What Is Corrosion Testing?
Corrosion testing is a general term for testing to confirm corrosion resistance under conditions that accelerate corrosion by extracting environmental factors that corrode materials.
Corrosion is one of the factors that cause products to break. Corrosion is caused by a complex combination of various environmental factors, and it is difficult to reproduce it completely. Even if it could be reproduced in a pseudo-realistic manner, it would require extensive testing. However, elemental testing can be performed simply by extracting the environmental factors that are thought to affect corrosion.
Since corrosion testing is conducted under conditions that dare to accelerate corrosion, it is possible to evaluate corrosion resistance in a relatively short period, and it is easy to compare the results with other materials.
Uses of Corrosion Testing
Corrosion testing is used as a standard for selecting materials and evaluating the corrosion resistance of products. For example, only materials that exceed a certain standard are used as materials.
There are also standardized corrosion evaluation standards which are used in a wide range of fields, including the automotive, home appliance, electrical appliance, civil engineering, and construction fields.
Principle of Corrosion Testing
Corrosion testing is performed using the mechanism of degradation caused by chemical reactions of materials. Degradation due to physical actions such as abrasion or scratches is not called corrosion, but only degradation due to chemical reactions.
First, in corrosion testing, the materials used in a product are placed in the environmental factors of the environment in which the product is likely to be used. For example, if the product is to be used in a coastal area, the environmental factors are the components of seawater, and if the product is to be used outdoors, the environmental factors are the components of acid rain.
The product is then left for a certain period under conditions that accelerate corrosion and observed. Over time, we will clarify the manner of corrosion and the time it took to corrode.
Types of Corrosion Testing
There are various types of corrosion testing, depending on the combination of materials and environmental factors. Among them, there are four typical tests that are commonly performed:
1. Real-World Exposure Tests
This corrosion testing is not an accelerated test, but rather a test to see how the material corrodes over time under actual environmental conditions. Also called weathering resistance testing, this test examines how corrosion progresses under the influence of light, humidity, water, and other factors.
It is often used to check the corrosion of bridges, buildings, machinery, vehicles, etc., which are mainly left outdoors for long periods of time. It can confirm the correct degree of corrosion, but it is not an accelerated test, and the test period is long.
2. Simulated Environmental Exposure Test
In this corrosion testing, the most corrosion-promoting conditions are selected according to the material to be tested, and the degree of corrosion is checked under the conditions that are most likely to promote corrosion.
Since the test is conducted under more severe conditions than corrosion that occurs in a real environment, it is possible to determine the limit value of the corrosion resistance strength of the material and to examine its corrosion resistance in a short period.
3. Electrochemical Corrosion Testing
In this corrosion testing, a pseudo-corrosive environment is created by adding electrochemical reactions, and the conditions under which corrosion occurs and its degree can be measured.
Specifically, corrosion resistance is evaluated using electrochemical measurement tests such as corrosion potential measurement, anodic polarization curve measurement, and impedance measurement testing. Evaluation combined with high-temperature, high-pressure water corrosion testing is also available.
4. Localized Corrosion Testing
In this corrosion testing, a material is immersed in a solution that is prone to corrosion, and stress is applied to cause strong corrosion in one area.
This test is used to evaluate metallic materials whose oxide film is destroyed by heat or force and corrodes at once.
Other Information on Corrosion Testing
Major Corrosion Factors Used in Corrosion Testing
Corrosion testing involves the use of various corrosion factors that can corrode materials. Commonly used corrosion factors are:
1. Salt Water
This factor is used for corrosion testing of materials left or used in coastal areas such as the sea. Tests using salt water include the salt spray test.
2. Acid Rain
This factor is used for corrosion testing of materials that are left or used near factories or in the open air. It is used, for example, in combined cyclic testing (CCT), which assumes atmospheric corrosion testing.
3. Gas and Ozone
This factor is used to examine the corrosion of materials used in factories and other places where corrosive gases are generated. Corrosive gases such as sulfur dioxide, hydrogen sulfide, nitrogen dioxide, chlorine, and ozone are used in gas corrosion testing.
4. Light
This factor is used for corrosion testing of materials that are left or used in places where they are exposed to sunlight. It is used for weathering resistance testing.
5. Low Temperature
This factor is used in corrosion testing of materials used in cold climates. It is used in temperature and humidity constant temperature and humidity cycling tests to examine coating hardening, embrittlement, and delamination due to low temperatures.
6. Wetting
This factor is used for corrosion testing of materials used in humid environments. It is used in water vapor oxidation tests, constant temperature and humidity, and temperature and humidity cycling tests.
7. Drying
A factor used in corrosion testing of materials used in low-humidity, dry areas. It is used in drying tests.
8. Chipping
This factor is used in corrosion testing that assumes corrosion that progresses from collisions and abrasions from road pebbles and other objects that are rolled up by driving automobiles and other vehicles. It is used in weathering tests.