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HIC resistant material is used since many years. Many published articles, such as test methods or recommendations from the likes of NACE, ISO or EFC, are mixed with the further requirements of oil and gas or engineering companies. Therefore, a variety of sour service specifications are applied for the plate purchasing process. In spite of this variety, the steel manufacturer has to find the appropriate way to provide high quality plates with homogeneous HIC resistance, combined with high availability.
The basic condition is a corrosion reaction creating a source of atomic hydrogen in a wet and sour environment, leading to the absorption of hydrogen by the steel. The presence of H2S as a promoter is necessary. The absorbed hydrogen migrates towards inclusions and imperfections where it recombines to form H2. This can lead to substantial pressures that cause cracks in the steel lattice with its reduced toughness due to the absorbed hydrogen. The various types of damage mechanisms can be found.
The simplest and most readily understood case of this is HIC, where no external stress is necessary for the damage. Cracks of this type are planar and sometimes appear step-wise. They are offen located in the mid-thickness of the plate. Hydrogen blistering is a Special case of HIC due to the close-ness of the cracks to the surface of the material.
The second case is a corrosion attack in combination with stress, known as sulfide stress cracking (SSC). SSC is primarily to be expected in the vicinity of welds at the hard area of heat affected zones. In recent years, another corrosion mechanism was under discussion, explained as a mix-ture of HIC and SSC. This is known as the phenomenon of stress orientated Hydrogen induced cracking (SOHIC).
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