How to Protect Metals

How to Protect Metals from Corroding

Corrosion is the natural deterioration that results from the chemical or electrochemical reaction of a metal or metal alloy with its environment. Like other natural threats — earthquakes, tornadoes, floods — corrosion can cause dangerous and expensive damage to everything from vehicles, home appliances, and water/treatment systems to pipelines, bridges, and public buildings. Corrosion differs from other natural disasters in that there are time-proven methods as well as new technologies that can help control and prevent corrosion thereby protecting people, assets, and the planet from its negative impact.

Many factors must be considered before determining the specific problem and/or solution to the prevention and control of corrosion including but not limited to:

  • environmental conditions (soil resistivity, humidity, and exposure to salt water on various types of materials)
  • type of product to be processed, handled, or transported
  • required lifetime of structure or component
  • proximity to corrosion-causing phenomena

Despite this seemingly complex interaction of factors and the near inevitability of metals rusting, corrosion is a controllable process when such widely used and effective methods of Materials Selection and Design, Protective Coatings, Measurement and Inspection, Cathodic Protection, Chemical Inhibitors, and Corrosion Management are considered.

Materials selection and design for corrosion control

Materials Selection and Design

Considering corrosion prevention and mitigation thoroughly and realistically during the materials selection phase of the design process is critical to preventing many types of failures.

Factors that can influence materials choices include corrosion resistance in the environment, availability of design and test data, mechanical properties, cost, availability, maintainability, compatibility with other system components, life expectancy, reliability, and appearance.

Integral to materials selection is appropriate system design, which considers process and construction parameters; geometry for drainage; avoidance or electrical separation of dissimilar metals; avoidance or the sealing of crevices; corrosion allowance; operating lifetime; and maintenance and inspection requirements.

While the use of metals and concrete are common design choices, material science offers corrosion engineers options in corrosion control with advanced materials. Engineered properties created through specialized processing and synthesis technologies give advanced materials superior performance over conventional materials and include ceramics, high value-added metals, electronic materials, composites, polymers, and biomaterials.

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Protective coatings for corrosion control

Protective Coatings

A corrosion study conducted by NACE International, now AMPP, shows that 50% of all corrosion costs are preventable – with roughly 85% of these specific to protective coatings.

Protective coatings, including paints, are thin layers of solid material applied to a substrate with the coating acting as a barrier to inhibit or prevent corrosion, wear, or exposure to water. Each liquid, liquefiable, or mastic composition is converted into a solid protective, decorative, or functional adherent film after application to a surface. Coatings may be sprayed on, welded on, plated on, or applied using hand tools depending on the coating surface, environment, and application goals.

Materials commonly used in organic coatings are epoxies, polyurethanes, or other polymers while materials typically found in inorganic metallic coatings include zinc, aluminum, and chromium.

After the preparation of a surface, coatings are applied in a 3-step process: first, a primer, then a full coating, followed by a sealant.

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Measurement and inspection for corrosion control

Measurement and Inspection

Coating inspections check industrial equipment and facilities as well as commercial properties and projects to ensure that protective coatings were correctly applied to minimize the risk of corrosion.

The discipline is critical to monitoring and measuring for corrosion control. It focuses on corrosion control, paint application and inspection, project management, and quality assurance. Also involved is the evaluation of the useful and remaining life of the structure, as well as repair and rehabilitation of the coating/structure.

Coating inspection helps strengthen the entire protective coatings industry and results in billions of dollars in corrosion cost savings.

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Cathodic protection for corrosion control

Cathodic Protection (CP)

Cathodic Protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. CP can be accomplished by sending a current into the structure from an external electrode and polarizing the metallic surface in an electronegative direction. This provides protection to the surface and extends the life of the asset.

CP systems protect a wide range of metal-based structures, including onshore/offshore pipelines, storage tanks, pier piles, ship and boat hulls, offshore oil platforms, and metal reinforcement components in concrete structures. Another CP technique to mitigate corrosion involves placing a zinc coating on galvanized steel components.

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Chemical inhibitors for corrosion control

Chemical Inhibitors

A corrosion inhibitor reduces the corrosion rate of a metal exposed to that environment by slowing down the chemical (corrosion) reaction.

To reduce the intensity of corrosion, they are commonly added in small amounts to acids, cooling waters, steam, and many other environments, either continuously or intermittently. When used as a coating, corrosion inhibitors are generally applied to clean surfaces and allowed to penetrate and dry.

Inhibition can be used internally with carbon steel pipes and vessels as an economic corrosion control alternative to stainless steels and alloys, coatings, or non-metallic composites, and can often be implemented without disrupting a process. Inhibitors can also be used to protect against the corrosion of reinforced steel bars (rebar) within concrete.

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Corrosion Management for corrosion control

Corrosion Management

More than technology is needed to prevent corrosion and lower its related costs; it requires a proactive corrosion management plan to improve the way critical assets are designed, operated, and maintained. Furthermore, these plans need to be founded on a change in how corrosion decisions are made within an organization.

According to a NACE study, those companies that are best at reducing corrosion’s negative effects follow certain practices with technical corrosion management plans integrated into their organization’s overall management system thereby reaching all levels of the organization. By getting every employee involved in the organization’s corrosion management plan, strategies can be implemented at every stage of a product or facility’s lifecycle, resulting in significant cost savings over the lifetime of an asset.

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