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Alawi_CHEMISTRY > Module 2: Chapter 7-11 > Flashcards

Module 2: Chapter 7-11 Flashcards

1
Q

two dissimilar metals are in closed vicinity & exposed to aqueous solution

A

GALVANIC CORROSION

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2
Q

ion transfer is high

A

GALVANIC CORROSION

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3
Q

PREVENTION OF GALVANIC CORROSION

*CCSSUE**

A
  1. Cathodic protection - sacrificial metal - ZINC
  2. Choose relative surface area, anodic metal > cathodic metal
  3. Separate dissimilar metals w/ non-conducting material
  4. Separate metals from conductive environment
  5. Use of poorly conducting electrolytes (water w/ no impurities)
  6. Eliminate metallic ions - (hastens corrosion)
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4
Q

Crevice corrosion is a type of

A

PITTING CORROSION

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5
Q

2 Types of Stress Corrosion Cracking

A
  1. Chloride Stress Corrosion Cracking
  2. Caustic Stress Corrosion Cracking
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6
Q

occurs where the anodic site becomes fixed in small area

A

PITTING

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6
Q

the formation of holes (deep attack) in an unaffected area due to localized (high and low) oxygen concentration

A

PITTING

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6
Q

It causes the corrosion cells, changing as surface and solution differences change

A

GENERAL OVERALL CORROSION

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6
Q

Presence of ____ promote pitting at areas of metal surface that are initially anodic w/ respect to adjacent area

A

OXYGEN

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6
Q

If the cells do not shift _____ results

A

PITTING

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7
Q

A ___ stainless steel tube and tube sheet of HEX suffered crevice corrosion due to its gap

A

TYPE 316

SWRO Desalination Plant

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7
Q

confined space w/c access of working fluid is limited (low)

A

CREVICE

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7
Q

It refers to localized attack on metal surface, adjacent to the gap or crevice between 2 joining surfaces

A

CREVICE CORROSION

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8
Q

___ cause pitting of iron and steel

A

CHLORIDE IONS

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9
Q

cause HIGHLY LOCALIZED DEFECTS in the passivating oxide layer on metal

A

CHLORIDE IONS

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10
Q

The ___ ___ will then be very large at anodic site and attack on metal will be rapid.

A

current density

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11
Q

attack wherein part of metal surface is in shielded or restricted environment, compared to the rest that is exposed to electrolyte

A

CREVICE CORROSION

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12
Q

a HAZARD due to rapid penetration of metal with little overall loss of mass

A

PITTING CORROSION

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13
Q

WAYS TO MINIMIZE PITTING CORROSION

AUADR

A
  1. Avoid stagnant conditions
  2. Use correct metals and alloys (less susceptible to corrosion)
  3. Avoid agents in medium that causes pitting
  4. Design system and components that has no crevices
  5. Remove dissolved gases and chlorides (corrodants)
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14
Q

PREVENTION CHEMISTRY CONTROL

PPCRP

A
  1. PASSIVATION - Pre-treatment/Pickling
  2. PASSIVATION - Passivators and Inhibitors
  3. Cathodic Protection
  4. Removing Corrosive Agents (Corrodants)
    -Mechanical
    -Chemical Addition
  5. pH Correction
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15
Q

involves careful control of coolant water chemistry and temperature during ____

A

PRE-TREATMENT/PICKLING

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16
Q

when a naturally active metal corrodes at very low rate due to oxide coating

A

PASSIVATION

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17
Q

chemical substances that are added to water to provide passivation by undergoing reduction at metal surface

A

PASSIVATORS OR INHIBITORS

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18
Q

common passivator

A

Pottasium Chromate (K2CRO4)

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19
Q

Other passivators

A

Erythorbic Acid (C6H806)
EDTA (Ethylenediaminetetraacetic Acid)

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20
Q

Cathodic protection by external current application

A

Impressed Current Cathodic Protection method

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21
Q

cathodic protection wherein an external electric current is applied to iron

A

IMPRESSED CURRENT

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22
Q

use of sacrificial anode

A

SACRIFICIAL ANODE METHOD

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23
Q

2 TYPES OF CATHODIC PROTECTION

A
  1. IMPRESSED CURRENT
  2. SACRIFICIAL ANODE
24
Q

iN WHAT PROCESS where corrodants are removed to reduce/eliminate the dissolved O, CO, dissolved solids, and insoluble solids

A

MECHANICAL MEANS/PROCESS
METHODS
-USE DAEARATORS
-FILTRATION AND DEMINERALIZATION

25
Q

use of
O scavenger (hydrazine N2H4)
CO2 scavenger (morpholine C4H9NO)

A

pH Correction - Chemical Addition

26
Q

Use of
1. Filming amines
2. phosphates
3. hydroxides
4. acids

to remove water hardness and adjust pH

A

pH Correction

27
Q

compounds that adjust pH and address water hardness

A

Trisodium phosphate (Na3PO4)
Disodium phosphate (Na2HPO4)

28
Q

Why use iron?

A

Cheap and Abundant

29
Q

how many % of earth’s crust and nearly all of earth’s core contains iron

A

5.6%

30
Q

how many % of metal contain iron

A

90%

31
Q

Alloy of iron (solvent) and carbon (solute)

A

STEEL

32
Q

4 TYPES OF STEEL

A

CAST

CARBON, ALLOY, STAINLESS, TOOL

33
Q

main alloy element is carbon, dependent on % of carbon present

A

CARBON STEEL

34
Q

0.04% to 0.30% CARBON

A

LOW CARBON STEEL (MILD STEEL)

35
Q

MEDIUM CARBON STEEL

A

0.31 - 0.60%

36
Q

0.61% to 1.5% Carbon

A

HIGH CARBON STEEL

37
Q

carbon steel that needs to be improved its properties (hardness, corrosion, resistance, retention of hardness and strength)

A

ALLOY STEEL

38
Q

Low Alloy Steel - other elements less than 4%

High Alloy Steel - “ “ more than 8%

A

Alloy Steel

39
Q

contains 10-20% Cr

A

Stainless Steel

40
Q

200x corrosion resistant to Gen. Corrosion than mild steel

A

STAINLESS STEEL

41
Q

SS SUBCATEGORIES

A

AFMDP

Austenitic
Ferritic
Martensitic
Duplex
Precipitation Hardening

42
Q

steels well-suited for tools

A

TOOL STEEL

43
Q

SUBCATEGORIES OF TOOL STEEL

WCHHSS

A

WATER HARDENING
COLD WORKING
HOT WORKING
HIGH SPEED
SPECIAL PURPOSE
SHOCK RESISTING

44
Q

It is the growth of crack formation in a corrosive environment subjected to tensile stress

A

STRESS CORROSION CRACKING

45
Q

Pure metals/iron is immune to what attack?

A

STRESS CORROSION CRACKING

46
Q

victims of SSC

A

alloyed metals - steel

47
Q

use for inspection of steel pipeline

A

magnetic particle inspection

48
Q

it is a result of an arrangement of atoms during solidification

A

CRYSTALLINE STRUCTURE

49
Q

SC
BCC
FCC

A

SIMPLE CUBE
BODY CENTERED CUBE
FACE CENTERED CUBE

50
Q

is a intergranular attack corrosion that occurs at grain boundaries under t.stress

A

STRESS C. CRACKING

51
Q

interface between two grains or crystallites in a polycrystalline material

A

GRAIN BOUNDARY

52
Q

defects in the crystal structure

A

GRAIN BOUNDARY

53
Q

it occurs in susceptible alloys

A

STRESS CORROSION CRACKING

54
Q

caused by chemisorption

A

SCC

55
Q

kind of adsorption w/c involves a chemical reaction between the surface and the adsorbate

A

CHEMISORPTION

56
Q

adhesion of atoms, ions, molecules. This creates a film of the adsorbate on surface of adsorbent

A

ADSORPTION

57
Q

formation of compound between metal atoms on surface as monomolecular layer of chemisorbed substance

A

CHEMISORPTION

58
Q

Susceptible Materials of Chloride SCC

A

Stainless Steel
High Carbon Steel
High Alloy Steel

59
Q

Susceptible Materials of Caustic SCC

A

Carbon S.
Alloy S.
Stainless S.
Tool S.

60
Q

3 Conditions for SCC to occur

A
  1. Chloride ions are present in envi
  2. Dissolved oxygen is present in envi
  3. Metal is under t. stress
61
Q

extensively used in power plants

A

stainless steel

62
Q

Environments containing O2 and Cl- ions can readily be created in _____

A

auxiliary water systems

63
Q

it enters via leaks in condensers and when there is cooled by unpurified cooling water

A

Cl- ions

64
Q

dissolved __ enter with feed and makeup water

A

O2

Alawi_CHEMISTRY (5 decks)

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