ANALYTICAL CHARACTERIZATION OF FLASH RUST FORMED ON CARBON STEEL AFTER UHP WATERJETTING

摘要

It is well established that when steel components are cleaned by high-pressure (HP) or ultra high pressure (UHP) waterjetting the surface begins to oxidize or ?flash rust? within a short period of time. Rusting per se is also observed after mechanical cleaning (abrasive blasting) of steel surfaces. However, it has been postulated that the rusting observed with the two cleaning methods are ?different? in nature. The present paper provides results of an in-depth investigation dealing with the composition, the thickness and other characteristics of the flash rust formed on steel surfaces after UHP waterjetting. Three levels of flash rusting; no flash rust (NFR), light flash rust (LFR), and moderate flash rust (MFR) were examined, using different surface analytical techniques. These included: (a) SEM examination to characterize the morphology of the oxide, (b) EDS analysis to determine elemental composition of the specimen surface, (c) XPS (or ESCA) analysis to obtain quantitative information about the composition and depth profile of the oxide layer, and (d) Raman Spectroscopy for characterizing the type of oxide. For comparison, an atmospherically corroded steel sample was also analyzed using the same techniques. Based on XPS and Raman Spectroscopy data the composition of the oxide film on flash rusted samples is a complex mixture of different forms of stoichiometric and non-stoichiometric oxides of iron but mainly FeO, Fe2O3, Fe3O4, hydrated Fe3O4 and FeOOH. Based on the depth profile data, the approximate average oxide thickness was found to be 473 nm (0.5 μm) for the NFR specimen, 2398 nm (2.4 μm) for the LFR specimen, and 18209 nm (18.2 μm) for the MFR specimen. The oxide on the atmospherically corroded sample is of a similar composition but with different distribution and proportion.