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 (SCC) 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, thus embrittlement, each can have very different causes.
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.
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.
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.
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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September/October 2005 Inspectioneering Journal
By John Reynolds at Intertek
Temper embrittlement is another form of metallurgical degradation resulting from exposure of susceptible low alloy steels to higher temperature ranges, usually in service, but can occur to some extent even during heat treatment. And, once again, if significant temper embrittlement has occurred, the equipment may be susceptible to catastrophic brittle fracture. |
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September/October 2005 Inspectioneering Journal
By John Reynolds at Intertek
Another form of metallurgical degradation at higher temperatures is called sigma phase embrittlement. As the name implies, a metallurgical phase change occurs in some stainless steels when they are heated above about 1000F (540C). |
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September/October 2005 Inspectioneering Journal
By John Reynolds at Intertek
Titanium (Ti) hydriding is another somewhat unusual metallurgical degradation phenomena that can result in brittle fracture. Unlike many other steel embrittlement phenomena, this one most often occurs in thin wall Ti tubes that have been selected for their superior corrosion resistance of overhead condensers. |
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July/August 2003 Inspectioneering Journal
By John Reynolds at Intertek
This is the name given to a form of embrittlement that occurs in 400 series of stainless steels, duplex SS's and less commonly in some 300 series stainless steels containing a metallurgical phase called ferrite. The embrittlement occurs from 600 F to 1000 F, but most readily at a temperature of 885 F, hence the name. |
