Pipeline failures attributed to internal corrosion in the oil and gas producing industry have not been decreasing despite the many corrosion mitigation, monitoring and inspection programs implemented. This Paper describes how preliminary investigations for evaluating the susceptibility of internal corrosion for wet sour gas pipelines have been based on integrating the latest knowledge in fluid flow and sour gas corrosion mechanisms. It is anticipated future efforts to correlate the onset of slug flow regime with historical corrosion and inspection data may lead to development of an improved criteria for predicting the onset of corrosive water traps and for triggering appropriate maintenance activities.
This Paper provides details of two corrosion failure Case Studies where application of flow modelling has improved the understanding of the operating hazards that contributed to the formation of a corrosive environment leading to high-rate initiation and growth of localized pitting corrosion. Preliminary analysis indicates slug flow pattern, and long water residence time of water within stagnant traps increases the likelihood of pitting corrosion.
According to statistics published by the industry Regulatory agency, pipeline failures attributed to internal corrosion in the oil and gas producing industry have not been decreasing despite the many corrosion mitigation, monitoring and inspection programs implemented. Causal analysis investigations of wet sour gas pipelines that have experienced damage or failure attributed to internal corrosion share a number of contributing factors:I
there is not an adequate response to changes inflow rates or fluid compositions;
inhibitor injection rates do not account for changes in water volumes, composition, or the presence of suspended solids;
low velocities contribute to the settling of water and suspended solids;
pigging and / or chemical inhibitor batching for removal and control of the hazards associated with stagnant water and settling solids is not performed at the correct frequency; and,
monitoring programs are not adequate to provide warning of system changes.
There is an opportunity to decrease the likelihood internal corrosion will initiate in wet sour gas pipelines by implementing a Corrosion Maintenance System (eMS) that prescribes a schedule for day-to-day mitigation activities in a manner consistently appropriate to the corrosion threat. The key to a successful CMS is therefore the technical evaluation of the hazard profile as a function of changes in the operating conditions.
An understanding of the fluid dynamics within the pipeline is essential to accomplish the goal of aligning mitigation activities with the corrosion threat. Recent studies have demonstrated the onset of slug flow pattern can have a significant effect on corrosion initiation and the rate of growth.2 Preliminary comparison of actual operating conditions with pipeline flow simulation data suggests an evaluation of the corrosion hazard must consider the flowing velocities of the gas and liquid phases, the liquid fraction profile within inclined pipe sections, locations for the onset of slug flow, and the residence time of the water within the slug flow regions.
