Learn about hydrogen sulfide corrosion in the petrochemical industry
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H2S-H2O: In H2S-containing aqueous solutions, steel suffers from general corrosion not only due to the formation of FeS as a result of anodic reactions, but also because hydrogen generated by cathodic reactions can penetrate into and diffuse within the steel, leading to hydrogen blistering (HB), hydrogen-induced cracking (HIC), stress-oriented hydrogen-induced cracking (SOHIC), and sulfide stress cracking (SSC). a. General corrosion: The corrosion of steel by hydrogen sulfide; generally, as the temperature increases, so does the degree of corrosion. The corrosion rate is highest at 80°C ； b. Hydrogen bubbling (HB): The hydrogen atoms generated by the cathodic reaction accumulate on the surface of the steel, and the penetration of hydrogen into the steel is accelerated due to the effect of HS-. When hydrogen atoms gather within the defects in steel and combine to form hydrogen molecules, their volume increases by about 20 times. Due to volume expansion, the hydrogen pressure in these areas gradually increases. If these defects are located just beneath the surface of the steel, the high-pressure hydrogen within the defects can cause the outer layer of metal to bulge, forming bubbles known as hydrogen embrittlement. Bubbling cracking occurs when the pressure inside the bubbles is sufficient to cause the metal surface to crack. The formation of hydrogen bubbles does not require external pressure. Typical cases: Hydrogen bubbling in aromatic reactor test blocks; c. Hydrogen-induced cracking (HIC). If defects are located deep within the steel, the accumulation of hydrogen in those areas can lead to an increase in hydrogen pressure, which in turn causes delamination or cracking within the metal. The banded distribution of MnS inclusions in steel increases the sensitivity to hydrogen-induced cracks. The formation of hydrogen-induced cracks also does not require external pressure. d. Stress-oriented hydrogen-induced cracking (SOHIC) Stress-oriented hydrogen-induced cracking occurs when, under stress influence, small cracks that form due to hydrogen accumulation at inclusions and defects develop in a direction perpendicular to the stress. That is, it develops in the direction of the steel’s wall thickness. Stress-induced hydrogen cracks often occur in the heat-affected zone of welded joints and in areas with high stress concentration. e. Sulfide stress cracking (SSC): Hydrogen atoms generated by sulfides penetrate into the steel, dissolving in the crystal lattice and causing brittleness. Cracking occurs under tensile stress or residual stress. Sulfide stress cracking typically occurs in the high-hardness zone of the weld heat-affected zone.
In the petrochemical industry, the corrosion of steel by hydrogen sulfide (H2S) manifests in the following ways: 1. General corrosion: The combination of hydrogen sulfide with aqueous solutions, along with increased temperatures, exacerbates corrosion, which is most severe at 80°C. 2. Hydrogen bubbling (HB): The cathodic reactions in a hydrogen sulfide environment cause hydrogen atoms to accumulate on the steel surface and penetrate inward, generating pressure that causes the metal to bulge, which may lead to surface cracking. 3. Hydrogen-induced cracking (HIC): If hydrogen atoms accumulate at deep internal defects in steel, it may cause internal delamination or cracking; this type of cracking occurs without the need for any external pressure. 4. Stress-oriented hydrogen-induced cracking (SOHIC): In the presence of stress, hydrogen accumulates at inclusions or defects, leading to the formation of rows of small cracks that develop perpendicular to the direction of the stress, such as in the weld heat-affected zone. 5. Sulfide stress cracking (SSC): Hydrogen atoms generated by hydrogen sulfide penetrate into the steel lattice, and cracking can easily occur under tensile stress or residual stress, especially in the high-hardness areas within the heat-affected zone of welds. .