Abstract: The brittleness phenomenon of pure nickel pipe in chemical equipment during service has been comprehensively investigated by means of OM (optical microscope), SEM (scanning electron microscope) and SAM (scanning auger microprobe). The present results indicated that under a certain condition of stress and temperature the S element originated from environmental medium can permeate into pure nickel matrix through grain boundary and segregate at the boundaries, leading to the enrichment of S and the formation of Ni₂S which could sharply decrease the strength, plasticity and corrosive resistance of the pure mickel and make rupture easily take place.