CORROSION

Question 1

when atomic hydrogen (H) penetrates into the material.

Answer 1

HYDROGEN EMBRITTLEMENT

Question 2

are necessary to
cause hydrogen embrittlement

Answer 2

Tensile stresses, susceptible material, and the presence of hydrogen

Question 3

How to prevent hydrogen embrittlement?

Answer 3

Control of stress level (residual or load) and hardness. • Avoid the hydrogen source. • Baking to remove hydrogen.

Question 4

best measure to take to reduce or completely eliminate stress corrosion

Answer 4

lower the magnitude of the stress

Question 5

termed stress corrosion cracking

Answer 5

STRESS CORROSION

Question 6

results from the combined
action of an applied tensile stress and a corrosive environment; both

Answer 6

STRESS CORROSION

Question 7

stainless steels stress corrode in solutions containing

Answer 7

chloride ions,

Question 8

brasses are especially vulnerable when exposed to

Answer 8

ammonia.

Question 9

arises from the combined action of chemical attack and mechanical
abrasion or wear as a consequence of fluid motion.

Answer 9

EROSION CORROSION

Question 10

commonly found in piping,

Answer 10

EROSION CORROSION

Question 11

Propellers, turbine blades, valves, and pumps are also susceptible to this form of corrosion

Answer 11

EROSION CORROSION

Question 12

One of the best ways to reduce erosion corrosion

Answer 12

change the design to eliminate
fluid turbulence and impingement effects.

Question 13

found in solid solution alloys and occurs when one element or
constituent is preferentially removed as a consequence of corrosion processes.

Answer 13

SELECTIVE LEACHING

Question 14

Dealloying, selective leaching and graphitic corrosion can be prevented through the
following methods

Answer 14

Select metals/alloys that are more resistant to dealloying
• Control the environment to minimize the selective leaching

Use sacrificial anode cathodic protection or impressed current cathodic protection

Question 15

occurs preferentially along grain
boundaries for some alloys and in specific environments.

Answer 15

INTERGRANULAR CORROSION

Question 16

This type of corrosion is especially prevalent in some stainless steels.

Answer 16

INTERGRANULAR CORROSION

Question 17

Stainless steels may be protected from intergranular corrosion by the following
measures:

Answer 17

sensitized material to a high-temperature heat treatment in which all the chromium carbide particles are re dissolved,

Question 18

another form of much localized corrosion attack in which small pits or holes
form.

Answer 18

PITTING CORROSION

Question 19

It is an extremely insidious type of corrosion, often going undetected and with very little material loss until failure occurs.

Answer 19

PITTING CORROSION

Question 20

Pitting corrosion can be prevented through:

Answer 20

Proper selection of materials with known resistance to the service environment • Control pH, chloride concentration and temperature • Cathodic protection and/or Anodic Protection • Use higher alloys (ASTM G48) for increased resistance to pitting corrosion

Question 21

to prevent crevice corrosion

Answer 21

Use welded butt joints instead of riveted or bolted joints in new equipment • Eliminate crevices in existing lap joints by continuous welding or soldering • Avoid creating stagnant conditions and ensure complete drainage in vessels • Use solid, non-absorbent gaskets such as Teflon. • Use higher alloys (ASTM G48) for increased resistance to crevice corrosion

Question 22

The major factors influencing crevice corrosion are:

Answer 22

crevice type: metal-to-metal, metal-to-non-metal • crevice geometry: gap size, depth, surface roughness • material: alloy composition (e.g. Cr, Mo), structure • environment: pH, temperature, halide ions, oxygen

Question 23

consequence of concentration differences
of ions or dissolved gases in the electrolyte solution and between two regions of the same metal piece.

Answer 23

Electrochemical corrosion

Question 24

solution becomes stagnant and there is localized depletion of dissolved oxygen.

Answer 24

Crevice corrosion

Question 25

prevent galvanic corrosion

Answer 25

• Avoid threaded joints for materials far apart in the galvanic series.

Question 26

alloys near the top of galvanic series

Answer 26

Cathodic and unreactive

Question 27

alloys bottom of galvanic series

Answer 27

Anodic

Question 28

occurs when two metals or alloys having different compositions are electrically coupled while exposed to an electrolyte.

Answer 28

Galvanic corrosion occurs

Question 29

experiences corrosion in galvanic

Answer 29

less noble or more reactive metal

Question 30

Inert metal protected from from corossion

Answer 30

Inert metal, cathode

Question 31

prevent uniform corrosion?

Answer 31

Use thicker materials for corrosion allowance • Use paints or metallic coatings such as plating, galvanizing or anodizing • Use Corrosion inhibitors or modifying the environment • Cathodic protection (Sacrificial Anode or Impressed Current -ICCP) and Anodic Protection

Question 32

is a form of electrochemical corrosion that occurs with equivalent intensity over the entire exposed surface and often leaves behind a scale or deposit.

Answer 32

UNIFORM ATTACK

Question 33

reactions occur randomly over the surface.

Answer 33

UNIFORM ATTACK

Question 34

most common form of corrosion

Answer 34

UNIFORM ATTACK

Question 35

is defined as the destructive and unintentional attack on a metal;

Answer 35

Corrosion

Question 36

Metallic corrosion is sometimes classified into eight forms:

Answer 36

uniform, galvanic, crevice, pitting, intergranular, selective leaching, erosion-corrosion, and stress corrosion.