In the gasoline stabilization distillation tower overhead condenser in the oil refining industry, the finished product cooler of the hydrodesulfurization unit, the stripper overhead condenser, and the oil field gathering and transportation pipelines, carbon steel and low alloy steel are exposed to an environment containing hydrogen sulfide. In the process, hydrogen generated due to corrosion invades the steel and accumulates locally, causing step-like cracking in the rolling direction of the steel. This phenomenon is called hydrogen-induced cracking, which also appears as bubbling. Hydrogen sulfide is one of the most corrosive and harmful media in oil and natural gas. In the process of natural gas transportation, hydrogen sulfide accounts for a large proportion of the stress corrosion of transmission pipelines. When used in a wet hydrogen sulfide environment, hydrogen sulfide can cause hydrogen bubbling (HB), hydrogen-induced cracking (HIC) and stress-oriented hydrogen-induced cracking (SOHIC) inside carbon steel. When pipes are exposed to acidic environments such as hydrogen sulfide, the hydrogen produced by corrosion invades the steel and causes cracks called hydrogen-induced cracking (HIC).
The mechanism of hydrogen-induced cracking: When steel is immersed in an environment containing hydrogen sulfide, the hydrogen generated due to corrosion penetrates into the steel, and the atomic hydrogen diffuses to the interface such as non-metallic inclusions, and is converted into molecular hydrogen at the defective parts, improving the cracking mechanism. the internal pressure of the cavity.
1) Hydrogen embrittlement: After the hydrogen atoms generated under various circumstances directly penetrate into the interior of the steel, the atomic bonding force between the steel grains is reduced, resulting in a reduction in the elongation and end shrinkage of the steel, and a change in the strength. Hydrogen embrittlement theory: A cathodic reaction corresponding to the anodic reaction occurs at the crack tip. Generated or processed hydrogen enters the steel causing hydrogen-induced cracking.
2) Hydrogen corrosion: Hydrogen reacts with the carbides in the steel to produce methane. The methane gas cannot diffuse out of the steel and accumulates between the grains to form local high pressure, causing stress concentration and causing micro-cracks or bubbling in the steel.
