Salt Spray Testing - Principles, Methods and Standards

Salt spray testing, also known as salt spray testing or salt corrosion testing, is used in various industries to evaluate the corrosion resistance of materials and coatings. This procedure simulates the effects of corrosion in marine environments or other harsh conditions with high concentrations of salt air, and is also used to test products for changes in their natural environment. Typically a test duration of 24-500 hours is sufficient to simulate corrosion changes in materials over days or even years. Here, we will delve into the full scope of salt spray testing, including principles, methods and test standard.

Principles of Salt Spray Testing

Salt spray testing is actually an accelerated corrosion process that typically uses a sodium chloride solution to simulate a corrosive medium. As the chloride ions in sodium chloride penetrate the oxidized and protective layers on the metal surface, an electrochemical reaction occurs with the metal resulting in corrosion of the product. Chlorine ions contain hydration energy, easy to be adsorbed in the pores of the metal surface, cracks crowded and replace the oxygen in the oxide layer, the insoluble oxides into soluble chlorides, so that the passivation of the state of the surface into an active surface. Therefore, the corrosion reaction in the salt spray test is caused by the electrochemical reaction between chloride ions and metals and the activation of metal surfaces.

Methods of Salt Spray Testing

Salt spray testing consists of four main methods, Neutral Salt Spray Test, Accelerated Acetate Spray Test with Copper Salt, Acetate Spray Test and Alternating Salt Spray Test.

1. Neutral salt spray test, also known as NSS test, is currently the most widely used and appeared the earliest of an accelerated corrosion test method. Generally 5% sodium chloride saline solution is used, and the solution PH value is adjusted in the neutral range (6.5-7.2), which is used as a spray. The test temperature is controlled at 35 ℃, the sedimentation rate of salt spray should be 1 ~ 2ml/80cm/h.

2. Copper salt accelerated acetate fog test, also known as CASS test, is a rapid salt spray corrosion test developed in recent years. Test temperature of 50 ℃, salt solution with a small amount of copper salt - copper chloride, with a strong corrosion-inducing ability, corrosion rate is about 8 times the NSS test.

3. Acetic acid salt spray test, also known as ASS test, is established on the basis of neutral salt spray test developed. Add glacial acetic acid in 5% sodium chloride solution, the PH value of the solution is reduced to about 3, the solution becomes acidic, and the final formation of salt spray also becomes acidic from neutral salt spray. The corrosion rate is about 3 times that of the NSS test.

4. Alternating salt spray test is a comprehensive salt spray test, which is based on the principle of neutral salt spray test plus constant humidity and heat test. Mainly used for cavity type machine products, through the penetration of the humid environment, so that the salt spray corrosion occurs both on the surface of the product, but also inside the product. Alternating salt spray test will be the product environment in the salt spray and humidity and heat under the two conditions of continuous replacement, and finally assess the whole product of the electrical and mechanical properties of the degree of change.

Test Standard of Salt Spray Testing

Test	Test Standard	Description
Salt Spray Testing	ISO 7253-1996	Corrosion tests in artificial atmospheres - Salt spray tests
	BS 3900-F12-1997	Methods of test for paints - Salt spray (fog) test
	BS 7479:1991	British Standard methods for resistance to atmospheres containing sulfur dioxide
	IEC 60068-2-11:1981	Environmental testing - Part 2: Tests - Test Ka: Salt mist
	GB/T 10125-1997	Corrosion tests in artificial atmospheres - Salt spray tests
	GB 2423.17-2008	Environmental testing for electric and electronic products - Part 2: Test method Test Ka: Salt mist
	DIN 50021-1988	Testing of metallic coatings - Salt spray testing
Acetic Acid Salt Spray Testing	ASTM B368-09	Standard test method for copper-accelerated acetic acid-salt spray (fog) testing (CASS Test)
	ISO 9227-2006	Corrosion tests in artificial atmospheres - Salt spray tests
	DIN 50021-1988	Testing of metallic coatings - Salt spray testing
	BS 7479:1991	British Standard methods for resistance to atmospheres containing sulfur dioxide
Copper Ion Accelerated Salt Spray Testing	ASTM B368-09	Standard test method for copper-accelerated acetic acid-salt spray (fog) testing (CASS Test)
	ISO 9227-2006	Corrosion tests in artificial atmospheres - Salt spray tests
	DIN 50021-1988	Testing of metallic coatings - Salt spray testing
	BS 7479:1991	British Standard methods for resistance to atmospheres containing sulfur dioxide
Cyclic Salt Spray Testing	ASTM D6899-2003	Standard practice for sliming resistance of coatings with copper accelerated acetic acid salt spray or copper accelerated acetic acid salt fog exposure
	ASTM G85-02e1 Annex A5	Standard practice for modified salt spray (fog) testing
	ISO 11997-1:2005	Paints and varnishes - Determination of resistance to cyclic corrosion conditions - Part 1: Wet (salt fog)/dry/humidity/UV light
	ISO 11997-2:2000	Paints and varnishes - Determination of resistance to cyclic corrosion conditions - Part 2: Wet (salt fog)/dry/UV light
	SAE J2334:2002	Laboratory Cyclic Corrosion Test
	WSK-M2G299	Corrosion test, cyclic
	GM4298P	Accelerated cyclic corrosion test
	GM4476P	Cyclic corrosion test
	GM9540P	Cyclic corrosion tests for vehicle components

Release time: 2024-02-22

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