Surface corrosion is the most common and predictable form of metal corrosion, causing significant economic losses annually in numerous industries. This phenomenon manifests as relatively uniform damage to the metal surface and, unlike localized corrosion, typically does not lead to sudden structural damage. This article examines in detail the mechanisms, causes, and methods for combating this type of corrosion.
Uniform corrosion mechanism
Basic electrochemical processes
Uniform corrosion is based on electrochemical principles and involves two main half-reactions:
Anodic (oxidation-reduction) half-reaction:
Fe → Fe²⁺ + 2e⁻
Cathode half-reaction (reduction):
O₂ + 2H₂O + 4e⁻ → 4OH⁻
These reactions take place in the presence of an electrolyte such as water or moisture and lead to the formation of corrosion products such as iron hydroxide.
Special features
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Evenly distributed over the metal surface
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The corrosion rate is relatively constant over time.
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A simple way to measure
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Formation of a uniform layer of corrosion products
Factors influencing the rate of uniform corrosion
1. Environmental conditions
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Humidity : High relative humidity accelerates corrosion.
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Temperature : For every 10 °C increase in temperature, the corrosion rate increases by 2 to 3 times.
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Environmental pH : Strongly acidic and alkaline pH values can increase corrosion.
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Presence of impurities : Sulphur dioxide, chlorides and other impurities can accelerate corrosion.
2. Material properties
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Chemical composition of alloys
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Crystal structure
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Presence of impurities
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residual stress
3. Physical factors
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The flow rate of a liquid coming into contact with a surface.
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Corrosion or vibration
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Wet and dry cycle
Uniform method for measuring corrosion
1. The most likely method
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Measures the weight loss of a sample over a given period of time.
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Calculate the corrosion rate in millimeters per year (mm/year) or millimeters per year (mpg).
2. Electrochemical method
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Linear polarization
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Polarization resistance
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Electrochemical impedance spectroscopy
3. Non-destructive methods
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Ultrasonic measurement of the residual thickness
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Visual inspection
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industrial radiography
Corrosion products in surface corrosion.
Formed compounds:
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Iron(II) hydroxide Fe(OH)₂
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Iron(III) hydroxide Fe(OH)₃
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Iron oxide Fe₂O₃ (hematite)
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Iron(II,III) oxide Fe₃O₄ (magnetite)
Properties of the wear layer:
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Adhesion to metal surfaces
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Porosity and permeability
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Protective effect (in some cases)
Industrial applications and practical examples
Common cases of common erosion:
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Vehicle bodies in wet areas
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External steel structure
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City water supply lines
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Chemical storage tanks
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Bridges and marine structures
Useful information:
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The corrosion rate of carbon steel in urban air: 50-80 µm/year
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Corrosion rate in marine environment : 200–500 micrometers/year
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Corrosion rate in industrial environments: 100-300 µm/year
Methods of control and prevention
1. Protective layer
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Organic coatings : paints, resins and enamels
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Metal coatings : zinc, aluminum, chrome.
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Conversion coating : phosphate and chromate
2. Cathodic protection
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Sacrificial anodes (magnesium, zinc, aluminum)
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applied current (ICCP)
3. Ecological transformation
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Humidity control
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Use corrosion inhibitors
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Adjustment of the pH value of the environment
4. Material selection
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Copper-nickel alloys
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reinforced plastic
Advantages and disadvantages of regular erosion
Special feature:
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predictability
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Please take increased thickness into account when designing .
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easy to recognize
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Relatively simple controls
Shortage:
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The material thickness continues to decrease.
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A regular maintenance schedule is required.
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Costs for spare parts
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Poor aesthetics
Relevant rules
Measurement criteria:
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ASTM G1 – Standard Method for Preparation, Cleaning, and Evaluation of Corrosion Test Specimens
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ASTM G31 – Standard Guide for Laboratory Tests of Metals for Corrosion Resistance by the Immersion Method
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ISO 9223 – Corrosion of metals and alloys – Atmospheric corrosion
Protection standards:
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ISO 12944 – Paints and varnishes – Corrosion protection of steel structures
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NACE SP0169 – External corrosion protection of buried or submerged metallic piping systems
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ASTM A123 – Standard Specification for Zinc Coatings (Hot-Dip Galvanized)
The latest developments in the field of uniform corrosion protection
New technologies:
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Intelligent coating : changes color when worn
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Nanocoating : Formation of a thin, permanent protective layer
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Ecologically safe inhibitors : alternatives to chromates
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Self-healing coatings : release inhibitors at the site of damage
New materials:
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Modern high-strength steel
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reinforced polymer composites
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Alloys with improved corrosion resistance
Conclusions and practical recommendations
Although common corrosion is considered the simplest form, ignoring it can have irreversible consequences . Understanding the basic mechanisms and factors contributing to its development enables the development of effective mitigation programs.
Important recommendations for the industry:
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Regular monitoring program : Establishment of a continuous corrosion monitoring system
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Conscious material selection : adapting materials to environmental conditions
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Proper design : Consider increasing the thickness to extend the life of the structure.
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Staff training : Raising staff awareness of the principles of corrosion control.
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Use of modern technologies : Use of modern conservation methods.
Implementing these solutions significantly extends the lifespan of equipment and metal structures and avoids unnecessary repair and replacement costs.