Development of a Customized Corrosion Testing Protocol For Evaluating Industrial Coatings On Steel

Micom Laboratories specializes in accelerated aging testing, typically relying on recognized standards such as ASTM B117 or ASTM G155. However, certain projects require the creation of customized protocols to meet specific needs. The following case study illustrates such a situation, in which we had to create a customized corrosion testing protocol.

The Challenge

Evaluate different coating suppliers to determine the best product capable of protecting steel exposed to concentrated solutions of an aggressive salt.

The Objectives

The mandate entrusted to us was to:

• Evaluate the corrosion resistance of coatings when exposed to a saturated solution of aggressive salt at high temperatures.
• Reproduce real-world operating conditions equivalent to more than 10 years of exposure in an industrial environment.
• Identify corrosion risks and ways to mitigate them.

The Technical Challenges and Constraints

The development of the protocol was influenced by several constraints related to the chemistry of the salt, the system design, and the duration of the tests:

• Solubility of the aggressive salt: At high temperatures, the salt dissolves in water at an approximate ratio of 1:1, which requires strict temperature control.
• Sample dimensions: Plates of different sizes required immersion baths of varying dimensions. To prevent cross-contamination, each sample needed its own bath.
• Exposure duration: The plates had to remain submerged for 18 months, which required long-term thermal and chemical stability.
• Heating method: Submersible heating elements posed a high risk of corrosion in a salt-saturated solution.
• Bath material: Plastic tanks were unsuitable due to their low thermal conductivity and the risk of deformation at high temperatures.

The Technical Choices and Implemented Solutions

To ensure the reliability, safety, and durability of the protocol, several technical decisions were made:

• Use of indirect heating via heating strips to avoid direct contact with the saline solution and reduce corrosion.
• Manufacturing of stainless steel immersion baths capable of holding up to 140 litres and offering excellent corrosion resistance, particularly at the welds. We considered inserting protective membranes inside the baths, but all budget-friendly solutions had a softening temperature well below the required temperature, rendering them unusable.
• Application of surface treatments (pickling, passivating) to enhance corrosion protection and extend the service life of the immersion baths.
• Addition of a pneumatic mixer, suitable for the baths, to ensure solution homogeneity and thermal stability.
• Airtight lids to limit evaporation and prevent oversaturation, which could lead to solid deposits.

The Corrosion Protection Measures

1. Surface Preparation: Polishing welds and heat-affected zones to remove impurities.
2. Pickling: Application of a pickling agent to restore corrosion resistance.
3. Passivation: Treatment using citric acid to reinforce the protective layer.
4. Sealing and coating: Application of a sealant and a Teflon-based epoxy paint for additional protection.

The Experimental Validation

A 4-litre scaled-down prototype containing 1.5 litres of high-temperature saturated solution was built in our materials testing laboratory in Montreal.

This model made it possible to:

• Validate the technical feasibility of the protocol
• Optimize the design of the baths
• Confirm the system’s stability and the corrosion resistance of the applied treatments
• Verify the ability to return the salt to solution following a power outage or partial crystallization

The results confirmed the validity of the final protocol, ensuring the reproducibility of the tests over the long term.

The Results

Thanks to this scientific and methodical approach, Micom Laboratories delivered a testing protocol that is:

• Reliable and compliant with industrial requirements
• Reproducible over long periods
• Adapted to real-world operating conditions
• Designed to minimize the risk of premature coating failure in industrial settings

This protocol enabled the selection of the highest-performing coating supplier while reducing uncertainties related to corrosion in a saline environment.

Conclusion

Using a systematic approach and innovative solutions, we have developed a robust protocol designed to minimize the risk of corrosion, maintain thermal and chemical stability, and ensure prolonged exposure of the samples. This protocol has enabled us to effectively compare the performance of coatings under extreme conditions, while paving the way for future improvements to enhance the reliability of the tests.

Whether your project calls for standard testing protocols or a fully customized solution, Micom Laboratories has the expertise to design and execute corrosion testing programs tailored to your specific conditions. Contact us today to discuss your corrosion testing needs and find out how we can help you select the right coating for your application.