Ph.D. Proposal Defense

 

 

 

A Mechanistic Study of CO2 Corrosion of Mild Steel in the presence of H2S

 

 

 

 

 

 

Kun-Lin John Lee

 

 

 

A Mechanistic Study of CO2 Corrosion of Mild Steel in the presence of H2S

 

 

Ph.D. candidate: Kun-Lin John Lee

 

Advisor: Srdjan Nesic

 

 

 

Research Abstract

 

A research project is currently undertaken with the aim to develop an integrated mechanistic model of CO2/H2S corrosion including all the important processes occurring such as: the electrochemical and chemical reactions, the transport processes within the boundary layer and the protective film formation. The existing mechanistic model of CO2 corrosion will be used as a basis for the future development of the combined CO2/H2S model. This research project will include addition of new species, chemical and electrochemical reactions arising from the presence of H2S.

 

 

Introduction

 

CO2/H2S combined internal corrosion attack has been a recognised problem in oil and gas industry for many years.  Although various research efforts have tried to analyse it in order to develop predictive models, the underlying corrosion mechanisms are still not fully understood.

Engineers in the oil and gas industry nowadays employ various models for CO2 corrosion1-16.  Depending on how firmly they are based on theory these predictive models can be classified into three categories: mechanistic, semi-empirical and empirical models.  Even for “pure CO2” corrosion, most research effort on the modelling are either semi-empirical or empirical1-10, that is, they are aimed at limiting the problem, but neglecting the physics behind it.  Only some of the more recent models have been based on mechanistic descriptions of the processes underlying CO2 corrosion11-16.  On the other hand, the predictive models for combined CO2/H2S corrosion attack are not only primitive but also unable to meet the demands of the industry.

Although several attempts were made to provide an equilibrium thermodynamic framework for the interpretation of Fe/CO2/H2S/H2O chemistry system16-18, there are no models existing for the interpretation of corrosion, transport and scaling phenomena in this system.  A research project is currently undertaken with an aim to develop an integrated mechanistic model of CO2/H2S corrosion that includes all the important processes occurring such as: the electrochemical and chemical reactions, the transport processes within the boundary layer and the protective film formation.  Film formation due to the presence of H2S and its effect on corrosion of mild steel is the main focus of this research as the formation of stable and metastable iron sulfide species are difficult to predict when taking various environmental factors into account.  The mechanistic model of FeCO3 film growth and the effect on CO2 corrosion of mild steel (Nesic and Lee, 2002)15 has shown that the concentrations of species near the metal surface are required in order to accurately predict the morphology of the film and its effect on the corrosion of the mild steel.  The model’s ability to calculate the concentration profile near the metal surface proves to be a strong advantage over other existing models and will be used as a basis for the future development of the combined CO2/H2S model. This research project will include addition of new species, chemical and electrochemical reactions arising from the presence of H2S. 

 

Overall, this research project not only provides the insight of the fundamental understanding of CO2/H2S corrosion with the inclusion of film formation, but also has a great practical purpose in the oil field related areas.

 

Some of the principal questions that need to be answered are:

 

  1. Can the complexity of iron sulfide formation be fully predicted when taking most of the important environmental parameters into account?
  2. How does the existence of several stable and metastable Fe-S compounds affect CO2 corrosion of mild steel?

 

 

Contributions

 

In the case of H2S corrosion and CO2/H2S corrosion, experimental studies have been performed by various studies.19-32 These studies included the effect of H2S on cathodic and anodic processes and the formation of various crystalline forms of iron sulfide scales. Several research efforts25,28-32 attempted to elucidate the mechanism of CO2/H2S corrosion.   However, the understanding of CO2/H2S corrosion in the presence of H2S is still limited and no predictive mechanistic models have been published in the open literature for H2S or CO2/H2S corrosion.  The purpose of this research project is to make the following contribution to the area of modelling of CO2 corrosion in the presence of H2S:

 

l          Develop a vapour-liquid equilibrium model for dilute aqueous solutions of

       CO2/H2S at different temperature with the aim to calculate the species concentrations in the presence of H2S.  Although similar model has been built previously33,34,35 It is essential to develop a model of our own to provide more flexibility and applicability of input and output because the equilibrium concentrations are used as initial and boundary conditions for the mechanistic corrosion model.  The equilibrium model is also a practical tool for experiments as it enables important parameter such as pH and H2S concentration to be compared and verified against the experimental measurements. 

l          Develop a mechanistic one-dimensional model of CO2/H2S corrosion including film growth.  Addition of new species, chemical and electrochemical reactions arising from the presence of H2S.

l          Performing small-scale experiments of CO2 corrosion in the presence of H2S to obtain missing physical constants.

l          Perform large-scale experiments to verify the overall performance of the model.

 

Progress to date

 

Three main areas are considered in the overview of the work accomplished: literature review, model development and experiments.  The tasks completed to date will serve as fundamental building blocks for the final model.

 

Model development

 

l          CO2 / H2S homogeneous chemistry equilibrium code for both open and closed system.

l          Implementation of implicit electrochemical boundary conditions to the CO2 corrosion code14.  This code will serve as a basis for all future developments.

l          Implementation of one dimensional film growth model into CO2 corrosion code from Nesic et al15.

 

Experiments

 

l          Mass-transfer and CO2 experiments using electrochemical techniques and a rotating cylinder.

l          Glass cell experiment in film forming conditions (high temperature and pH) in order to obtain missing physical parameters for film growth model15.

l          Small scale CO2 ­/H2S experiments using electrochemical measuring techniques and a rotating cylinder.

 

 

Current work

 

Small-scale experiments of CO2 corrosion in the presence of H2S are performed using RCE/glass cell arrangement (shown in Figure 1) to obtain missing physical constants.  At this stage, conditions are chosen to avoid forming sulfide films at various H2S concentrations, focusing on the main effects of H2S on the cathodic and anodic reactions present in CO2 corrosion.  Both the potentiodynamic sweep technique and Electrochemical Impedance Spectroscopy are employed in order to capture the insight of electrochemical reactions caused by CO2­/H2S interaction.  Several studies36-39 have demonstrated that the electrochemical behaviour of iron in the acidic solutions containing H­2S can be investigated by means of AC impedance measurement together with the potentiodynamic sweep technique.  However, no systematic investigation has been reported on the influence of H2S concentration on the dissolution of iron in CO2/H2S solution.   Once the fundamental understanding of the effects of H2S has been established, a new set of test matrix condition will be devised to investigate the effect of H2S on the film formation in order to address principle questions 1 and 2.  The mechanistic one-dimensional model of CO2 ­/H2S corrosion including films is developed at the same time as more in-depth understanding of the H2S effects are grasped.

 

 

Future plans

 

Basically, the work that remains to be done can be classified into two sections, namely, the modelling section and experimental section.  Small-scale experiments are required to obtain the missing physical constants in the model.  Large-scale experiments will be conducted to verify the overall performance of the final model.

 

 

Milestones for achieving the goals:

 

  1. Performing small-scale experiments of CO2 corrosion in the presence of H2S to obtain missing physical constants.
  2. Develop a mechanistic one-dimensional model of CO2-H2S corrosion including films.  Addition of new species, chemical and electrochemical reactions arising from the presence of H2S.
  3. Performing the large-scale experiments to verify the overall performance of the final model
  4. Writing-up and submitting PhD thesis.

 

 

A timeline is provided below to serve as a guide to achieve discrete goals in each period.

 

 

 

September 2002

January 2003

June  2003

 February 2004

June    2004

Milestone 1

 

 

 

 

Milestone 2

 

 

 

Milestone 3

 

 

 

 

Milestone 4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Publications

 

There will be at least three publications submitted to the NACE conferences and the  Corrosion Journal.  Two publications have already been submitted to the NACE conferences.  The paper that describes iron carbonate film growth model15 has already been accepted by the corrosion journal. The schedule for writing-up and presenting these papers are shown below. 

 

April, 2002

 

Presenting the iron carbonate film growth model15 in the NACE conference.

 

Summer and fall quarter 2002

 

Writing-up the paper on vapour-liquid equilibrium model for the 2003 NACE conference and Corrosion Journal.

 

Summer and fall quarter, 2003

 

Writing-up the paper on CO2-H2S corrosion model for the 2004 NACE conference and Corrosion Journal.

 

April, 2004

 

Presenting the CO2-H2S corrosion model in the NACE conference.

 

June, 2004

 

Submitting the final NACE and Corrosion Journal publication.

 

 

 

Reference

 

1.    C. de Waard and D.E Milliams, “Predictive Model for CO2 Corrosion

       Engineering in Wet Natural Gas Pipelines”, Paper No.577, CORROSION/91

 

2.    C. de Waard and U Lotz, “Prediction of CO2 corrosion of carbon steel”, Paper

       No.69, CORROSION/93

 

3.    C. de Waard,  U Lotz, and A Dugstad, “Influence of liquid flow velocity on CO2

       corrosion: a semi-empirical model”, Paper No.128, CORROSION/95

 

4.    M. R. Bonis, J-L. Crolet, “Basics of the prediction of the risks of CO2 corrosion

       in oil and gas wells”, CORROSION/89, paper no. 466, (Houston Texas: NACE

       International, 1995)

 

5.    Y.M. Gunaltun. “Combining research and field data for corrosion rate prediction”.

       CORROSION/96, paper no. 27. (Houston Texas: NACE International, 1996).

 

6.    C.D. Adams, J.D. Garber, R.K. Singh, “Computer modelling to predict corrosion

       rates in gas condensate wells containing CO2", CORROSION/96, paper no. 31,

       (Houston Texas: NACE International, 1996).

 

7.    S. Srinivasan, R.D. Kane, “Prediction of Corrosivity of CO2 / H2S production

       environments”, CORROSION/96, paper no.11, (Houston Texas: NACE

       International, 1996).

 

8.    R.C. John et al, “SweetCor: An information system for the analysis of corrosion

       of steels by water and carbon dioxide”, CORROSION/98, paper no.20, (Houston

       Texas: NACE International, 1998).

 

9.    W.P. Jepson, C. Kang, M. Gopal and S. Stitzel, “Model for sweet corrosion in

        horizontal multiphase slug flow”, CORROSION/97, paper no.11, (Houston

        Texas: NACE International, 1997).

 

10.   R.Zhang, M.Gopal and W.P. Jepson, “Development of a mechanistic model for

        predicting corrosion rate in multiphase oil/water/gas flows”, CORROSION/97,

        paper no.601, (Houston, TX: NACE International, 1997).           

 

11.   B.F.M. Pots, “Mechanistic models for the prediction of CO2 corrosion rates

         under multi-phase flow conditions”, paper no. 137, CORROSION/95.

 

12.   S. Nesic, J. Postlethwaite and S. Olsen, “An Electrochemical Model for

        Prediction of CO2 Corrosion”, paper no.131, CORROSION/95.

 

13.   E. Dayalan, F.D. deMoraes, J.R. Shadley, S. A. Shirazi, E. F. Ribicki, “CO2

            corrosion prediction in pipe flow under FeCO3 scale-forming conditions”,

        CORROSION/98, paper no. 51, (Houston, TX: NACE International, 1998)  


14.    S. Nesic, M. Nordsveen, R. Nyborg and A. Stangeland, “A Mechanistic Model

         for CO2 Corrosion with  Protective Iron Carbonate Films”, CORROSION/2001,

         paper no. 40, (Houston, TX: NACE International, 2001).

 

15.    S. Nesic and K.J. Lee, “The mechanistic model of iron carbonate film growth

        and the effect on CO2 corrosion of mild steel”, Paper No.237, CORROSION/02

 

16.    A. Anderko and R. Young, ”Simulation of CO2 / H2S corrosion using

         thermodynamic and electrochemical models”, Paper No.31, CORROSION/99

 

17.    D.D. MacDonald and J.B. Hyne, “The thermodynamics of the    

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18.    D.W. Shoesmith, “Formation, Transformation and Dissolution of phases formed

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20.    J.B. Sardisco, W. B. Wright, E. C. Greco, Corrosion, v.19, p. 354t (1963)

 

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22.    K.Videm, J. Kvarekval, Corrosion, v.51, p.260-269 (1995).

 

23.    A.Ikeda, M.Ueda and S. Mukai, “Influence of environmental factors on

         corrosion in CO2 source well”, advance in CO2 corrosion.

 

24.    D.R. Morris, L.P. Sampaleanu, D.N. Veysey, “The corrosion of steel by aqueous

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25.    Z.A. Iofa, V. V. Batrakov, Cho-Ngok-ba, Electrochim. Acta, V. 9, p. 1645

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26.    D.W. Shoesmith, P. Taylor, M.G. Bailey, B.Ikeda,Electrochim. Acta, v. 23,

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27.    D.W. Shoesmith, M.G. Bailey, B.Ikeda, Electrochim. Acta, v.23, p. 1329-1339

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28.    D.W. Shoesmith, P. Taylor, M.G. Bailey, D. Owen, J. Electrochem. Soc., v. 127, 

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29.    T.A. Ramanarayanan and S.N. Smith, “Corrosion of iron in gaseous

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30.    S.N. Smith, “A proposed mechanism for corrosion in slightly sour oil and gas

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        1993.

 

31.   H.Vedage, T.A. Ramanarayanan, J.D. Mumford and S.N. Smith,

        “Electrochemical growth of iron sulfide films in H2S-saturated chloride media”,

        corrosion, v. 49, no.2, p.114-121 (1993).

 

32.   S.N. Smith and E.J. Wright, “Prediction of minimum H2S levels required for

        slightly sour corrosion”, Paper NO.11, CORROSION/94

 

33.   B. E. Roberts and P.R. Tremaine, “Vapour Liquid Equilibrium Calculations

        for Dilute Aqueous Solutions of CO2, H2S, NH3 and NaOH to 300oC”, The

        Canadian Journal of Chemical Engineering, 63, (1985): p.294-300.

 

34.   R.D. Deshmukh and A.E. Mather, “A Mathematical Model for Equilibrium

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35.   A. Miyasaka, “Thermodynamic Estimation of pH of Sour and Sweet

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36.   H.Y. Ma, X.L. Cheng, S.H. Chen, C. Wang, J.P. Zhang. H.Q. Yang, J.

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