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All metals and certain ceramics and polymers are susceptible to corrosion, that is typically created by the presence of moisture in the air or direct contact with water. In metals this technique is oxidation: the alteration of electrostatic charge where salts or oxides are produced, causing damage to the metal's structure. Rusting, the production of red oxide within an iron structure, is a very common example of this. The word 'degradation' is applied to the corrosion of non-metals, nevertheless the process is similar: the corroding material surrenders electrons in a chemical reaction and drops its structural integrity. Corrosion testing can be applied for the following forms of damage.

Galvanic corrosion happens when two metals come into contact within the electrolytic medium or one metal is confronted with two different electrolytes. Microbiologically Influenced Corrosion is brought on by micro-organisms attacking a metallic or non-metallic material either with or without the presence of oxygen; for example Accelerated Low Water Corrosion damages steel piles round the low-water mark, leaving behind an orange sludge for a deposit. Aerospace materials, engines or power-generation materials are typical instances of substances vulnerable to  High Temperature Corrosion. Metal Dusting happens in high-carbon-dioxide contexts, creating a tell-tale film of graphite on metal and reducing the metal to powder.

Corrosion testing requires the promotion of degradation in test samples to ascertain the extent and rate of any damage by corrosion within the environment. Accelerated Corrosion Testing is an approach which is designed to calibrate the long-term effects on the system of alternating wet and dry cycles, inducing the output of partially dry corrosion agents that worsen degradation within the system. Typical is the ISO 11474 test, which employs an outdoor intermittent salt-water spray.

Weld testing for corrosion damage or any other structural compromise can be achieved via Dye Penetrant Inspection. Penetrant is used to a test surface and left for 5-30 minutes. Developer, either dry powder or Non-Aqueous Wet Developer (e.g. acetone), draws penetrant from defects in a visible ‘bleed-out’ process. Different weld testing methods involve Magnetic Particle Testing, X-rays, 3D X-rays and microscopy: all considered as Non-Destructive Inspection approaches. [http://columbusbbw.com/activity/p/499831/ ColumbusBBW ]