Influence of the gas hydrates on the corrosion rate of gas gathering pipelines

Abstract

Abstract The regularities of corrosion degradation of the low carbon ferrite pearlite St 20 (0.2C) steel of gas gathering pipeline under the mutual effect of corrosion environment, mechanical stresses and hydrate formation were determined. A change in corrosion mechanism in chloride media at increasing chloride concentration from 2.5 mol/L to higher concentration was found. The revealed more significant influence of mechanical stress on localized corrosion rate than on uniform corrosion one was associated with the formation of local galvanic elements on the metal surface and intensification of the metal dissolution in the tensile zone due to the weakening of interatomic interaction caused by increase the distance between grains. Fatigue tests of the pipe steel specimens after exposure to gas hydrate showed a significant decrease in durability (by 15 – 25% depending on test environment), the reason of which was obviously associated with increasing of corrosion damaging of the specimen surface as a result of the aggressive action of gas hydrates.