A Statistical Study Of Pipeline Corrosion In A High-Pressure Simulated Flow Loop
Authors: Fli Shi Liang , Bluth M.J. , Choi Ho Jin 
Published: October 2008

A high pressure, high temperature recirculating flow loop was constructed for the study of corrosion in pipelines. An empirical method based on a 23factorial design was used to establish a model that describes the effects of pressure, temperature, velocity, and their interactions on corrosion. Statistical analyses of the flow loop data result in an interaction model which adequately predicts corrosion rates under flowing conditions. The model suggests that the corrosion rate is dependent upon all three variables as well as upon their interactions. The corrosion rate increases with the increase of these variables and their interactions. Both temperature and pressure display the strongest effects on varying corrosion rates. This is followed by the effect of the temperature pressure interaction. The effects of velocity and its interaction with either pressure or temperature are relatively less significant. The current model provides a good quantitative comparison of the importance of each variable and their interactions on corrosion under flowing conditions.

INTRODUCTION

Corrosion is the most common problem that causes pipeline failures in the oil and gas production industry (1). A typical type of corrosion is "sweet corrosion", which involves the presence of carbon dioxide (C02). Carbon dioxide dissolves in brine to form carbonic acid that ionizes to yield a low pH value. The resulting acidic solution consequently causes the carbon steel pipes and joints to corrode. in recent years, the presence of carbon dioxide in produced fluids is encountered more frequently due to the use of enhanced oil recovery (EOR)techniques involving C02 injection into reservoirs. The sweet corrosion problem also occurs in gas production from deeper wells. Replacement of corroded pipes often results in a big capital loss due to the cost of pipe replacement and the cost of production shutdown. Therefore, vast amounts of time and energy have been devoted to combating this problem in the field. This has been achieved through material selection and the application of inhibitors. A significant amount of effort has also been made in the laboratory to support the field work.

One major challenge in the laboratory is to have the ability to predict corrosion rates under various field conditions. A good estimate on corrosion rates could provide field engineers with useful information for better pipeline design and proper material selection. Corrosion prediction is normally based on a model which is established by either a mathematical approach or by an empirical method. Mathematical modelling is based on the principles of transport phenomena, fluid dynamics, and electrochemistry. Assumptions are usually made in order to achieve an analytical solution to the mathematical model. The empirical method requires conducting some experiments to gather data for constructing the model. Since flow induced corrosion is one of the most common corrosion problem in pipelines, most models are focused on factors such as velocity, mass transfer rate, and turbulent intensity (2–4). Additional factors may be added to emphasize a specific corrosion problem such as cavitation corrosion and erosion corrosion. The validity of these models is then verified in laboratory simulation units (2,5)