The application of the polarization resistance method for monitoring the degradation of steel in port crane metal structures

Abstract

The problem associated with the application of the polarization resistance method for monitoring the degradation of steel structures of port cranes has been examined. The experience of operating port equipment indicates that its individual components and elements are subjected to significant cyclic loading, which is super- imposed on the usual static loading according to regulations, due to the constant and random influence of various factors (such as wind loads, vibration from abnormal opera- tion of electric drives, jerks from the switching on/off of mechanisms for lifting cargo, rotation, changes in trajectory, movement, etc.). In low-alloy steels, under the influence of prolonged combined action of static and cyclic loads, significant changes occur in their structure and properties, mainly due to the development of deformation aging, known as operational steel degradation. These changes, often referred to as operational aging of steels, do not always affect their strength, but significantly reduce their resis- tance to brittle fracture, especially at low temperatures. Deformation aging is caused by the presence of carbon and nitrogen impurities in the metal, which, interacting with the dislocation structure, strengthen the steels and complicate the relaxation of elastic stresses due to plastic deformation. Correlation dependencies between polarization resistance and impact toughness of operated steels have been established, which form the basis for the development of an electrochemical method for predicting the resistance to brittle fracture of long-term operated metal. The metal diagnostic procedure of portal crane nodes included preparation of a portable potentiostat for operation, connection of auxiliary and reference electrodes, activation of the automatic mode of potentiodynamic polarization, export of data to graphic programs, and calculation of the polarization resistance value. The obtained data of polarization resistance and impact toughness for different nodes of investigated port cranes indicate a significant decrease in these characteristics during prolonged operation. In particular, impact toughness decreases much faster, making it the most conservative and informative parameter for determining the operational degradation of port crane steels. To verify the proposed approach using metal cutting from crane nodes, samples were manufactured and tested for strength. The obtained results of mechanical tests correspond to the diagnosed data, confirming the effectiveness of the proposed approach.