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

1
Q

The most common method of preventing
corrosion is the

A

selection of proper metal
or alloy

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2
Q

Not stainless; Not the most
corrosion-resistant material

A

stainless steel

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3
Q

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.

A

stainless steel

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4
Q

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

A

they do not resist all corrosives.

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5
Q

stainless steel are
less resistant than ordinary structural steel:

A

Chloride-containing medium
Stressed structures

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6
Q

also more susceptible
to localized corrosion than ordinary
structural steels

A

Stainless steel

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7
Q

Frequently, the quality of stainless steel is checked

A

with a magnet

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8
Q

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

A

nonmagnetic

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9
Q

There is ___________ between magnetic
susceptibility and corrosion resistance

A

no correlation

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10
Q

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

A

Indiscriminate selection of stainless steels

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11
Q

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

A

pure metal

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12
Q

are usually
expensive and relatively soft and weak

A

pure metals

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13
Q

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

A

Aluminum

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14
Q

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

A

ARC-MELTED ZIRCONIUM

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15
Q

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

A

Nonmetallics

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16
Q

The five general classes of nonmetallics
are

A

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

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17
Q

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

A

rubbers and plastics

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18
Q

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

A

ceramics

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19
Q

Good corrosion resistance,
electric and heat conductivity
Fragile

A

carbon

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20
Q

frequently as
important as the choice of materials of
construction.

A

design of a structure

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21
Q

Design should consider ________ together with an _____ for corrosion

A

mechanical and strength requirement, allowance

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22
Q

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

A

thickness

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23
Q

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

A

Wall thickness

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24
Q

Wall thickness must meet the mechanical
requirements such as

A

pressure, weight, and stress
considerations

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25
Q

________rather than
rivet tanks and
other containers

A

Wield

26
Q

Design tanks and
other containers for

A

easy draining, easy cleaning

27
Q

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

A

blanketing

28
Q

heterogeneity must be _____

A

avoided

29
Q

Design to ______ air

A

exclude

30
Q

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

A

Sir Humphry Davy 1824

31
Q

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

A

Cathodic protection

32
Q

achieved by
supplying electrons to the metal structure
to be protected

A

Cathodic protection

33
Q

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

A

if current enters it from the electrolyte

34
Q

Types of cathodic protection

A

Galvanic/Sacrificial
Impressed current method

35
Q

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

A

Galvanic/Sacrificial

36
Q

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

A

sacrificial anode

37
Q

Sacrificial metals used for cathodic protection consist of

A

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

38
Q

serve essentially as sources of
portable electrical energy

A

sACRIFICIAL ANODES

39
Q

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

A

1V (1.3 if in seawater)

40
Q

The potential of zinc is less
than that of magnesium

A

-0.8V in seawater

41
Q

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

A

aluminum

42
Q

Advantages of galvanic/sacrificial method

A

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

43
Q

Disadvantages of galvanic/sacrificial method

A

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

44
Q

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

A

IMPRESSED CURRENT METHOD

45
Q

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

A

tank, graphite or Duriron

46
Q

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

A

backfill
consisting of coke breeze, gypsum, or
bentonite

47
Q

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

A

high

48
Q

FACTORS THAT INFLUENCE CURRENT
REQUIREMENTS

A

Environment
Coating

49
Q

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

A

organic coating

50
Q

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

A

magnesium

51
Q

are the
most widely used anode materials for impressed anodes.

A

Steel, graphite, and silicon-iron

52
Q

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

A

Edeleanu.

53
Q

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

A

Anodic protection

54
Q

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

A

Anodic protection

55
Q

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

A

electrochemical technique

56
Q

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

A

potentiostat

57
Q

The terminals of a potentiostat is

A

connected to the tank,
auxiliary cathode,
reference electrode.

58
Q

Advantages of anodic protection

A

Applicability in extremely corrosive
environments.
Low current requirements

59
Q

Limitation of anodic protection

A

Only applicable to passive metals and
alloys

60
Q

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

A

Type 316 SS

61
Q

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

A

molybdenum