Hydrogen Gas Evolution from Cathodically Protected Pipeline Steel Surfaces Exposed to Chloride-Sulfate Solutions

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Abstract
An experimental study of the conditions for hydrogen discharge and the associated pH changes in chloride-sulfate solutions was conducted for different pipeline steel surface conditions. The highest potential for gas discharge is shown to be in reasonable agreement with the value quoted in the literature (−1.15 V Cu-CuSO4) for pipeline surfaces exposed to other solutions, although somewhat higher potentials can prevail if the surface has previously been exposed to lower potentials. The extent of gas evolution is essentially determined by the magnitude of the current flowing at the surface, which varies with the polarization characteristics of different surfaces and solution compositions. The associated pH value increases in the solution, a matter of considerable importance in relation to coating disbondment or the generation of a potent stress corrosion cracking (SCC) environment, are dependent upon solution composition as well as the amount of gas evolved. Thus, for similar initial pH values, chl...

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