Q Explain Hydrogen embrittlement or HSC?
Hydrogen embrittlement occurs where hydrogen migrates out of its normal structure in steel, causing a failure of reliability to the metal’s normal properties.
The failure may be immediate in use or may occur in a delayed manner. The primary problem in the industry is a specific form of hydrogen embrittlement, called Hydrogen Stress Cracking (HSC), a result of hydrogen absorption.
Ferrous alloys, especially those with relatively large quantities of carbon are prone to hydrogen embrittlement.
Low carbon materials zinc-plated or hot-dip galvanized are not subject to hydrogen embrittlement. B7 material zinc plated and B7 hot-dip galvanized is not subject to hydrogen embrittlement.
Materials plated that are subject to hydrogen embrittlement:
-B7 cadmium plated
-Grade 8 Alloy zinc plated
To relieve HSC, it is required that the material be baked after plating at high temperatures for an extended time (375 degrees F for 4 hours). In addition, the efficiency of the plating process will affect HSC and the required baking.
Historic Example of Hydrogen Embrittlement: Six months prior to opening, the East Span of the Oakland Bay Bridge failed during testing. Catastrophic failures occurred in anchor rods in the span, after only two weeks of service, with the failure attributed to embrittlement, possibly from the environment.
