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. The color of the flash rust is typically orange, red, or brown of various shades depending on the color of the underlying steel, the nature of the surrounding environment, and the duration of exposure to the environment. Standard terminology has been developed by NACE and SSPC to categorize the grade (or level) of flash rust. These are light flash rust (LFR), moderate (or medium) flash rust (MFR) and heavy flash rust (HFR). 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. Surface analytical techniques consisting of X-ray Photon Spectroscopy (XPS) and Raman Spectroscopy, were used in the study. 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. The oxide on the atmospherically corroded sample is of a similar composition but with different distribution and proportion.
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. Similar rusting is also observed after mechanical cleaning (abrasive blasting) of steel surfaces. However, it has been postulated by some that the rusting observed with the two cleaning methods are ?different? in nature. The color of flash rust after waterjetting is typically orange, red, or brown of various shades depending on the color of the underlying steel, the nature of the surrounding environment, and the duration of exposure to the environment. Standard terminology has been developed by SSPC and NACE to categorize the grade (or level) of flash rust. These are as follows:
? No Flash Rust (NFR): A steel surface which when viewed without magnification, exhibits no visible flash rust.
? Light Flash Rust (LFR): A surface which, when viewed without magnification, exhibits small quantities of a yellow/brown rust layer through which the steel substrate may be observed. The rust or discoloration may be evenly distributed or present in patches, but it is tightly adherent and not easily removed by light wiping with a cloth
? Moderate Flash Rust (MFR): A surface which, when viewed without magnification, exhibits a layer of yellow/brown rust that obscures the original steel surface. The rust layer may be evenly distributed or present in patches, but it is reasonably well adherent and lightly marks a cloth that is lightly wiped over the surface.
? Heavy Flash Rust (HFR): A surface which, when viewed without magnification, exhibits a layer of heavy red/brown rust that hides the initial surface condition completely. The rust may be evenly distributed or present in patches, but the rust is loosely adherent, easily comes off, and leaves significant marks on a cloth that is lightly wiped over the surface.
Due to lack of research into the effects of flash rusting on coating performance, most paint specifications require reworking a flash-rusted surface to reveal bare steel. Additionally, most paint manufacturers will not accept liability if their products are applied over certain grades of flash rust.
