51314-3828-The Effect of Surfactant Additions on the Mechanism of Sulfur Corrosion in Aqueous Sour Systems

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Product Number: 51314-3828-SG

ISBN: 3828 2014 CP

Author: Larry Chen

Publication Date: 2014

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The Effect of Surfactant Additions on the Mechanism of Sulfur Corrosion in Aqueous Sour SystemsLarry Chen Nihal Obeyesekere and Jonathan WyldeClariant Oil ServicesAbstractIt is well known that one of the most difficult jobs for corrosion control is in an aqueous system that the high H2S gas (>5% H2S mol%) and elemental sulfur are present at the same time which will lead to an accelerated and localized corrosion on a carbon steel. The accelerated attacks occur predominantly in the vicinity of sulfur particles in direct contact with the metal surface. In such a environment rarely a corrosion inhibitor will remain effective even at very high dose rates.Some have reported that when elemental sulfur is in contact with H2S various polysulfide species of the general formula H2Sx+1 in which x is greater than or equal to 1 are formed. Authors of this paper believe that these polysulfides are surface active and will compete with the molecules of the corrosion inhibitors which are also surface active species in cohesioning to the metal surface and damage the uniformity of the iron sulfide layer initially formed over the entire metal surface after it is exposed to the sour environment shortly and the protective layer from the addition of the corrosion inhibitors.Authors of this paper began from the hypothesis that certain surfactants that might be surface active and bear the proper electrochemical properties for this aqueous sour gas system that containing elemental sulfur will fend off the elemental sulphur and polysulfide attachments onto the metal surface to achieve an energy equilibrium with other groups of surface active species – such as corrosion inhibitors elemental sulfur and polysulfides. An ideal balanced system is that the surfactants keep washing off the elemental sulfur or polysulfides from being pasted onto the metal surface and in the meantime to facilitate the corrosion inhibitors to perform effectively.A number of surfactants were evaluated at moderate temperature (140oC/284oF) and pressure (13.8bar/200psi) following a varied elemental sulfur surfactants and corrosion inhibitor addition matrix in an aqueous environment containing sour-gas (15% H2S and balanced with CO2 based on mol%) with LPR bubble and autoclave tests. The carbon steel specimens were evaluated and studied before and after these tests.