Influence of O on the erosion-corrosion performance of 3Cr steels in CO containing environment.

With the introduction of O during oil and gas production, the erosion-corrosion rate of tubing steels increases; the objective of this report is to explore the reason for this. Erosion-corrosion experiments were performed in environments of CO and CO-O, respectively. Macrographs, microstructures, and the compositions of erosion-corrosion scales were investigated using a digital camera, scanning electron microscope (SEM), Kevex-SuperDry energy spectrometer (EDS) and X-ray diffraction (XRD). The results show that the erosion-corrosion products are composed of large FeCO particles and some amorphous product in the CO environment, while they are made up of FeCO, FeO, FeO, and bits of amorphous product in the CO-O environment. The interface between erosion-corrosion scales and the substrate of 3Cr steel is smooth, and Cr enrichment obviously exists in the erosion-corrosion products in the CO condition. However, the erosion-corrosion scale is loose and porous with little Cr enrichment in the CO-O environment, which makes the protectiveness of the erosion-corrosion scale weak, and pitting corrosion occurs. The addition of O may destroy the protective FeCO scale and Cr enrichment in the erosion-corrosion scale, which may be the main reason for the decline in the level of protectiveness of the erosion-corrosion scale, making it weak in terms of preventing the corrosive medium from diffusing to the substrate.