Hydrogen-induced cracking, or hydrogen embrittlement, is a chemical phenomenon that causes metal alloys to fracture due to a build-up of hydrogen molecules within the crystal lattice structure. This is a unique mode of mechanical failure that most commonly affects low alloys and high-hardness steel grades such as titanium (Ti). Often, components will develop increased susceptibility to hydrogen-induced cracking due to the introduction of excess hydrogen molecules into the metal structure during forming or finishing processes.
The most common concern with respect to hydrogen-induced cracking, however, is the gradual diffusion of hydrogen atoms into a component’s structure throughout its service life. This is an ongoing issue in industries such as sour service and wet hydrogen sulfide (H2S) applications.
This blog post will explore the mechanics of hydrogen-induced cracking in more detail, with a focus on HIC-resistant steel grades.
How Does Hydrogen-Induced Cracking Occur?
Hydrogen-induced cracking occurs when the crystal lattice of an alloy becomes saturated with diffuse hydrogen atoms. This typically occurs at higher rates in extreme temperatures, given the proportional relationship between the solubility and temperature of hydrogen. These atoms diffuse through the metal and may recombine to form larger hydrogen molecules, which can accumulate in minuscule pockets of space within the metal structure.
Hydrogen concentration increases the internal pressure on the component, restricting key properties such as ductility and tensile strength. This localized flaw can propagate through the surface of the metal, causing fractures.
The mechanism of hydrogen-induced cracking most commonly affects vessels and pipes in hydrogen and hydrogen sulfide processing or containment facilities. It is a complex form of corrosion that can be extremely costly and represents a risk to human health if plant personnel are exposed to hydrogen sulfides.
What are HIC-Resistant Steel Grades?
HIC-resistant steel grades are novel metal alloys that have been engineered to resist hydrogen-induced cracking and provide long-lasting service in wet H2S processing applications. They are envisaged as a comprehensive solution for pressure vessel manufacturing in the oil and gas, and petrochemical sectors.
These innovative steels grades feature a high carbon content (<0.2%) and are manufactured using a proprietary electric arc technique. This enables the construction of a high-purity, homogeneous steel through ladle refining and vacuum degassing, following robust desulphurization and dephosphorization processes. Eliminating common impurities is essential in ensuring that an HIC-resistant steel grade will perform to specification, but they must also be tested to guarantee that the theory translates well to practical application.
Hydrogen-Induced Cracking Solutions with Masteel
Masteel provides a range of MASTERHIC carbon steel grades for wet H2S applications, with outstanding resistance to hydrogen-induced cracking. We ensure this by subjecting our HIC-resistant steels to rigorous testing, including: ultrasonic measurements that screen products for voids and flaws; impact testing at -50°C; and hardness testing according to NACE.