Discussing hydrogen corrosion in the petrochemical industry and its control methods

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1. Hydrogen bubbling: In low-strength steels, especially those containing a large amount of non-metallic inclusions, the hydrogen atoms generated in the solution can easily diffuse into the metal. Most of this hydrogen combines with other elements on the other side of the material’s surface to form H2 and escape, but a small amount of hydrogen remains trapped in the voids within the steel, where it also combines to form H2. Since hydrogen molecules cannot diffuse, this accumulation leads to high internal pressures, causing bubbles to form on the surface of the steel, or even causing it to rupture. 　　When the environment contains toxins such as sulfides, cyanides, and phosphorus-containing ions that prevent the hydrogen release reaction, hydrogen atoms enter the steel and cause bubbling. Materials in the petroleum industry often contain the aforementioned toxins, and hydrogen bubbling is a common hazard. Prevention method: Removing such toxins is the most effective approach ； Hole-free calm steel can also be used as a substitute for boiling steel, which contains numerous holes. Furthermore, linings made of austenitic stainless steel or nickel, which are impermeable to hydrogen, or rubber, plastic, ceramic tiles, along with the addition of corrosion inhibitors, can be used. 2. Hydrogen embrittlement: In high-strength steels, the lattice undergoes significant deformation; when hydrogen enters, the lattice changes further, which reduces toughness and ductility and leads to embrittlement, allowing the material to crack under external forces. However, hydrogen embrittlement is reversible before rupture; by undergoing appropriate heat treatment to allow hydrogen to escape, the metal can regain its original properties. Generally, the higher the strength of steel, the greater its susceptibility to hydrogen embrittlement fracture. Its mechanism is not yet fully understood; there are various theories, such as: the accumulation of hydrogen molecules creating high internal pressure ； The adsorption of hydrogen reduces the surface energy, or affects the bond strength of atomic bonds, thereby promoting dislocation movement, etc. Some indications suggest that ferritic and martensitic ferroalloys react with hydrogen at the crack tips, while metals such as titanium and tantalum, which readily form hydrides, tend to react with dissolved hydrogen at high temperatures to produce brittle hydrides. Hydrogen can also cause decarburization at high temperatures. 　　Hydrogen that enters metals is often generated during operations such as electroplating, welding, pickling, and cathodic protection. After the crack tip is acidified due to stress corrosion, hydrogen embrittlement also occurs, but anodic corrosion has caused permanent damage, which is different from simple hydrogen embrittlement. Hydrogen embrittlement is not related to voids in steel; therefore, the prevention methods differ slightly from those used to prevent hydrogen blistering: in environments where hydrogen embrittlement is likely to occur, it is advisable to avoid using high-strength steels, and Ni or Cr alloyed steels can be used instead ； Use low-hydrogen welding electrodes during welding, and keep the environment dry (water is the main source of hydrogen) ； The plating solution needs to be selected, and the current must be controlled ； A corrosion inhibitor is added to the pickling solution. Once hydrogen has entered the metal, low-temperature baking can be used to remove it; for steel, dehydrogenation generally takes place at 90–150°C.