Stress-corrosion cracking:

Another form of stress-corrosion cracking is hydrogen embrittlement. While embrittlement of materials takes several forms, hydrogen embrittlement in high strength steels has the most devastating effect since of the catastrophic nature of the fractures while they occur. A Hydrogen embrittlement is the procedure through that steel loses its ductility and strength because of tiny cracks which result from the internal pressure of hydrogen (H₂) or methane gas (CH₄) that forms at the grain boundaries. Within zirconium alloys, hydrogen embrittlement is caused through zirconium hydriding.  At nuclear reactor facilities, the word "hydrogen embrittlement" commonly refers to the embrittlement of zirconium alloys caused through zirconium hydriding.