Surface Characterisation and Fatigue Strength of Corroded Armour Wire

Abstract

Tensile armour wire from two flexible risers was fatigue tested for assessment of SN-curves. Both risers had been subjected to sea water flooding of the annulus for several years. The wire was corroded in the form of pits, however, the cross section was not significantly reduced. Reference wire from the same batches of material that had not been subjected to corrosion was also tested. Testing was carried out in air, to investigate the effect of accumulated corrosion damage in terms of a fatigue notch factor. The fatigue strength of the corroded wire was significantly reduced, corresponding to a fatigue notch factor in the range 1.5–1.7. The wire was examined by optical and by electron scanning microscopy and the surface defects were characterised.