Influence of Iron Boride Coating on Flow-Accelerated Corrosion of Carbon Steel

Flow-accelerated corrosion (FAC) often occurs in piping systems made of carbon steels and other steels and alloys in power generation and mineral processing, when the products are subjected by extremely high-velocity corrosive fluid flows. Under these extreme conditions, dissolution and subsequent degradation and thinning of the metallic surfaces occur due to corrosion-erosion resulting in a quick rupture of the piping products. Herein, iron boride-based coatings obtained through the proprietary thermal diffusion process are selectively applied onto the inner surface of carbon steel A106B piping sections to protect the steel against FAC. The coated and uncoated steel piping sections are tested using the high-turbulence corrosion loop device with flow rates up to 120 gal min(-1) (approximate to 450 L min(-1)) in boric acid-based solutions. Changes of wall thickness of the piping sections and their structures are examined and evaluated. The pipe sections with iron boride coatings demonstrate significantly lower degradation in the studied FAC conditions compared with the bare carbon steel. Promising behavior of the coating can be explained by its well-consolidated double-layer structure composed of iron borides with high hardness, chemical inertness, and strong diffusion-induced bonding between the protective layers and the steel substrate.