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The HIC hydrogen-induced cracking test is also known as the resistance to hydrogen-induced cracking test or the resistance to hydrogen embrittlement test. The full English name for hydrogen-induced cracking (HIC) is Hydrogen induced cracking, abbreviated as HIC. Compared to metal atoms, hydrogen atoms are very small, allowing them to diffuse into the interior of the metal matrix from the gaps between metal atoms. There, they undergo physicochemical reactions with the matrix, thereby reducing the mechanical properties of the metal matrix. Principle of hydrogen-induced cracking: When steel is exposed to an environment containing hydrogen sulfide, hydrogen generated as a result of corrosion penetrates into the steel. Atomic hydrogen diffuses to interfaces such as non-metallic inclusions, where it transforms into molecular hydrogen at those defect sites, thereby increasing the internal pressure within the voids. (1) In all cases of hydrogen embrittlement, hydrogen atoms that penetrate directly into the steel reduce the atomic bonding forces between the steel grains, resulting in a decrease in the ductility and end-face contraction rate of the steel, as well as changes in its strength. Hydrogen embrittlement theory: At the crack tip, a cathodic reaction corresponding to the anodic reaction occurs. The hydrogen generated or processed enters the steel, causing hydrogen-induced cracking. (2) Hydrogen corrosion: Hydrogen reacts with the carbides in steel to produce methane. This methane gas cannot diffuse out of the steel, so it accumulates between the grains, creating localized high pressures that lead to stress concentration. This, in turn, causes microcracks or bulging in the steel. The sources of hydrogen can be divided into internal hydrogen and external hydrogen: (1) Internal hydrogen refers to the hydrogen that is already present within the material before it is used, mainly arising from processes such as smelting (moisture in raw materials), pickling (acids), electroplating (hydrogen evolution at the cathode), welding (failure to dry the material before welding), and heat treatment (quenching, etc.) ； (2) External hydrogen or ambient hydrogen refers to the hydrogen absorbed by the material during use. When operating in H2 or H2S gas or an aqueous solution of H2S, H2 or H2S can release H into the components or specimens. Under hydrogen pressure, adjacent hydrogen blister cracks at different levels connect with each other, forming internal cracks with a stepped pattern; this phenomenon is known as hydrogen-induced cracking. The cracks can sometimes also extend to the metal surface. The occurrence of HIC also does not require external stress; it is generally associated with high-density, large-planar inclusions in the steel, or with the irregular microstructure resulting from the segregation of alloying elements within the steel. Hydrogen-induced cracking (HIC) is now widely used to describe this type of crack, and it has been adopted by NACE International. Test plan and standards: NACE TM0284 – Method for evaluating resistance to hydrogen-induced cracking in pipeline steels and pressure vessels; GB/T 8650 – Method for evaluating resistance to hydrogen-induced cracking in pipeline steels and pressure vessel steels. Sample requirements: Sample dimensions: length 100 mm, width 20 mm. 1) Thickness < 30mm: Sample in parallel; 1 set of samples per product, with 3 samples in each set ； 2) 30mm ≤ thickness < 88mm: Staged sampling; 1 set of samples is taken per product, with a quantity of 3 samples ； 3) Thickness ≥ 88 mm: Sampling in stages; if the thickness of 1 sample is < 30 mm, the maximum number of samples shall be taken based on the actual thickness. HIC test procedure 1: Solution A is a distilled water solution containing 5% sodium chloride by mass and 0.50% glacial acetic acid ； 2. The HIC hydrogen-induced cracking test procedure is as follows: (1) Prepare the specimen ； (2) Place in the test container ； (3) Prepare the solution ； (4) Measure the pH of the initial solution ； (5) Pass nitrogen gas at a rate of 100 ml/min/L to remove oxygen for two hours ； (6) Pass H2S at a rate of 200 ml/min/L for at least 1 hour until the solution is saturated ； (7) Measure the pH value and H2S content of saturated H2S solutions ； (8) Maintain a positive H2S pressure until the end of the test ； (9) pH value of the solution at the end of the test ； (10) Test result verification.