How about the performance of stainless steel square pipe?

Metals in the atmosphere can react with oxygen to form an oxide film on the surface. Iron oxide formed on ordinary carbon steel will continue to oxidize, so that the corrosion continues to expand, and eventually the formation of holes. This CAN be DONE BY COATING THE SURFACE of the carbon STEEL WITH PAINT OR BY PLATING AN OXIDIZED METAL, BUT THIS coating is only a thin film. If the coating is destroyed, the underlying steel will begin to rust again. Whether the stainless steel tube is corroded is related to the content of chromium in the steel. When the content of chromium in the steel reaches 12%, in the atmosphere, the surface of the stainless steel tube generates a layer of passivated and dense chromium-rich oxide to protect the surface, which can prevent further reoxidation. This oxide layer is extremely thin, through which the natural shine of the steel surface can be seen, giving stainless steel a unique surface. If the chromium film once destroyed, the chromium in the steel and oxygen in the atmosphere to regenerate the passivation film, continue to play a protective role. In some special environments, stainless steel will also appear some local corrosion and failure, but stainless steel and carbon steel is different, will not appear uniform corrosion and failure, so the corrosion allowance for stainless steel pipe is not meaningful.