THE EFFECT OF CATHODIC PROTECTION POTENTIAL ON CORROSION-FATIGUE CRACK-GROWTH RATE OF AN OFFSHORE STRUCTURAL-STEEL

Duplicate tests have been performed to determine the effect of cathodi c protection potential on corrosion fatigue crack growth rate of a mod ern offshore structural steel, produced by thermomechanically controll ed processes. The experiments were carried out using compact tension s pecimens exposed to artificial seawater at 10 degrees C and subjected to constant amplitude loading at 0.35 Hz. Reproducible results showed that the merits of cathodic protection potentials are strongly depende nt on stress intensity ratio R and stress intensity range Delta K. It appears that a specific value of cathodic potential may not give compr ehensive protection against corrosion fatigue within the spectrum of v ariable amplitude loading experienced in service. Fractography showed the initiation of secondary cracks on the fracture surface to be assoc iated with the dissolution of calcium sulphide inclusions, regardless of imposed cathodic potential.