Successful nondestructive field tests to detect corrosion on stainless steel (SS) were recently conducted using a novel gel-like pad system developed by the German Institute for Materials Research and Testing (Berlin, Germany), and made available by TÜV SÜD Chemie Service (Leverkusen, Germany).
In the presence of water and oxygen, a chromium oxide (Cr2O3) layer typically forms on the surface of SS, which helps prevent dissolution of the underlying material. However, certain conditions in manufacturing, transport, or storage operations can result in defects of the passive layer.
The KorroPad system tests the Cr2O3 layer within 15 min. The system can be used on assets such as piping systems or tanks that are frequently exposed to extreme environmental conditions, including fluids with high concentrations of chloride; acids; or corrosive gases.
Wherever the passive layer is missing or defective, a potassium hexacyanoferrate indicator in the test pad reacts with the iron ions. These ions, present at the sites of defects, cause a chemical reaction that changes the test pad’s color at the exact point of damage. Results are documented by either taking photographs of the affected area or scanning it.
Field tests were carried out on austenitic chromium nickel steels as well as martensitic, ferritic, and duplex steels. Since surface quality plays a key role in whether a material is prone to corrosion, the tests used steels that are considered particularly resistant or prone to corrosion. Testing was carried out both on materials as delivered and on steels subjected to dry or wet grinding in manual and machine processing.
Results of the testing confirmed the effectiveness of the method and correlated well with results obtained through electrochemical measurements.