Stainless steel is covered by a protective chromium oxide layer, also called a passive layer. Due to errors in processing, the protective layer might not form everywhere on the surface, which could lead to local rust formation. BAM has developed a rapid colour indicator test to check the surface of stainless steels quickly, inexpensively, and without any special expertise. Conventional methods such as salt spray testing are time and cost intensive and destruct the steel surface. The BAM KorroPad corrosion test, however, enables steels to be tested quickly and non-destructively by making emitted iron ions immediately visible using a colour indicator. KorroPad is simple to use and the state of the passive layer can be estimated without any prior knowledge. The application possibilities are very diverse and range from incoming and outcoming inspection to process monitoring and optimisation or testing weld seam processing.