Corrosion resistance

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Salt spray test

Salt spray refers to the dispersion system composed of small droplets containing salt in the atmosphere. Salt spray corrosion is one of the most common and destructive atmospheric corrosion. The corrosion of the metal surface by salt spray is caused by the electrochemical reaction between the chloride ion and the inner metal through the oxide layer and the protective layer on the metal surface. The quality of salt fog corrosion resistance of products or metal materials can be tested.

1. Neutral salt spray test (NSS test) is the earliest and most widely used accelerated corrosion test method. It uses 5% NaCl solution, and the pH of the solution is in neutral range (6~7) as a spray solution. The test temperature is 35 ℃, and the sedimentation rate of salt spray is required to be between 1-2ml / 2000px · H.

2. The acetate spray test (ASS test) is developed on the basis of neutral salt spray test. It is to add some glacial acetic acid into 5% sodium chloride solution to reduce the pH value of the solution to about 3, the solution becomes acidic, and finally the salt mist formed changes from neutral salt mist to acid. Its corrosion rate is about three times faster than NSS test.

3. Copper salt accelerated acetate spray test (lrhs-663p-ry) is a kind of rapid salt spray corrosion test newly developed abroad. The test temperature is 50 ℃, and a small amount of copper salt copper chloride is added into the salt solution to strongly induce corrosion. Its corrosion rate is about 8 times that of NSS test.

4. Alternating salt spray test is a comprehensive salt spray test, which is actually a neutral salt spray test plus a constant heat and humidity test. It is mainly used for the whole machine products of cavity type. Through the infiltration of damp environment, salt spray corrosion occurs not only on the product surface, but also inside the product. It is the product in salt fog and hot and humid two environmental conditions alternate conversion, the final assessment of the electrical and mechanical properties of the whole machine products have no change.

Determination methods of salt spray test results: rating determination method, weighing determination method, corrosives occurrence determination method, corrosion data statistical analysis method.

Method standard GB / t1771-2007 paints and varnishes - Determination of resistance to neutral salt spray

Corrosion test in artificial atmosphere GB / T 10125-1997 ASTM B 117-2011

Total corrosion

Comprehensive corrosion test corrosion test occurs on all or most of the metal surface, also known as uniform corrosion test. In most cases, a protective corrosion test product film will be formed on the metal surface, which will slow down the corrosion test. Some metals, such as steel, dissolve rapidly in hydrochloric acid without forming a film. Generally, the average corrosion test rate (i.e. the loss of several millimeters of material thickness per year) is used to measure the degree of uniform corrosion test and also as the principle of material selection. Generally, the annual corrosion test rate is less than 1-1.5mm, which can be considered as applicable (with reasonable service life).