Chapter 8: Corrosion and Degradation of Materials

Question 1

there is actual
material loss either by
dissolution (corrosion) or by
the formation of nonmetallic
scale or film (oxidation).

Answer 1

metals

Question 2

are relatively resistant to deterioration, which
usually occurs at elevated temperatures or in rather extreme
environments

Answer 2

Ceramic materials

Question 3

For polymers, mechanisms and consequences differ from those for
metals and ceramics, and the term ___ is most frequently
used

Answer 3

degradation

Question 4

Polymers may dissolve when exposed to a liquid solvent, or they may
absorb the solvent and swell; also, ___
(primarily ultraviolet) and heat may cause alterations in their
molecular structures

Answer 4

electromagnetic radiation

Question 5

*___ of an object occurs as a result of the interaction between the environment or with the materials that form the object

*several ways in which ceramics break down physically and chemically

Answer 5

degradation

Question 6

it is in the nature of all the materials used for construction to eventually ___ and ___

Answer 6

degrade and deteriorate

Question 7

the destructive electrochemical attack of a material

Answer 7

corrosion

Question 8

why metals corrodes?

Answer 8

redox reaction (reduction-oxidation)

Question 9

two reactions necessary in corrosion of zinc in acid

Answer 9

oxidation reaction and reduction reaction

Question 10

occurs when the iron in the metal oxidises

Answer 10

steel rusting

Question 11

solution for steel rusting

Answer 11

alloying with chromium (stainless steel)
painting/coating the metal

Question 12

generated by
coupling to the standard
hydrogen electrode, standard
half-cells for various metals
and ranking them according
to measured voltage

Answer 12

electromotive force (emf)

Question 13

the rate of
material removal as a consequence of
the chemical action, is an important
corrosion parameter

Answer 13

corrosion penetration rate (CPR)

Question 14

The variables in the corrosion environment, which include ___ can have a decided
influence on the corrosion properties of the materials that are in
contact with it.

Answer 14

fluid velocity, temperature, and composition

Question 15

In most instances, increasing fluid velocity enhances the rate of
corrosion due to

Answer 15

erosive effects

Question 16

Increasing the concentration of the corrosive species (e.g., H+
ions in acids) in many situations produces a more rapid rate of

Answer 16

corrosion

Question 17

forms of corrosion

Answer 17

stress corrosion
erosion-corrosion
pitting
crevice
galvanic
intergranular
selective leaching
uniform attack

Question 18

work together at crack tips

Answer 18

stress corrosion

Question 19

break down of passivating layer by erosion (pipe elbows)

Answer 19

erosion-corrosion

Question 20

downward propagation of small pits & holes

Answer 20

pitting

Question 21

between two pieces of the same metal

Answer 21

crevice

Question 22

Dissimilar metals are physically joined. The more anodic one corrodes

Answer 22

galvanic

Question 23

corrosion along grain boundaries, often where special phases exist

Answer 23

intergranular

Question 24

preferred corrosion of one element/constituent

Answer 24

selective leaching

Question 25

oxidation & reduction occur uniformly over surface also known as general attack corrosion most common type of corrosion and is caused by a chemical or electrochemical reaction greater amount of corrosion destruction but safe form of corrosion predictable, manageable and preventable

Answer 25

uniform attack

Question 26

it specifically attacks one area of the metal structure

Answer 26

localized corrosion

Question 27

classification of localized corrosion

Answer 27

pitting corrosion crevice corrosion filiform corrosion

Question 28

results when a small hole, or cavity, forms in the metal, usually as a result of de-passivation of a small area produces localized galvanic reaction often difficult to detect due to the fact that it is relatively small

Answer 28

pitting corrosion

Question 29

similar to pitting it occurs at a specific location often associated with stagnant micro-environment

Answer 29

crevice corrosion

Question 30

occuring under painted or plated surfaces when water breaches the coating begins with small defects in the coating and spreads to cause structural weakness

Answer 30

filiform corrosion

Question 31

occurs when two different metals are located together in a corrosive electrolyte forms between two metals, where one becomes anode and one becomes cathode

Answer 31

galvanic corrosion

Question 32

three conditions must exists for galvanic corrosion to occur

Answer 32

-electrochemically dissimilar metals must be present -the metals must be in electrical contact -the metals must be exposed to an electrolyte

Question 33

is a corrosion process that can result from a combination of environmental conditions affecting the metal

Answer 33

environmental cracking

Question 34

types of environmental cracking

Answer 34

-stress corrosion cracking (SCC) -corrosion fatigue -hydrogen-induced cracking -liquid metal embrittlement

Question 35

___ or flow-accelerated corrosion, results when a protective layer of oxide on a metal surface is dissolved or removed by wind or water, exposing the underlying metal to further corrode and deteriorate

Answer 35

flow-assisted corrosion (FAC)

Question 36

-occurs as a result of repeated wearing, weight and/or vibration on an uneven, rough surface -often found in rotation and impact machinery

Answer 36

fretting corrosion

Question 36

-is a chemical or electrochemical atttack on the grain boundaries of a metal -often occurs due to impurities in the metal which tend to be present in higher contents near grain boundaries and these boundaries can be more vulnerable to corrosion than the bulk of the metal

Answer 36

transgranular and intergranular corrosion

Question 36

de-alloying also called

Answer 36

selective leaching

Question 36

can also be caused by high temperature oxidization, sulfidation and carbonization

Answer 36

high temperature corrosion

Question 37

-is the selective corrosion of a specific element in an alloy -the most common type of it is de-zincification of unstabilized brass -the result of corrosion in such cases is a deteriorated and porous copper

Answer 37

de-alloying

Question 38

corrosion prevention

Answer 38

-through the judicious selection of materials -cost may be a significant factor -changing the character of the environment -lowering the fluid temperature and/or velocity -increasing or decreasing the concentration of some species

Question 39

are substances or mixtures that in low concentration and in aggressive environment inhibit, prevent or minimize the corrosion

Answer 39

inhibitors

Question 39

3 mechanism of the inhibitor

Answer 39

-inhibitor is chemically adsorbed on the surface of the metal -inhibitor leads a formation of a film by oxide protection of the base metal -inhibitor reacts with a potential corrosive component

Question 40

examples of application of inhibitors

Answer 40

petroleum industry packaging industry sour gas systems potable water systems engine coolants

Question 40

environmental types of corrosion inhibitor

Answer 40

neutralizer scavanger

Question 41

adsorption (mixed) 2 types of corrosion inhibitor

Answer 41

chemical physical

Question 41

inorganic 2 types

Answer 41

anodic cathodic

Question 41

green 2 types of corrosion inhibitor

Answer 41

extract oil

Question 41

2 cathodic types of corrosion inhibitor

Answer 41

poisonous precipitation