Study and Modeling of the Localized Nature of Top of the Line Corrosion

The occurrence of localized corrosion in Top of the Line Corrosion (TLC) was investigated in a sweet (CO2-dominated) environment, with a focus on understanding the influence of the environmental parameters on localized TLC in order to develop a narrative for the mechanism. A unique setup was developed for the experimental work, involving the use of carbon steel inserts exposed to three different levels of cooling at the same time. This concept was quite successful in simulating realistic localized features. A series of long term exposure (oneto three-month) experiments was conducted to investigate the controlling parameters. The occurrence of localized corrosion could be very clearly correlated to the condensation rate, the gas temperature and the organic acid content. Additional statistical information related to the morphology of localized TLC features could be made, providing useful insight on the mechanisms involved. INTRODUCTION When significant heat exchange is present between the wet gas pipelines and the surroundings (frozen land, deep-sea water, etc.), water and hydrocarbon vapor can condense on the inner pipe wall and lead to severe corrosion issues [1]. This phenomenon called Top of the line corrosion (TLC) is inherently a localized process. Corrosion occurs in specific areas along the line and the attack is not usually extended to large sections. This localized aspect is often related to situations where high condensation rates occur, i.e. where the gradient of temperature between the produced fluid and the outside environment is large. In sweet environments (CO2-dominated), the corrosion process is often characterized as a mesa attack: the steel is not uniformly corroded but the pits are usually wide, often flat-bottomed and bare of any layers, surrounded by areas with intact corrosion product layers. The localized nature of TLC is still not well understood. The corrosion features observed in the field can be so large that the corrosion process is often referred to as “localized uniform corrosion” instead of a just “localized corrosion”. The unique TLC scenario where droplets of condensed water appear and are