Views: 0 Author: Site Editor Publish Time: 2026-01-07 Origin: Site
Corrosion is a silent enemy, gradually wearing down metal structures. Did you know corrosion costs industries billions annually? For industries relying on CNC machining, corrosion can cause expensive damage and reduced performance.
In this article, we will explore the seven main types of corrosion. You will learn how to identify them and, most importantly, how to prevent their destructive effects on metal. Understanding these corrosion types is crucial for maintaining the integrity of machinery and infrastructure in CNC machining and beyond.
Uniform corrosion is a type of corrosion that affects the entire surface of a metal, causing an even loss of material. This process occurs when metals like steel, copper, and aluminum are exposed to harsh environments such as water, air, or chemicals. As the corrosion spreads uniformly across the metal surface, it leads to a predictable thinning over time, which weakens the material.
Metals such as iron, copper, and aluminum are particularly vulnerable to uniform corrosion when they come into contact with oxygen and moisture. For example, iron undergoes oxidation when exposed to both oxygen and water, forming iron oxide (rust). This rust gradually eats away at the metal, weakening its structure and integrity. The rate at which uniform corrosion occurs depends on environmental factors like humidity, temperature, and the presence of pollutants or chemicals.
In environments with high humidity, such as coastal areas or places with heavy rainfall, uniform corrosion can accelerate. Similarly, pollutants in the air, such as sulfur compounds, can increase the rate of corrosion, making it crucial for industries to take preventive measures.
Location | Description |
Steel Structures | Steel beams, pipelines, and outdoor equipment exposed to moisture and air. These structures are prone to rust and corrosion over time. |
Outdoor Equipment | Items like fences, railings, and storage tanks are exposed to environmental elements like rain, sun, and air, leading to faster deterioration. |
● Corrosion-Resistant Materials: Using corrosion-resistant metals like stainless steel can significantly reduce the likelihood of uniform corrosion. These metals form a protective oxide layer, preventing further rusting.
● Protective Coatings: Applying protective coatings such as paints, galvanization, or powder coating creates a physical barrier that prevents corrosive elements like water and oxygen from reaching the metal surface.
● Environmental Control: Reducing humidity and moisture levels around metal structures is essential. Utilizing dehumidifiers in enclosed areas or coating outdoor equipment with protective layers helps maintain the metal's integrity over time.
Galvanic corrosion occurs when two different metals are electrically connected in a corrosive electrolyte environment. One metal (the anode) corrodes at an accelerated rate while the other metal (the cathode) corrodes at a slower rate or not at all. This process is driven by the electrochemical potential difference between the metals when they come into contact in an electrolyte, like seawater or saltwater.
Location | Description |
Plumbing Systems | Copper and steel pipes often come into contact in plumbing systems, creating a potential for galvanic corrosion. |
Marine Structures | Ships, offshore oil rigs, and marine equipment that use different metals can experience galvanic corrosion, especially in saltwater environments. |
● Choose Metals Close in the Galvanic Series: When selecting materials for different parts of a system, choose metals that are close to each other on the galvanic series to reduce the risk of corrosion.
● Use Non-Conductive Materials: Insulating materials can be used to separate different metals, preventing electrical contact and reducing galvanic corrosion.
● Apply Protective Coatings: Protective coatings can act as a barrier, preventing the metals from coming into contact with the corrosive environment.
Pitting corrosion is a localized form of corrosion that creates small, deep holes or pits in the surface of the metal. Unlike uniform corrosion, which affects the entire surface, pitting corrosion attacks specific areas, often leading to more severe structural damage. This form of corrosion is particularly dangerous because it may go unnoticed until the damage is significant. It often occurs in stainless steel and aluminum, particularly when exposed to chloride ions.
Pitting is initiated when the protective oxide layer on the metal’s surface is damaged, exposing the underlying metal to aggressive agents like chloride ions. These agents create anodic areas where metal loss occurs rapidly, leading to the formation of pits that can spread over time.
Location | Description |
Stainless Steel | Stainless steel, particularly in environments containing chlorides (like seawater), is highly susceptible to pitting corrosion. |
Aluminum | Aluminum, despite its inherent resistance to corrosion, can also experience pitting when exposed to environments with high levels of chloride ions. |
● Regular Inspection: Regularly inspect metal surfaces, especially those made from stainless steel or aluminum, to detect early signs of pitting.
● Control Chloride Ions: Reduce the presence of chloride ions in the environment, particularly in marine and industrial applications.
● Pit-Resistant Alloys: Use alloys that are specifically designed to resist pitting corrosion, such as those with higher chromium content.
Intergranular corrosion occurs at the grain boundaries of metals, often leaving the bulk of the metal largely intact. This corrosion is common in stainless steel, particularly after welding or heat treatment. The grain boundaries are more susceptible to corrosion due to the segregation of alloying elements or depletion of critical elements like chromium in stainless steels.
This form of corrosion is often invisible at first, as the metal itself may appear unaffected. However, as the grain boundaries deteriorate, the overall structural integrity of the material is compromised.
Location | Description |
Welded Stainless Steel | Stainless steel parts that have been welded or heat-treated are particularly prone to intergranular corrosion due to the changes in the alloy composition at the grain boundaries. |
Austenitic Steel | This type of corrosion is also common in austenitic stainless steels, which are used in high-stress environments like pressure vessels or reactors. |
● Low-Carbon or Stabilized Alloys: Use low-carbon stainless steels or stabilized alloys that resist chromium carbide formation at the grain boundaries.
● Proper Heat Treatment: Ensure correct post-weld heat treatment to avoid the creation of corrosive zones at the grain boundaries.
● Avoiding Corrosive Environments: Minimize exposure to environments that exacerbate intergranular corrosion, such as high-temperature or chloride-rich environments.
Stress-corrosion cracking (SCC) occurs when a material is exposed to tensile stress in a corrosive environment, causing the material to crack. These cracks can propagate without any visible external damage, making SCC particularly insidious. This form of corrosion is commonly found in metals subjected to high-stress conditions, such as those used in infrastructure, pipelines, and aerospace applications.
SCC is driven by a combination of mechanical stress and environmental factors, such as the presence of chloride ions or high temperatures. The cracks usually form perpendicular to the direction of applied stress and can lead to sudden failure if not detected early.
Location | Description |
Bridge Cables | The cables in suspension bridges, which are under constant tensile stress, are vulnerable to SCC when exposed to corrosive environments. |
Pipeline Welds | Welded joints in pipelines that carry pressurized liquids or gases can be susceptible to SCC, especially if the pipeline is exposed to aggressive chemicals. |
● Use SCC-Resistant Materials: Select materials that are resistant to stress-corrosion cracking, such as high-quality stainless steels or titanium alloys.
● Environmental Control: Control the exposure to corrosive environments, such as reducing the presence of chloride ions.
● Stress-Relief Methods: Implement design changes that reduce stress on critical components, such as applying annealing techniques to relieve residual stress.
Erosion corrosion is the accelerated degradation of metal due to the combined effects of mechanical erosion and chemical corrosion, usually caused by high-velocity fluid or gas flow. This form of corrosion is most common in systems where fluids move at high speeds, such as pipelines, valves, and turbine blades.
The impact of high-velocity fluids wears down the metal surface, while simultaneously, the corrosive environment (such as acidic fluids) accelerates the corrosion process. Erosion corrosion is particularly problematic in industries dealing with fluid transport systems, such as oil and gas pipelines.
Location | Description |
Pipes and Valves | Components like pipes, valves, and impellers in fluid systems are highly susceptible to erosion corrosion, especially at points where the fluid flow is turbulent. |
Turbine Blades | Turbine blades used in gas or steam systems can also suffer from erosion corrosion due to high-velocity fluid interactions. |
● Erosion-Resistant Materials: Use harder alloys and materials designed to withstand mechanical wear and corrosion, such as ceramic-coated metals.
● Control Fluid Velocities: Design systems that reduce fluid velocity in critical areas where erosion corrosion is likely to occur.
● Streamlined Fluid Paths: Redesign pipes and valves to minimize turbulent flow, which contributes to erosion.
Choosing the right materials is the first step in preventing corrosion. Stainless steel is a popular choice for its resistance to rust, but it may not be suitable for all environments. Materials should be selected based on their resistance to specific corrosion types, such as galvanic or pitting corrosion.
Protective coatings, such as galvanization, anodizing, and paint, provide a barrier between the metal and the corrosive environment. These coatings are essential for preventing the metal from coming into direct contact with moisture, oxygen, or chemicals.
Controlling environmental factors such as temperature, humidity, and exposure to chemicals can greatly reduce the risk of corrosion. In industrial settings, using dehumidifiers or reducing temperature fluctuations can help preserve the integrity of metal components.
Cathodic protection is a widely used method that prevents corrosion by converting the metal into a cathode, thus preventing the oxidation process. This technique is commonly used in pipelines, storage tanks, and marine structures to protect them from corrosion.
This article covered the seven main types of corrosion and prevention strategies. Understanding these corrosion mechanisms is essential to prolong the life of metal components. Companies, such as Suzhou Welden Intelligent Tech Co., Ltd., offer innovative products that effectively combat corrosion. Their solutions provide long-lasting protection, helping businesses reduce maintenance costs and improve operational efficiency.
A: The seven types of corrosion include uniform corrosion, galvanic corrosion, pitting corrosion, intergranular corrosion, stress-corrosion cracking (SCC), erosion corrosion, and galvanic corrosion. Understanding these types is essential, especially in industries like CNC machining, where corrosion can significantly affect the longevity and performance of metal parts.
A: Corrosion in CNC machining can weaken metal components, leading to costly repairs and reduced equipment efficiency. It can also affect the precision and durability of machined parts. Regular surface treatment methods like coating and anodizing can help mitigate corrosion in CNC machined parts.
A: Surface treatment helps create a protective barrier that prevents corrosion by isolating the metal from environmental factors like moisture, oxygen, and chemicals. Techniques such as galvanizing, anodizing, and coating are commonly used in CNC machining to extend the lifespan of metal components.
A: Pitting corrosion is particularly dangerous because it causes localized damage, leading to deep holes or pits that weaken the metal significantly. This is especially problematic in CNC machining, where precise parts are critical. Regular inspection and surface treatment can reduce the risks of pitting corrosion.
A: To prevent stress-corrosion cracking (SCC) in CNC machining, use materials that are resistant to SCC, control the environment to minimize exposure to corrosive agents, and apply surface treatment techniques like coating and heat treatment to reduce the risk of cracking.
A: Using corrosion-resistant materials in CNC machining helps ensure that components last longer, perform better, and require less maintenance. These materials, when combined with effective surface treatment, offer increased durability and resistance to various forms of corrosion.
A: While surface treatment can significantly reduce the risk of many types of corrosion, it may not eliminate all forms, especially in extreme environments. However, it remains a critical strategy for protecting CNC machining components from most common corrosion types.
