What causes pitting?
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Material: 316L; Pipe diameter: DN50; Medium: Vinyl chloride in gas phase; Temperature: ~60°C; Pressure: -0.086~1.09 MPa; Corrosion condition: Pitting and perforation. What causes this?
Vinyl chloride should require hydrogen chloride; could there be a leak causing chloride ions to cause corrosion?
The medium contains not only vinyl chloride but also hydrogen chloride and chloride ions. It is mainly the corrosion and damage to metal surfaces caused by hydrogen chloride and chloride ions.
There should be trace amounts of hydrogen chloride in the vinyl chloride medium; could trace amounts of chlorine cause corrosion of 316L? No other pipelines in the same system are corroded, so I suspect there is an issue with the material.
There is chloride corrosion; ordinary materials are likely not suitable
The first is a material issue； Second, the chloride ion level is above the limit ； Third is temperature and pressure (under certain temperature and pressure conditions, even low concentrations of chloride ions can cause corrosion of 316L material) ； The concentrations of other organic acids are above the limit
If I don’t understand, I’ll ask. May I ask, does chloride-induced corrosion of stainless steel fall under intergranular corrosion? Can this type of corrosion be seen with the naked eye? This pitted appearance is typical of pitting corrosion; it’s likely due to a problem with the material or prolonged use, with various ions such as chloride ions and acidic ions causing electrochemical corrosion that results in pitting.
I also suspect there’s a problem with the material; in the past, we used patch welding to address it, but it still leaks； Currently, the solution is to replace the pipes; for now, 304 material will be used (316L pipes need to be purchased, and the lead time for procurement is long)