Design of Multiphase Offshore Gas Pipelines with High Risk of Sweet Top of the Line Corrosion

During the last fifteen years several methods, techniques, tools and products have been developed for the prediction, control and monitoring of top of the line corrosion (TLC) and also for the design of wet gas pipelines. However, most of the knowledge used for dealing with TLC was based on the field experience, pipeline simulation packages and empirical correlations. With time, the real mechanism of TLC was understood and the roles of important parameters were identified and quantified. Knowledge provided by R&D increased significantly and started to be used in the prediction, control and monitoring of TLC and also in the design of pipelines. Then during the last five years significant efforts have been made to correlate predictions and field data and also to evaluate the efficiency of corrosion control and monitoring systems. Performance and reliability of prediction tools are improved. While some of the corrosion control systems still remain at the stage of "better than nothing" some others have reached a high level of efficiency and reliability. However, more efforts are needed to demonstrate that these systems can now be considered as "standard" for the design of pipelines as there is no consensus, among the users, about their level of reliability. Another aspect is the impact of environment protection on the pipeline design as the risk of pipeline failure by TLC is more important than by typical CO2 corrosion. This paper is the first attempt to discuss (i) impact of the TLC mechanism on the pipeline design (ii) overall performances of the existing prediction, corrosion control and monitoring tools and products, (iii) level of confidence expressed by the industry in these systems, (iv) impact of environment protection on the pipeline design. Design requirements for sensitive and highly sensitive environments are proposed. The primary objective of the paper is to initiate discussions on the standardization of pipeline design for sweet TLC service.