Hydrogen induced cracking (HIC)

Hydrogen induced cracking (HIC) is a type of failure that occurs in metals and alloys when they are exposed to hydrogen under tensile stress. This phenomenon can have devastating consequences, as it can cause the material to crack and ultimately fail.

What is Hydrogen Induced Cracking?

Hydrogen induced cracking is a type of failure that occurs in metals and alloys when they are exposed to hydrogen under tensile stress. The hydrogen enters the material through various means, such as corrosion or chemical reactions, and accumulates at the microstructural defects such as dislocations, grain boundaries or voids. When hydrogen atoms accumulate, they cause localised embrittlement, which reduces the material's toughness and resistance to fracture. As a result, the material becomes more prone to cracking and ultimately fails.

How does HIC occur?

Hydrogen induced cracking occurs in three stages:

Hydrogen absorption: Hydrogen atoms diffuse into the material's microstructure, typically through a process known as hydrogen ingress. This occurs when the material is exposed to an environment that contains hydrogen gas or hydrogen ions, such as water.

Hydrogen diffusion: Once hydrogen has entered the material, it diffuses through the microstructure, seeking areas of high stress. The hydrogen atoms can accumulate at microstructural defects such as dislocations, grain boundaries or voids.

Hydrogen-induced cracking: When hydrogen accumulates in high-stress areas, it can cause embrittlement. This leads to cracking, which can ultimately result in failure of the material.

Real-World Examples of HIC

HIC can occur in a wide range of materials, including steel, aluminum, and titanium alloys. It is a major concern in the oil and gas industry, where it can cause pipeline failures, resulting in environmental damage, injury, and loss of life. Here are two real-world examples of HIC:

The USS Thresher Submarine Disaster:

In 1963, the USS Thresher, a United States Navy submarine, sank during a deep-diving test mission. It was discovered that the submarine's piping system had experienced hydrogen-induced cracking due to a combination of factors, including improper welding and inadequate quality control. This led to the formation of cracks, which ultimately caused the submarine to sink.

The Sour Gas Pipeline Failure in Canada

In 2000, a sour gas pipeline in Canada failed due to HIC. The pipeline was carrying natural gas that contained high levels of hydrogen sulphide. The hydrogen sulphide reacted with the steel pipe, causing hydrogen to enter the material. The hydrogen accumulated at microstructural defects and caused embrittlement, which led to the formation of cracks. The cracks grew over time, causing the pipeline to fail and resulting in a release of toxic gas into the surrounding environment.