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MPI > 5: Discontinuities > Flashcards

5: Discontinuities Flashcards

1
Q

What should you do with “discontinuities” producing a weak or questionable indication?

A

Test with another method

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2
Q

What is a butt joint?

A

2 pieces joined together on SAME plane

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3
Q

What is a t-joint?

A

2 pieces joined that are 90 degrees to each other

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4
Q

What is a lap joint?

A

2 pieces joined by overlapping and welding seam between them

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5
Q

What are corner joints?

A

2 pieces joined that are 90 degrees, forming an “L”

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6
Q

Elongated porosity is called what?

A

Wormholes

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7
Q

Where does lack of fusion occur?

A

Between weld & parent metal OR between weld metal & and weld metal

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8
Q

Slag inclusions are found in welds produced by a process that uses what? (SMAW, SAW, FCAW)

A

Flux

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9
Q

Oxide inclusions produce similar indications to what?

A

Porosity

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10
Q

What type of inclusions are virtually undetectable using MPI?

A

Tungsten

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11
Q

What type of cracking may appear as longitudinal, traverse or star shaped?

A

Hot cracking

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12
Q

What is a common cause of hot cracking?

A

Shrinkage stresses during solidification

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13
Q

What can occur immediately on cooling or after a period of hours/days?

A

Cold/under-bead cracking

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14
Q

Where does lamellar tearing occur?

A

Base metal of structural welded shapes

Found at plate edges/areas of cut cross section

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15
Q

What are the 3 main causes of service discontinuities?

A
  1. Over-stress
  2. Fatigue stress
  3. Corrosion
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16
Q

80% of failures involving non-stationary parts are attributable to what?

A

Fatigue

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17
Q

Fatigue properties are usually related to what?

A

Yield point

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18
Q

What type of fatigue can result in fracture?

A

Thermal fatigue

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19
Q

Describe creep:

A

A solid material that tends to move slowly/deform under mechanical stress

20
Q

What are the 2 key contributors to creep?

A
  1. Cyclic stresses

2. High temp

21
Q

What is cyclic stress?

A

Distribution of forces that change over time in a repetitive fashion

22
Q

What type of fatigue can lead to rapid failure and is important to detect ASAP?

A

Corrosion fatigue

23
Q

If a part contains internal stresses, what will appear on surface where stresses are the highest?

A

A pit or notch (corrosion or oxidation)

24
Q

What is stress corrosion cracking?

A

Constant tensile stresses in a corrosive environment

25
Q

What is the difference between corrosion fatigue cracking and stress corrosion cracking?

A

Corrosion fatigue can start from 1 PIT but stress corrosion requires a larger area

26
Q

Stress and corrosion combined leads to crack growth along what?

A

Grain boundaries

27
Q

What is erosion corrosion?

A

Degrading of material by abrasion

28
Q

What are the 2 types of erosion corrosion? Describe them

A
  1. Fretting corrosion: 2 components rubbing together causing small particles on surface to bond together, then torn away by continued rubbing
  2. Cavitation corrosion: pitting accelerated due to constant flow of liquid against surface
29
Q

What’s the easiest way to minimize fretting corrosion?

A

Less movement and a looser fit

30
Q

What is hydrogen cracking?

A

Fracturing that occurs due to corrosive environments produced by hydrogen media while exposed to applied tensile/residual stress

**follows grain boundaries

31
Q

How can hydrogen be introduced?

A

Electroplating, pickling or welding in a moist area

32
Q

What is the first step in distinguishing relevant and non relevant indications?

A

Know whether the part was in service or not

33
Q

What does magnetic writing result from?

A

One ferromagnetic part rubbing against another, both will contain some residual magnetism, magnetic poles will be created, revealing themselves in lines or “writing”

34
Q

How can longitudinal magnetism in a coil or yoke legs create false indications?

A

Magnetic poles will be created at the ends where lines of force are most densely packed so particles will accumulate there

35
Q

How can a part that was subjected to cold working cause false indications?

A

The change in permeability to that area will attract magnetic particles when magnetized

36
Q

Non relevant indications where there is an abrupt change of section will appear how?

A

More fuzzy and broad

37
Q

How do cracks appear in areas with abrupt changes of section?

A

They flow with less uniformity and are more jagged

38
Q

If subsurface discontinuities are not a concern, what should be used whenever possible? And why?

A

AC will reduce non relevant indications and improve sensitivity

39
Q

When are magnetic rubber inspections used?

A

Surface/subsurface discontinuities with poor visual access

40
Q

What do magnetic rubber inspections form?

A

A cast replica

41
Q

What does Alginate impression compounds involve?

A

“Lifting” magnetic particles from inaccessible areas which can’t be accurately viewed using black light

42
Q

Where are flash line found and what are they caused by?

A

Cracks that may be found on a forging sheet to improper trimming of flash

43
Q

What type of defects are seams and what are they caused by?

A

Processing defects caused by surface cracks that are stretch out and lengthened during rolling operations of a bar

44
Q

What type of discontinuity is segregation?

A

Inherent

45
Q

What is pipe caused by?

A

failure to remove a shrink cavity that forms at top of ingot

46
Q

Where is a toe crack found?

A

Where face of weld joins base metal

47
Q

When do hot cracks develop?

A

During cooling process of weld due to shrinkage

MPI (10 decks)

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