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corrison when carbon steel and stainless steel
Jan 05, 2018

Why pipe component and pipe support parts which made from stainless steel and non ferrous metal cannot touch carbon steel during storage?

For the matter of touch between stainless steel and carbon steel, mainly to avoid galvanic corrosion. There is natural potential difference between different metal material. When the difference reach some value and there is electrolyte external, electron will shift happen when different metal get in touch, which called current flow and corrosion will happen together with the flow. And which metal will get corrosion is determined by their electromotive series. Such as copper and zinc, natural potential of zinc is lower than copper, so zinc will get corrosion if they touch each other. The battery use this theory, just copper is replaced by graphite.

The natural potential between stainless steel and carbon steel is big, corrosion will happen if they get touch and there is water or other conducting medium around. In regular environment it is carbon steel to get rust. But if there is chloridion(such as sea water), carbon steel get just a little rust and stainless steel will get dots rust. This is because the oxygen film on stainless steel surface get damaged very quickly under chloridion affect and galvanic corrosion will happen in this situation. But carbon steel will have no dots rusted.

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