What Is Corrosion: Types, Causes, and Prevention Methods in Steel
Corrosion is the process by which materials lose their chemical and physical integrity as a result of reactions with their environment. In industrial projects and structural steel applications, the use of corrosion-resistant materials is a fundamental engineering decision that determines the lifespan and maintenance budget of infrastructure systems. In this article, we will examine in detail the electrochemical causes of corrosion, the different forms of damage occurring on steel, and protection methods that comply with international standards to optimize the cost of your project.
The scientific answer to the question “What is corrosion?” is the tendency of refined metals to revert to their naturally stable states of oxide, sulfide, or hydroxide. For this destructive electrochemical reaction to begin, four basic components must be present simultaneously:
Anode: The active metal surface that begins to dissolve (corrode) by losing electrons.
Cathode: The metal region that collects electrons and physically stabilizes the reaction.
Electrolyte: A conductive medium that allows ion flow, such as water, moisture, or soil.
Conductive Path: The direct metallic contact between the anode and cathode.
Are Corrosion and Rust the Same Thing?
Although corrosion and rusting are often used interchangeably in the industry, they are not the same thing from a metallurgical perspective. Corrosion is a broad term referring to the degradation of materials, including polymers, ceramics, and all metals, due to environmental factors. Rusting, on the other hand, is the formation of reddish-brown iron oxide in iron and iron alloys (especially carbon steel) in the presence of water and oxygen.
The answer to the question frequently asked by engineers on construction sites – whether corrosion and rusting are the same in reinforcing steel – is practically yes; because reinforcing steel is made of carbon steel and rusts when it corrodes by oxidizing. However, copper, for example, forms a green patina when it corrodes, while aluminum is covered with a white powder layer; both metals corrode but do not “rust”.
What are the most common types of corrosion in steel?
Steel structures can fall victim to a wide variety of corrosion mechanisms depending on the chemical environment they are exposed to and their design geometry. Understanding these mechanisms is a critical step in comprehending the structural weaknesses underlying the question “what is corrosion in construction?” The most common types of corrosion encountered in projects are listed below:
Uniform (General) Corrosion: This is the most common but easiest to control type, progressing at approximately the same rate across the entire exposed surface of the metal. Since the wear rate can be calculated, the risk can be eliminated by adding corrosion allowance to the steel thickness during the design phase or by coating the surface with a suitable barrier system.
Pitting Corrosion: This begins with the localized breakdown of the passive film protecting the metal surface by chloride ions (seawater or de-icing salts). These tiny holes, starting as small as a pinhead on the surface, rapidly penetrate deep into the metal, leading to sudden perforation of the material. The highest level of protection against pitting corrosion is achieved by using specific alloys such as 316 grade stainless steel with molybdenum additive.
Crevice corrosion occurs in microscopic cavities where oxygen cannot penetrate, such as bolt bottoms, flange connections, lap weld joints, or the undersides of sealing gaskets. The difference in oxygen concentration creates a severe electrochemical cell in this narrow gap. Isolating these cavities with filler materials or using continuous welding methods during the design phase prevents commercial losses.
What is galvanic corrosion and what causes it?
| Contacting Metals | Galvanic Corrosion Risk | Recommended Isolation Material |
|---|---|---|
| Aluminum & Carbon Steel | High | Teflon or Nylon Washer |
| Stainless Steel & Copper Alloys | Low | Direct Contact Is Generally Acceptable |
| Zinc-Coated Steel & Carbon Steel | Safe (Zinc Acts as the Sacrificial Anode) | Galvanizing Principle (No Isolation Required) |
Corrosion Protection Methods in Construction and Industry
The decision on the most suitable corrosion protection methods for industrial steel structures should be made according to the atmospheric environmental classes (from C1 mild environment to C5-M harsh marine environment) specified in the international ISO 12944 standard. Choosing the right system optimizes the life cycle cost (LCC) of the installation.
Material Selection and Natural Corrosion Resistance: Corrosion resistance is defined as the natural resistance of an alloy to oxidation. Instead of using carbon steel and requiring constant paint maintenance, using stainless steel, which forms an invisible chromium-oxide layer that self-renews itself due to its chromium content, is more cost-effective in the long run, especially in food and chemical plants. In architectural applications, Corten steel, which forms a protective, dense rust layer on its surface, can be preferred.
Barrier Coatings and Surface Insulation: These are systems applied to physically prevent the steel from coming into contact with water and oxygen. After cleaning the surface with industrial sandblasting (Sa 2.5), applying a zinc-rich epoxy primer and polyurethane topcoat paint will stop corrosion for years. The answer to the frequently asked question by investors – whether epoxy paint or galvanizing provides better corrosion resistance – depends on the application. Epoxy paints excel in acidic and chemical environments, while hot-dip galvanizing offers excellent resistance to mechanical impacts during transportation and installation.
Cathodic Protection (Sacrificial Anode Systems): When calculating the cost of corrosion prevention in underground steel pipelines, a cathodic protection budget is determined, taking into account the impossibility of painting massive pipelines. In this method, “sacrificial anodes” with a high tendency to donate electrons, such as magnesium or zinc, are attached to the steel structure to be protected. When the reaction begins, these sacrificial anodes melt instead of the steel. In larger industrial facilities, corrosion is completely stopped by keeping the steel continuously under a negative (cathode) charge using external current (direct current) systems.
Effects of Corrosion on Reinforced Concrete Structures
General inquiries such as “What is corrosion in a building?” usually refer to the condition of the structural steel within the concrete. The high pH level of healthy concrete creates a natural shield protecting the steel reinforcement from rusting. However, the penetration of chloride ions into the concrete over time due to carbon dioxide in the air or the use of sea sand breaks down this shield. When the reinforcement corrodes, its volume increases; this expansion strains the concrete from the inside, causing it to spall. To eliminate this danger at the design stage, corrosion inhibitors (retardant chemicals) or epoxy-coated rebars should be used.
Frequently Asked Questions
What does 304 stainless steel mean?
Corrosion is the process by which metals lose their physical integrity through electrochemical reactions with water, moisture, oxygen, or aggressive chemicals. It occurs because the metal attempts to return thermodynamically to its stable ore form found in nature.
Are corrosion and rust the same thing?
Corrosion and rusting are not the same thing. Corrosion is a general deterioration process that can occur in all materials. Rusting, on the other hand, is the oxidation of iron and steel alloys specifically due to the effects of moisture and oxygen.
What does corrosion mean in medicine?
In medical terminology, corrosion is a burn or tissue damage that occurs when chemical substances, such as acids or strong alkalis, come into contact with living tissues. This is sometimes searched using terms like “what is burn corrosion”.
Where does corrosion occur?
Corrosion is most prevalent in ports exposed to seawater, underground steel pipelines, chemical plants, ship hulls, and open-air industrial facilities with high humidity levels.
Do you need steel bars in custom sizes?
Contact Uyar Çelik’s expert team. You can receive technical support and a price quote for our hot-rolled and cold-drawn steel bar varieties.
Telephone: +90 (212) 485 9898 | Web: uyarcelik.com
Diğer Gönderiler
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.
