/
AI Flashcards
Save to my account
Sign up
AI Flashcards
Corrosion Control Methods
Study
1
Question
What is meant by 'Material Selection' as a corrosion control method?
Page 1
Answer
Choosing materials that resist corrosion, such as corrosion-resistant alloys or non-metallic materials (plastics, ceramics, composites), to minimize or prevent corrosion.
2
Question
Give two common coating approaches used to protect metals from corrosion.
Page 1
Answer
1) Applying a corrosion-resistant metal layer (cladding), e.g., galvanizing steel with zinc. 2) Applying organic coatings such as paints and epoxy coatings.
3
Question
What is the basic principle of cathodic protection?
Page 1
Answer
Preventing corrosion by making the protected metal the cathode of an electrochemical cell, either by attaching a more anodic metal or by applying an external current to counteract the electrochemical potential.
4
Question
How does the sacrificial anode method work and give an example?
Page 1
Answer
A more anodic (electrochemically active) metal is attached to the structure so the anode corrodes instead of the protected metal; example: zinc anodes used to protect steel structures in seawater.
5
Question
What is impressed current cathodic protection (ICCP)?
Page 1
Answer
A cathodic protection method that uses an external power source to apply a small electrical current which counteracts the electrochemical potential and prevents corrosion of the protected metal.
6
Question
What is anodic protection and when is it suitable?
Page 1
Answer
Anodic protection maintains the metal surface at a specific electrochemical potential where a passive protective film forms, reducing corrosion rate; suitable for metals like stainless steel and some carbon steels in certain acidic environments.
7
Question
Why do crevices and sharp corners promote localized corrosion?
Page 1
Answer
Crevices and sharp corners trap moisture and aggressive ions, creating stagnant microenvironments that promote localized corrosion.
8
Question
What design modification can reduce crevice formation and thus localized corrosion?
Page 1
Answer
Using rounded designs and avoiding sharp corners to prevent trapping of moisture and aggressive ions.
9
Question
How does ensuring proper drainage and ventilation help control corrosion?
Page 1
Answer
Proper drainage and ventilation prevent stagnant moisture accumulation, which reduces conditions that favor corrosion.
10
Question
Why might designers use thicker materials to mitigate corrosion?
Page 1
Answer
Designing components with increased thickness provides extra material to compensate for expected corrosion losses over time, extending service life.
11
Question
Name three environmental control strategies used to reduce corrosion.
Page 1
Answer
1) Reducing exposure to corrosive agents (moisture, salts, industrial pollutants). 2) Dehumidification to control humidity in storage or operation. 3) Temperature control—lowering temperatures to decrease corrosion rates in many metals.
12
Question
How does dehumidification reduce the rate of atmospheric corrosion?
Page 1
Answer
By lowering and controlling the humidity in storage or operational environments, it reduces the availability of moisture required for electrochemical corrosion processes.
13
Question
Why is lowering temperature effective at decreasing corrosion rates for many metals, especially at high temperatures?
Page 1
Answer
Lower temperatures generally slow the chemical and electrochemical reaction rates that drive corrosion, making corrosion processes less aggressive, particularly where high-temperature corrosion mechanisms are active.
14
Question
What is shot peening (as a surface treatment)?
Page 2
Answer
Shot peening is a process that involves blasting the metal surface with small beads to create compressive stress on the surface.
15
Question
How does the compressive stress produced by shot peening affect corrosion resistance?
Page 2
Answer
The compressive stress produced on the metal surface from shot peening can improve corrosion resistance by altering surface stresses (reducing tensile stresses that promote crack initiation and corrosion progression).
16
Question
What is passivation in the context of metal surface treatment?
Page 2
Answer
Passivation is treating metals (such as stainless steel) with acid to remove free iron from the surface and form a protective oxide layer.
17
Question
Specifically, how does passivation protect stainless steel surfaces?
Page 2
Answer
Passivation removes free iron from the stainless steel surface and promotes formation of a protective oxide layer that shields the metal from further corrosion.
18
Question
What are chemical corrosion inhibitors?
Page 2
Answer
Chemical corrosion inhibitors are chemicals added to the environment that reduce the corrosion rate by forming a protective film on the metal surface or by neutralizing corrosive agents.
19
Question
What are the two main ways chemical inhibitors reduce corrosion?
Page 2
Answer
• Forming a protective film on the metal surface • Neutralizing corrosive agents in the environment
20
Question
How are chromates used as corrosion inhibitors in water systems (example from the text)?
Page 2
Answer
Chromates are added to water systems as chemical inhibitors that help reduce corrosion, typically by contributing to formation of a protective film or by neutralizing corrosive agents.
21
Question
How are phosphates used as corrosion inhibitors in water systems (example from the text)?
Page 2
Answer
Phosphates are added to water systems as chemical inhibitors that help reduce corrosion by forming protective films on metal surfaces or neutralizing corrosive species.
22
Question
What are volatile corrosion inhibitors (VCIs)?
Page 2
Answer
Volatile Corrosion Inhibitors (VCIs) are chemicals that vaporize and form a protective layer on metal surfaces via the vapor phase.
23
Question
How do VCIs protect metal surfaces?
Page 2
Answer
VCIs vaporize and the vapor deposits on metal surfaces to form a protective layer that inhibits corrosion.
24
Question
In what common application are VCIs often used, according to the text?
Page 2
Answer
VCIs are often used in packaging for metal parts to protect the parts from corrosion during storage and transport.
25
Question
What is a practical distinction between chemical inhibitors and volatile corrosion inhibitors (VCIs)?
Page 2
Answer
Chemical inhibitors are added directly to the environment (for example, dissolved in water systems) to form protective films or neutralize corrosives, whereas VCIs vaporize and protect metal surfaces by depositing a vapor-phase protective layer (commonly used in packaging).
26
Question
Which surface treatment from the text specifically uses acid to alter the metal surface, and what does it achieve?
Page 2
Answer
Passivation uses acid to treat the metal surface; it removes free iron and promotes formation of a protective oxide layer on the metal.