Magnetic Particle Inspection MT Flashcards
And inspection method in which an initial magnetizing force is applied to a part and then reduce to a lower continuous value was called
Surge method
The 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 is
Impedance
Discontinuities in plate , sheet or strip caused by internal fissures, inclusions, or blow holes in the original ingot which after rolling, are usually flat and parallel to the outside surface are called
Laminations
The cumulation of particles at a site on the part surface, collected at and held to the site by the magnetic leakage field, is called
An indication
The leakage field strength is controlled by
The materials permeability, the depth and width of the discontinuity and the relative strength of the applied magnetic flux
Primarily a qualitative inspection, detecting changes in volume
Magnetic flux leakage - tank floor scanning, in line inspection of pipelines, wire rope, coil tubing and rail inspections
Relatively thin coating of paint or plating on the surface can cause a surface crack to appear as
Broad and fuzzy
When matters is place within an external magnetic field, the magnetic moments of that material’s electrons maybe reorientated. When this occurs the material produces its own macroscopic magnetic field this is known as
Faraday’s Law of magnetic induction
Any material with a negative relative permeability that is slightly less than one is
Diamagnetic - Mercury gold bismuth and zinc
When the internal magnetic field of a material is aligned in the same direction as the applied external field, and the material has a small positive suspect ability and a positive relative permeability that is slightly more than one the material is called
Paramagnetic- aluminum platinum copper sulfate and wood
When the internal magnetic field of the material is aligned in the same direction as the applied external field, and the material has a high positive suspect ability and a high positive permeability that is much greater than one, the material is called
Ferromagnetic
When an electric current is passed through the part the part is the conductor of the electric current and a circling magnetic field is established both within the inside and outside the conductor
Direct magnetization
Magnetism that results when a ferromagnetic material is influenced by an external field. Devices such as central conductors, coil’s, and yokes
Indirect magnetization
Coil where the length is greater than the diameter
Solenoids
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
Impedance
Lines of force that form a path around the crack in a ring magnet
Magnetic lines
Earths field this week, how week?
0.3 gauss
Particle sizes for wet method testing ranges from
1 to 25 µm (micrometer)
When magnetic material reaches its curie temperature, the material becomes
Paramagnetic
Which type of radiation can most damage human tissue?
UV-B
µ =
Permeability =B/H
B =
Flux density measured in gauss (SI units measured in tesla)
Best technique for testing of large flat area
Prods
H =
Magnetizing force measured in oersted
Most common wattage of mercury vapor bulbs florescent MT exams
100 W
Amp turns L/D, yoke, coil around part are all types of this field
Longitudinal
Prods, central conductor, headshot, passing current directly through part or all types of this field
Circular
The field established in a part when it is placed next to a conductor carrying a current, which should be avoided
Parallel magnetization
Useful when orientation of discontinuities are unknown (proper sequence) magnetize, apply particles, shut off current, and inspect
Multidirectional magnetization
Produced by simultaneously imposing two magnetizing forces in two directions where one is stronger than the other upon a magnetizable article
Vector field
N*I =
N= number of turns I = current (amps)
45,000/(L/D)
Advantage to demagnetize a part
Position east to west
Check concentration of particles for wet method
Settling test
Unit of viscosity
Centistokes
MT machine is calibrated with
A shunt and a calibrated ammeter
Determines amperage being used
Ammeter
Fill factor equals
10% or 10 to 1
One line of flux per square centimeter is
Gauss (flux density)
Interruption or break in the normal physical structure
Discontinuity
Accumulation of particles
Indication
Plated parts can be reliably tested at what thickness
.1 mm or.004
To retain a magnetic field
Retentivity or remnant
The ease which something can be magnetized
Permeability
Best subsurface inspection
Dry continuous half wave DC with prods (Deepest Penetration)
Best surface and subsurface
Half wave rectified AC with dry particles (most effective with greatest particle mobility)
Best surface
Wet fluorescent continuous AC shallowest penetration
Easiest to demagnetize
Longitudinal fields
Harder to demagnetize
Circular fields
Current for skin affect
AC
Greater in hard materials than soft materials
Resistance to demagnetization
When a magnetic field is at 90° to the defect, it will cause an abrupt change in this of the part
Permeability
Sub microscopic regions inside of material
Magnetic domains
Permeability less than one
Diamagnetic
One or slightly more
Paramagnetic
Many more times more than one
Ferromagnetic
MT particles need to have
High permeability and low retentivity
Human vision range is
380nm to 770 nm violet to red
A nano meter equals
Billionth of a meter
Black light is how far outside of the humans range
365 nm
Fluorescent particles absorb at
365 nm or 3650 angstroms
Fluorescent particles released at
550 nm or 5500 Å yellow green
Required visible light for visible MT
100 foot candles
Magnetic particle building from the discontinuity the strongest one the discontinuity is orientated
90° to the magnetic flux flow
The number of lines of flux intercepting in area perpendicular to the flux
Flux density
Prod spacing less than___________is usually not practical because the particles tend to band around the prize, making interpretation difficult
3 inches
The source that supplies the most power for magnetizing is
Three phase alternating current, full wave rectified
Half wave direct current is obtained from
Single phase alternating current power
Full wave, three phase rectified alternating current produces
Low ripple direct current
The timer on a bench should have an accuracy of
+/-.1 second
Field that is easiest to detect, but hardest to demagnetize
Circular
Field that is easier to demagnetize
Longitudinal
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 parts
Quick break
Typical average output for mobile equipment is
1.5 KA to 4000 amperes
Single phase equipment require how many more times then three phase unit
1.73
Alternating current is available in voltages ranging from
120 to 440 V
The level of fluorescent particles and suspension should be maintained consistently, from
.1 to .4 mL in 100 mL settling test
Most military and commercial specifications require the test site to be darkened to
20 luxs or 2 ftc
The settling rate is inversely proportional to the
Liquids viscosity
Skin depth for 60 Hz alternating current fields is typically about
1 mm or .04 inch
Detects field strength because the fields creates a voltage difference between two sides of the sensor in proportion to the field strength
Hall Effect Probe
The hall effect probe sensitivity is increased using a ferrite ring because
Increased permeability and higher B value
Most likely subsurface discontinuity detectable by Mt
Stringer
Most difficult to detect by MT
Porosity
Longer shots are required with magnetic rubber due to
Higher viscosity
Provides information about particle concentration, magnetic properties of the particles, and the functioning of magnetizing machine
Ketos Ring Test
The magnetization of a ferromagnetic substance by increasing magnetic field takes place in discontinuous steps rather than continuously
Barkhausen Effect
A single shot magnetization method using discharge from the bank of capacitors. A means by which electrical current is built up and stored until a sufficient level is achieved to provide a predetermined magnetic field in a test object, usually saturation
Capacitor discharge method
A potential difference developed across a conductor at right angles to the direction of both the magnetic field and the electric current. Produce when a current flows along the rectangular conductor subjected to a transverse magnetic field. The magnitude of the voltage is proportional to the applied field.
Hall Effect
Radiant energy generated to the 400 to 700 nm or 4000 to 7000 angstroms wave range
Visible light
Yokes produce either alternating current or alternating current half wave direct current output from
120 V or 240 V alternating current single phase
The shot timer is typically adjustable from
.5 seconds to 1 second
Why is the shot timer usually set between .6 seconds and .9 seconds?
Because the timing device used to calibrate the timer has an accuracy of plus or minus .1 second
Mobile power supply normally operate on
240 V or 480 V
Mobile power supplies provide both alternating current and half wave direct current output up to
6000 A
Amps per 1 inch diameter of cross-section with alternating current
500 to 600 A
Amps per 1 inch of diameter or cross section with direct current or rectified alternating current
800 to 1000 A
The level of visible particles and suspension should be maintained consistently, from
1.2 to 2.4 100 mL
The most visible indications generally result when the depth exceeds
Five times the width
