If you’ve been around plumbing products for a while, you’ve probably heard the term “salt spray test.” And if you’re new to it, the first question that usually comes up is: why does stainless steel—of all materials—need to be tested for corrosion?
The short answer is that stainless steel isn’t truly stainless. It’s stain-resistant.
What makes stainless steel resist rust is a thin chromium oxide layer that forms naturally on its surface. Under normal indoor conditions, that layer stays intact and does its job. But in certain environments—coastal areas with salt air, industrial zones with chemical exposure, or even settings where chlorine-based cleaners are used frequently—that protective layer can break down.
Once the layer is compromised, corrosion starts. It might begin as tiny pinprick spots, but over time they spread. For a faucet that sits in a humid bathroom or kitchen day after day, that’s a real risk if the material or surface finish isn’t up to standard.
Salt spray testing is essentially a way to accelerate that process. It simulates years of exposure in a matter of days, so we can see exactly how a product will hold up before it ever reaches a job site.
How Salt Spray Testing Works
1. The Test Method
The principle is straightforward. A faucet or component goes into a sealed chamber where a salt solution—usually 5% sodium chloride—is atomized into a fine fog. The temperature is kept steady at around 35°C. The product stays inside for a set period, and at the end, we take it out and inspect the surface for any signs of corrosion.
The test runs continuously. A few days inside the chamber can replicate years of exposure in a harsh environment. It’s not uncommon to see poor-quality finishes show rust spots within 48 hours, while properly treated surfaces come out looking the same as they went in after 200 or 300 hours.
2. Common Testing Standards
Different markets and different clients ask for different standards. The most widely used internationally is ASTM B117, which comes from the American Society for Testing and Materials. In Europe, ISO 9227 is the go-to. China follows GB/T 10125.
The underlying principles are similar across these standards—they all use a salt fog chamber at controlled conditions—but there are differences in how samples are prepared, how long they’re tested, and how results are evaluated. When we produce for a specific market or client, we test according to whichever standard they require. Some large-scale projects also come with their own custom test protocols that go beyond the standard requirements.
3. Test Duration and Rating
How long a product can last in salt spray tells you a lot about its real-world corrosion resistance.
For standard residential faucets intended for indoor use, 24 to 48 hours of salt spray testing is usually enough to confirm the surface finish is adequate. For coastal hotels, outdoor kitchens, or other high-exposure installations, we typically test to 96 hours, 120 hours, or even longer.
When the test is done, it’s not just a pass-or-fail check. We evaluate the results using a rating system. The rating looks at two things: how much of the surface area is affected by corrosion, and the type of corrosion that occurred. A rating of 10 means no change at all. A 9 might show a few tiny spots that are barely visible. Anything below a 7 usually indicates the surface treatment didn’t hold up.
4. Surface Finishes and Corrosion Resistance
Not all stainless steel faucets handle corrosion the same way. The material grade matters, but so does the surface finish.
Brushed and polished finishes are the most common. Brushed surfaces are mechanically abraded to create a consistent grain; polished surfaces are smoothed to a shine. Neither of these adds a protective coating—they rely entirely on the base material for corrosion resistance. With good-quality 304 stainless steel, that’s usually fine for indoor use.
Electroplating adds a layer of another metal—often chrome or nickel—over the stainless steel. A well-applied electroplated layer can significantly improve corrosion resistance. The catch is that if the plating has micro-pores or is too thin, those weak points can become the first places where corrosion starts.
PVD—physical vapor deposition—is a different approach. In a vacuum chamber, metal ions are deposited onto the product surface to form a dense, uniform coating. PVD coatings are harder and adhere better than electroplated finishes. We’ve run side-by-side salt spray tests comparing the two: at 96 hours, electroplated surfaces often show early signs of corrosion, while PVD-treated surfaces remain completely clean.
Then there’s the material itself. 316 stainless steel contains molybdenum, which gives it much better resistance to chloride corrosion than 304. Even with a simple brushed finish, 316 will outperform 304 in coastal environments. For a seaside installation, 316 plus PVD is about as durable as it gets.
In practice, we match the material and finish to the project’s environment. For a typical indoor residential or commercial project, 304 with a quality PVD coating is more than enough. For a beachfront property or an outdoor installation, 316 with PVD gives you the longest service life with minimal risk.
Salt spray testing isn’t just about meeting a requirement on a spec sheet. It’s about turning an unknown—how long will this faucet actually last—into measurable data. For us as a manufacturer, it’s how we make sure what leaves the factory will still look and perform as it should years down the line. For anyone specifying or buying faucets, it’s one of the most reliable indicators of long-term quality.
At Inoxbath, we run salt spray testing on all our faucets, with durations tailored to the intended installation environment. If you’re working on a project and want to know what level of corrosion resistance makes sense for your conditions, feel free to reach out. We can walk you through the test data and help you choose what fits.
