A Review of Trends for Corrosion Loss and Pit Depth in Longer-Term Exposures

Abstract

For infrastructure applications in marine environments, the eventual initiation of corrosion (and pitting) of steels (and other metals and alloys) often is assumed an inescapable fact, and practical interest then centres on the rate at which corrosion damage is likely to occur in the future. This demands models with a reasonable degree of accuracy, preferably anchored in corrosion theory and calibrated to actual observations under realistic exposure conditions. Recent developments in the understanding of the development of corrosion loss and of maximum pit depth in particular are reviewed in light of modern techniques that permit much closer examination of pitted and corroded surfaces. From these observations, and from sometimes forgotten or ignored observations in the literature, it is proposed that pitting (and crevice corrosion) plays an important role in the overall corrosion process, but that longer term pitting behaviour is considerably more complex than usually considered. In turn, this explains much of the, often high, variability in maximum depths of pits observed at any point in time. The practical implications are outlined.

Predicting long-term corrosion of metal alloys in physical infrastructure

“…For improved understanding, particularly of pitting and crevice corrosion phenomena, understanding of precisely the conditions at every point on a metal surface is unlikely, and statistic techniques would seem to be inevitable. For pit depth at least there is a long history of invoking statistical methods 99 and also for exploring pit interactions 72,100 but more generally for corrosion modelling much remains to be explored.…”

Experimental correlation using ANOVA and DOE studies on corrosion behavior of Fe and Ni-based alloy under different media

“…The %Ni and %Cr equivalents are calculated from the alloy composition data listed in table 1 for the given alloys by using equations developed by Pickering and Schneider [17,18] as the following; Analysis of variance (ANOVA) is used to detect the design parameters significantly influencing the corrosion rate. Using the limited data that were available at the time, it was supposed that the modal characteristic also valid to longer-term trends for maximum and average pit depths [16]. ANOVA is used to decide which model Figure 1(a) illustrates that increasing the temperature and/or time increases the weight loss, (mg) while increasing the %Ni eq., %Cr eq.…”

“…The weight loss measurement is a very reliable more accurate technique to study the corrosive behavior of the Fe and Ni-based alloys and also very useful to corroborate the obtained data from the electrochemical analysis [14,15]. Almost all theories for the initiation and development of pitting concentrate on the way a pit can initiate on what is close to a perfect surface, with material imperfections, inclusions and local alloy constituents producing only very small differences in local potential to drive dissolution leading to pit initiation [16]. Initial pitting usually is considered to initiate at multiple sites on the surface of metal than some stable pits able to propagate with time.…”

Corrosion Behaviour of SMAW and GMAW Welded Mild Steel Attacked by Hydrochloride Acid

“…Rusting of steel by water and oxygen results in hydrated iron oxide. In addition, rusting is a term reserved for steel and iron which having corrosion degradation.Although many others metals elements in its composition, it is still referred to steel compared to other oxides when corrosion occurs [13,14].…”