lecture8 - corrosion prevention and control
Post on 05-Apr-2018
227 Views
Preview:
TRANSCRIPT
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
1/33
Corrosion Prevention and Control
Degradation of Materials
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
2/33
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
3/33
Primary and Secondary Mechanisms
Primary Corrosion Mechanism
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
4/33
Primary and Secondary Mechanisms
Secondary Corrosion Mechanism
Contributions from people, designers,
manufacturers
Influence of a remote subsystem: effect of ac/dc Unpredictability in the environment
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
5/33
Corrosion Prevention
Materials Selection
Design Factors
Life Prediction Analysis
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
6/33
Materials Selection
Cost Availability
Raw materials
Quantity
Production costs
Labor requirements
Anticipated service
life
Made to order
Bought from
manufacturer
Available off the
shelf
Tooling required
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
7/33
Materials Selection
Material Properties
Mechanical: hardness,creep, fatigue, stiffness,
compression, shear,impact, tensile, wear
Physical
Electrical
Magnetic
Thermal
Chemical
Corrosion resistance
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
8/33
Design-Related Causes
Use of dissimilar metal
Poor drainage
Presence of crevices
Relative motion between two interacting parts orbetween a metal and the environment
Selective leaching of a metal in an alloy
Inability to clean the surface thoroughly
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
9/33
Design Considerations
Environment
Stress
Shape
Compatibility Movement
Temperature
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
10/33
Environment
Natural Chemical
Air
Waters
Soils
Urban and industrial
atmospheres
Environmental
pollutants
Chemical plant
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
11/33
Environment
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
12/33
Stress
Static Fluctuating
Stress Corrosion
Cracking
Corrosion Fatigue
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
13/33
Stress
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
14/33
Shape
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
15/33
Compatibility
Within the metal
Within the environment
Contact with other materials
Welds
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
16/33
Compatibility
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
17/33
Movement
Flowing fluids
Parts moving in the fluid
Two-phase and multi-phase fluids
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
18/33
Temperature
Environmental factors
Sources of heat
Condensation
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
19/33
Corrosion Protection
Choice of Materials
Addition of Inhibitors
Use of Protective Coatings
Cathodic and Anodic Protection
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
20/33
Addition of Inhibitors Purpose:
Suppress the corrosion reaction
Produce a competent corrosion product
Example Chemicals:
Zinc/polyphosphates Chromates
Phosphonates
Polymers
Nitrates Vanadates
Arsenates
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
21/33
Addition of Inhibitors
Cathodic Inhibitors Anodic Inhibitors
Inhibit the hydrogen
evolution in acidic
solution or reductionof oxygen in neutral or
alkaline solution
Effective in the pH
range 6.5-10.5
Increase in potential
to reach passivation
region; dependent on
concentration of
inhibitor
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
22/33
Protective CoatingsApplication of PAINTS as protective barriers PAINTS
Source of insulation of the metal from the corrosiveenvironment
HOW TO ACHIEVE CORROSION CONTROL BYCOATING? Barrier coating mitigates current transfer between
anode and cathode
Cathodic protection as in the case of Zn-containingpigments
Inhibitive primer which forms passive films or layers
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
23/33
Composition of Paints
Vehicle: liquid that gives the paint its fluidity anddries or evaporates to form a solid film
Pigment: suspended in the vehicle, the pigment
controls the corrosion rate or the rate of diffusion
of the reactants through the dry film
Additives or Fillers: these accelerate the drying
process or better enable the dry coating to
withstand the working environment
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
24/33
Protective Coatings
Barrier coatings must be: Impermeable to ionic species
Impermeable to oxygen
Able to maintain adhesion under wet conditions
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
25/33
Metallic Coatings
provide enhanced corrosion resistance of metalsas either barrier coatings or sacrificial coatings
Durable, usually easy to form but sometimes
porous
Examples: Nickel, lead, zinc, copper, cadmium,
tin, chromium
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
26/33
Inorganic Coatings
inorganic, nonmetallic coatings that act as abarrier between the corrosive environment and
the base material being protected
Oxide film
Useful for providing high temperature corrosion
protection
Examples: chromate films, phosphate coatings
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
27/33
Cathodic Protection
Two Types: Impressed Current
Sacrificial Anode
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
28/33
Cathodic Protection
Impressed Current
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
29/33
Cathodic Protection
Impressed Current
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
30/33
Cathodic Protection
Sacrificial Anode
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
31/33
Cathodic Protection
Sacrificial Anode
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
32/33
Anodic Protection
Make metal an anode and drive it into its passiveregion
Applicable only to metals which exhibit an active-
passive behavior such as Cr, N, Fe, Ti, Al and
alloys containing these elements
-
7/31/2019 Lecture8 - Corrosion Prevention and Control
33/33
Cathodic vs. Anodic Protection
top related