Modeling the Contribution of Gas Hydrate to Corrosion Rate Along the Subsea Pipelines

Abstract

This study developed a corrosion predictive model along the deepwater gas pipelines with hydrate as the corroding agent. The model was developed and simulated with primary focus on the thermodynamic properties of each component of the gas mixture and a solution algorithm written with Matlab 6.5 code. The model was validated by comparing the generated results with the outputs of already established laboratory and mathematical corrosion studies; and the trends of the results obtained comparatively agreed with these studies to confirm its reliability. The model correctly predicted the relationships between corrosion rate and other thermodynamic parameters such as temperature, pressure, wall shear stress, velocity loss and pH. This study showed that hydrates can initiate galvanic corrosion, stress cracking corrosion and erosion-corrosion amongst others. Furthermore, the resulting corrosion rate from the hydrates could be as high as 174mm/year (0.48mm/day). This is extremely alarming compared to the industry's aim to operate below 2mm/year. At this rate, an underwater pipeline would be subjected to full bore rupture within some days if corrective measures are not quickly taken; hence, the need for further studies.

Influence of Hydrate Formation and Concentration of Salts on the Corrosion of Steel 20 Pipelines

“…In the same way, the lumps of hydrate accumulate over time and form larger pipes, which in turn requires more gas transportation along the pipe wall surface [9,23]. This movement induces relative movement between the pipe wall and the hydration plug and activates the development of large-scale erosion corrosion [5,6,14]. Studies [15,17] have shown an increase in the level of localization of corrosion processes, but no explanation for this phenomenon has been provided.…”

“…In general, most of the results reported in the literature describe hydrate formation during offshore gas [4,23,25] and gas transportation by offshore or onshore pipelines [9,16,20]. Mathematical models of corrosion effects of gas hydrates [1,2,3,6,21,22,24] do not take into account the effect on the metal or passive films of the hydrate itself, but only the pH of the medium or the concentration of CO2 in the gas. Also, the effect of mechanical stresses and hydrate formation on internal corrosion has not been sufficiently studied.…”

Heat transfer study in the exploitation of argillaceous‐silt natural gas hydrate reservoirs

“…The second vital problem hindering the long‐term exploitation of NGH is secondary gas hydrate formation inside the wellbore. Several researchers, such as Koh, 36 Obanijesu et al, 37 Guo et al, 38 Chaudhari et al, 39 and Yu et al, 40 have identified and assessed the blockage risk in the natural gas transportation pipe. Field trial production cases already showed the serious damage caused by secondary gas hydrate formation including blockage of pipes, plugging of valves, and shutting down the production 41–44 .…”