Types of corrosion testing methods

Companies across industries conduct corrosion testing to verify material durability, predict service life, and meet regulatory standards. Particularly in safety-critical sectors, rigorous testing safeguards assets and lives.

In this article, we'll review common corrosion mechanisms and how they impact materials. We'll also detail eight standardized testing methods engineers use to predict corrosion performance.

Understanding corrosion testing

Corrosion testing involves exposing materials or components to controlled, accelerated corrosive environments—such as salt spray, elevated humidity, or chemical solutions—to measure resistance and forecast longterm durability.

These tests serve multiple functions: They confirm product integrity, extend service life, and reduce warranty claims. They also accelerate product development and lower corrosion-related returns. In sectors like automotive and aerospace where reliability must meet strict standards, lab-based corrosion testing is a standard practice for product development and quality assurance.

Types of corrosion

Environmental conditions and material properties dictate which corrosion type takes hold. Each type attacks metal through a distinct mechanism that can threaten product performance and service life. Engineers match each corrosion mechanism with a targeted accelerated test to ensure lab results mirror real-world service life.

Let's consider common types of corrosion.

Uniform corrosion

Uniform corrosion evenly attacks a metal surface. The corrosion progresses at a consistent rate across the entire exposed area, resulting in uniform material thinning. This process typically occurs in metals exposed to atmospheric conditions or immersed in corrosive solutions.

Engineers assess uniform corrosion by measuring mass loss over a defined time, converting results into corrosion rates—often expressed in mils per year. This standard test method helps predict the overall lifespan and corrosion resistance of materials and protective coatings under standard environmental conditions.

Pitting corrosion

Pitting corrosion is a localized attack that forms small, deep holes on metal surfaces. It often occurs in passivated metals or under damaged coatings, especially in chloride-rich environments. Because each pit expands inward, the damage can progress rapidly. Notably, this focused attack can lead to sudden, unexpected failures.

Stress corrosion cracking

Stress corrosion cracking is the formation of cracks in metal under the simultaneous influence of tensile stress and a corrosive environment. These cracks often develop at or near the surface, where stress concentrations occur.

Over time, small fissures can grow—reducing load-bearing capacity and jeopardizing structural integrity. Engineers monitor crack initiation and growth rates to assess susceptibility. Material testing typically involves controlled loading and corrosive media to replicate service conditions.

Crevice corrosion

Crevice corrosion is a localized form of attack that occurs in narrow gaps between metal parts or where metal connects with non-metal surfaces. These tight spaces trap moisture and limit oxygen flow, creating an acidic environment that accelerates metal deterioration.

The process typically starts at the crevice opening and progresses inward, often causing severe damage before it is detected. Notably, the ratio of crevice depth to width strongly influences corrosion rates, with deeper, narrower spaces creating more aggressive conditions.

Salt corrosion

Salt corrosion occurs when soluble salts—especially chlorides—deposit on metal surfaces and attract moisture. The resulting electrolyte triggers electrochemical reactions that dissolve protective films and corrode the underlying metal.

The process intensifies under cyclic wet-dry conditions, as drying concentrates the salts and elevates local acidity. Plus, salt corrosion can initiate pitting, crevice corrosion, and stress corrosion cracking. Even trace amounts of residual salts can significantly speed up the corrosion process and undermine protective coatings over time.

Galvanic corrosion

Galvanic corrosion occurs when two dissimilar metals electrically connect in a conductive environment, such as moisture. This contact forms an electrochemical cell where one metal (anode) corrodes faster, while the other (cathode) corrodes slower or remains protected. The greater the difference in the metals' electrochemical potentials, the faster the corrosion rate.

Notably, the surface area ratio between the anode and cathode materials significantly impacts corrosion intensity. Recognized by galvanic corrosion testing methods, small anodes connected to large cathodes experience accelerated degradation due to the concentration of the corrosion current over a limited area.

8 corrosion testing methods

Corrosion testing methods systematically assess how materials perform under corrosive conditions. Engineers rely on the following standardized tests to ensure materials and coatings withstand their intended environments, preserving structural integrity and extending service life.

Depending on the type of corrosion, engineers select tests that precisely replicate specific environmental and mechanical conditions. In particular, matching test methods to corrosion mechanisms ensures accurate forecasting of material performance and reliable service life predictions.

1. Weight loss (mass loss) testing

Weight loss testing exposes a cleaned, weighed metal coupon to a controlled corrosive environment for a defined period. After exposure, technicians remove surface films, reweigh the specimen, and record the difference.

The mass loss converts to a corrosion rate—typically expressed in mils per year—using equations specified in ASTM G31. The straightforward procedure applies to most alloys, solutions, and temperatures—providing a versatile baseline for validating accelerated or electrochemical tests.

2. Salt spray (fog) testing

Salt spray testing exposes metal or coated specimens to a continuous saline mist inside a sealed chamber. In practice, technicians dissolve 5% sodium chloride in distilled water, atomize the solution, and maintain the chamber at 35 °C to replicate a harsh marine-like environment.

As salt droplets settle, they accelerate corrosion processes that would normally occur over months or years. Observers can measure the time until visible rust or coating failure appears and use that interval to rank protective finishes or compare material formulations. The method delivers rapid, repeatable insights for quality control.

3. Immersion testing

Immersion testing submerges a cleaned metal or coated coupon in a controlled corrosive solution and tracks degradation over time. In practice, engineers set solution chemistry, temperature, agitation, and gas sparging according to ASTM G31 to replicate specific service fluids.

After the defined exposure, they then remove, clean, and weigh the specimen to calculate uniform corrosion rates or inspect for pitting and film failure. This material testing method's straightforward setup, low cost, and direct mass-loss data make it a baseline for screening materials and validating inhibitor performance.

4. Potentiodynamic polarization

Potentiodynamic polarization provides a rapid electrochemical snapshot of a metal's behaviour under controlled conditions. Using a potentiostat, the test steadily sweeps the specimen's potential and records the current response—generating a polarization curve.

Key features on this curve—corrosion potential, corrosion current density, and passive or pitting regions—translate into uniform corrosion rates and highlight susceptibility to localized attack. Standards such as ASTMG59 and G5 codify the procedure, helping engineers rank alloys, validate inhibitors, and study surface film stability with reproducible results.

5. Electrochemical impedance spectroscopy (EIS)

Electrochemical impedance spectroscopy (EIS) gauges a coating's barrier health or a metal's corrosion rate by applying a minute alternating signal to the metal-electrolyte system and measuring the impedance across a spectrum of frequencies.

The resulting impedance plot functions as a fingerprint: high resistance and low capacitance indicate robust protection, whereas declining values reveal early degradation. Because the excitation is non-destructive, engineers can monitor the same sample over time. ASTM G106 defines standard conditions that ensure results remain comparable across laboratories.

6. Stress corrosion cracking (SCC) testing

Stress corrosion cracking (SCC) testing determines a material's tendency to crack when static tensile stress interacts with a specific corrosive environment. Common laboratory protocols expose pre-stressed specimens—U-bend bars, C-rings, or smooth tensile coupons—to controlled media while maintaining a constant load, displacement, or very slow strain rate.

Using this method, engineers monitor time-to-fracture or elongation loss to rank susceptibility and identify threshold stress intensity factors. Standards, such as ASTM G36, G38, and G129, use accelerated chloride or caustic solutions to reveal cracking within hours or days, instead of years.

7. Atmospheric exposure testing

Atmospheric exposure testing exposes metal or coated panels to real outdoor conditions to see how they corrode in actual service climates. In practice, engineers mount the panels on racks at a representative site, then let sun, rain, salt, and pollutants work naturally.

They then conduct periodic checks to record weight change and visible damage—creating a reliable baseline for selecting materials and validating faster lab tests. Because the test captures the full spectrum of real environmental stressors, it delivers the most service-like durability picture—although programs often span months or years.

8. Cyclic polarization testing

Cyclic polarization testing subjects a metal sample in solution to a slow, controlled voltage sweep that first climbs and then retraces its path. The resulting current-versus-potential loop flags the point where the protective film breaks on the way up and the point where it heals on the way down.

Engineers compare these two landmarks to judge how readily an alloy pits or repassivates, making the technique a quick screen for localized-corrosion risk before longer tests. Plus, ASTM G61 codifies the procedure for common iron-, nickel-, and cobalt-based alloys.

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