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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
Occurs when a metal is exposed to a corrosive environment under tensile stress
Stress cracking corrosion
26
Prevention of stress cracking corrosion
* Lowering Stress * Changing Alloy * Cathodic protection * Inhibitors * Coating
27
Degradation that occurs when hydrogen penetrates the surface of a metal
Hydrogen Damage
28
Can lead to various forms of damage like embrittlement, blistering, and cracking
hydrogen damage
29
Prevention of hydrogen damage
* Material selection * Hydrogen removal * Corrosion inhibitors * Proper handling
30
Steel with ________________ is a corrosive combination
Concentrated Sulfuric acid
31
Stainless steel with ____________ is a corrosive combination
nitric acid
32
Occurs in the presence of a liquid containing ions (electrolyte) * Electrochemical process. * Follows thermodynamic laws and electrochemistry kinetics
Wet corrosion
33
High temperature corrosion occurs at elevated temperatures above __________ from gases, solid or molten salts, or molten metals.
400°C (750ºF)
34
Follows thermodynamic laws and chemistry kinetics of heterogeneous reactions.
High temperature corrosion
35
The kinetics of wet corrosion are influence by various factors such as
temperature, pH, and presence of impurities.
36
is commonly used to describe corrosion kinetics, relating the current density to factors like activation energy and overpotential
Tafel equation
37
This type is not primarily electrochemical in nature, but involves chemical attacks from gases, solid or molten salts, or molten metals at elevated temperatures
High temperature corrosion
38
The kinetics of high temperature corrosion are influenced by factors such as
The kinetics are influenced by factors such as
39
Iron and its alloys
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
generic term that applies to high carbon-iron alloys containing silicon.
Cast iron
41
Contain 2% to 4% carbon and 1% to 3% silicon. * Considered as the least expensive of the engineering metals.
Gray cast iron
42
White cast irons have practically all of the carbon in the form of
IRON CARBIDE
43
These are produced by high temperature heat treatment of white iron of proper composition
Malleable cast iron
44
In malleable cast iron, The graphite forms as __________ instead of flakes and the material shows good ductility
rosettes or clusters
45
The graphite is present as nodules or spheroids as a result of a special treatment of the molten metal.
Ductile cast iron
46
The mechanical properties of ductile irons can be altered by ______________similar to ordinary steel.
heat treatment
47
due to presence of chlorides
Crevice and pitting corrosion
48
For cast iron, intergranular corrosion occurs due to
presence of NH4NO3 that caused the depletion of Cr
49
Selective leaching happens in cast iron due to
graphite corrosion
50
When the silicon content of gray cast iron is increase to 14%, it becomes extremely corrosion resistant to many environment
high silcon cast iron
51
The excellent corrosion resistance of high silicon irons is due to the formation of a ____________surface late
passive SiO2
52
contains about 14.5% silicon and 0.95% carbon. It becomes _________ after the addition of 3% molybdenum
Duriron, durichlor
53
Composed of up to 2.14% carbon
Steels
54
Two types of steels
Plain carbon, alloyed
55
Contained at least 11% chromium
Stainless steel
56
Types of stainless steels
Martensitic, Ferritic, Austenitic, and Precipitation-hardened
57
Can be hardened by heat treatment similar to ordinary steel. * Heat treatment increases tensile strength.
Martensitic Stainless Steels
58
Essentially nonmagnetic and cannot be hardened by heat treatment. Can only be hardened by cold working
Austenitic Stainless Steels
59
Cannot be hardened by heat treatment. Can only be hardened by cold working, just like Austenitic stainless steel
Ferritic Stainless Steels
60
Hardened and strengthened by solution-quenching, followed by heating for substantial times at temperature approximately in the range of 800 to 1000 F.
Precipitation-hardened Stainless Steels
61
different from most other metals in that it combines corrosion resistance with high electrical and head conductivity, formability, machinability, and strength when alloyed
copper
62
alloys have better physical properties than copper alone, and they are also more resistant to impingement attack
Copper-zinc alloys
63
used in preference to copper for condenser tubes
brass
64
factors due to high temperatures, stagnant solutions, and porous inorganic scale formation.
Dezincfication or Dealloying
65
Type of corrosion for Cu-Zn alloys due to ammonia
Stress-Corrosion Cracking (Season Cracking)
66
Lightweight metal having good corrosion resistance to the atmosphere and most aqueous media
Aluminum
67
Aluminum corrosion can occur at
extreme pH (>8, <4)
68
Has the lowest density of all structural metals
Magnesium
69
Pure magnesium readily forms a layer of
MgO2
70
Magnesium alloys are sought after for its
high strength-toweight ratio
71
Magnesium is alloyed with metals such as____________ to improve hardness, ductility, corrosion resistance etc. of the resulting alloy
Al, Zi, Mn and Zn
72
Magnesium and magnesium alloys are resistant to
1. Atmosphere 2. Distilled water 3. Alkalis
73
Magnesium and magnesium alloys are not resistant to:
1. Hard water 2. Seawater 3. Organic acid, inorganic acid and acid salts 4. Methanol 5. Leaded gasoline mixtures 6. Freon plus wate
74
ductile and tough mainly because of its face-centered cubic structure
Pure nickel
75
Nickel metal is resistant to the following:
1. Alkalis and fused alkalis 2. Dilute nonoxiding inorganic and organic acids.
76
The resistance of nickel metal is improved if acids are _____
deaerated
77
Nickel metal is not resistant to the following:
1. Oxidizing acids 2. Oxidizing salts 3. Aerated ammonium hydroxide 4. Alkaline hypochlorites 5. Seawater 6. Sulfur or sulfur - containing reducing environments
78
Consists of 10-30% copper and 70-90% nickel
Cupronickels
79
n seawater, ____________forms a stable layer of Cu2O that provides excellent resistance to biofouling
cupronickels
80
Also known as Nichrome
Ni-Cr alloys
81
The mixture of formed oxides (NiO and Cr2O3 ) combine to form nickel chromite (NiCr2O4 ) that protects it from oxidation.
Ni-Cr alloys
82
FACTORS AFFECTING METAL CORROSION
Metal composition Crystal structure pH Level Temperature Aeration Moisture Stress Microbial activity
83
In some environments, microorganisms like bacteria can accelerate corrosion through various mechanisms, a phenomenon known as
microbiologically influenced corrosion (MIC)
84
can make it more susceptible to corrosion, especially localized forms like stress corrosion cracking
Mechanical stresses on the meta
85
essential for most corrosion processes to occur, as it provides the necessary conductive medium for ionic movement.
presence of moisture
86
often plays a crucial role in many corrosion processes, acting as an oxidizing agent
oxygen
87
Generally, __________ temperatures accelerate corrosion reactions
higher
88

Corrosion Engineering (6 decks)

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