What are the hazards of acidic water with a pH of 9.5 in hydrogenation cold high-pressure processes?
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The pH value of the acidic water from hydrodesulfurization is 9.5; what harm does it cause to carbon steel and stainless steel?
Corrosion, right. . . . This is the most obvious, right?
Could you explain the corrosion mechanism? Thank you.
The pH value of the hydrogenated and cooled high-acidity water is 9.5, and it does have a corrosive effect on carbon steel and stainless steel. Here, the overall usage conditions need to be considered, such as the medium used, temperature, pH value, etc. The acidic water here contains a certain amount of H2S, NH3, as well as various other substances such as CO2 and CN‑oil, with a pH value of 9.5. If the pH value in the medium is 9.5 and other factors are not considered, corrosion is minimal. However, there are also corrosive factors in the form of acidic water here; as a result, corrosion occurs under the combined influence of the medium, pH value, temperature, pressure, etc., with stress corrosion being the main type. Cracks appear mainly in the weld bead and its heat-affected zone.
Master, I’m still confused. An increase in PH indicates an increase in the levels of ammonia and ammonium salts, as the solubility of hydrogen sulfide is 1:2.6, meaning it is slightly soluble； But I haven’t considered how carbon dioxide and cyanide ions react to produce it ； The stress corrosion you mentioned – what element causes it, and is it related to a high pH level?
Corrosion condition: After high-pressure air cooling, the temperature is reduced to around 50°C before entering the cold high-pressure separator; this area is of the low-temperature H2S-H2O-NH3 type. H2S undergoes bipolar dissociation in water to produce HS‑, S2‑, and H‑; when combined with NH3, it forms NH4HS, which is highly corrosive. Due to the low temperature of the separator, crystallization occurs in the NH4HS solution, leading to under-scale corrosion. Furthermore, a certain amount of Cl (about several dozen PPM) is present in the medium water, and it reacts with NH3 to form NH4Cl. When the water volume is low, crystallization occurs easily; the resulting NH4Cl, upon absorbing moisture, creates locally highly acidic solution conditions, leading to severe under-scale corrosion. Under low-temperature conditions, these corrosive agents tend to form ammonium hydrosulfide and ammonium sulfide deposits in areas of equipment and pipelines where fluidity is poor, leading to under-deposit corrosion of the equipment.