When you source chains, springs, hooks, or other metal hardware, a supplier may tell you that a plated or coated product can pass 96, 240, or 500 hours of salt spray testing. You may have seen these numbers without knowing how the test works, what it measures, or how to judge the result. This article explains what salt spray testing is, why it is used, how the common methods differ, and what the results can and cannot tell you.
What Is Salt Spray Testing?
Salt spray testing, also called a salt spray corrosion test, is a laboratory test that exposes metal or coated samples to a controlled salt fog to accelerate corrosion. You may also see the terms salt spray test, salt fog testing, and salt fog test in technical documents.
The test is mainly used to compare the corrosion resistance of materials, plated finishes, coatings, and other surface treatments. Manufacturers can also use it to check whether a product meets a specified requirement or whether surface treatment remains consistent between production batches. A salt spray test shows how a sample performs under defined laboratory conditions. It does not fully reproduce outdoor, coastal, or industrial environments. You therefore cannot convert salt spray hours directly into years of service life.
Why Is Salt Spray Testing Used?
Salt spray testing can reveal weak areas in corrosion protection more quickly under controlled conditions. For purchasing and quality control, it is commonly used to:
- Compare different options. When the substrate, sample condition, and test method are the same, you can compare the corrosion resistance of different platings or coatings.
- Verify a specified requirement. The test can help confirm whether a product meets the technical requirements in a product specification or purchase agreement.
- Check production consistency. If one production batch corrodes earlier than another, the manufacturer may need to review cleaning, pretreatment, plating, coating, or curing.
- Find local weak points. A surface treatment can be harder to apply evenly around pores, edges, welds, complex shapes, and chain-link contact points. These areas may corrode before a flat surface.
Salt spray testing covers only part of a product’s corrosion-related performance. It cannot replace dimensional inspection, tensile or load testing, coating adhesion testing, wear testing, or validation under real service conditions.
How Does Salt Spray Testing Work?
Before testing begins, the test standard, sample condition, exposure time, and acceptance criteria must be defined. Without these details, a completed test may not provide a result that you can use for acceptance.
A typical salt spray test follows these steps:
- Select representative samples. The samples should represent the actual substrate, formed or welded condition, pretreatment, and final surface finish.
- Position the samples. The laboratory places the samples in the chamber according to the applicable method and prevents them from interfering with one another.
- Create a controlled salt fog. The chamber operates under specified temperature, solution, and atomization conditions, keeping the samples exposed to a salt fog.
- Inspect at defined times. The laboratory checks the samples at the required intervals. The inspection should not disturb the test or affect other samples.
- Record the findings. The inspector records the type, location, area, and time of corrosion and takes photographs when required.
- Judge the result against the specification. Whether a result passes or fails depends on the applicable product specification, drawing, or customer acceptance criteria.
As a buyer, you do not need to know every chamber setting. You do need to confirm that the method, samples, and acceptance criteria match the product you are buying.
What Are the Main Types of Salt Spray Tests?
Salt spray testing is not a single method. Neutral salt spray, acetic acid salt spray, and copper-accelerated acetic acid salt spray use different solutions and environments. They are also intended for different materials and finishes.
| Test type | Basic environment | Common use | Important limitation |
|---|---|---|---|
| Neutral Salt Spray (NSS) | A continuous fog produced from a neutral sodium chloride solution | Comparing and controlling the quality of many metals, electroplated coatings, conversion coatings, and organic coatings | It is the most common method, but it is not suitable for every material or service environment |
| Acetic Acid Salt Spray (AASS) | Acetic acid is added to the salt solution to create an acidic environment | Certain metallic and decorative coatings and specified surface treatments | It should not be treated simply as a universally more severe NSS test; select it only when the relevant specification calls for it |
| Copper-Accelerated Acetic Acid Salt Spray (CASS) | Copper salt is added to an acidic salt solution to create a more corrosive environment | Certain decorative copper-nickel-chromium, nickel-chromium, and other applicable decorative coatings | CASS hours cannot be converted directly into NSS hours |
Do not choose a method simply because it appears to be more severe. The correct method must match the material, surface treatment, product specification, and purpose of the test. When comparing suppliers or products, first confirm that they used the same method and acceptance criteria.
What Do ASTM B117 and ISO 9227 Specify?
Two of the most common references for salt spray testing are ASTM B117 and ISO 9227. Both relate to salt spray testing, but neither standard name alone defines a complete product acceptance requirement.
ASTM B117 mainly explains how a laboratory creates and maintains the salt spray environment, including the equipment, operating procedure, and test conditions. It does not set one test duration or one acceptance criterion for every product.
ISO 9227:2022 specifies the equipment, reagents, and procedures for NSS, AASS, and CASS testing. It can be applied to unprotected metallic materials and to metal products with permanent or temporary corrosion protection. The applicable product specification must still define the exposure time, samples, and interpretation of results.
For purchasing, it is not enough to write “test according to ASTM B117” or “comply with ISO 9227.” You also need to specify the test method, sample condition, exposure time, inspection requirements, and failure criteria.
How Should You Read Salt Spray Test Results?
Do not read a salt spray test result as an hour value alone. You also need to know what was tested, which method was used, and what surface change counted as failure.
Test Duration Alone Does Not Define a Pass
A report that only says “passed 48 hours of salt spray testing” is incomplete. You still need to confirm the standard and method, whether the test used a flat panel, a component, or the finished product, and whether the sample received the required preparation.
The acceptance criteria should also define the inspection intervals, end time, acceptable type and area of corrosion, or required rating. If these conditions differ, two reports that both state “48 hours” may not be comparable.
White Corrosion and Red Rust Mean Different Things
For zinc-plated steel products, white corrosion products and red rust on the substrate are different failure conditions. White corrosion is generally associated with corrosion of the zinc layer. Red rust normally shows that the steel substrate has started to corrode. A product specification may set different limits for each condition.
For painted, powder-coated, or electrophoretically coated products, the inspection may also cover blistering, peeling, corrosion creep from a scribe, and local edge corrosion. Writing only “no rust” in a purchase specification is usually too vague.
A Test Panel Does Not Automatically Represent the Finished Product
A standard flat panel is useful for checking the basic performance of a coating or process. However, it does not have all the edges, welds, joints, recesses, and local coating-thickness variations found on a finished product. If you are buying hardware with a complex shape, confirm whether the acceptance requirement applies to a panel, a component, or the finished product.
For example, a chain has contact areas between links, and a welded chain also has weld zones. Coating coverage, local friction, and corrosion behavior in these locations may differ from a flat panel. A panel can support process comparisons, but it should not be treated as proof of finished-product performance without product-level validation.
What Products and Surface Treatments Are Commonly Tested?
Salt spray testing is often used for products that require an assessment of metal or coating corrosion resistance. Different surface treatments protect metal in different ways. Results are meaningful together only when the materials, samples, and test conditions are the same or otherwise comparable.
| Product or finish | What the test commonly checks | What you need to consider |
|---|---|---|
| Electroplated zinc parts | The time and extent of white corrosion products and red rust on the substrate | Plating thickness, passivation, and sealing can affect the result |
| Hot-dip galvanized parts | The corrosion behavior of the zinc layer under the specified test environment | Constant salt fog does not fully represent how zinc corrodes in a real atmosphere |
| Electrophoretically coated, painted, and powder-coated parts | Blistering, peeling, edge corrosion, and corrosion creep from a scribe | Pretreatment, film thickness, curing, and whether the sample is scribed can affect the result |
| Nickel, chromium, and decorative multilayer coatings | Pores, local corrosion, and the protective performance of the coating system | Select NSS, AASS, or CASS according to the actual coating system |
| Conversion coatings and temporary protective coatings | Coating continuity, sealing, and relative corrosion resistance | The method and acceptance criteria must match the applicable product specification |
| Finished chains, springs, hooks, and connecting parts | Weak areas around complex shapes, welds, edges, and contact points | Confirm whether the test uses a panel or a finished product that matches the purchase specification |
For example, welded chain requires attention around welds and link contact points. On lighter weldless products such as double loop chain, single loop chain, and jack chain, overlapping or contacting areas may be harder to coat evenly.
Compression springs, S hooks, and other wire forms may also require closer inspection around bends and ends. These products should not share one vague test requirement. Select representative finished samples based on the actual product shape.
When comparing two surface treatments, do not place their highest salt spray hour claims side by side without checking the details. First compare the material, sample shape and construction, pretreatment, coating system, test method, and failure criteria. Otherwise, the hour values can be misleading.
What Are the Limitations of Salt Spray Testing?
Salt spray testing uses stable conditions, which makes it useful for comparing samples and checking production consistency. The chamber environment is much simpler than a real service environment, so the test also has important limitations.
- Hours cannot be converted directly into service life. Real environments include wet-dry cycles, ultraviolet exposure, temperature changes, pollutants, wear, and maintenance. A traditional salt spray test does not reproduce all of these factors.
- Hour values for different materials and finishes may not be comparable. When the substrate, pretreatment, coating, or protection mechanism differs, the same exposure time can have a different meaning.
- A small sample cannot represent every product in a batch. Sampling can help you judge production and batch consistency, but it cannot prove that every item will perform identically.
- Constant salt fog may not be the most suitable simulation. If a product repeatedly experiences wet, dry, or changing-temperature conditions, cyclic corrosion testing or another supplementary method may be more appropriate.
Salt spray testing is therefore better at answering, “How did this sample perform under the specified conditions?” It cannot answer on its own, “How many years will this product last in service?”
What Salt Spray Test Requirements Should You Specify When Purchasing?
You do not need to define every laboratory operating detail. You do need to set a clear method, sample, and acceptance criteria so that the supplier and laboratory work to the same requirement.
| Item to confirm | What you need to specify |
|---|---|
| Standard and method | The applicable standard and NSS, AASS, CASS, or another specified method |
| Test item | A standard panel, a component, or a finished product matching the purchase specification |
| Sample condition | Substrate, pretreatment, plating or coating system, and whether a scribe is required |
| Exposure time | Total exposure time and required inspection intervals |
| Failure definition | Acceptable limits for white corrosion, red rust, blistering, peeling, or corrosion creep from a scribe |
| Acceptance range | Permitted corrosion area, rating, or another agreed evaluation method |
| Report requirements | Sample description, test conditions, inspection records, photographs, and whether a third-party report is required |
If you write only “salt spray testing required,” different suppliers may use different methods. Even when the reports show the same number of hours, the results may come from different conditions and cannot be compared directly.
Frequently Asked Questions About Salt Spray Testing
Is There a Difference Between a Salt Spray Test and a Salt Fog Test?
Usually, no. Salt spray testing and salt fog testing generally refer to the same type of test. The chamber creates a uniform salt fog and keeps the samples exposed under controlled conditions. It does not rinse the product with a direct stream of salt water.
Does ASTM B117 Specify How Many Hours a Product Must Be Tested?
No. ASTM B117 explains how to create and maintain the salt spray environment, but it does not set one duration for your product. Whether the test runs for 48, 96, 240 hours, or longer depends on the product specification, drawing, or purchase requirement. You must also define what condition counts as a failure.
Can a Sample Still Be Used After Salt Spray Testing?
It should not normally be used as a saleable product. Continuous corrosive exposure may affect both the finish and the underlying metal, even when the sample shows little visible change. Treat test samples as consumable items when planning the quantity to submit.
How Many Samples Are Needed for a Salt Spray Test?
There is no fixed number for every product. The quantity should follow the product specification, sampling plan, part size, and purpose of the test. When comparing materials, finishes, or production batches, prepare representative samples for each option. The quantity should also be sufficient to show whether the result is consistent.
Can Stainless Steel Be Salt Spray Tested?
Yes, but the result must be interpreted carefully. Stainless steel performance can be affected by the grade, part shape, crevices, surface condition, and test conditions. Salt spray testing can compare samples or support a quality check under the same conditions. It cannot prove by itself that one stainless steel grade is suitable for every service environment.
When Should You Use Cyclic Corrosion Testing?
Cyclic corrosion testing may be more representative when a product will repeatedly experience salt, moisture, drying, or temperature changes. Select the method according to the service conditions, likely corrosion problems, and applicable specification. Do not choose a test simply because it runs longer or appears more severe.
Final Thoughts
Salt spray testing can help you compare the corrosion resistance of metals and surface treatments, but it cannot directly predict how many years a product will last. When reviewing a result, check the method, sample, and acceptance criteria instead of looking only at the hour value. Tuohai can arrange different salt spray tests for chains, springs, hooks, and other wire-formed products according to your requirements and provide the agreed test report. If you are unsure which method or acceptance criteria to specify, contact us to review the requirements.
For related product details and practical comparisons, you can also read about Safety Chain and What Is Tensile Testing? Methods, Results, and Hardware Applications.
English 
Russian 
Spanish 
Czech 
German