Corrosion margin issue
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The corrosion margin value indicated on the drawing represents the corrosion margin for that duration of time.
The corrosion margin is the annual corrosion rate multiplied by the expected service life; it is usually provided by the process engineering team in design firms, and if no process design has been carried out, it can only be provided by the user. It’s difficult to specify the expected lifespan; generally, 10 years or 20 years is indicated.
The amount of corrosion is determined based on the material’s corrosion rate toward other materials and its service life.
As mentioned by the previous speakers, it refers to the amount of corrosion that occurs on a device during its service life (the typical service life is specified in construction drawings or similar documents; if not specified, it is generally assumed to be 20 years), depending on the media it comes into contact with.
Design service life. 15 years is common.
It is generally considered based on a service life of 10 years.
The corrosion margin should be determined based on the expected service life B of the container and the corrosion rate K of the medium on the metal material, that is: C2=K*B. The typical service life of containers is considered to be 10 years, while that of towers, reactors, etc. is considered to be 20 years. The corrosion rate can be obtained from corrosion handbooks, chemical property handbooks, and relevant foreign materials, or determined through actual \"test coupon\" experiments. The following parameters can also be used as a reference for determination: 1. Degree of corrosion: no corrosion, corrosion rate less than 0.05 mm/year, corrosion margin of 0 mm ； 2. Degree of corrosion: Mild corrosion, with a corrosion rate of 0.05–0.13 mm/year; the corrosion margin is 1 mm or more ； 3. Degree of corrosion: Corrosion is present; the corrosion rate is 0.13–0.25 mm/year, with a corrosion margin of 2 mm or more ； 4. Degree of corrosion: Severe corrosion, with a corrosion rate greater than 0.25/year; the corrosion allowance is 3 mm or more.
The person who asked this question didn’t understand what a corrosion allowance is. A corrosion allowance is something that prevents pressure-bearing components from losing thickness due to corrosion or mechanical wear; it is determined based on the design service life and the rate at which the metal material is corroded by the surrounding medium.