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Corrosion Engineering > CORROSION OF METALS AND ALLOYS > Flashcards

CORROSION OF METALS AND ALLOYS Flashcards

1
Q

Types Of Metallic
Corrosion

A

Uniform
Crevice
Galvanic
Pitting
Intergranular
Selective leaching
Erosion corrosion
Stress cracking corrosion
Hydrogen damage

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2
Q

Most common form of corrosion

A

uniform

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3
Q

Characterized by a chemical or
electrochemical reaction that
proceeds uniformly over the entire
exposed surface

A

uniform corrosion

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4
Q

Prevention of uniform corrosion includes

A

(1) proper materials, including coatings,
(2) inhibitors, or
(3) cathodic protection.

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5
Q

Metal deterioration that
happens in tight spaces where
a stagnant liquid gets trapped

A

crevice corrosion

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6
Q

Prevention of crevice corrosion

A
  • Design considerations
  • Corrosion-resistant materials
  • Coatings
  • Cleaning and maintenance
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7
Q

Exists between two dissimilar
metals with potential difference
in a conductive solution

A

galvanic corrosion

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8
Q

In galvanic corrosion, the rate of
attack on the anode is
______________, compared to the
rate when the metal is
uncoupled.

A

accelerated

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9
Q

serious threat because it accelerates the
deterioration of the less resistant metal.

A

galvanic corrosion

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10
Q

Prevention of galvanic corrosion

A
  • Electrical insulation
  • Use of compatible metals
  • Sacrificial anodes
  • Cathodic Protection
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11
Q

A highly localized form of attack that eats away at the metal,
creating small holes or cavities

A

pitting corrosion

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12
Q

One of the most destructive and insidious forms of corrosion. It can penetrate deep into the metal, leading to sudden and
unexpected failures even when overall material loss seems
___________

A

Pitting corrosion; minimal

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13
Q

Prevention of pitting corrosion

A
  • Corrosion-resistant materials
  • Protective coatings
  • Environmental modification
  • Cathodic protection
  • Regular maintenance
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14
Q

List metals based on increasing pitting resistance

A

Type 304 stainless steel
Type 316 stainless steel
Hastelloy F, Nionel, or Durimet 20
Hastelloy C, Chlorimet 3
Titanium

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15
Q

Metals are made up of tiny
crystals called

A

grains

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16
Q

The boundaries where these grains meet are susceptible to

A

intergranular corrosion

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17
Q

Intergranular corrosion happens due to chemical composition difference at __________ from the ________

A

grain boundaries, bulk of the grain

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18
Q

Prevention of intergranular corrosion

A
  • Material selection
  • Heat treatment
  • Corrosion inhibitors
  • Design modifications
  • Electrochemical techniques
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19
Q

This type of corrosion
targets alloys, which are
mixtures of different metals

A

Selective leaching

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20
Q

During selective leaching,
one specific component of
the alloy is preferentially
_______________ by the corrosive
environment

A

dissolved and removed from
the surface

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21
Q

Prevention of selective leaching

A
  • Alloy selection
  • Protective coatings
  • Environmental modification
  • Cathodic protection
  • Regular maintenance
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22
Q

Occurs when a metal surface is repeatedly exposed to a fluid with abrasive particles

A

Erosion corrosion

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23
Q

The repeated impact of the particles can cause loss
of material that leads to

A

pits, grooves, or cavities.

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24
Q

Prevention of erosion corrosion

A
  • Protective coatings
  • Flow control
  • Design modifications
  • Regular maintenance
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25
Q

Occurs when a metal is
exposed to a corrosive
environment under tensile
stress

A

Stress cracking corrosion

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26
Q

Prevention of stress cracking corrosion

A
  • Lowering Stress
  • Changing Alloy
  • Cathodic protection
  • Inhibitors
  • Coating
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27
Q

Degradation that occurs
when hydrogen penetrates
the surface of a metal

A

Hydrogen Damage

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28
Q

Can lead to various forms of
damage like embrittlement,
blistering, and cracking

A

hydrogen damage

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29
Q

Prevention of hydrogen damage

A
  • Material selection
  • Hydrogen removal
  • Corrosion inhibitors
  • Proper handling
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30
Q

Steel with ________________ is a corrosive combination

A

Concentrated Sulfuric acid

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31
Q

Stainless steel with ____________ is a corrosive combination

A

nitric acid

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32
Q

Occurs in the presence of a
liquid containing ions
(electrolyte)
* Electrochemical process.
* Follows thermodynamic
laws and electrochemistry
kinetics

A

Wet corrosion

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33
Q

High temperature corrosion occurs at elevated temperatures above __________ from gases, solid or molten salts, or molten metals.

A

400°C (750ºF)

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34
Q

Follows thermodynamic laws
and chemistry kinetics of
heterogeneous reactions.

A

High temperature corrosion

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35
Q

The kinetics of wet corrosion are influence by various
factors such as

A

temperature, pH,
and presence of impurities.

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36
Q

is commonly
used to describe corrosion kinetics,
relating the current density to
factors like activation energy and
overpotential

A

Tafel equation

37
Q

This type is not primarily
electrochemical in nature, but
involves chemical attacks from
gases, solid or molten salts, or
molten metals at elevated
temperatures

A

High temperature corrosion

38
Q

The kinetics of high temperature corrosion are influenced by
factors such as

A

The kinetics are influenced by
factors such as

39
Q

Iron and its alloys

A

Cast
Gray cast
White cast
Malleable cast
Ductile Cast
High Silicon cast
Steels
Stainless steel
Martensitic SS
Austenitic SS
Ferritic SS
Precipitation hardened SS

40
Q

generic term that
applies to high carbon-iron
alloys containing silicon.

A

Cast iron

41
Q

Contain 2% to 4% carbon and
1% to 3% silicon.
* Considered as the least
expensive of the engineering
metals.

A

Gray cast iron

42
Q

White cast irons have practically
all of the carbon in the form of

A

IRON CARBIDE

43
Q

These are produced by high temperature heat treatment of
white iron of proper
composition

A

Malleable cast iron

44
Q

In malleable cast iron, The graphite forms as __________ instead of flakes
and the material shows good
ductility

A

rosettes or clusters

45
Q

The graphite is present as
nodules or spheroids as a
result of a special treatment of
the molten metal.

A

Ductile cast iron

46
Q

The mechanical properties of
ductile irons can be altered by
______________similar to
ordinary steel.

A

heat treatment

47
Q

due to
presence of chlorides

A

Crevice and pitting corrosion

48
Q

For cast iron, intergranular corrosion occurs due to

A

presence of NH4NO3
that caused the
depletion of Cr

49
Q

Selective leaching happens in cast iron due to

A

graphite corrosion

50
Q

When the silicon content of gray cast
iron is increase to 14%, it becomes
extremely corrosion resistant to
many environment

A

high silcon cast iron

51
Q

The excellent corrosion resistance of
high silicon irons is due to the
formation of a ____________surface
late

A

passive SiO2

52
Q

contains about 14.5% silicon
and 0.95% carbon. It becomes _________ after the addition of 3% molybdenum

A

Duriron, durichlor

53
Q

Composed of up to 2.14%
carbon

A

Steels

54
Q

Two types of steels

A

Plain carbon, alloyed

55
Q

Contained at least 11%
chromium

A

Stainless steel

56
Q

Types of stainless steels

A

Martensitic, Ferritic, Austenitic, and
Precipitation-hardened

57
Q

Can be hardened by heat
treatment similar to ordinary
steel.
* Heat treatment increases
tensile strength.

A

Martensitic
Stainless Steels

58
Q

Essentially nonmagnetic and
cannot be hardened by heat
treatment. Can only be hardened by cold
working

A

Austenitic
Stainless Steels

59
Q

Cannot be hardened by heat
treatment. Can only be hardened by cold
working, just like Austenitic
stainless steel

A

Ferritic
Stainless Steels

60
Q

Hardened and strengthened by
solution-quenching, followed
by heating for substantial times
at temperature approximately in
the range of 800 to 1000 F.

A

Precipitation-hardened
Stainless Steels

61
Q

different from
most other metals in that it
combines corrosion
resistance with high
electrical and head
conductivity, formability,
machinability, and
strength when alloyed

A

copper

62
Q

alloys have better
physical properties than copper
alone, and they are also more
resistant to impingement
attack

A

Copper-zinc alloys

63
Q

used in preference to copper for
condenser tubes

A

brass

64
Q

factors due to high temperatures,
stagnant solutions, and porous
inorganic scale formation.

A

Dezincfication or Dealloying

65
Q

Type of corrosion for Cu-Zn alloys due to ammonia

A

Stress-Corrosion Cracking
(Season Cracking)

66
Q

Lightweight metal having good
corrosion resistance to the
atmosphere and most aqueous
media

A

Aluminum

67
Q

Aluminum corrosion can occur at

A

extreme pH (>8, <4)

68
Q

Has the lowest density of all
structural metals

A

Magnesium

69
Q

Pure magnesium readily
forms a layer of

A

MgO2

70
Q

Magnesium alloys are sought
after for its

A

high strength-toweight ratio

71
Q

Magnesium is alloyed with
metals such as____________ to improve hardness,
ductility, corrosion resistance
etc. of the resulting alloy

A

Al, Zi, Mn and
Zn

72
Q

Magnesium and magnesium alloys are resistant to

A
  1. Atmosphere
  2. Distilled water
  3. Alkalis
73
Q

Magnesium and magnesium alloys are not resistant to:

A
  1. Hard water
  2. Seawater
  3. Organic acid, inorganic acid and acid salts
  4. Methanol
  5. Leaded gasoline mixtures
  6. Freon plus wate
74
Q

ductile and
tough mainly because of its
face-centered cubic
structure

A

Pure nickel

75
Q

Nickel metal is resistant to the following:

A
  1. Alkalis and fused alkalis
  2. Dilute nonoxiding inorganic and organic acids.
76
Q

The resistance of nickel metal is improved if acids are _____

A

deaerated

77
Q

Nickel metal is not resistant to the following:

A
  1. Oxidizing acids
  2. Oxidizing salts
  3. Aerated ammonium hydroxide
  4. Alkaline hypochlorites
  5. Seawater
  6. Sulfur or sulfur - containing reducing environments
78
Q

Consists of 10-30% copper
and 70-90% nickel

A

Cupronickels

79
Q

n seawater, ____________forms a stable
layer of Cu2O that provides
excellent resistance to
biofouling

A

cupronickels

80
Q

Also known as Nichrome

A

Ni-Cr alloys

81
Q

The mixture of formed
oxides (NiO and Cr2O3
)
combine to form nickel
chromite (NiCr2O4
) that
protects it from oxidation.

A

Ni-Cr alloys

82
Q

FACTORS AFFECTING METAL CORROSION

A

Metal composition
Crystal structure
pH Level
Temperature
Aeration
Moisture
Stress
Microbial activity

83
Q

In some environments,
microorganisms like
bacteria can accelerate
corrosion through
various mechanisms, a
phenomenon known as

A

microbiologically
influenced corrosion
(MIC)

84
Q

can make it
more susceptible to
corrosion, especially
localized forms like
stress corrosion
cracking

A

Mechanical stresses on
the meta

85
Q

essential
for most corrosion
processes to occur, as it
provides the necessary
conductive medium for
ionic movement.

A

presence of moisture

86
Q

often plays a
crucial role in many
corrosion processes,
acting as an oxidizing
agent

A

oxygen

87
Q

Generally, __________ temperatures
accelerate corrosion
reactions

A

higher

88
Q
A

Corrosion Engineering (6 decks)

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