Corrosion

Incorporation of protective film formation kinetics into CO2 corrosion models for robust corrosion management – a combined experimental and modelling approach

Supervisors: Prof Anne Neville, Dr Richard Barker, Dr Thibaut Charpentier, Prof Harvey Thompson

Project Summary: Safe and efficient recovery of hydrocarbons is of paramount importance in the oil and gas industry. One of the main obstacles to successful oil production is internal pipeline corrosion, which can cause catastrophic and unexpected failures, leakages, down-time and severe environmental damage. The natural formation of an iron carbonate (FeCO3) corrosion product on the inside of steel pipework is one of the most important factors governing the corrosion rate of the underlying steel; the rate of corrosion can be orders of magnitude lower when FeCO3 is present. Understanding the associated kinetics of FeCO3 formation as well as the conditions conducive to its removal (mechanically or chemically) is of great interest to the oil and gas industry.

There now exists a strong understanding of the CO2 corrosion mechanism within literature and this is reflected in the numerous mechanistic, semi-empirical and empirical models openly available. However, one aspect where greater ambiguity lies is around the subject of FeCO3 formation and understanding how environmental/physical conditions relate formation kinetics and protective nature. This subject area is challenging as the solution chemistry at the interface of a corroding sample dictates the nucleation and growth behaviour and this can be markedly different to that of the bulk solution.

This project adopts a new, combined experimental and computational approach to relate the solution composition in the near surface region to the precipitation kinetics and protective nature of FeCO3 over a range of physical and environmental conditions.

Tasks and expected milestones/deliverables:

Task 1 – Design of a flow cell for controlled hydrodynamics and precipitation experiments:

The initial stages of work will focus on the development of a thin channel flow cell for constant composition experiments. This will facilitate a controlled environment which will yield reproducible and reliable data in relation to FeCO3 precipitation behaviour. The flow cell will cover a range of hydrodynamic conditions to enable the effect of flow rate on the surface species concentration to be evaluated.

Task 2 – Implementation of computational modelling to predict surface concentration of species within flow cell

A computational model will be developed for the thin channel cell within COMSOL Multiphysics. The model will cover the following processes:

  • Integration of Leeds in-house mechanistic model for CO2 corrosion to predict corrosion rate at the steel surface based on the hydrodynamics within the system (which will be validated experimentally)
  • Coupling the surface flux of species, hydrodynamics and the bulk equilibrium reactions for CO2 systems in COMSOL to determine the concentration gradient of species from the surface out into the bulk solution.

Task 3 – Correlation of surface concentration with precipitation kinetics, nucleation and growth behaviour and level of film protection

Mass gain measurements and optical microscopy will be used to analyse the precipitation of FeCO3 from experiments performed in the flow cell under different hydrodynamic and environmental conditions. This will yield information on precipitation rate, surface coverage, crystal size and nucleation and growth behaviour, which can all be linked with surface species concentration.

Task 4 – Development of a semi-empirical model for precipitation of FeCO3

The precipitation data extracted from the flow cell will be compared with the surface concentration of species. The data will then be linked to mechanistic precipitation models to provide accurate prediction of precipitation rates and film protectivity over a range of environmental and hydrodynamic conditions.

Task 5 – Integration into more complex geometries and validation of developed model

The established precipitation model will be integrated into a time-dependent computational model for a range of more complex geometries which will predict the local film growth processes, providing more accurate quantification of corrosion rate behaviour is film-forming CO2 systems. The establish model will be compared with other models from literature to quantify the level of improvement.

Academic requirements: Degrees in Engineering, Materials Science, Physics and Chemistry are particularly suitable.  The successful candidate will join the School of Mechanical Engineering and will work as part of the Institute of Functional Surfaces (iFS) a vibrant and supportive international community of researchers who collaborate with each other and the engineering community. You will be extensively trained for a career as a professional engineer, which will set you on the right track for a future in industry or academia. Follow the links to find out more about what we offer in the institute of Functional Surfaces, https://institutes.engineering.leeds.ac.uk/functional-surfaces/

Understanding the influence of brine chemistry on CO2 corrosion and film formation

Supervisors: Prof Anne Neville, Dr Richard Barker, Dr Thibaut Charpentier

Project Summary: Carbon dioxide (CO2) corrosion of carbon steel presents a serious problem for the oil and gas industry. CO2 can be naturally present in oil and gas reservoirs, or purposely injected as part of enhanced oil recovery techniques to facilitate higher levels of extraction from wells. Additionally CO2 can be injected into depleted oilfields for the purposes of geological storage in an effort to mitigate its effects on the environment.

Despite its low corrosion resistance, carbon steel still remains the most widely used pipeline material based on its widespread availability and low cost. The CO2 corrosion mechanism involves a complex combination of chemical, electrochemical and transport processes. In addition to these, deposition or precipitation processes occur which result in the formation of corrosion products or mineral scales on the steel surface. Typically, in ‘simple’ CO2-saturated solutions with distilled water or only NaCl as the salt present, iron carbonate (FeCO3) is the most commonly observed corrosion product. The importance of the formation of this crystalline layer has been well documented in its ability to reduce steel corrosion rate.

The structural and protective properties of the FeCO3 layer have been shown to be highly dependent upon the concentration of ionic species, temperature, pH and partial pressure of the system in question. However, one potentially influential aspect which has surprisingly received less attention is that of the brine chemistry and the effect of cations such as calcium (Ca2+) and magnesium (Mg2+) which can readily be found in production fluids. The presence of divalent salts can reduce CO2 solubility and result in the precipitation of mineral scales (such as the formation of calcium carbonate (CaCO3) in the case of Ca2+ presence). Despite MgCl2 and CaCl2 salts being commonly found in the fluids of geological formations, their role on FeCO3 film formation, morphology, structure and chemical properties, particularly in supercritical CO2 conditions is limited. This project addresses the knowledge gap through the systematic evaluation of corrosion films on steel surfaces across a range of pressures, temperatures and brine chemistries. The goal is to determine the effects of complex brine chemistries on the susceptibility of carbon steel to both general and localised corrosion in both low and high pressure environments, typical of production and downhole conditions, respectively.

Tasks and expected milestones/deliverables:

Task 1 – Low pressure testing in the absence of corrosion products and mineral scales – Ca2+, Mg2+, K+, Na+, Cl, SO42- effects on general and localised corrosion

The initial stages of work will focus on understanding the role of various monovalent and divalent cations and anions on the anodic and cathodic CO2 corrosion reactions, as well as the general and localised corrosion behaviour in conditions where no film formation occurs (i.e. below the solubility limit of FeCO3, CaCO3, MgCO3 etc.). The work will systematically evaluate how each specie influences the initiation and propagation of localised attack, and the extent of uniform corrosion.

Task 2 – Low pressure testing in corrosion product forming/mineral scaling conditions

Based on the initial work, a subset of anions and cations will be selected to test in conditions where their respective mineral scales are above their solubility limit within the CO2 brine. This work will consider the relative effects of saturation ratio for each scale/corrosion product, to determine how this influences the film kinetics, morphology and the level of protection afforded to the steel substrate in terms of general and localised corrosion.

Task 3 – High pressure testing in film forming conditions

The final series of experiments will contrast the thin films formed at low pressure with the much thicker corrosion product layers generated at high pressure over the same time-frame. These experiments will enable further insight to be gained into properties of the film through conducting a combination of dissolution experiments and mechanical measurements to determine the resistance of the films to mechanical damage and chemical dissolution.

Academic requirements: Degrees in Engineering, Materials Science, Physics and Chemistry are particularly suitable.  The successful candidate will join the School of Mechanical Engineering and will work as part of the Institute of Functional Surfaces (iFS) a vibrant and supportive international community of researchers who collaborate with each other and the engineering community. You will be extensively trained for a career as a professional engineer, which will set you on the right track for a future in industry or academia. Follow the links to find out more about what we offer in the institute of Functional Surfaces, https://institutes.engineering.leeds.ac.uk/functional-surfaces/

Experimental and Numerical Investigation of Flow Accelerated Corrosion in Power Plant Piping Networks

Supervisors: Dr Richard Barker, Prof Anne Neville, Prof Harvey Thompson

Project Summary: Corrosion is the degradation of a material, due to chemical reactions with the surrounding environment. Flow Accelerated Corrosion (FAC) occurs in piping systems and leads to thinning of larger areas on pipelines, particularly in fossil and nuclear power plants and in oil and gas pipelines. This can cause pipeline breakage, even plant shutdown and personal injury, and several catastrophic failures have been reported at power plants around the world due to FAC. Piping elbows are particularly prone to FAC, due to secondary flows and and/or flow separation. The project will carry out an experimental and numerical investigation of the corrosion rates caused by mass transfer in power plant piping elbows. Mass transfer rates and mass transfer coefficients in pipe elbows will be measured experimentally using electrochemical (EC) sensors integrated into multiple designed elbow pipes to assess local mass-transfer rates within each elbow at different radial positions. Computational Fluid Dynamics (CFD)-based models for FAC will be developed, the first of which will use Chilton-Colborn correlations for mass transfer coefficient as a function of wall shear stress, mean velocity and Schmidt number, and a second, more accurate model which accounts for species transport caused by molecular diffusion and turbulent convection. These CFD models will be validated by comparting their predictions against existing experimental mass transfer data from the literature and experimental wall thickness measurements from the damaged elbows.

The validated model will be used to explore the effect of flow velocities, static pressures and shear stresses on corrosion rate distributions over elbow geometries, and the influences of the key parameters will be ranked statistically.

Tasks and Milestones:

Task 1 – Project orientation: literature survey on FAC, familiarisation with experimental and numerical methods. Literature survey completed (month 6).

Task 2 – Experimental studies: AE measurements of mass transfer and wall thinning in elbow geometries Initial validation data completed (month 12), Experimental study of key parameters completed (month 18).

Task 3 – CFD modelling of FAC: familiarisation with CFD methods; develop initial CFD models with RNG k-ε turbulence model and Chilton-Colborn correlations; extend CFD model to account for species transport using highly refined structured grids to resolve mass transfer boundary layer; validate CFD models against experiments and explore effect of key parameters, using Plackett-Burman analyses. CFD models validated (month 18); Parameter studies and risk evaluations completed (month 33);

Task 4 – Write up journal papers and thesis: journal papers and thesis (months 30,36).

Background of student required: Graduate in an Engineering subject (Mechanical, Chemical), Mathematics or Physics, preferably with experience and knowledge of fluid mechanics.