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MPI > 2: Methods & Techniques > Flashcards

2: Methods & Techniques Flashcards

1
Q

What are 3 ways to figure out the magnetic field direction?

A
  1. Right Hand Rule
  2. Pie Gauges
  3. Quantitative Quality Indicators (QQI’s)
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2
Q

What units do magnetic field indicators measure in?

A

Gauss or Tesla

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3
Q

What is a digital type of Gauss Meter?

A

Hall Effect Meter

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4
Q

Main difference between circular and longitudinal magnetism?

A

Longitudinal has external poles

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5
Q

Solenoids produce what kind of field?

A

Longitudinal

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6
Q

How do defects show up?

A

Same direction as current

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7
Q

What is one of the best ways to detect subsurface discontinuities when using half wave DC or half rectified AC?

A

Circular magnetization with prods

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8
Q

Coils are typically around what type of frame?

A

Molten

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9
Q

What is a pole piece?

A

Stuck on the end of a part to create length

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10
Q

Parts less than what require a pole piece?

A

Two

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11
Q

Parts exceeding what max length need to be inspected in separate pieces?

A

18 inches (26 cm)

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12
Q

What is the fill factor?

A

Diameter of part compared to diameter of coil

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13
Q

When using DC current, amps depend on what thickness?

A

Cross-sectional thickness

Direct Contact Formula

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14
Q

What are QQI’s used for?

A

Ensure proper technique is used

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15
Q

Wet fluorescence is often referred to as what? (2)

A

Background or background fluorescent

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16
Q

How is furring caused?

A

Excessive longitudinal field

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17
Q

Contact area is referred to what?

A

Cross section

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18
Q

What is the rule for how close prods are together?

A

2”-8”

6” is good

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19
Q

When using prods and a material less than 3/4” ..what amperage should you use?

A

90-115 amps/inch of spacing

3.5-4.5 amps/mm

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20
Q

When using prods and a material more than 3/4” thick, what amperage should you use?

A

100-125 amps/inch

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21
Q

What is the formula for low fill factor in a coil?

A

45,000/(L/D) x 1/n

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22
Q

What is the formula for high fill factor in a coil?

A

35,000/(L/D)+2 x 1/n

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23
Q

An effective inspection area is what?

A

4x diameter of the conductor

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24
Q

What is amperage based on when using a central conductor?

A

Wall thickness and diameter of centre conductor

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25
Q

Doubling the radius will do what to the flux density?

A

Cut flux density in half

26
Q

What are the 6 basic steps on an MPI?

A
  1. Part prep
  2. Mag methods
  3. Application of particle
  4. Inspection & Interpretation
  5. Demagnetization
  6. Post Cleaning
27
Q

What type of cleaner do you HAVE to have around welders?

A

Non-chlorinated

Will create lethal phosgene

28
Q

What is the disadvantage of ferromagnetic coatings on a part you are trying to inspect?

A

Could provide false indications and mask discontinuities

29
Q

What best results, are characteristics of particles do we want?

A

High permeability and low retentivity

30
Q

What is the idea particle density?

A

5-8x thicker than water

31
Q

In wet applications, what is required in order to avoid settling of particles?

A

Constant agitation

32
Q

What are “contrast aid paints”?

A

White pigment suspended in quick drying, colourless solvent

33
Q

Choosing particles depends on what 3 things?

A
  1. Type of defect
  2. Size of surface defect
  3. Convenience
34
Q

1 advantage and 1 disadvantage of dry visible method?

A

Less sensitive to tiny surface defects but better for finding sub surface flaws

35
Q

What are pie gauges made out of?

A

Low carbon steel pie sections, furnace brazed and copper plated

36
Q

What is a multidirectional unit?

A

Capable of producing both field at the same time

37
Q

Describe the current in the central conductor method?

A

Strong circular field around conductor and specimen BUT no current through specimen itself

38
Q

AC is used to induce eddy currents into parts during which method because it can’t be properly inspected using direct contact or central conductor techniques?

A

Induced current technique

39
Q

Core material should have a minimum length of what?

A

Equal to diameter of ring shaped test piece BUT no less than 152 mm long

40
Q

What is the most common method to test welds?

A

Prod method

41
Q

Inspection of tubes, pipes, shafts or small ferromagnetic parts are generally done with what?

A

Portable coils

42
Q

Why would Vector Fields occur?

A

Imbalanced circular and longitudinal fields in multidirectional magnetization

43
Q

How do you calculate amperage for a low fill conductor?

A

12-32 amps/mm of (CC diameter + 2x wall thickness)

44
Q

Where is the field strength strongest in a solid nonmagnetic conductor?

A

Surface of part

45
Q

What is the field strength proportional to in a solid nonmagnetic conductor?

A

Size of conductor

Will increase proportionally to increase in current

46
Q

Where is the field strength greatest in a solid MAGNETIC conductor?

A

Below the surface

47
Q

For ferromagnetic conductors, field strength within is dependant on what?

A

Permeability

48
Q

What is the field strength of a hollow nonmagnetic AND magnetic conductor?

A

Zero in centre of hollow section and greatest at outer surface

49
Q

What is referred to as “skin effect”?

A

AC’s tendency to flow near surface of conductor

50
Q

Detergent and aqueous cleaners are usually used for what contaminants?

A

Light oils, grime, soil/dirt and mild grease

51
Q

Solvent cleaners (like non halogenated petroleum naphtha) are most commonly used for what contaminants?

A

Mild - moderate grease and oils

However they may leave a thin film or residue

52
Q

Describe steam cleaning:

A

A form of alkaline or detergent cleaning where the solution is pressurized

53
Q

Vapour degreasing is very effective for removing what?

A

Heavy souls, grease and oils

54
Q

Steels become brittle with what type of cleaner?

A

Acid based

55
Q

Titanium and nickel alloys are attacked by what type of cleaner?

A

Products containing halogen and sulphur

56
Q

Particle selection is based on what?

A

Sensitivity required and suspected discontinuities

57
Q

Choice of current is primarily governed by what?

A

Type and location of suspected discontinuities

58
Q

What is the tail stock?

A

The moveable section of headstock

59
Q

Describe the magnetic field while using indirect current with a central conductor:

A

Field on inside surface is smaller and opposite than what’s produced on outside

60
Q

In a stationary magnetizing coil, the field direction is…

A

Parallel to axis of coil

61
Q

Ratio of length to diameter must be at least what for coil magnetization to be effective?

A

2:1

62
Q

Longer parts can actually be demagnetized by the earths magnetic field, therefor the axis should always be placed in what direction?

A

Long axis east to west direction

MPI (9 decks)

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