6 - Corrosion Prevention Techniques

Question 1

Excellent corrosion and high
temperature resistance. Brittle and has lower tensile
strength

Answer 1

Ceramics

Question 2

Weaker, softer, and more
resistant to chloride ions but
less resistant to strong sulfuric
acid and oxidizing acids

Answer 2

Rubbers and Plastics

Question 3

Good corrosion resistance,
electric and heat conductivity. Fragile

Answer 3

Carbon

Question 4

Corrosion resistance of pure metal =
better vs corrosion resistance of metal
with impurities

Answer 4

METAL PURIFICATION

Question 5

Not expensive in a fairly pure state
(99.5% pure). Used for handling hydrogen peroxide

Answer 5

Aluminum

Question 6

Generic name for a series of more than
30 different alloys. Does not resist all corrosives. Natural metal-corrosive combination.

Answer 6

Stainless steel

Question 7

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

Answer 7

Arc-melted Zirconium

Question 8

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

Answer 8

CATHODIC PROTECTION

Question 9

He said copper could be successfully protected
against corrosion by coupling it to iron
or zinc in 1824

Answer 9

Humphry Davy

Question 10

Uses a more reactive metal (sacrificial
anode) that corrodes preferentially to
the metal structure (cathode) that
needs to be protected

Answer 10

Galvanic or Sacrificial Anode
Method

Question 11

CATHODIC PROTECTION ADVANTAGES

Answer 11

• No external power source required so it
  can be used remotely
• Lower installation cost
• Minimum maintenance is required
• Systems seldom cause adverse effects
  on their structure

Question 12

CATHODIC PROTECTION DISADVANTAGES

Answer 12

• Limited driving potential and current
  input
• Can be ineffective in high resistivity
  environments
• Not generally applicable for poorly
  coated structures
• Life of anodes are relatively short
  depending on the load
• Existence can easily be forgotten by
  maintenance personnel

Question 13

External power supply is connected to
an underground tank. The negative
terminal of the power supply is
connected to the tank, and the positive
to an inert anode such as graphite or
Duriron.

Answer 13

Impressed Current Method

Question 14

Impressed Current Method ADVANTAGES

Answer 14

• There is a larger driving voltage
• More flexible control of voltage and
  current
• Applicable to uncoated parts, high
  resistivity environments, large objects,
  etc.

Question 15

Impressed Current Method DISADVANTAGES

Answer 15

• Higher installation and maintenance
  costs for small systems
• Can cause adverse effects on nearby
  structures

Question 16

Aggressive corrosives require prohibitively high currents;
lower currents are needed to protect
steel in less severe environments. What is this called?

Answer 16

PROTECTIVE CURRENTS

Question 17

FACTORS THAT INFLUENCE CURRENT
REQUIREMENTS

Answer 17

• Environment
• Coating

Question 18

Achieved by exhibiting an active
passive behavior to form a passive film

Answer 18

ANODIC PROTECTION

Question 19

Practical application and use of
potentiostat was first suggested by

Answer 19

Edeleanu

Question 20

ANODIC PROTECTION ADVANTAGES

Answer 20

• Applicable in extremely corrosive
  environments
• Low current requirements

Question 21

ANODIC PROTECTION DISADVANTAGES

Answer 21

• Only applicable to passive metals and
  alloys

Question 22

Electronic device that maintains a
metal at a constant potential with
respect to a reference electrode in
order to anodically protect a structure

Answer 22

POTENTIOSTAT

Question 23

What are the terminals of Potentiostat?

Answer 23

o Connected to the tank,
o Auxiliary cathode,
o Reference electrode

Question 24

Can be accurately and rapidly determined by electrochemical measurements

Answer 24

Anodic protection

Question 25

Must usually be determined by empirical testing

Answer 25

Cathodic protection

Question 26

Range of corrosive is from weak to aggressive

Answer 26

Anodic protection

Question 27

Range of corrosive is from weak to moderate

Answer 27

Cathodic protection