Relationship between temperature and corrosion of metals by sulfides in petrochemical refining
Thread Content
1. At t≤120℃, sulfides do not decompose; in an anhydrous environment, there is no corrosion of the steel； However, when moisture is present, various H2S-H2O types of corrosion occur in the light oil sections of various units in the refinery, resulting in corrosion areas that are difficult to control. 2. For 120℃＜t≤240℃, the active sulfides in crude oil remain undecomposed, so they cause no corrosion to steel. 3. For 240℃＜t≤340℃, the sulfides begin to decompose, producing hydrogen sulfide; corrosion of the steel then starts, and this corrosion intensifies as the temperature rises. 4. For 340℃＜t≤400℃, H2S begins to decompose into H2 and S. The corrosion reaction equations for steel at this stage are: H2+S → Fe+S→ FeS; R-S-H (thiol) + Fe → FeS+unsaturated hydrocarbons. The FeS film formed acts as a barrier against further corrosion; however, in the presence of acids such as hydrochloric acid or naphthenic acid, these acids react with FeS and destroy the protective film, allowing corrosion to proceed further and intensifying the effect of sulfides on corrosion. 5. For 420℃＜t≤430℃, high-temperature sulfur causes the fastest corrosion of steel. 6. When t > 480℃, the sulfides are nearly completely decomposed, and the corrosion rate decreases. 7. When t > 500℃, it is not within the range of sulfide corrosion; at this temperature, high-temperature oxidative corrosion occurs.
In the petroleum refining process, the relationship between sulfides’ corrosion of metals and temperature includes the following points: 1. When the temperature is below 120°C, sulfides remain undecomposed, and they will only cause corrosion to steel in the presence of water. 2. Between 120°C and 240°C, the active sulfides in crude oil have not yet decomposed, so they do not cause corrosion to steel. 3. When the temperature is between 240°C and 340°C, sulfides begin to decompose, producing hydrogen sulfide; as the temperature rises, the corrosion of steel intensifies as well. 4. When the temperature exceeds 340°C but is below 400°C, hydrogen sulfide decomposes into hydrogen and sulfur; the resulting iron sulfide (FeS) film can prevent further corrosion, but this protective film is destroyed in the presence of acid. 5. Between 420°C and 430°C, at high temperatures, sulfur causes the fastest corrosion of steel. 6. Above 480°C, the sulfides decompose almost completely, and the corrosion rate begins to decline. 7. When the temperature exceeds 500°C, it is no longer a problem of sulfide corrosion; instead, high-temperature oxidation corrosion becomes the dominant factor. .