Oxygen-free Phosphorus-containing Copper
High electrical conductivity coppers are distinct from coppers deoxidized by the addition of phosphorus in the smelting process. Oxygen-free phosphorus-containing copper (CuOFP) is typically used for structural and thermal applications where the copper material will be subject to temperatures high enough to cause hydrogen embrittlement or more exactly steam embrittlement. Examples include welding/brazing rods and heat exchanger tubing.
Indeed, copper alloys which contain oxygen as an impurity (in the form of residual oxides present in the metal matrix) can be embrittled if exposed to hot hydrogen. The hydrogen diffuses through the copper and reacts with inclusions of Cu2O, forming H2O (water), which then forms pressurized water steam bubbles at the grain boundaries. This process can cause the grains to literally be forced away from each other, and is known as steam embrittlement (because steam is produced, not because exposure to steam causes the problem).
CuOFP has been selected as corrosion resistant material for the overpack of spent nuclear fuel in the KBS-3 concept developed in Sweden and Finland to dispose high-level radioactive waste in crystalline rock formations.
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