10179 Hydrogen Flux and Corrosion Rate Measurements on Hydrogen Induced Cracking Susceptible and Resistant A516 Steels in Various Sour Environments

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Product Number: 51300-10179-SG

ISBN: 10179 2010 CP

Author: Frank W. H. Dean, Christopher Mark Fowler, Robert T. Farnell and Samuel J. Mishael

Publication Date: 2010

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Two A516 16 mm plate steels were simultaneously exposed to various sour saturated solutions at 20^oC over two week trials. One plate was known to be highly resistant to HIC cracking, the other to be highly susceptible to HIC cracking. Flux and corrosion rates of the two plates decreased after a few days in non-buffered acid solutions, whereas in buffered acid conditions they maintained a steady state. Crack surface ratios of HIC susceptible plates post-trial were approximately proportional to the total wall flux passed. In ammonium bisulfide solutions, flux was only induced by addition of cyanide. In all trials, flux from the two plates co-trended extremely closely.

Computed hydrogen diffusivities, entry concentrations, and permeabilities of the HIC resistant and susceptible plates were similar. Diffusion coefficients varied between 8 and 12 x 10^-6 cm².s^-1, consistent with other data for A516 steels. There was good correlation between corrosion rate and steady state flux for the first day of measurement, except from pH 2.7 solutions, where an additional, non-hydrogen occluding corrosion of 0.5 mm/yr corrosion rate was attributed to similar corrosion measured prior to sour saturation. Apart from this, no pH effect on the correlation was evident between pH 2.7 and pH 9.

Key words: hydrogen permeation, hydrogen flux, hydrogen induced cracking, crack ratio, sour corrosion