What defects, and how did they form?
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For 20-grade steel, the surface has a scale-like appearance, but it feels smooth to the touch. How did this come about? Is it a defect?
The fish-scale-like pattern on the surface of steel may be caused by uneven surface temperatures during the cooling process. When steel cools, the cooling rates at the surface and within the material differ, which can result in irregular compressive stresses and lead to a fish-scale-like texture on the surface. This situation is more common in some alloy steels or specially treated steels. If the surface feels smooth to the touch and it does not affect performance, then this fish-scale-like pattern is not necessarily a defect, but it may affect the appearance of the material. In applications that require precision surface finishing or have special surface quality requirements, this may be considered a defect. You can evaluate whether it is acceptable based on specific uses and technical requirements. .
The description is unclear. What operating conditions, how long it will be used, internal medium. It needs to be mentioned.
His titles aren’t clear enough; it’s not obvious how the work is carried out in practice. What he seems to mean is why the surface is rough, and it’s unclear whether it’s related to equipment or pipes. I don’t know what to express.