Diffusion controlled corrosion of pipelines under turbulent flow conditions

Abstract

The rate of diffusion controlled corrosion of copper tube in turbulently flowing 8M H₃PO₄ (Schmidt number Sc=49860) was studied by measuring the limiting anodic current during dissolution of the tube wall in two position: in a short pipe section under fully developed flow; and downstream of a sudden contraction. Also, the effect of drag reducing polymers on the rate of corrosion was tested. For a short pipe section, the data were described by the equation: Sh = 0·055Sc^0.33Re^0.8(d/L)^0.33, where Sh is the Sherwood number, Re the Reynolds number, d pipe diameter, and L length of transfer section. This equation is useful in predicting the rate of local diffusion controlled corrosion. For a given Re, the mass transfer coefficient downstream of a sudden contraction was higher than the fully developed value by a factor in the range 1·19–1·57. Under the present conditions, where highly concentrated acid was used, the drag reducing polymer was found to have a negligible effect on the rate of dissolution. Comparison of the present results with previous studies has shown that the Sc range plays an important role.