07501 Modeling the Effect of Chloride Content on H2S Corrosion by Coupling of Phase and Polarization Behavior

Available for download

Product Number: 51300-07501-SG

ISBN: 07501 2007 CP

Author: Hans Hoffmeister

Publication Date: 2007

Member Price: $0.00

Non Member Price: $20.00

Price: $20.00

Qty:

In a previous work a deterministic H2S-corrosion model for calculation of precipitation of FeS2 together with respective acidification at the anodic sites of an assumed corrosion system for pure Fe was described. The model is based on coupling the anodic polarization resistances to the precipitated equilibrium masses of FeS2 which in a “closed loop” time stepwise procedure are calculated from the solute concentrations in a diffusion boundary layer. With the cathodical process controlled by hydrogen diffusion the precipitation of FeS2 enforces local pH reductions at the anodic site depending on the total concentrations of HS-, Fe++ and H+ in the assumed diffusion layer. In the present work the effects of chlorides on ion migration, sulfide solubility, anodic polarization resistances and solid phase precipitations of FeS2 together with FeCl2 are integrated into the model. As a result the increase of chloride contents accelerates the anodic acidification and increases the mean corrosion currents. This effect is more pronounced at higher H2S partial pressures depending on bulk pH levels. As in the previous work, the reduction of bulk pH accelerates acidification and increases the corrosion currents drastically. As a specific result for pH levels below 7, the effect of H2S partial pressures is characterized by an initial drop of corrosion currents followed by a pronounced increase at higher H2S contents. Also, the increase of total pressures at a constant H2S volume content enhances corrosion rates due to the respective effect of increasing H2S partial pressures. The results are shown to reflect presently known experimental and sour service field corrosion experiences for carbon steels. As a prerequisite for sulfide stress cracking following localized corrosion of higher alloyed steels the local anodic acidification by H2S-cloride – corrosion is quantitatively explained.