POTENTIAL-PH EQUILIBRIUM DIAGRAMS FOR THE SYSTEM S-H2O FROM 25-DEGREES-C TO 150-DEGREES-C - INFLUENCE OF ACCESS OF OXYGEN IN SULFIDE SOLUTIONS

Equilibrium potential-pH diagrams were constructed using a large set of thermodynamic data for a number of sulphur compounds, from 0 to 150-degrees-C. These diagrams were used to determine how access of oxygen in H2S bearing solutions influences corrosion. It is shown that occasional access of limited amounts of oxygen is not necessarily corrosive, but that continuous access of even traces of oxygen to a same volume of H2S solution can produce an important pH drop which may be the cause of corrosion. In the present state of knowledge concerning the reversibility or irreversibility of the reactions, these equilibrium diagrams should be considered as a guide for experimental researches involving systematic electrode potential and pH measurements, which might lead to a perfect understanding and mastering of the corrosions.