A T-piece from a copper hot water system failed. Microscopic examination of a polished section revealed a main crack and branching transcrystalline cracks running from the outer surface of the pipe into the pipe wall. The crack appearance indicated disintegration by stress-corrosion cracking. Although copper is not susceptible in the pure state, it is prone to stress-corrosion cracking under tensile stress in the presence of other elements in a damp ammoniacal atmosphere. The material was not defective, but a phosphorus-deoxidized copper type. The residual phosphorus combined with oxygen to form phosphorus pentoxide. Hard soldering in turn prevented the formation of cuprous oxide, and hydrogen embrittlement occurred.
Egon Kauczor, Cracked T-Piece from a Copper Hot Water System, ASM Failure Analysis Case Histories: Buildings, Bridges, and Infrastructure, ASM International, 2019, https://doi.org/10.31399/asm.fach.bldgs.c9001180
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