Initially, roughing is hard to detect. Visual inspection using handheld flashlight can be used to evaluate these rouging. It is not easy to determine the degree of rouging in early stages. Instruments can easily be used either online or for interval sampling to find rouging. Some of the sensors measure the luster or reflectance of steel surface with light source. After finding the rouge, the process of derouging starts. It calls for production downtime. There are mechanical cleaning processes that remove all the visible particles which adhere to the surface loosely and they are limited to the areas which are easy to access.
Chelating agents and inorganic acids are the most widely used media to derouge the steel surface. Nitric acid is used more commonly. Some of the common acids for re-passivation treatments are citric, phosphoric and other oxidizing acid liquids. If used well, these acids can be used to restore corrosion resistance of S.S. steel systems by re-oxidizing or removing the layer of stainless steel. Be careful when using acid as it may damage the surface. Be sure to avoid organic acids as they don’t have same solubilizing ability like concentrated acids. The chemical compounds with chelating agent and metal ion, chelants can remove iron oxides and various other elements.