The effects of oxygen and iron in feedwater on erosion-corrosion of mild steel tubing

Erosion-corrosion downstream of an orifice in single phase water in the pH range 9.0-9.4 and at 1450C has been investigated under both reducing and oxidising conditions. It has been found that a concentration of only 5 μg kg-1 oxygen is required to stop erosion-corrosion which, under reducing water chemistry, was proceeding at 0.5-0.8 mm/year. In the absence of oxygen, and at pH 9.4 increasing the concentration of iron from about 7 to 14 μg kg-1 is also found to stop erosion-corrosion although this does not offer a practicable palliative because of the consequential increases in pressure drop. The application of these results to control of erosion-corrosion in high pressure once-through AGR boilers is discussed and the mechanistic aspects are considered