Alloy 718 comprises 51% of the total weight of the Space Shuttle Main Engine. It is used for more than 1,500 individual parts in hydrogen, oxygen, and hydrogen-rich steam at temperatures ranging from-253°C to 760°C. The severe operating conditions of the SSME lead to potential problems such as hydrogen-cnvironment embrittlement and oxygen ignition. This paper will discuss how these potential problems are controlled through design,, protective barriers, and heat treatment. Operational experiences, fabrication tcchniqucs, and welding microfissures will also be discussed.

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