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Alawi_CHEMISTRY > Module 2: Chapter 7-11 > Flashcards

Module 2: Chapter 7-11 Flashcards

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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
Other passivators
Erythorbic Acid (C6H806) EDTA (Ethylenediaminetetraacetic Acid)
20
Cathodic protection by **external current** application
Impressed Current Cathodic Protection method
21
cathodic protection wherein an **external electric current** is applied to iron
IMPRESSED CURRENT
22
use of sacrificial anode
SACRIFICIAL ANODE METHOD
23
2 TYPES OF CATHODIC PROTECTION
1. IMPRESSED CURRENT 2. SACRIFICIAL ANODE
24
iN WHAT PROCESS where corrodants are removed to reduce/eliminate the dissolved O, CO, dissolved solids, and insoluble solids
MECHANICAL MEANS/PROCESS METHODS -USE DAEARATORS -FILTRATION AND DEMINERALIZATION
25
use of O scavenger (**hydrazine N2H4**) CO2 scavenger (**morpholine C4H9NO**)
pH Correction - Chemical Addition
26
Use of 1. Filming amines 2. phosphates 3. hydroxides 4. acids to remove **water hardness** and adjust pH
pH Correction
27
compounds that adjust pH and address water hardness
Trisodium phosphate (Na3PO4) Disodium phosphate (Na2HPO4)
28
Why use iron?
Cheap and Abundant
29
how many % of earth's crust and nearly all of earth's core contains iron
5.6%
30
how many % of metal contain iron
90%
31
Alloy of iron (solvent) and carbon (solute)
STEEL
32
4 TYPES OF STEEL
**CAST** CARBON, ALLOY, STAINLESS, TOOL
33
main alloy element is carbon, dependent on % of carbon present
CARBON STEEL
34
0.04% to 0.30% CARBON
LOW CARBON STEEL (MILD STEEL)
35
MEDIUM CARBON STEEL
0.31 - 0.60%
36
0.61% to 1.5% Carbon
HIGH CARBON STEEL
37
carbon steel that needs to be improved its properties (hardness, corrosion, resistance, retention of hardness and strength)
ALLOY STEEL
38
Low Alloy Steel - other elements less than 4% High Alloy Steel - " " more than 8%
Alloy Steel
39
contains 10-20% Cr
Stainless Steel
40
200x corrosion resistant to Gen. Corrosion than mild steel
STAINLESS STEEL
41
SS SUBCATEGORIES
**AFMDP** Austenitic Ferritic Martensitic Duplex Precipitation Hardening
42
steels well-suited for tools
TOOL STEEL
43
SUBCATEGORIES OF TOOL STEEL WCHHSS
WATER HARDENING COLD WORKING HOT WORKING HIGH SPEED SPECIAL PURPOSE SHOCK RESISTING
44
It is the growth of **crack** formation in a corrosive environment subjected to tensile stress
STRESS CORROSION CRACKING
45
Pure metals/iron is immune to what attack?
STRESS CORROSION CRACKING
46
victims of SSC
alloyed metals - steel
47
use for inspection of steel pipeline
magnetic particle inspection
48
it is a result of an arrangement of atoms during solidification
CRYSTALLINE STRUCTURE
49
SC BCC FCC
SIMPLE CUBE BODY CENTERED CUBE FACE CENTERED CUBE
50
is a **intergranular attack corrosion** that occurs at grain boundaries under t.stress
STRESS C. CRACKING
51
interface between two grains or crystallites in a polycrystalline material
GRAIN BOUNDARY
52
defects in the crystal structure
GRAIN BOUNDARY
53
it occurs in susceptible alloys
STRESS CORROSION CRACKING
54
caused by chemisorption
SCC
55
kind of adsorption w/c involves a chemical reaction between the surface and the adsorbate
CHEMISORPTION
56
adhesion of atoms, ions, molecules. This creates a film of the adsorbate on surface of adsorbent
ADSORPTION
57
formation of compound between metal atoms on surface as monomolecular layer of chemisorbed substance
CHEMISORPTION
58
Susceptible Materials of Chloride SCC
Stainless Steel High Carbon Steel High Alloy Steel
59
Susceptible Materials of Caustic SCC
Carbon S. Alloy S. Stainless S. Tool S.
60
3 Conditions for SCC to occur
1. Chloride ions are present in envi 2. Dissolved oxygen is present in envi 3. Metal is under t. stress
61
extensively used in power plants
stainless steel
62
Environments containing O2 and Cl- ions can readily be created in _____
auxiliary water systems
63
it enters via leaks in condensers and when there is cooled by unpurified cooling water
Cl- ions
64
dissolved __ enter with feed and makeup water
O2

Alawi_CHEMISTRY (5 decks)

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