Asnt Mt Level Iii Notes

MT Level III Notes

MT Level III Notes By: Charles Hansen ASNT Level III MT Wave Forms

Charles Hansen ASNT Level III

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MT Level III Notes

Field Strength and Distribution in Symmetrical Objects

Charles Hansen ASNT Level III

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MT Level III Notes

Charles Hansen ASNT Level III

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MT Level III Notes Impedance: Term used to refer to the total opposition to flow of current represented by the combined effect of resistance, inductance and capacitance of a circuit. Magnetic Lines: Lines of force that form a path around a crack in a ring magnet Earth field is weak, how weak? 0.3 gauss Demagnetization is required: the object is to be electric arc welded, could interfere with instruments in service, or could attract chips or particles in service Particle sizes for wet method testing ranges from: 1 to 25 micrometer When magnetic material reaches its curie temperature, the material becomes: paramagnetic Which type of radiation can most damage human tissue? UV-B Best technique for testing a large flat area? Prods µ = Permeability = B/H B = Flux Density measured in Gauss (SI Units measured in Tesla) H = Magnetizing force measured in Oersted Most common wattage of mercury vapor bulbs for fluorescent MT exams = 100 watts Longitudinal field = amp turns (L/D), Yoke, Coil around part Circular field= Prods, central conductor, head shot, passing current directly through part Parallel magnetization= should be avoided (field is established in a part when it is placed next to a conductor carrying current.) Multidirectional Magnetization: Useful when orientation of discontinuities are unknown (Proper Sequence) Magnetize, apply particles, shut off current, and inspect. Vector field= produced by simultaneously imposing two magnetizing forces in two directions where one is stronger than the other upon a magnetizeable article. N*I = 45,000 L/D

N= number of turns I= current (amps)

Advantage to demagnetize a part: Position East-West Centistokes: unit of viscosity Settling test: check concentration of particle for wet method Calibrate MT Machine- Use shunt with calibrated ammeter Ammeter: determine amperage being used Fill Factor= 10% or 10:1 Gauss= 1 line of flux per square centimeter = Flux Density

Charles Hansen ASNT Level III

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MT Level III Notes Discontinuity= interruption or break in the normal physical structure Indication= accumulation of particles Plated parts can be reliably tested = 0.1mm (0.0004 in) thick Retentivity or Remanent: retain magnetic field Permeability: ease with which it can be magnetized Inductance: The magnetism produced in a ferromagnetic body by some outside magnetizing force. Forging defects- laps, burst Casting defects- shrinkage, gas, misruns, cold laps, sand inclusion, hot tears Best Subsurface: Dry continuous HWDC with Prods (Deepest Penetration) Best Surface and Subsurface: HW Rectified AC with Dry Particles (Most effective) (Greatest Particle Mobility) Best Surface: Wet Fluorescent Continuous AC (Shallowest Penetration)

Easier to demagnetize: Longitudinal fields Harder to demagnetize: Circular fields Skin affect: AC Resistance to demagnetization: Greater in hard materials than soft materials When a magnetic field is at 90° to the defect, it will cause an abrupt change in the permeability of the part. Magnetic domains: submicroscopic regions inside material Medium: refers to particles that have the ability to be strongly attracted to leakage fields. **Permeability of Materials** Diamagnetic: less than 1.0 Paramagnetic: 1.0 or slightly more Ferromagnetic: many many times more than 1.0 MT particles need to have: High permeability / Low Retentivity Human vision range is: 380nm to 770nm (violet to red) Nm = nanometer - billionth of a meter Black light = 365nm, outside of human’s range Fluorescent particles absorb 365nm (3650 angstroms) and release at 550nm (5500 angstroms) (Yellow/Green) 100 ft candles- Visible light for visible MT Magnetic particle building from a discontinuity is strongest when the discontinuity is orientated: 90 degrees to the magnetic flux flow.

Charles Hansen ASNT Level III

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MT Level III Notes Strongest magnetic field in a coil is at the: inside edge Field meter: equipment used to determine if a part has been demagnetized. They read a maximum of 10 to 20G or 10 to 20 MT. (The positive corresponds to the North pole on one end of the part, and the negative to the South pole on the other end of the part. Circular field is easiest to detect, but hardest to demagnetize Longitudinal field is easier to demagnetize Flux Indicator: small device, generally a metal strap or disk, containing artificial discontinuity used to determine when the correct magnetizing condition or magnetic field direction has been achieved. Fill Factor: is given by 𝐷𝑝2 /𝐷𝑐2 Wet ferromagnetic particles have lower permeability and higher Retentivity compared to dry powder. Advantages of Magnetic Rubber: 1. Replica of the geometry is created. 2. A record is created. 3. The indication can be viewed under a microscope. Magnetic Rubber Inspection takes a long time because: curing the magnetizing rubber solution. Typical amperage output for mobile equipment is 1.5Ka to 4000 amperes. Hall Effect probe: detects field strength because the field strength creates a voltage difference between two sides of the sensor in proportion to the field strength. Quick Break: shuts off current at its maximum causing the collapsing magnetic field to produce eddy currents that compensate for decreased flux density at the ends of a part. Cobalt glass filter provides peak transmission of what wavelength? 3650 angstroms or 365nm Advantages of batteries for MT: can be operated using low current line chargers. Ketos Ring Test: provides information about particle concentration, magnetic properties of the particles, and the functioning of the magnetizing machine. Hall Effect probe sensitivity is increased using a ferrite ring because? Of increased permeability and higher B value. You should wear UV absorption eyewear while performing fluorescent MT, because if light shines in your eye, a cloudy sensation may occur do to liquid in the eye ball fluoresce. Depth to width of a crack for detection.

Have seen 1:1 and 1:5.

Stringer: most likely subsurface discontinuity detectable by MT Porosity: most difficult to detect by MT. Contact pads used during a head shot are necessary to? reduce arcing and current density through contact area. Longer shots are required with magnetic rubber due to? Higher Viscosity

Charles Hansen ASNT Level III

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