Webinar Recap: Laboratory Corrosion Testing – Improving Realism and Reproducibility with Modern Methods

Selecting the right corrosion test method is essential for accurately evaluating material durability, coating performance, and long-term product reliability. In our webinar Laboratory Corrosion Testing – Realism and Reproducibility with Modern Methods, Q-Lab reviewed how corrosion testing has evolved from traditional salt spray methods to modern cyclic corrosion tests, and how today’s laboratory equipment supports improved realism, repeatability, and reproducibility. 

Overview of Accelerated Corrosion Test Types

Accelerated corrosion tests serve different purposes depending on the testing objective. Our technical experts outlined four primary categories, which have evolved over time as both scientific understanding of corrosion and laboratory technology have matured.

1. Quality Control Corrosion Tests – Short-duration, pass/fail tests used to verify compliance with material or coating specifications.
2. Qualification and Validation Tests – Medium- to long-term tests that compare results against reference materials or established performance criteria.
3. Correlative Corrosion Tests – Tests designed to rank materials and compare laboratory results with natural outdoor exposure at benchmark sites.
4. Predictive Corrosion Tests – Long-duration tests intended to estimate service life using acceleration factors relative to real-world environments.
    

Understanding these distinctions helps laboratories and manufacturers choose corrosion tests that align with performance goals and industry requirements. 

Continuous Salt Spray Testing (ASTM B117)

Continuous salt spray testing is over 100 years old, but remains one of the most widely-used corrosion test methods, particularly for quality control of metallic and conversion coatings. ASTM B117 specifies exposure to a continuous 5% sodium chloride fog at 35°C with neutral pH.

While salt spray testing is useful for screening purposes, it has important limitations. Results often show poor correlation with outdoor exposure, generate corrosion products that differ from those seen in service environments, and provide limited insight into long-term corrosion performance. 

Wet/Dry Cyclic Corrosion Tests

Wet/dry cyclic tests, such as the Prohesion® test, introduce alternating salt spray and dry-off phases to better simulate environmental cycling. These methods are commonly used for evaluating higher-performance coatings, including architectural aluminum systems tested under AAMA 2605.

Although these represent a step forward in realism compared to continuous tests, simple wet/dry cyclic corrosion tests often suffer from poor repeatability and reproducibility, especially for automotive and industrial coatings due to variability in drying rates and chamber conditions.

Evolution of Automotive Cyclic Corrosion Tests

First-generation automotive cyclic corrosion tests made a further improvement in test realism, adding fully-humid “wetting” steps to existing Fog/Dry-Off cycles. However, these lacked precise control of transition times and environmental conditions, resulting in inconsistent test severity and poor inter-laboratory reproducibility.

Modern automotive corrosion test standards address these issues through advanced chamber design and tighter control of test parameters. Examples discussed included Toyota TSH1555G, GMW 14872, Volvo ACT 1 and ACT 2, and ISO 16701. These modern cyclic corrosion tests offer significantly improved realism and reproducibility compared to earlier methods.

Verifying Corrosion Test Performance

Modern corrosion tests often require users to verify the performance of test chambers. Several techniques are used, often in combination, including:

1. Mass-loss corrosion coupons to measure corrosion rates
2. Pluviometry to quantify collected for or shower solution
3. Independent monitoring of temperature and relative humidity

Performing these verifications in test chambers loaded fully with test specimens help ensure consistent, repeatable results across laboratories.

Need help selecting the right corrosion test standard or chamber? Q-Lab experts can help you understand corrosion testing standards & equipment, evaluate test methods, and improve test realism and reproducibility for your specific application.

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Frequently Asked Questions

Q: What is the purpose of accelerated corrosion testing?

A: Accelerated corrosion testing is used to evaluate material durability, coating performance, and long-term product reliability in a shortened timeframe. These tests help manufacturers assess corrosion resistance, compare materials, and verify compliance with specifications.

Q: What are the main types of accelerated corrosion tests?

A: Accelerated corrosion tests generally fall into four categories:

• Quality Control Tests for short, pass/fail screening
• Qualification and Validation Tests for medium- to long-term performance evaluation
• Correlative Tests for ranking materials against natural outdoor exposure
• Predictive Tests for estimating service life using acceleration factors

Each type serves a different testing objective and application.

Q: When is salt spray testing (ASTM B117) most appropriate?

A: Salt spray testing, such as ASTM B117, is commonly used for quality control of metallic and conversion coatings. It is effective for pass/fail screening but is not intended to accurately simulate most real-world service environments or predict long-term corrosion performance.

Q: What are wet/dry cyclic corrosion tests?

A: Wet/dry cyclic corrosion tests, such as the Prohesion® test, alternate between salt spray and dry-off phases to better simulate environmental cycling. These tests are often used for evaluating higher-performance coatings, including architectural aluminum systems.

Q: How do I choose the right corrosion test method for my application?

A: The right corrosion test depends on your performance goals, industry standards, materials, and whether you need screening, comparison, correlation, or service-life prediction. Selecting the appropriate test method is critical for obtaining meaningful and reliable results. Our experts can help you identify which tests and equipment would work best for your specific product needs.