Common Types of Corrosion Identified Through Failure Analysis
Corrosion is one of the leading causes of material degradation and unexpected equipment failure across industries such as oil & gas, construction, power generation, marine, and manufacturing. When corrosion-related failures occur, they can lead to costly downtime, safety hazards, and regulatory non-compliance. This is where Corrosion and Failure Analysis plays a critical role. By systematically investigating damaged components, failure analysis helps identify the exact type of corrosion involved, its root cause, and preventive measures to avoid recurrence.
This article explores the most common types of corrosion identified through corrosion and failure analysis, along with their characteristics, causes, and industrial impact.
What Is Corrosion and Failure Analysis?
Corrosion and Failure Analysis is a scientific investigation process used to determine why materials, components, or structures have failed prematurely. It combines visual inspection, metallurgical examination, chemical analysis, mechanical testing, and non-destructive testing to identify corrosion mechanisms and contributing factors such as environment, material selection, design flaws, or operational conditions.
Accurate identification of corrosion types is essential for implementing corrective actions and extending asset life.
1. Uniform (General) Corrosion
Uniform corrosion is the most common and easily recognizable form of corrosion. It occurs evenly across the exposed surface of a metal when it reacts with its environment.
Key Characteristics:
Even material loss across the surface
Predictable corrosion rate
Gradual thinning of components
Identified Through Failure Analysis:
Failure analysis reveals uniform corrosion through thickness measurements, weight loss studies, and surface examination. Although predictable, failure can occur if corrosion allowance is underestimated.
Common Industries Affected:
Water pipelines
Storage tanks
Structural steel components
2. Pitting Corrosion
Pitting corrosion is localized and highly destructive, often leading to sudden failures with minimal overall material loss.
Key Characteristics:
Small, deep pits on metal surfaces
Difficult to detect visually
Can cause leaks or rupture
Role of Corrosion and Failure Analysis:
Failure analysis uses microscopy and surface profiling to detect pit morphology and depth. Chemical analysis often reveals the presence of chlorides or aggressive ions responsible for pit initiation.
Typical Applications:
Stainless steel equipment
Marine and coastal installations
Chemical processing plants
3. Crevice Corrosion
Crevice corrosion occurs in confined spaces where stagnant solutions are trapped, such as under gaskets, bolts, washers, or deposits.
Key Characteristics:
Localized attack in shielded areas
Often hidden from visual inspection
Accelerated corrosion rates
Identified Through Failure Analysis:
Corrosion and failure analysis helps uncover crevice corrosion by dismantling assemblies and analyzing affected zones. Environmental conditions such as oxygen depletion and chloride concentration are assessed.
Common Failure Locations:
Flanged joints
Fasteners
Heat exchanger tube sheets
4. Galvanic Corrosion
Galvanic corrosion occurs when two dissimilar metals are electrically connected in the presence of an electrolyte, causing the less noble metal to corrode faster.
Key Characteristics:
Accelerated corrosion of anodic metal
Dependent on metal pairing and environment
Often design-related
Failure Analysis Insights:
Failure analysis evaluates material compatibility, electrical continuity, and environmental exposure. Electrochemical testing helps confirm galvanic interactions.
Affected Industries:
Marine structures
HVAC systems
Construction assemblies
5. Stress Corrosion Cracking (SCC)
Stress corrosion cracking is a dangerous form of corrosion that combines tensile stress and a corrosive environment, leading to sudden brittle failure.
Key Characteristics:
Fine cracks with little surface corrosion
Rapid and catastrophic failure
Difficult to detect early
Detection Through Failure Analysis:
Advanced metallurgical examination, fractography, and crack pattern analysis are used in corrosion and failure analysis to identify SCC. Residual stress and environmental factors are closely evaluated.
Common Applications:
Pipelines
Pressure vessels
Aerospace and power plant components
6. Intergranular Corrosion
Intergranular corrosion attacks the grain boundaries of metals, often weakening the material without significant surface damage.
Key Characteristics:
Corrosion along grain boundaries
Loss of mechanical strength
Often related to improper heat treatment
Failure Analysis Techniques:
Metallographic analysis reveals grain boundary attack. Chemical testing identifies sensitization effects, especially in stainless steels.
Typical Industries:
Welding-intensive fabrication
Chemical processing equipment
Heat-treated components
7. Erosion-Corrosion
Erosion-corrosion occurs when mechanical wear from fluid flow accelerates corrosion damage.
Key Characteristics:
Directional wear patterns
Accelerated metal loss
Occurs in high-velocity environments
Identified Through Corrosion and Failure Analysis:
Failure analysis evaluates flow conditions, material hardness, and surface morphology to distinguish erosion-corrosion from pure mechanical erosion.
Common Examples:
Pumps and valves
Pipe bends
Heat exchangers
8. Microbiologically Influenced Corrosion (MIC)
MIC is caused by microorganisms that create corrosive environments on metal surfaces.
Key Characteristics:
Localized pitting
Biofilm formation
Occurs under deposits or stagnant zones
Failure Analysis Approach:
Corrosion and failure analysis includes microbiological testing, surface analysis, and chemical profiling to identify bacterial activity such as sulfate-reducing bacteria.
High-Risk Areas:
Underground pipelines
Water systems
Storage tanks
Importance of Identifying Corrosion Types Through Failure Analysis
Identifying the correct corrosion mechanism through corrosion and failure analysis enables industries to:
Implement targeted corrosion control measures
Improve material selection and design
Reduce unplanned shutdowns
Enhance safety and regulatory compliance
Extend equipment service life
Incorrect diagnosis can result in repeated failures and increased operational costs.
Conclusion
Corrosion manifests in many forms, each with unique causes and consequences. Through systematic Corrosion and Failure Analysis, testing laboratories can accurately identify corrosion types such as uniform corrosion, pitting, crevice corrosion, galvanic corrosion, stress corrosion cracking, and more. Understanding these mechanisms allows industries to implement effective preventive strategies, optimize maintenance practices, and ensure long-term reliability of critical assets.
Partnering with an experienced corrosion and failure analysis laboratory is essential for minimizing risk, improving performance, and safeguarding infrastructure across industries.
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