Effects of carbon steel corrosion on the methane hydrate formation and dissociation

Pipeline surface corrosion and gas hydrate plugging are two tricky problems with security risks to the oil-gas production and transportation. The surface morphology, induction time, normalized formation rate and percentage conversion of water to methane hydrate were in situ monitored on the carbon steel (CS) coupon inserted in the SDS solution, which was corroded by soaking in the seawater for different times (0-336 h) before use. The water distribution and methane hydrate cages formation on the metal surfaces with different physical structures were also investigated by microsecond molecular dynamics (MD) simulation. Results indicated that the presence of CS coupons could facilitate the hydrate nucleation via reducing the induction time by about 37%. CS corrosion led to 60% decrease in the induction time compared with the pristine CS, but insignificant difference was found for the CS coupons with different corrosion time. Moreover, the CS coupons had insignificant effects on the normalized hydrate formation rate, but were able to significantly enhance the percent conversion of water to hydrate and inhibit the hydrate dissociation. Overall tendency observed from experiments agreed with the MD simulations, which highlighted the contribution of the changes in the physical structure (formation of grooves with different sizes) other than the chemical components (formation of rust) to the hydrate formation.