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The entire or most of the metal surface is corroded, with the degree of corrosion being roughly uniform. Generally, a layer of corrosion product film on the surface can slow down corrosion; high-temperature oxidation is an example of this. Similarly, easily passivated metals such as stainless steel, titanium, and aluminum form an extremely thin passivation film in an oxidizing environment, which provides excellent protection and essentially stops corrosion. The oxide film (rust) formed on iron in the atmosphere and water has very low protective properties. Generally, uniform corrosion is quite severe. There are also cases of uniform corrosion that do not produce a surface film, such as iron dissolving rapidly and completely in dilute sulfuric acid or hydrochloric acid. Full-scale corrosion without a membrane is very dangerous, but it occurs rarely in real life, unless there is a serious mistake in material selection, such as using iron or aluminum equipment to store and transport hydrochloric acid. The degree of uniform corrosion can be expressed by the corrosion rate. Two units are commonly used: one is the weight lost per unit area per unit of time, expressed in g/(m2·h) ； The other is the average corrosion thickness per unit time, expressed in mm/year. The conversion relationship between the two is as follows: lmm/year = 8.76 g/(m2·h) × 1/d, where d is the density of the material. The expected service life of equipment can be estimated from the thickness corrosion rate, and this method is more widely used.