Investigating the role of CO2 corrosion products in localised corrosion
Lead Research Organisation:
University of Leeds
Department Name: Mechanical Engineering
Abstract
Localised carbon dioxide (CO2) corrosion of carbon steel remains one of the most aggressive forms of corrosion. The rate of localised material loss experienced by carbon steel pipelines can be very difficult to predict and orders of magnitude greater than the overall uniform corrosion rate. A number of environmental, operational and metallurgical factors have been attributed to the onset of localised corrosion in carbon steel pipelines. Recently, the development of surface corrosion products and mineral scales has been linked to the propensity of localised attack to occur, generating significant scientific interest.
Under CO2-containing conditions, a variety of different surface films can develop; the most common of these in laboratory environments include iron carbide (Fe3C) and iron carbonate (FeCO3). However, deposits such as calcium carbonate (CaCO3) and barium sulphate (BaSO4), as well as mixed corrosion products (FeXCayCO3) can also form, resulting in complex mixtures of corrosion products and mineral scales existing on the same steel surface. Research has indicated that in the case of FeCO3 formation, when partial corrosion product coverage exists, galvanic interactions occur between bare and filmed areas on the same steel surface, helping explain the propagation of localised corrosion under 'pure' CO2 corrosion conditions with NaCl brines.
In most of the published studies on pitting corrosion on carbon steels the pitting corrosion is generated in laboratories over several tens or up to two hundred hours and whilst there is no doubt that localized corrosion is occurring, depths of only hundreds of microns are achieved. In this study we will create laboratory simulations that will enable us to answer questions relating to how pits can grow or be stifled in realistic configurations.
The questions to answer from the study include:
i. What conditions in the fluid in the vicinity of a deep pit and at the metal/corrosion product interface need to exist for pits to grow?
ii. How does transport of chemical species through the corrosion product layer affect pit growth when the corrosion product depth is in the order of mm thick?
iii. Can pit propagation be controlled by inhibitors if deep pits exist with thick corrosion product layers?
This project will seek to answer these key questions through a series of specifically designed experiments, coupled with state-of-the-art surface characterisation, imaging and microscopy techniques.
Objectives
The objectives of the study are as follows:
To develop an integrated methodology which will enable aspects of (a) pit propagation (b) transport of inhibitors through layers of corrosion products (c) understanding the interstitial fluid composition in deep pits to be investigated
To determine what the limitations are for current inhibition strategies to halt the growth of already existing deep pits
Under CO2-containing conditions, a variety of different surface films can develop; the most common of these in laboratory environments include iron carbide (Fe3C) and iron carbonate (FeCO3). However, deposits such as calcium carbonate (CaCO3) and barium sulphate (BaSO4), as well as mixed corrosion products (FeXCayCO3) can also form, resulting in complex mixtures of corrosion products and mineral scales existing on the same steel surface. Research has indicated that in the case of FeCO3 formation, when partial corrosion product coverage exists, galvanic interactions occur between bare and filmed areas on the same steel surface, helping explain the propagation of localised corrosion under 'pure' CO2 corrosion conditions with NaCl brines.
In most of the published studies on pitting corrosion on carbon steels the pitting corrosion is generated in laboratories over several tens or up to two hundred hours and whilst there is no doubt that localized corrosion is occurring, depths of only hundreds of microns are achieved. In this study we will create laboratory simulations that will enable us to answer questions relating to how pits can grow or be stifled in realistic configurations.
The questions to answer from the study include:
i. What conditions in the fluid in the vicinity of a deep pit and at the metal/corrosion product interface need to exist for pits to grow?
ii. How does transport of chemical species through the corrosion product layer affect pit growth when the corrosion product depth is in the order of mm thick?
iii. Can pit propagation be controlled by inhibitors if deep pits exist with thick corrosion product layers?
This project will seek to answer these key questions through a series of specifically designed experiments, coupled with state-of-the-art surface characterisation, imaging and microscopy techniques.
Objectives
The objectives of the study are as follows:
To develop an integrated methodology which will enable aspects of (a) pit propagation (b) transport of inhibitors through layers of corrosion products (c) understanding the interstitial fluid composition in deep pits to be investigated
To determine what the limitations are for current inhibition strategies to halt the growth of already existing deep pits