Accelerating corrosion in a laboratory set-up for corrosion-fatigue of offshore steels

Abstract

Corrosion-fatigue is a dangerous failure mechanism that is not yet fully understood. Structures subjected to corrosion-fatigue are over conservative in design, which is economically unfavourable. To counter this, representative laboratory experiments simulating the corrosion-fatigue conditions of an offshore structure should be performed. Lab testing is, for obvious reasons, performed at frequencies much higher than these of wave and wind actions. However, this means that corrosion needs to be accelerated in the same manner. In this work two different ways to accelerate corrosion were selected, namely temperature and oxygen content adaptation. S-N curves were determined in different test conditions in order to evaluate the damage evolution. It has been found that high temperatures and high levels of oxygen content will result in earlier failure. The fracture surfaces are somewhat different than fracture surfaces obtained due to fatigue in air. More crack initiation sites can be observed and the fracture surface is generally rougher due to corrosion.