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Don't be fooled by "1000-hour salt spray reports" anymore; scientific testing is the true protection.

A question:

In the manufacturing industry, you often hear conversations like this:

"How many hours can your salt spray test last?"

"1000 hours, no problem!"

"Okay, I'll choose you."

And then what? After product delivery, the customer reports rust problems. Why do the lab data look good, but reality is a disaster?

Today, we'll talk about the necessity and correct methods of salt spray testing—helping you truly understand this "corrosion protection report card."

01 Why is salt spray testing necessary?

Salt spray is everywhere; corrosion is an "invisible killer."

Salt is one of the most common compounds in the world. It can be found in oceans, the atmosphere, land surfaces, lakes, and rivers. Therefore, it's impossible to completely prevent items from being exposed to salt spray.

The impact of salt spray environments on electrical and electronic products is second only to temperature, vibration, humidity, and dusty environments. It has three major destructive effects:

Corrosion effect: As an electrolyte, the salt spray accelerates the electrochemical corrosion of metals, leading to rust, blistering, and component damage.

Electrical effect: The conductivity of the salt solution significantly reduces the surface resistance of insulators, causing open circuits or short circuits in fine wires and breakage of component leads.

Physical effect: Blockage or adhesion of mechanical parts or components, causing moving parts to jam or malfunction.

Salt spray testing: A "time machine" for accelerated evaluation.

Theoretically, to verify whether metal parts on a product will corrode when exposed to the atmosphere, the product could be placed in its operating environment for a sufficiently long time—for example, a full lifespan. However, this is both time-consuming and labor-intensive, and rarely used in practice.

Salt spray testing is the answer to this problem.

It is an accelerated corrosion resistance evaluation method using an artificial atmosphere: a certain concentration of salt water is atomized and sprayed into a sealed, temperature-controlled chamber, and the changes in the sample are observed over a short period (days or even hours), thus quickly evaluating its corrosion resistance performance.

Three Core Values of Salt Spray Testing

According to industry experts, the necessity of salt spray testing is mainly reflected in three aspects:

Value Dimension

Specific Functions

Assessing Product Durability

Detecting potential corrosion problems early, ensuring product quality and reliability

Selecting Appropriate Materials and Coatings

Different materials have different resistance to salt spray corrosion, helping to make the right selection

Compliance with Standards and Regulations

Meeting industry standards and regulatory requirements, ensuring product compliance

02 Three Methods of Salt Spray Testing: Choosing the Right Method is Key to Effectiveness Salt spray testing is mainly divided into three types, selected according to the product's usage environment and testing purpose:

Neutral Salt Spray Test (NSS) The most widely applicable and basic testing method.

Salt solution: 5% sodium chloride solution, pH 6.5~7.2 (neutral)

Test temperature: 35℃±2℃

Application scenarios: Metal materials, metal coatings (zinc plating, chrome plating, etc.), organic coatings, anodized films

Acetic Acid Salt Spray Test (AASS) Corrosion rate approximately 3 times that of NSS

Salt solution: 5% sodium chloride solution + glacial acetic acid ... pH value around 3 (acidic)

Test temperature: 35℃±2℃

Application scenarios: Copper + Nickel + Chromium or Nickel + Chromium decorative coatings, aluminum anodized films

Copper Accelerated Acetic Acid Spray Test (CASS)

Corrosion rate is approximately 8 times that of NSS, the most stringent

Salt solution: 5% sodium chloride solution + copper chloride + glacial acetic acid, pH value around 3

Test temperature: 50℃

Application scenarios: Rapid evaluation of decorative coatings, high-requirement products

Alternating Salt Spray Test

The testing method closest to the real environment

It doesn't just continuously spray salt spray, but simulates complex working conditions such as humidity differences, alternating wet and dry conditions, and high temperature and high humidity in the real environment through a multi-stage cycle of salt spray → drying → humid heat.

Significant advantages:

More realistic dynamic environment simulation

Faster corrosion acceleration effect

Can evaluate the salt absorption and degradation problems of non-metallic materials (such as plastics and rubber)

03 7 Key Steps for Correct Testing

Based on the latest national standard GB/T 2423.17-2024 (Officially implemented March 1, 2025), the following procedures must be strictly followed for salt spray testing:

Step 1: Sample Preparation

Cleansing: Samples must be thoroughly cleaned using appropriate methods before testing, but any intentionally applied protective organic film should not be removed.

Protection: For cut samples, the cut area should be protected with paint, paraffin wax, or tape.

Identification: Mark the sample number with a corrosion-resistant label.

Step 2: Salt Solution Preparation

Concentration: 50 g/L ± 5 g/L (density 1.029~1.036 g/cm³ at 25℃)

Water Quality: Use distilled or deionized water with a conductivity ≤20 μS/cm (25℃±2K).

Purity: Total mass fraction of heavy metals (copper, nickel, lead) in sodium chloride ≤0.005%, total mass fraction of impurities ≤0.5%.

pH Value: At 25℃±2K, the pH value of the collected solution is 6.5~7.2.

Important: Solution must not be reused.

Step 3: Equipment Inspection and Preparation

Equipment Water Refill (Use only purified or distilled water; tap water is strictly prohibited):

Sealed Water Tank: Fill to the marked "Standard Water Level Line"

Heating Water Tank: Fill to the specified mark to prevent the heating element from drying out.

Air Saturator: Water level controlled between 1/2 and 2/3 of the saturator's volume.

Pipeline Inspection:

Sprayer Water Hose: No bends or cracks; connections secure.

Exhaust Pipe: Unobstructed and unblocked.

Air Source Connection Pipe: Pressure adjusted to 0.07~0.1MPa

Step 4: Sample Placement (Critical!)

The proper placement of the sample directly affects the uniformity of salt spray contact:

Angle: Unless otherwise specified, the sample should be at a 20°±5° angle to the vertical, with the test surface facing upwards.

Distance: The distance between the sample and the inner wall of the chamber should be ≥50mm; maintain a ≥30mm interval between samples.

Avoid Contact: Samples must not come into contact with each other. Or in contact with the chamber, droplets on the sample must not fall onto other samples.

Support: Should be made of inert non-metallic material (e.g., PTFE)

Suspension material: Should not be metal, but should be insulating material such as synthetic fiber or cotton thread.

Step 5: Parameter Setting and Operation

Core Parameters:

Temperature: 35℃±2K

Salt spray deposition rate: 1.5mL/h±0.5mL/h (80cm² horizontal collection area)

Spray pressure: 70kPa~170kPa (commonly 98kPa±10kPa)

Duration (preferred): 16h, 24h, 48h (2d), 96h (4d), 168h (1 week), 336h (2 weeks), 672h (4 weeks)

Step 6: Test Process Control

Minimize Interruptions:

Total daily chamber opening time should not exceed 1 hour.

If opening is necessary, first turn off the spray and heating systems, and wait for the pressure to drop to atmospheric pressure. Open the door slowly.

Operation time should be controlled within 5 minutes.

Safety Protection:

Wear acid and alkali resistant gloves, goggles, and protective clothing.

If salt spray comes into contact with skin, immediately rinse with plenty of running water for at least 15 minutes.

Step 7: Post-Test Treatment and Evaluation

Sample Cleaning:

Small Samples: Rinse under tap water for 5 minutes, then rinse with distilled or deionized water.

The temperature of the cleaning water should not exceed 35℃.

Shake or use airflow to dry and remove water droplets.

Recovery Treatment:

Let it sit under standard recovery conditions for at least 1 hour and no more than 2 hours.

Result Evaluation:

Evaluation Methods

Applicable Scenarios

Judgment Basis

Rating Judgment Method

Flat Plate Samples

Percentage of Corrosion Area to Total Area

Weighing Judgment Method

Corrosion Resistance Assessment of a Certain Metal

Weight Loss Before and After Corrosion

Judgment Method for the Appearance of Corrosion Products

General Product Standards

Whether Corrosion Occurs

Common Rating Standards:

GB/T GB/T 1766—2008 "Rating Method for Aging of Paint and Varnish Coatings"

GB/T 6461—2002 "Rating of Specimens and Test Pieces of Metallic and Other Inorganic Coatings on Metallic Substrates After Corrosion Testing"

04 Common Misconceptions and Truths about Salt Spray Testing

❌ Misconception 1: The longer the salt spray test time, the more reliable the product.

Truth: Salt spray testing is an accelerated test and has no direct conversion relationship with actual service life. The performance of different materials and coatings in salt spray testing cannot be simply equated with their service life in real-world environments.

❌ Misconception 2: Passing 1000 hours of salt spray testing means the product can be used for 10 years.

Truth: Single salt spray resistance performance cannot represent resistance to other media. Salt spray test results cannot be used as a direct guide to the corrosion resistance performance of the tested material in all environments. Factors such as temperature changes, ultraviolet radiation, alternating wet and dry conditions, and complex pollutants in real-world environments all affect actual corrosion behavior.

❌ Myth 3: Results from different standards can be compared.

Truth: Salt spray test results from different standards cannot be compared. While standards such as ASTM B117, ISO 9227, and GB/T 10125 share similar principles, their specific parameters and operational details differ, making direct comparison meaningless.

✅ Correct Approach: Comprehensive Evaluation

Outdoor corrosion of metal parts is often influenced by a combination of factors. Past salt spray test results show that although constant salt spray testing is widely accepted, it has no correlation with actual natural corrosion testing.

More Reliable Methods:

Cyclic Corrosion Testing (CCT): Introduces parameters such as high temperature, humidity, low temperature, and dryness to obtain test results with a higher correlation to the natural environment.

Salt Spray UV Cyclic Exposure: Introduces the effects of ultraviolet radiation and condensation, more realistically reflecting the natural environment.

05 Four Suggestions for Manufacturing Enterprises

Clarify the testing purpose and choose the right testing method

Evaluate conventional metal coatings? → Neutral Salt Spray Test (NSS)

Evaluate decorative coatings? → Copper Accelerated Acetic Acid Salt Spray Test (CASS)

Simulating complex environmental conditions? → Alternating Salt Spray Test

Look beyond the results, examine the process. Request a complete test report and pay attention to:

Whether the sample placement angle meets the standard.

Whether the salt spray deposition rate is within the range of 1.5±0.5mL/h.

Whether there were any abnormal interruptions during the test.

Whether there are process photos.

Integrate salt spray testing into the quality control system.

Establish a regular testing mechanism.

Translate test parameters into production inspection standards.

Determine the minimum compliant protection standards through testing to optimize costs.

Choose a qualified third-party testing organization.

Prioritize laboratories with CMA/CNAS accreditation.

Check the calibration certificate of the salt spray chamber equipment.

Confirm whether they have experience testing similar products.

Let salt spray testing return to its essence. Salt spray testing itself is not wrong; it is a useful tool.

The mistake lies in treating the tool as the answer.

The original intention of salt spray testing is to help manufacturers assess the durability of products in salt spray environments and identify potential corrosion problems in advance, not to provide a number to "show off."

The next time you see an advertisement for "1000 hours of salt spray testing," please ask:

What testing method was used? (NSS/AASS/CASS/Alternating?)

How were the samples arranged?

Were the testing procedures recorded?

Truly reliable protection isn't a number in a lab, but rather lasting protection in real-world environments.