Where can I find a coating that is chloride and sulfur corrosion-resistant?
Thank you very much for your inquiry. We get questions like this all the time, and they are far more complex than most people realize.
First, to be clear, we are consultants who do this for a living. But, we are unusual even in that regard, as we are vendor neutral. That is, all we do every day, in this response and in our work, is tell the technical truth about issues such as this.
The way virtually all coating material selection procurement takes place is by an owner asking the question you did— what material will work in a given situation. And the problem even in asking the question is that as soon as the owner stumbles upon a coating company (or engineering or architectural firm as a proxy or "pass through" to a coating company), folks typically think the hard part is over.
But that’s a dangerous and wrong assumption. That would be like going to a Ford dealership and asking what type of hybrid they recommend, or an Apple store, and asking them to recommend a phone. You’re only going to get what they have to sell.
It may not be what you need, so you’ll want to keep looking. You’ll need to contact a number of different coating companies and thoroughly technically vet what they have to offer in order to get the optimal coating system for your use. (For an in-depth discussion, read Methods & Pitfalls in Selecting Coating Systems for Specification.)
Some of the complex issues you’ll be facing include:
- The temperature is almost certainly cyclical, meaning that the temperature will range from ambient up to about 1380°F (750°C). That means that during peak or nominal operating temperatures, there won’t be any liquids in the system. But during cycling, there may be condensates at varying temperatures and concentrations. If you design a coating system for only 1380°F and don’t take cycling into consideration, and there ends up being condensate, a failure may be lurking right around the corner.
- For the most part, coating systems don’t know or care about the substrate to which they are adhered. You’re gaining a physical bond with the substrate through physically abrading it, typically via dry abrasive blasting. Ferritic stainless steel is difficult to abrasive blast and requires a highly experienced technician to ensure proper blast profile. If you don’t have the proper blast profile, you will be 100% guaranteed to have an immediate and catastrophic failure. (For further reading, see Myth or Fact: Higher Surface Profile Increases Coating Adhesion.)
- Understanding the coating system is vital. The most complex process in all of this is not finding a coating system that will work (if there is one), but finding the optimal system and understanding how it works. We worked on a project similar to this a couple of years ago. We found an optimal coating, and the manufacturer specified the dry film thickness (DFT) to be between 5 and 8 mils. The final specification we developed (with the support of the manufacturer), however, came in with a DFT of between 14 and 18 mils.
Why? Because we calculated that the increased thickness would provide a roughly 100% increase in service life, for an additional total installed cost of only a fraction of a percent, thus saving the client an estimated $800,000 over the course of eight years. There are other equally important considerations, but these are the big ones.
When we approach a project like this, we do the following:
- Thoroughly understand the asset and operating environment through all phases of operation.
- Develop a document that we call a "Request for Coating Compatibility" and submit it to various pre-vetted coating vendors.
- Evaluate the responses.
- Write a site-specific, asset-specific coating and application specification.
I hope this information was more useful than confusing.
More Q&As from our experts
- High-Temperature Corrosion
- Ferritic Steel
- Abrasive Blasting
- Dry Film Thickness
- Sulfonic Acid
- Ferritic Stainless Steel
- Surface Topography
- Coating Specification
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