Corrosion and protection of steel structures Corrosion: Flashcards

1
Q

How much does corrosion cost per year to the US economy?

A

$ 276 billion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How much of an industrialised country GDP is spent on corrosion?

A

3.5%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How much of the annual world wide production of iron and steel is used to replace material lost through corrosion?

A

15%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is corrosion?

A

Degradation in properties and appearance and loss of material due to dissolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where does it occur?

A

Surface of material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the corrosion costs from Drinking Water and Sewer Systems?

A

$36 billion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the second biggest source for corrosion costs?

A

Motor vehicles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the direct losses from corrosion on the economy?

A
  • Component replacement
  • Painting and other preventative measures
  • Use of expensive corrosion-resistant materials
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the indirect losses from corrosion on the economy?

A
  • Plant shutdown
  • Loss of product e.g. in pipes
  • Loss of efficiency
  • Contamination of product
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What effect is the corrosion of metals?

A

Electrochemical effect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens in the chemical reaction?

A
  • Electrons are transferred
  • REDOX reaction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What occurs at the anode during metal corrosion?

A

During metal corrosion, metal atoms are oxidized at the anode, meaning they form positive ions and release electrons. This site is where the anodic reaction occurs and where corrosion typically happens.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

In the provided examples, what happens to iron (Fe) when it oxidizes?

A

When iron (Fe) oxidizes, it forms Fe2+ ions and releases 2 electrons (2e-)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does aluminum (Al) react in an oxidation reaction?

A

In an oxidation reaction, aluminum (Al) forms Al3+ ions and releases 3 electrons (3e-)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the oxidation state and number of electrons released when zinc (Zn) corrodes?

A

When zinc (Zn) corrodes, it forms Zn2+ ions and releases 2 electrons (2e-)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What happens during the corrosion of Zn in an acidic solution?

A

During the corrosion of Zn in an acidic solution, Zn corrodes into Zn2+ at the anode, and electrons are transferred to the cathode forming hydrogen gas, with H+ being reduced to hydrogen at the cathode.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does the nature of the cathodic reaction depend on?

A

Environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

When electrons formed what are he transferred to?

A

Electrons formed are transferred to another chemical species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Where is the H+ ions reduced?

A

Cathode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Where do electrons go to form hydrogen gas?

A

Cathode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How is iron oxide formed and why is it energetically favorable for iron to form rust?

A

Iron oxide, or rust, is formed when iron reacts with oxygen in wet conditions. It is energetically favorable for iron to form rust because iron found as iron oxide in iron ore tends to revert to the oxide as part of an electrochemical process.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What happens to iron extracted?

A

Tends to reform the oxide in an electrochemical process

23
Q

What initiates the process of rust formation on iron?

A

Rust formation is initiated when oxidizing iron supplies electrons at the edge of the water droplet to reduce oxygen from the air.

24
Q

What role does the iron surface inside the droplet play in rust formation?

A

The iron surface inside the droplet acts as the anode, where oxidation occurs as iron loses electrons.

25
Q

What happens to the electrons generated at the anode during the rust formation process?

A

Electrons generated at the anode move through the iron to the outside of the water droplet, where reduction occurs at the cathode.

26
Q

Describe the process that occurs within the droplet leading to the precipitation of iron(II) hydroxide.

A

Inside the droplet, hydroxide ions can move to react with the iron(II) ions coming from the oxidation region, resulting in the precipitation of iron(II) hydroxide.

27
Q

How is rust produced from iron(II) hydroxide?

A

Rust is produced by the further oxidation of the precipitated iron(II) hydroxide.

28
Q

What kind of process drives the formation of rust?

A

The formation of rust is driven by an electrochemical process.

29
Q

What command is rust?

A
  • FeOH
30
Q

What does the Galvanic Series indicate?

A

The Galvanic Series gives the relative reactivity of some common materials in seawater, listing metals in decreasing order of their tendency to corrode, with the most noble (least reactive) at the top.

31
Q

What are some of the most cathodic (noble) materials in the Galvanic Series?

A

The most cathodic (noble) materials in the Galvanic Series are Platinum, Gold, and Graphite.

32
Q

Which metals are considered the most anodic and likely to corrode in the Galvanic Series?

A

The most anodic metals, which are most likely to corrode, are Zinc, Magnesium, and Cadmium.

33
Q

How can corrosion be avoided in materials?

A

Corrosion can be avoided by using materials resistant to corrosion, providing a physical barrier like paint to the surface of the component, using galvanic or cathodic protection, and galvanizing.

34
Q

What is the challenge associated with using coatings such as paint for corrosion protection?

A

It is difficult to ensure that coatings like paint will last over time, especially in structures.

35
Q

What does galvanic protection involve?

A

Galvanic protection involves using a galvanic couple where the metal to be protected is connected to a more reactive metal, such as Magnesium or Zinc, to prevent its corrosion.

36
Q

What is cathodic protection and how does it work?

A

Cathodic protection is a method that supplies electrons from an external source to force the oxidation reaction to reverse, thereby protecting the metal from corrosion.

37
Q

What is the purpose of a polymer-coated steel pipe, and what does it typically consist of?

A

The purpose of coating a steel pipe with polymers, such as HDPE and an epoxy layer, is to protect it against corrosion. This method is quite expensive but effective.

38
Q

What is the purpose of connecting a steel pipe to an active metal like magnesium in galvanic protection?

A

The purpose is to form a sacrificial anode with magnesium, which is oxidized in preference to the iron in the steel pipe, protecting the pipe from corrosion.

39
Q

Why is magnesium used in galvanic protection for steel pipes?

A

Magnesium is used because it will act as the anode in the FeMg voltaic cell, oxidizing in preference to the steel, and it’s easier to replace the magnesium rod than the steel pipe.

40
Q

What role does the steel pipe play in the FeMg voltaic cell in galvanic protection?

A

In the FeMg voltaic cell, the steel pipe is involved in a cathodic reaction, which means it is protected from oxidation.

41
Q

How is galvanising achieved, and what is its benefit?

A

Galvanising is achieved by applying a layer of zinc to steel through hot dipping, creating a galvanic circuit to the steel. It has a low carbon footprint and can be recycled.

42
Q

Why is zinc used for hot dip galvanising coatings, and what happens when it corrodes?

A

Zinc is used for hot dip galvanising coatings because it corrodes in preference to steel and sacrifices itself, which is beneficial since zinc is abundant. The corrosion products from zinc are deposited on the steel, resealing it from the atmosphere and stopping further corrosion.

43
Q

What happens if a galvanised coating is damaged and reveals the bare steel?

A

If the galvanised coating is damaged, the steel can still be protected because the zinc provides both barrier and sacrificial protection.

44
Q

How does the rate of weathering of zinc in a galvanised coating benefit the steel it protects?

A

The zinc in a galvanised coating weathers at a very slow rate, which provides a long and predictable life for the steel it protects.

45
Q

What is one of the sacrificial protection benefits of galvanised coatings on steel?

A

Galvanised coatings provide sacrificial protection to small areas of steel exposed through drilling, cutting, or accidental damage, as the coating corrodes preferentially.

46
Q

How does galvanising prevent sideways creep on larger damaged areas of steel?

A

If the damaged area on the steel is larger, the sacrificial protection offered by the galvanising prevents sideways creep which can undermine coatings.

47
Q

What is the significance of the coating toughness in galvanised steel?

A

The coating toughness is significant because the galvanised coating is bonded metallurgically to the steel, which makes it very durable.

48
Q

Why is galvanising considered to have the lowest lifetime cost?

A

Galvanising is considered to have the lowest lifetime cost because of its durability and the fact that the protective coating lasts more than 40 years, reducing the need for frequent maintenance or replacement.

49
Q

What makes the inspection of galvanised steel easy?

A

The ease of inspection for galvanised steel is due to the obvious visual signs of wear or damage to the zinc coating, allowing for straightforward assessments of the coating’s integrity.

50
Q

What is the main principle behind cathodic protection?

A

Cathodic protection works by redirecting current to flow from a sacrificial anode to the soil-water electrolyte, instead of from an anode area on a pipeline or other metallic structure, thereby protecting the structure from corrosion.

51
Q

What is the role of the protective anode in cathodic protection?

A

The role of the protective anode in cathodic protection is to corrode in place of the metallic object it is designed to protect.

52
Q

How is the negative end of the power supply used in cathodic protection?

A

The negative end of the power supply is attached to the metal to be protected, ensuring that the metal acts as the cathode and does not corrode.

53
Q

Where is the positive terminal of the power supply connected in a cathodic protection system?

A

The positive terminal is attached to an inert (usually graphite) protective anode that is buried in the soil, which is where the corrosion occurs.

54
Q

What happens to the current in a cathodic protection system for buried pipelines?

A

In a cathodic protection system for buried pipelines, the current flows from the protective anode through the soil and towards the pipeline, which is protected as the cathode.