Overview of Embrittlement

Embrittlement is the process of a material becoming brittle due to a loss of ductility. Hydrogen embrittlement, temper embrittlement, liquid metal embrittlement, and sulfide stress cracking (SSC) are all examples of embrittlement. Embrittlement can be a very dangerous mechanism, leaving it unchecked can lead to cracking or even catastrophic brittle failure.

While each of the above mentioned mechanisms are similar in that the symptom of the mechanism is loss of ductility (embrittlement), each can have very different causes.

Hydrogen embrittlement occurs when atomic hydrogen diffuses into certain metals and those metals are put under applied tensile stresses, it can affect metals under both high and low temperature conditions. This type of embrittlement can affect materials during any number of operations such as welding, applying cathodic protection, pickling, phosphating, electroplating, forming, or finishing operations.

Temper embrittlement is caused by the presence of impurities of certain elements in the steel, such as antimony, phosphorous, tin, or arsenic when heating the metal from either 250 to 400 °C or from 450 to 650 °C. Unlike many other types of embrittlement, temper embrittlement can sometimes be reversible.

Liquid metal embrittlement is a type of embrittlement that can occur when molten metals come in contact with certain materials. This type of embrittlement is particularly dangerous because cracking rates from this mechanism can be exceedingly rapid and failure can occur within seconds.

Sulfide Stress Cracking (SSC) can occur at locations where atomic hydrogen is able to diffuse at sites of high internal stress, such as grain boundaries, inclusions and regions of triaxial stress at notches. When placed in proximity to tensile stresses this can lead to embrittlement.

Because of all this, it’s important that any operators be aware of any causes of embrittlement that can affect their in service equipment. Embrittlement is an insidious condition, but with awareness and preparation it can be prevented.

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