typically contains 0.1 to 0.4 mL settled particles per 100 mL; visible wet bath typically 1.2 to 2.4 mL per 100 mL.
- UV-A intensity requirement
- Fluorescent magnetic particle examination typically requires at least 1,000 µW/cm² UV-A at the part surface and white light below about 20 lux.
- Two-direction magnetization
- Examine each area with two magnetizing directions approximately 90 degrees apart, because defects perpendicular to flux lines are best detected.
- System performance check
- Periodic checks with a known-defect reference piece or lift test verify that equipment, particles, and viewing conditions still detect discontinuities.
- ASTM E709
- Standard guide for magnetic particle testing that covers equipment, techniques, and general procedures; often used as a method reference.
- ASTM E1444
- Standard practice for magnetic particle testing, widely referenced for aerospace and general industry; includes requirements for equipment and process control.
- ASME Section V Article 7
- Boiler and pressure vessel code article that specifies magnetic particle examination method requirements; acceptance criteria are found in the applicable construction section.
- ISO 9934 series
- International standards for magnetic particle testing, covering general principles, detection media, equipment, and examination of ferromagnetic components.
- SNT-TC-1A
- ASNT recommended practice for personnel qualification and certification in nondestructive testing; employers use it to establish written practice for Levels I, II, and III.
- Acceptance criteria source
- The construction code or contract specification defines acceptable indication size and type; the MT method standard usually does not set acceptance limits.
- Relevant indication
- An indication caused by an actual discontinuity or defect that must be evaluated against the acceptance criteria.
- Nonrelevant indication
- An indication caused by part geometry, permeability changes, or edge effects rather than a defect; it is not cause for rejection.
- Magnetic writing
- A false indication caused by residual magnetism from contact with a magnet or current-carrying conductor; demagnetization and re-examination usually remove it.
- Surface versus subsurface
- Surface indications are usually sharp and dense; subsurface indications tend to be broad and fuzzy because leakage fields spread before reaching the surface.
- Reporting essential data
- Reports should identify the part, material, technique, current, particle type, coverage, indications, acceptance status, examiner, date, and governing standard.
- Linear indication
- An indication whose length is at least three times its width; it is often treated more severely than a rounded indication in acceptance criteria.