Long-term General Corrosion Behavior of Hot Extruded Tubing Alloy 690 in High Temperature Water

The general corrosion behavior and mechanism of three areas (namely head A, middle B and tail C) of hot extruded tubing alloy 690 in high temperature de-aerated water were studied by means of long-term immersion, and the oxide film was analyzed by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). The results show that the general corrosion process of A, B and C specimen reaches a stable state after immersion for 2 500 h, and their corrosion rates are all lower than 5 mg/(month•dm²). The corrosion rate of head A is equal to that of tail C, and which are obviously lower than that of middle B. The oxide film is characterized by a double layer structure. The outer layer is rich in Fe and Ni, while the inner layer is rich in Ni and Cr. There is a chrome barrier in the middle of the oxide film of A and C specimen, however, the C specimen has no obvious chrome barrier.