Corrosion fatigue (CF) of duplex stainless steel X2CrNiMoN22-5-3 was investigated in situ under geothermal conditions of Northern German Basin (NGB) aquifer solution. The specimens, which were placed in the corrosion chamber, underwent purely alternating axial cyclic push/pull load to failure. The circulating electrolyte of the NGB was heated to 369 K to simulate geothermal environment. The experiments covered an extended range of mechanical loads, whereby the influence of a distinct electrical insulation of the experimental setup was additionally investigated. The electric insulation resulted in the stabilization of open-circuit potential (OPC), its more noble initial values, increased deterioration of the alloy and negative shift of the CF life span of the material. Corrosion fatigue damage, such as cracks and pits, were investigated via micro-sectional analysis and scanning electron microscope (SEM). Multiple fatigue cracks accompanied by pitting corrosion exhibited horizontal grain attack exposing preferable degradation of austenitic phase in the pit’s cavity. This phenomenon corresponded well with the measured Pitting Resistance Equivalent Number (PREN) of austenitic and ferritic phases.

Subject
Scanning electron microscopy, Test methods, Geothermal energy, Corrosion fatigue, Materials, Insulation, Machinery, Free corrosion potential, Corrosion cracking, Mechanical failure, Steel, Pitting, Electrode potential
Keywords:
corrosion fatigue, duplex stainless steel (DSS), geothermal energy
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2016
Association for Materials Protection and Performance (AMPP)
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