Cracks have appeared in multiple stainless steel units used for low-temperature methanol washing – what is the cause?
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Cracks have appeared in multiple stainless steel units used in low-temperature methanol washing. Two cracks occurred near the weld seam of the head of the methanol flash tank, two cracks appeared at the head of the rich methanol filter, and as many as ten cracks appeared at the head of the second lean methanol cooler. Yet the process was operating normally with no abnormalities detected – what could be the reason for this? Dear sea friends, please share your valuable opinions!
I often saw cracks in stainless steel in many dyeing and printing factories, and later learned that this was caused by chloride corrosion. I’m not familiar with the chemical industry, but I hope this can be of some reference to you.
It’s because it’s washed too much..... Pity!~~~~~~ It has little to do with the equipment itself! Actually, your chemical industries are fine; the worst situation is in pharmaceutical factories... The equipment is fine at first, but they keep washing it over and over again, maybe twice a week, and then... cracks appear. In the end, I’m the one who suffers; even when my own equipment is fine, I still have to pay to have it repaired for free.
Another type is chemical corrosion, which includes electrochemical corrosion. Chemical corrosion is a direct chemical reaction, such as the reaction between chlorine and iron. Electrochemical corrosion is caused by the unevenness of pipeline materials; factors such as uneven potential and uneven lattice structure can all lead to corrosion. The corrosion of stainless steel by liquid chlorine is mainly pitting corrosion, a type of corrosion that is difficult to detect and prevent. Theoretically, the more easily passivated a metal is, the more sensitive it is to pitting corrosion. In other words, pitting is more likely to occur. This is because metals in a passivated state still possess a certain degree of reactivity, meaning that the dissolution and restoration of the passivation film are in a dynamic equilibrium. When the corrosive medium contains active anions (such as chlorine, which is common), the equilibrium is disrupted and dissolution becomes dominant. The reason is that chloride ions preferentially adsorb onto the passivation film of stainless steel, displacing oxygen atoms; they then combine with the cations in the passivation film to form soluble chlorides. As a result, small pits (20 to 30 micrometers in size) are formed at specific points on the newly exposed base metal, known as pitting nuclei. Subsequently, when the pitting nucleus grows to over 30 micrometers, it becomes a source of pitting, after which pitting accelerates corrosion under autocatalytic acidification.
From the perspective of device manufacturing and processing, is it possible that excessive stress was generated during production and not eliminated, resulting in this issue?