Corrosion is a primary cause of premature failure in metals and alloys. It arises from electrochemical and chemical reactions between a material and its environment, leading to loss of material, reduced strength and ultimately component failure if left unchecked. Understanding the different forms of corrosion is essential for designing against it and for choosing protective measures that minimise unplanned downtime and maintenance costs.
Uniform corrosion, sometimes called general corrosion, is the most common form. It reduces material thickness evenly across exposed surfaces, making it relatively predictable and allowing engineers to design corrosion allowances into components. Although considered less dangerous than localised forms, it still leads to long-term weakening and costly replacements.
Pitting is a highly localised and aggressive form of corrosion that produces deep, narrow cavities while leaving much of the surface untouched. It is particularly problematic because pits penetrate quickly, can be extremely small at the surface and are difficult to detect until they cause leakage or failure.
Crevice corrosion occurs in confined spaces where stagnant liquid alters the local chemistry, creating aggressive conditions inside the crevice. It is especially challenging because it forms in hidden areas, such as under seals or fasteners and can progress rapidly once started.
Galvanic corrosion arises when two dissimilar metals are coupled in an electrolyte, setting up an electrochemical reaction where one metal corrodes faster than it would in isolation. This process can dramatically accelerate damage if materials are not carefully selected or electrically insulated.
Intergranular corrosion selectively attacks grain boundaries rather than the grains themselves, effectively weakening the internal structure of the metal. This makes the material appear sound externally but brittle and prone to failure under load.
Stress corrosion cracking is one of the most dangerous forms of corrosion because it combines mechanical and chemical effects. Tensile stress and a specific corrosive environment act together to produce cracks that propagate with little visible warning, often leading to catastrophic failure.
All of these corrosion mechanisms reduce equipment life and drive up operational costs, but some (particularly pitting, SCC, and crevice corrosion) can cause sudden and unpredictable failures. Traditional coatings such as hard chrome and thermal spray offer some defence but are prone to micro-cracks and porosity, leaving substrates vulnerable.
By contrast, Chemical Vapour Deposition (CVD) tungsten carbide coatings provide a dense, pore-free barrier that resists uniform, localised and stress-assisted corrosion. These coatings can be applied evenly across complex geometries and internal surfaces, delivering long-term protection in harsh environments and reducing maintenance interventions.
Corrosion takes many forms from gradual uniform attack to localised mechanisms like pitting, crevice corrosion and stress corrosion cracking. Each reduces component life and reliability, leading to costly and unexpected failures.
Traditional coatings can leave weaknesses, but Hardide CVD tungsten carbide coatings provide a dense, pore-free barrier that protects against uniform, localised and stress-driven corrosion, even on complex geometries.
For a deeper understanding of the mechanisms that affect component life, download our full guide on design for longevity below.