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Home > Answers > How to determine the degree of rust on steel plates?
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Q: How to determine the degree of rust on steel plates?

11/08/2025 17:09:55 2    answers in: Other
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A

The degree of rust on steel surfaces is classified into four levels according to the national standard GB/T 8923-1.

Grade A: The steel surface is completely covered with mill scale, with no visible rust, as if tightly encased by a thick protective layer.
Grade B: The steel is showing signs of rust, with some mill scale beginning to flake off, and rust stains appearing. Surface rust is beginning to show, and the protective layer is no longer intact.
Grade C: As rust progresses, large sections of mill scale flake off, and pitting corrosion occurs. Rust becomes increasingly noticeable on the steel surface, and pitting gradually emerges.
Grade D: The mill scale is completely removed, and pitting corrosion is widespread on the steel surface, leaving numerous holes and rust stains.

A

The degree of rust on steel plates can usually be determined through observation, measurement, and the use of specialized tools. Visual inspection is the basis for assessing the overall rust condition, but a more precise assessment requires the use of instruments.

Color and Rust Area: The surface color of steel can reflect the degree of rust. Generally, the appearance of reddish-brown or brown spots on the surface indicates the beginning of rust. If these spots appear in multiple areas, the rust is more severe. You can compare the rust level with a standard photograph or a rust grade chart to determine the approximate rust level.

A layer of rust will form on the surface of steel. This rust will change the surface texture, making it rough, uneven, and even bumpy. When this surface texture becomes more pronounced, the rust is more severe.

The thickness of the surface can be used to determine the degree of rust. You can roughly estimate the thickness of the rust layer by visual inspection or using simple tools like calipers. Generally speaking, the more rust on the surface, the thicker the steel. A thicker rust layer on the steel surface may indicate more severe corrosion.

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