Mass transfer and erosion corrosion in pipe bends

In recent years, there have been several instances of serious corrosion damage to pipework of nuclear once-through steam-generators in which the feed-water purity is maintained at the highest levels. Maximum mass transfer rates in pipe bends under single phase flow conditions occur on the outside or side wall of the bend depending on the flow rate and bend length. Mass transfer rates up to 60% greater than the straight tube case have been found. It has been proposed that because the solubility of magnetite is itself increased by high rates of erosion-corrosion, the rate of metal loss can, in practice, vary as the cube of the mass-transfer coefficient. Under adverse conditions, the observed increased mass-transfer coefficients in the bend would therefore result in a disproportionate increase in the erosion-corrosion rate