Unusual corrosion of nickel‐aluminium bronze in a hydroelectric power plant

Abstract

Localized phase selective corrosion of turbine runners made from the bronze CuAl10Fe5Ni5 was observed in a hydroelectric power plant. Routine investigation of the corrosion system did not provide a satisfactory explanation for this specific type of corrosion which seems uncommon to occur in freshwater. Corrosion potential measurements of the stainless steel runner rings, galvanically coupled to the runners, indicated ennoblement, creating an effective galvanic couple driving the bronze to corrode. This mechanism was verified by on‐site, in situ electrochemical experiments. Biofilm formation by diatoms was identified as the cause of ennoblement.

Design of a multichannel potentiostat and its application to corrosion testing of a nickel‐aluminum bronze

“…Conversely, a significant susceptibility of NAB to localized corrosion in fresh water appears at potentials which may be established by galvanic coupling to biofilm ennobled SS, as was observed in Ref. and which is known similarly from sea water applications …”

“…These potential limits were estimated from the experiences gained. [1] The potential of WE 1 is 95 mV above the open circuit potential of NAB observed in fresh water, which was estimated by ca. −50 mV SCE .…”

“…In all tests, the specimen at the lowest potential (WE 1 ) was polarized to +45 mV SCE and the potential spacing was set to dE = +15 mV, resulting in polarization of WE 8 to +150 mV SCE . These potential limits were estimated from the experiences gained . The potential of WE 1 is 95 mV above the open circuit potential of NAB observed in fresh water, which was estimated by ca.…”

Tribocorrosion behavior of nickel aluminum bronze in seawater: Identification of corrosion‐wear components and effect of pH

“…Firstly, E corr are shifted cathodically compared with that in the absence of sliding. Such a cathodic shift is due to that, in the contact areas, friction can wipe off the protective oxide layer on the metal surface, leading to the exposure of fresh underlying metal with a low equilibrium potential to the corrosive solutions and the increase in the corrosion susceptibility of NAB . Secondly, i corr are increased greatly by nearly one order of magnitude with respect to those without rubbing at each pH value.…”

“…Such a cathodic shift is due to that, in the contact areas, friction can wipe off the protective oxide layer on the metal surface, leading to the exposure of fresh underlying metal with a low equilibrium potential to the corrosive solutions and the increase in the corrosion susceptibility of NAB. [30] Secondly, i corr are increased greatly by nearly one order of magnitude with respect to those without rubbing at each pH value. During tribocorrosion, the passive film on the metal surface will be destroyed by rubbing, which initiates a galvanic coupling between the activated wear track areas (anode) and surrounding passivated areas (cathode), and yields an accelerated corrosion rate.…”