Corrosion
Learning objectives
At this pdf we discuss on following topic:
• Explain various components of corrosion
• Discuss the factors affecting corrosion
• Explain types of corrosion
• Distinguish various methods of corrosion
• Discuss methods to prevent corrosion
Corrosion
Corrosion is a natural process, which converts refined metal to their more stable oxide. It may be of physical, chemical or electro-chemical process
It is the gradual destruction of materials (usually metals) by chemical reaction with their environment (chemical terminology- Corrosion)
In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen
Corrosion is the oxidation of a metal due to an electrochemical reaction.
The oxidizing agent is most often O2 (atmospheric corrosion) or H+ (chemical corrosion) or both
Corrosion can also be defined as the degradation of a material due to a reaction with its environment
Degradation implies deterioration of physical properties of the material
Recipe for corrosion
– Active metal
– Water
– Oxygen (atmospheric corrosion)
– Acid (chemical corrosion)
– Salt
– High temperature
Corrosion product: The compound that is formed during corrosion
Corroded: The metal surface that has undergone corrosion
Corrosion media: Generally liquids (mostly aqueous solutions, solids and gases
Types of Corrosion in Pharmaceutical Industries
In the pharmaceutical industry, as in other sectors, corrosion is a prevalent concern that can lead to various issues, including product contamination, equipment failure, and increased maintenance costs. Understanding the different types of corrosion that can occur in pharmaceutical settings is essential for effective corrosion management. Below are some common types of corrosion that are particularly relevant to the pharmaceutical industry:
- General Corrosion: This is the most common type of corrosion in which the entire surface of a metal is uniformly corroded over time. In pharmaceutical equipment, this can result from exposure to corrosive chemicals, cleaning agents, or environmental conditions. Regular inspection and maintenance are crucial to mitigate general corrosion.
- Pitting Corrosion: Pitting corrosion is localized and can create small holes or pits on the metal surface. In pharmaceutical applications, pitting corrosion can be especially problematic as it may lead to the formation of crevices where contaminants can accumulate. Proper material selection and surface finish are important in preventing pitting corrosion.
- Crevice Corrosion: Corrosion in crevices or tight spaces is a significant concern in pharmaceutical equipment with joints, gaskets, and seals. These hidden areas can trap moisture and chemicals, creating ideal conditions for crevice corrosion. Regular inspection and maintenance, along with appropriate gasket and seal materials, can help prevent this type of corrosion.
- Intergranular Corrosion: This type of corrosion occurs along the grain boundaries of metal. In pharmaceutical industries, intergranular corrosion can be a result of improper welding or heat treatment processes. Proper quality control and material selection are essential to prevent this type of corrosion.
- Stress Corrosion Cracking (SCC): SCC is a severe form of corrosion that occurs under tensile stress. In pharmaceutical equipment, stress corrosion cracking can be induced by residual stresses from fabrication, temperature fluctuations, or exposure to specific chemicals. Using stress-relieving processes during fabrication and avoiding stress concentrations are vital in preventing SCC.
- Microbiologically Influenced Corrosion (MIC): In pharmaceutical processes involving water or other aqueous solutions, MIC can be a significant concern. Microorganisms, such as bacteria, can accelerate corrosion by producing corrosive byproducts. Maintaining proper sanitation practices and using biocides can help prevent MIC.
- Galvanic Corrosion: Galvanic corrosion arises when two dissimilar metals come into contact in the presence of an electrolyte. In pharmaceutical equipment, different metal components may be used, leading to the potential for galvanic corrosion. Isolation of dissimilar metals or the use of sacrificial anodes can prevent this type of corrosion.
- Erosion Corrosion: In pharmaceutical processing, high-velocity fluid flow can lead to erosion corrosion. This occurs when the protective layer on the metal surface is mechanically removed, exposing it to corrosion. Proper design and material selection can minimize erosion corrosion.
- Hydrogen Embrittlement: In environments where hydrogen is present, such as during the use of acid cleaning solutions, hydrogen embrittlement can occur. This can lead to the loss of mechanical integrity in metal components. It’s crucial to avoid exposure to hydrogen when selecting materials and processes.
Dry or Wet type Corrosion
|
DRY / Chemical Corrosion |
WET / Electrochemical Corrosion |
| Involves the direct attack of dry gases (air and oxygen) on the metal through chemical reactions | Involves the directs attack of aqueous media (strong or dilute, acidic or alkaline) on metal through electrochemical reactions |
| As a result an oxide layer is formed over the surface | The moisture and oxygen are also responsible |
| Not very common | Occurs at anodic area and is quite common |
Corrosion Prevention Methods:
- Protective Coatings: One of the most common methods to prevent corrosion is the application of protective coatings. These coatings act as a barrier between the metal surface and the surrounding environment, preventing direct contact with corrosive agents. Common coatings include paint, epoxy, and galvanization.
- Cathodic Protection: This method involves using sacrificial anodes or impressed current systems to protect the metal from corrosion. Sacrificial anodes are metals that corrode more easily than the protected metal, diverting the corrosion away from the critical structure. This is particularly useful for underground pipelines and storage tanks.
- Corrosion Inhibitors: Corrosion inhibitors are chemical compounds that, when added to the environment, mitigate the corrosive effects. They work by forming a protective layer on the metal’s surface or altering the electrochemical reactions that cause corrosion. Inhibitors are often used in cooling systems and water treatment.
- Material Selection: Choosing the right materials for the intended application is crucial in corrosion prevention. Using corrosion-resistant alloys or non-metallic materials, such as plastics or fiberglass, can significantly reduce the risk of corrosion.
- Proper Design: Good engineering practices, including designing equipment to minimize areas where moisture or corrosive agents can accumulate, can help prevent corrosion. Smooth and easily cleanable surfaces reduce the likelihood of corrosion-prone areas.
Importance of Corrosion Control:
- Safety: Corrosion control is vital to ensure the safety of structures and equipment. Corrosion-induced failures can lead to accidents, compromising the safety of individuals and the environment.
- Cost Savings: Effective corrosion control measures help extend the lifespan of equipment and infrastructure. This reduces the need for frequent repairs and replacements, leading to substantial cost savings for individuals and industries.
- Product Quality: In industries like pharmaceuticals and food processing, maintaining corrosion-free equipment is essential to prevent contamination of products. Corrosion control ensures product quality and safety.
- Environmental Protection: Corrosion can release harmful materials into the environment. Proper corrosion control minimizes these environmental impacts and contributes to ecological sustainability.
- Operational Efficiency: Corrosion can lead to reduced efficiency and downtime. By preventing corrosion, operations can run smoothly, minimizing disruptions and maximizing productivity.
- Infrastructure Longevity: In sectors like transportation and infrastructure, corrosion control is essential to extend the lifespan of bridges, pipelines, and buildings. This, in turn, promotes the economic well-being of communities.
Factors Affecting Corrosion
• Material related factors
• Solution pH
• Oxidising agents
• Temperature
• Velocity
• Surface films
• Constituents of the reaction media
• Other factors
FAQs
1. Why does corrosion occur? Corrosion occurs due to the reaction of metals with their environment, typically involving oxygen and moisture.
2. What are the common types of corrosion? Common types of corrosion include rusting, pitting, crevice corrosion, and galvanic corrosion.
3. How can corrosion be prevented? Corrosion prevention methods include protective coatings, cathodic protection, and the use of corrosion inhibitors.
4. What is the environmental impact of corrosion? Corrosion can lead to the release of harmful materials into the environment, posing environmental risks.
5. Why is corrosion control important in industries? Corrosion control is essential for industries to prevent equipment damage, maintenance costs, and ensure the longevity of assets.
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