C O R R O S I O N P R E V ENT I O N T E CHNI Q UE S

Question 1

The most common method of preventing
corrosion is the

Answer 1

selection of proper metal
or alloy

Question 2

Not stainless; Not the most
corrosion-resistant material

Answer 2

stainless steel

Question 3

t is a generic name for a
series of more than 30
different alloys containg 11.5
to 30% chromium and 0 to
22% nickel, together with
other alloy addition.

Answer 3

stainless steel

Question 4

Stainless steel have widespread applications in resisting
corrosion but it should be remembered that
____________

Answer 4

they do not resist all corrosives.

Question 5

stainless steel are
less resistant than ordinary structural steel:

Answer 5

Chloride-containing medium
Stressed structures

Question 6

also more susceptible
to localized corrosion than ordinary
structural steels

Answer 6

Stainless steel

Question 7

Frequently, the quality of stainless steel is checked

Answer 7

with a magnet

Question 8

__________ stainless steels represent good alloys
and stainless steels that are magnetic are inferior

Answer 8

nonmagnetic

Question 9

There is ___________ between magnetic
susceptibility and corrosion resistance

Answer 9

no correlation

Question 10

A large number of corrosion failures
can be directly attributed in the

Answer 10

Indiscriminate selection of stainless steels

Question 11

The corrosion resistance of a_________is
usually better than that of one containing
impurities or small amounts of other
elements

Answer 11

pure metal

Question 12

are usually
expensive and relatively soft and weak

Answer 12

pure metals

Question 13

Not expensive in a fairly pure
state - 99.5% plus.
Used for handling hydrogen
peroxide

Answer 13

Aluminum

Question 14

More corrosion-resistant
than induction-melted
zirconium.
Used in atomic-energy
application.

Answer 14

ARC-MELTED ZIRCONIUM

Question 15

This category involves integral or solid
nonmetallic construction and also sheet
linings or coverings of substantial
thickness

Answer 15

Nonmetallics

Question 16

The five general classes of nonmetallics
are

Answer 16

rubbers, natural, and synthetic;
plastics;
ceramics;
carbon and graphite;
and wood.

Question 17

Compared with metals and
alloys: weaker, softer, and
more resistant to chloride
ions but less resistant to
strong sulfuric acid and
oxidizing acids.

Answer 17

rubbers and plastics

Question 18

Has excellent corrosion and
high-temperature resistance.
Brittle and has lower tensile
strength.

Answer 18

ceramics

Question 19

Good corrosion resistance,
electric and heat conductivity
Fragile

Answer 19

carbon

Question 20

frequently as
important as the choice of materials of
construction.

Answer 20

design of a structure

Question 21

Design should consider ________ together with an _____ for corrosion

Answer 21

mechanical and strength requirement, allowance

Question 22

Corrosion is a penetrating action. Hence, it is
necessary to make allowances for the reduction of _________ n designing pipes, tanks, and other
components that can corrode

Answer 22

thickness

Question 23

is usually made twice the
thickness that would give the desired life.

Answer 23

Wall thickness

Question 24

Wall thickness must meet the mechanical
requirements such as

Answer 24

pressure, weight, and stress
considerations

Question 25

________rather than rivet tanks and other containers

Answer 25

Wield

Question 26

Design tanks and other containers for

Answer 26

easy draining, easy cleaning

Question 27

Provide for __________ with dry air or inert gas if vessels "inhale" moist marine atmosphere while being emptied.

Answer 27

blanketing

Question 28

heterogeneity must be _____

Answer 28

avoided

Question 29

Design to ______ air

Answer 29

exclude

Question 30

As a result of laboratory experiments in salt water, __________ that copper could be successfully protected against corrosion by coupling it to iron or zinc

Answer 30

Sir Humphry Davy 1824

Question 31

is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell

Answer 31

Cathodic protection

Question 32

achieved by supplying electrons to the metal structure to be protected

Answer 32

Cathodic protection

Question 33

f current is considered to flow from ( + ) to ( -' ), as in conventional electrical theory, then a structure is protected _______________

Answer 33

if current enters it from the electrolyte

Question 34

Types of cathodic protection

Answer 34

Galvanic/Sacrificial Impressed current method

Question 35

This type of CP uses a more reactive metal (the sacrificial anode) that corrodes preferentially to the metal structure (the cathode) that needs to be protected

Answer 35

Galvanic/Sacrificial

Question 36

_______protecting the underlying metal will continue to degrade over time until the sacrificial anode is no longer capable of supplying protection.

Answer 36

sacrificial anode

Question 37

Sacrificial metals used for cathodic protection consist of

Answer 37

magnesium-base and aluminum-base alloys and, to a lesser extent, zinc

Question 38

serve essentially as sources of portable electrical energy

Answer 38

sACRIFICIAL ANODES

Question 39

The open - circuit potential difference of magnesium with respect to steel is about

Answer 39

1V (1.3 if in seawater)

Question 40

The potential of zinc is less than that of magnesium

Answer 40

-0.8V in seawater

Question 41

as a sacrifi cial anode is that it tends to become passive in water or in soils with accompanying shift of potential to a value approaching that of steel

Answer 41

aluminum

Question 42

Advantages of galvanic/sacrificial method

Answer 42

No external power source is required so it can be used remotely. It has a lower installation cost. Minimum maintenance is required. Systems seldom cause adverse effects (interference) on their structure

Question 43

Disadvantages of galvanic/sacrificial method

Answer 43

There is limited driving potential and current output. It can be ineffective in high resistivity environments. It is not generally applicable for poorly coated structures. The life of the anodes tends to be relatively short, depending on load. Its existence is easily forgotten by maintenance personne

Question 44

This type of CP uses an external power source (impressed current) to provide the electrons required to cathodically protect the structure.

Answer 44

IMPRESSED CURRENT METHOD

Question 45

The negative terminal of the power supply is connected to the __________, and the positive to an inert anode such as ________

Answer 45

tank, graphite or Duriron

Question 46

The anode usually surrounded by ____________, which improves electric contact between the anode and the surrounding soil.

Answer 46

backfill consisting of coke breeze, gypsum, or bentonite

Question 47

Aggressive corrosives such as hot acids require prohibitively___________currents, whereas much lower currents are needed to protect steel in less severe environments (concrete)

Answer 47

high

Question 48

FACTORS THAT INFLUENCE CURRENT REQUIREMENTS

Answer 48

Environment Coating

Question 49

Pipes with ________ require much lower currents since the only areas requiring protection are defects or "holidays" in the protective layer

Answer 49

organic coating

Question 50

Of the sacrificial anodes, _________ is the most widely used.

Answer 50

magnesium

Question 51

are the most widely used anode materials for impressed anodes.

Answer 51

Steel, graphite, and silicon-iron

Question 52

Practical application of anodic protection and use of the potentiostat was first suggested by

Answer 52

Edeleanu.

Question 53

n is the formation of a protective film on metals by externally applied anodic currents

Answer 53

Anodic protection

Question 54

achieved by exhibiting an active-passive behavior in order to form a passive film

Answer 54

Anodic protection

Question 55

Anodic protection is an ____ for maintaining passive a metal with an active–passive behavior when placed in an aggressive environment

Answer 55

electrochemical technique

Question 56

It is an electronic device that maintains a metal at a constant potential with respect to a reference electrode in order to anodically protect a structure

Answer 56

potentiostat

Question 57

The terminals of a potentiostat is

Answer 57

connected to the tank, auxiliary cathode, reference electrode.

Question 58

Advantages of anodic protection

Answer 58

Applicability in extremely corrosive environments. Low current requirements

Question 59

Limitation of anodic protection

Answer 59

Only applicable to passive metals and alloys

Question 60

known for its excellent corrosion resistance properties, particularly against corrosive environments like sulfuric acid.

Answer 60

Type 316 SS

Question 61

Type 316 SS contains _______, which enhances its resistance to pitting and crevice corrosion, making it suitable for such harsh environments.

Answer 61

molybdenum