What is Hydrogen induced corrosion cracking?

Hydrogen induced corrosion cracking is a corrosion mechanisms that occurs under moderate temperatures and natural environments. Alloys and high strength steels are more susceptible to this type of corrosion, but it will only occur under specific conditions. A source of hydrogen would be required and tensile stress needs to be present in the material.

Sources of Hydrogen

Hydrogen can come from many different sources. Hydrogen is one of the foremost present atoms on the planet. Hydrogen can be enclosed into the material through the production process. In the event that it diffuses through the material, it can become a source of hydrogen embrittlement. Another source for hydrogen is the environment. There are many possible sources, but one most commonly overlooked is that Micro-organisms can produce and consume hydrogen. Within microbial processes, hydrogen is an important carrier of electrons. Micro-organisms can either utilise available hydrogen or produce hydrogen as a result of affiliates processes.

Another source of hydrogen that is resularly neglected is the hydrogen produced by cathodic protection. Cathodic protection and especially, impressed current systems can produce hydrogen (and other constructs) as a result of the energy that is transferred to water.

Tensile stress

certainly alloys, but also plain carbon steel does not exist out of a single atom (Fe). In the case of alloys, you have different metals that are put together to create specific properties. But even in de case of carbon steel, also other atoms are intrinsically present into the material. A particular interesting element is carbon (C) and Hydrogen (H). Thos elements are sitting together in a matrix. Hydrogen is however a very small atom, quickly moving through the material. Carbon steel is however not a uniform matrix without any disturbances. There are small Crystallites, which are small, microscopic crystals that are formed during cooling and or heating of the metals. These Crystallites are also referred to as grains. When a material is put under stress conditions, grain boundaries are susceptible to Hydrogen induced corrosion cracking.

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