The HIC corrosion test involvesexamining several samples taken from pipes (base metal or welded area) or sheets by immersing them for a specified time (typically 96 hours) in two saturated solutions of hydrogen sulfide. Solution A includes sodium chloride (NaCl) and acetic acid (CH3COOH), while solution B contains synthetic seawater. The test is carried out at room temperature and at atmospheric pressure. After the test period, the samples are extracted, polished and examined metallographically. The cracks found are measured and their dimensions (depth and length) are related to those of the samples. The results are expressed through the values of CSR (Crack Sensitivity Ratio), CLR (Crack Length Ratio) and CTR (Crack Thickness Ratio).

NACE standard TM 0284, first introduced in 1984, was created to provide a set of standard test conditions for evaluating steel pipes and for comparing results obtained by different laboratories. Recently, the focus on damage caused by hydrogen-induced cracking (HIC) also on steel fittings and flanges has led to these components also being included in the most recent revision of the standard. Therefore, the current scope of the standard includes steels in the form of pipes, plates, fittings and flanges used in the manufacture of pipelines and pressure vessels.

Description of the HIC phenomenon

Hydrogen adsorption generated by corrosion of steel in a wet environment containing hydrogen sulfide (H2S) can cause several effects, which depend on the properties of the steel, the mode of fabrication and forming processes, the characteristics of the environment, and other variables. One of the observed adverse effects is the development of cracks along the rolling direction of the steel, which can connect by forming grooves along the thickness. These cracks can reduce wall thickness until the stress to which pipes or pressure vessels are subjected becomes excessive, leading to rupture. This phenomenon is sometimes accompanied by surface blisters.

Terminology and history of the phenomenon

Terms such as stepwise cracking, hydrogen pressure cracking, blister cracking or hydrogen-induced stepwise cracking are now considered obsolete. The U.S. NACE International Institute has adopted the term hydrogen-induced cracking, abbreviated HIC. This type of corrosion is closely related to the formation of hydrogen bubbles, a phenomenon that has been critically studied since the 1940s but only recognized as problematic for pipelines since the 1970s, after some pipelines ruptured.