Effects of Size Parameters of Stepwise Corrosion Pit on Stress Concentration of Steel and Its Computation Model Establishment

Stepwise corrosion pit (SCP) nucleated in late corrosion period can make corroded steel surface more irregular, and lead to the severe stress concentration, even failure of steel member, so the stress concentration caused by SCP needed to be carefully investigated and studied. In this work, a non-contact 3D scanner was employed to measure the profile measurements of corroded steel specimens produced from an artificially accelerated corrosion test. The corrosion pitting parameters of SCP were surveyed and used for statistical analysis. And then the effects of pitting parameters on stress concentration were systematically analyzed by means of the finite element simulation. The results showed that the stress concentration caused by SCP was the most obvious on the corroded steel surface compared with any other type of corrosion pit, and the stress concentration factor (SCF) relied on all of the pitting parameters of SCP, of which the weights were varied depending on the type of SCP (such as bilateral stepwise pit (BSP), partial bilateral stepwise pit (PSP) and unilateral stepwise pit (USP)). For all kinds of SCP, each pitting parameter had a different influence on SCF, and the corresponding weight was also different. So, a calculation model (written as SCP-SCF) was established to calculate SCF by using the least square method, based on the relationships between SCF and pitting parameters of SCP. By contrast, it was found that the error between the theoretical value of SCF calculated by the SCP-SCF method and the true value obtained by the FEM with the actual corroded surface was within 5%.