ANTICORROSION PERFORMANCE OF CHRYSOPHYLLUM ALBIDUM AND A SYNTHETIC INHIBITOR IN SIMULATED DRILLING FLUID

 

ABSTRACT

The anti-corrosive performance of ethanol extracts of Chrysophyllum albidum and  a synthetic inhibitor was investigated using weight loss and potentiodynamic polarization technique on mild steel. Results from weight loss analysis revealed that inhibition efficiency increased with increase in concentration of the inhibitors while corrosion rate decreased with increase in concentration of the inhibitors due to the adsorption of the organic molecules on the metal surface. Highest inhibition efficiency of 96.6% at 218.2 ml/L was recorded after five days for the ethanol extracts of Chrysophyllum albidum and 96.05%  at 250ml/L after three days for the synthetic inhibitor both in a simulated drilling fluid. Temperature studies carried out also revealed the efficacy of the ethanol extracts of Chrysophyllum albidumas compared to the synthetic inhibitor at the temperature ranges of 313K and 333 K. From the values of activation energy obtained, the mechanism of the adsorption process was proposed to be  predominantly of  chemisorption for both inhibitors.Thevalues ofΔG obtained were all negative which  reveals  spontaneity  of  the  process  while  ΔH_ads  reveals  endothermic reactions for both inhibitors in the simulated drilling fluid medium.Potentiodynamic polarization results showed that both the anodic and cathodic reactions were inhibited indicating that the inhibitors are of mixed type. The experimental data obtained fits well with Langmuir adsorption isotherm indicating that the inhibitors were adsorbed uniformly on the metal surface.

 

Key Words:   Chrysophyllum Albidum, Corrosion Inhibition, Weight Loss, Mild Steel, Synthetic Inhibitor.

 

TABLE OF CONTENTS

 

Cover  Page                                                                                                                              i

Title page                                                                                                                                 ii

Certification                                                                                                                            iii

Dedication                                                                                                                                         iv

Acknowledgements                                                                                                                           v

Table of Contents                                                                                                                             vi

List of Tables                                                                                                                                  viii

List of Figures                                                                                                                                    x

 

List of Abbreviation                                                                                                                 xii

 

 

CHAPTER ONE: INTRODUCTION

1.1  Background  Information                                                                                                   1

1.2  Problem Statement                                                                                                            10

1.3  Objectives of Study                                                                                                           10

1.4  Justification of Study                                                                                                         11

1.5  Scope of Study                                                                                                                  11

 

CHAPTER TWO: LITERATURE REVIEW

  

2.1  Metallic Corrosion Inhibitor of Plant Origin                                                                     12

 

 

CHAPTER THREE: MATERIALS AND METHOD

 

3.1  Materials                                                                                                                            25

3.2  Material Preparation                                                                                                          25

3.3  Preparation of Inhibitors                                                                                                   26

3.4  Corrosion System                                                                                                              26

3.5  Experimental Set- up  and Monitoring                                                                              26

3.6  Electrochemical Measurement                                                                                           27

3.7  Temperature Studies                                                                                                           28 CHAPTER FOUR: RESULTS AND DISCUSSION

 

4.1  Results                                                                                                                               30

4.2  Analysis of Results from Gravimertic Measurement                                                        40

4.3  Analysis of Results from Potentiodynamic Polarization Measurements                          45

4.4  Discussion of Gravimetric Results                                                                                    49

4.5  Discussion of Potentiodynamic Polarization Result                                                         50

4.6  Adsorption Considerations                                                                                               50

 

4.7  Langmuir Adsorption Isotherm                                                                                        51

4.8  Temkins Adsorption Isotherm                                                                                          58

4.9   Effect of Temperature                                                                                                      62

4.10  Discussion of Results from Temperature Studies                                                           64

4.11  Thermodynamic Studies                                                                                                  65

 

CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS

 

5.1  Conclusion                                                                                                                        73

5.2  Recommendations                                                                                                            74

5.3  Contribution to Knowledge                                                                                              74

REFERENCES                                                                                                                        75

 

CHAPTER ONE

INTRODUCTION

1.1       BACKGROUND  INFORMATION

1.1.1  PREAMBLE

The uses of mild steel cut across several sectors. These include petrochemical, food, sugar, leather, textile industries etc. Corrosion of metals is a common problem that has economic as well as environmental impact. Many of the corrosion problems encountered in our industries are engendered by acids such as HCl, H₂SO₄, and to a reduced extent H₂CO₃, (Sastri, 1998). In the oil industries, corrosion in various forms is the major cause of drilling pipe failures that add significantly to drilling costs (Kermani&Morshed, 2003). The trends toward drilling of deeper wells, use of higher strength steels, presence of higher stresses, and use of lower pH drilling fluids contribute to increased susceptibility of metals to failure because of corrosion (Anom, 2006).

Corrosion is the principal cause of damage to metals in wells and production facilities. Corrosion attacks metals in drilling and producing operations through electrochemical processes in the presence of electrolytes and corrosive agents in drilling, completion, packer, and produced fluids. The components in fluids that promote the corrosion of steel in drilling and producing operations are majorly oxygen, carbon dioxide, hydrogen sulphide (Chilingarian, Mourhatch, & Al-Qahtani, 2008).

Because it is almost impossible to preventcorrosion, it is becoming more apparent thatcontrolling the corrosion rate may be themost economical solution. Corrosion engineers are therefore increasingly involved inestimating the cost of their solutions to corrosion prevention and estimating the useful life of equipment (Singh & Krishnathasan, 2009).

Recent researches in the field of corrosion have been geared towards reduction if not complete eradication through the use of synthetic and inorganic inhibitors. This is simply so owing to the health and environmental hazards posed by this class of inhibitors. Apart from being hazardous, synthetic inhibitors are expensive, not readily available, non – biodegradable, non-renewable and more especially, are not eco- friendly (Oguzie, Onuoha, &Ejike, 2007; Sastri, 1998).

Corrosion inhibitors from plant origin (roots, stems, leaves and seeds) are known to contain lone pair of electrons present on a hetero-atom ( i.e  oxygen, phosphorous, sulphur and nitrogen), pi- bond, triple bond  (e.gcyano group) in their functional group which are characteristics of a good corrosion inhibitor (Odiongenyi, 2006).

1.1. 2 Definition of Corrosion

Corrosion is defined as the deterioration of materials by chemical interaction with the environment causing slow, steady and irreversible deterioration of the metal in both physical and chemical properties (Sastri, 1998). It is also defined as an electrochemical process by which metallic surfaces reacts with their environment causing the metal to lose its material properties due to surface deterioration (Boyanzier & Hammounti, 2004).

Virtually all metals with exception of gold and platinum corrode in an oxidizing environment forming compounds either in their oxides, hydroxides and sulphates (Ashworth, 1996; Nasa-Nasa, 1994; Vasant & Bansal, 2013). Corrosion causes important material and economical loses due to partial or total replacement of equipment and structures and plant repairing shutdowns (Fontana et al., 1967; Sastri, 1998).

1.1.3  FORMS OF CORROSION

1. a) Classification by Mechanism

Corrosion can be classified into the following forms based on the chemistry of their occurrence.

Sweet (CO₂) Corrosion

Carbon dioxide corrosion, also called ―sweet‖ corrosion, is often encountered in oil and gas production wells and is the main cause of material failures.  There are three main reasons for this observed prevalence of CO₂ corrosion.   

1. The actual CO₂ corrosion mechanism itself is still not fully understood.
2. The existing long-term prediction models are unreliable.

• The carbon and low-alloy steels, widely used in oil and gas production wells, have poor resistance against CO₂ corrosion (Kermani & Morshed, 2003).

 

Sweet corrosion is gaining additional attention due to the increased use of CO₂ injection method for enhanced oil recovery (EOR).  Dry CO₂ gas is not corrosive at the temperatures occurring in oil and gas production wells and requires an aqueous phase.  The main cause of the corrosion is that CO₂ dissolves in water, yielding a weak acid, H₂CO₃ which can be corrosive (Kermani & Morshed, 2003).

 

The equilibrium makes it difficult to identify the rate-determining step (RDS) in the reaction between the dissolved CO₂ and the steel surface(Chukwudeme et al., 2009)

CO₂ + H₂O  CO₂ – H₂O ≈ H₂CO₃ H⁺ + HCO₃^–                       (1.1)

Although CO₂ corrosion itself generally doesn’t cause catastrophic failures, such as the cracking associated with H₂S corrosion, its high corrosion rate can, in the end, be even more damaging.  CO₂ corrosions often occur as general corrosion or localized corrosion, such as pitting, mesa-attack, and flow-induced localized corrosion, (Newton &Hausler, 1984).

Sour (H₂S) Corrosion

H₂S reacts with steel to form a semi-protective film of iron sulfide (FeS). Because the FeS film is normally not uniform and can be removed by liquid flow, fresh metal is exposed to H₂S. The exposed area is anodic and small in area compared to the surrounding iron sulfide film. Hence, the exposed metal preferentially corrodes causing pitting.  When H₂S concentrations are low, however, sulphide stress cracking (SSC), a form of hydrogen stress cracking (HSC), can occur (Felipe & Mize, 1994; Schroder et al., 1999).  .  

The role of H₂S in SSC formation is to provide hydrogen at the metal surface by corrosion and to prevent hydrogen escaping into the surrounding fluid. In the absence of H₂S, hydrogen normally formed at a cathode in a production well would simply bubble off. However, sulfide in surrounding fluids prevents the escape of hydrogen (H₂S poison effect). The hydrogen thus finds an alternative path through the metal due to the small size of the hydrogen atom. At high temperatures the migration of the hydrogen atoms is rather easy; but, at low temperature migration is restricted and, therefore, the concentration of hydrogen atoms inside the metal (where temperature is lower than in the surrounding fluid) builds up (Bellarby, 2009).  

Microbiologically Influenced Corrosion

Microbiologically influenced corrosion (MIC) is also known as biocorrosion or microbial corrosion.  It occurs when micro-organisms complicate matters in the environment.   The type of metal used in construction, the microstructures, the metal surfaces, metal alloys, all play a part in affecting MIC.  An understanding of MIC requires an understanding not only of corrosion but of microbiology. Describing the types of corrosion, bacteria, algae and fungi all play a role; and the average dimensions of these microbes is typically in the range of micrometres.  Their small size makes their dispersion in the environment and into crevices and many hard to access areas possible gives the definition of MIC as ―The electrochemical process, here the participation of microorganisms, is able to facilitate, or accelerate the corrosion reactions without changing its electrochemical nature‖(Videla, 1996).

Bacteria can be quite detrimental and to further complicate the problem they are able to withstand extreme conditions; often from below freezing to quite high temperatures. Another problematic characteristic they possess is their ability to enter a ―spore‖ form once they are dehydrated together with their ability to remain in a spore stage until an acceptable environment allows them to germinate later(Borenstein, 1994). All natural waters contain bacteria and often MIC is observed in stagnant process waters.   

Bacteria can work to instigate MIC in a number of ways:

1. They can destroy protective films on the metals. ii. They can produce localized acid environments. iii. They can form corrosive environments. iv. They can alter anodic/ cathodic reactions.
2. b)              Physiochemical Classification

Physiochemically, corrosion is divided into the following seven categories as follows:- uniform corrosion, pitting corrosion, corrosion by erosion, stress corrosion cracking, galvanic or bimetallic corrosion, corrosion via hydrogen embrittlement and blistering and

corrosion by cavitation                                                                                                            Uniform corrosion: This is the most common type characterized by the corrosion occurring uniformly over the metal surface and it has a high corrosion rate. The loss of the metal surface occurs at the anodic sites while the appearance of the corroded surface is

relatively uniform and manifests roughness (Levy, 2002).

Piting corrosion: This is a form of localized attack where some part of the metal surfaces are free of corrosion but small localized area corrode quickly. This occurs when any solid corrosion product or neutralization salt are located on the metal surface causing deep holes known as ―piting‖, these areas are the most susceptible to the corrosion process(Marcus et al., 2008).

Corrosion by erosion: This type of corrosion provokes uniform thinning of the metal surface which is associated with the exposure to high velocity fluid which causes the erosion product to be stripped from the metal surface resulting in the exposure of the bare metal surface which can corrode again causing an accelerated attack (Levy, 2002). Stress corrosion cracking:  This type of corrosion promotes the formation of a fracture in the metal structures due to mechanical stress and a chemically aggressive medium, (Sieradzki & Newman, 1987).  

Galvanic or Bimetallic corrosion: This occurs when there is a potential difference between dissimilar metal immersed in a corrosive solution, the potential difference produces flow of electrons between the metals where the less resistance is the anode ( metal active) and  the most resistance is the cathode (noble metal). The attack can be destructive dramatically accelerating the corrosion rate of the most reactive metal (Song et al., 2004). Corrosion via hydrogen Embrittlement and Blistering: This is associated with the hydrogen atoms that can be produced on the metal surface in an aqueous medium, a reduction reaction occur when atomic hydrogen penetrates the metal. The presence of defects allow the interaction between the hydrogen atoms  and the metal  forming molecular hydrogen which can be trapped by the metal producing enough pressure to form blisters resulting to micro-cracks. This occurs mainly in basic media where there are compounds such as sulphides or cyanide, (Hotlets et al., 2007).  

Corrosion by Cavitation: This is a form of corrosion caused by the formation and rupture of vapour bubbles in the fluid near the metal surface causing sequence of pits in the form of small but deep cracks (Ali & Folaud, 2012).

 

1.1.4  CORROSION MEASUREMENT AND MONITORING.

Corrosion monitoring is a series of quantitative method by which the effectiveness of corrosion control and prevention technique can be evaluated. The overall aim of monitoring corrosion is because it provides a feedback which enables corrosion control and prevention methods to be optimized. A variety of technique can be employed and they are:

1. Non destructive testing:

This includes use of ultrasound testing, radiography, thermography, eddy current / magnetic flux and intelligent pigs in measuring the effectiveness of a corrosion control and prevention technique (Devalapura et al., 1994). It also involves pH measurement, dissolved gas (O₂,CO₂ H₂S) evaluation, metal count (Fe^2+.Fe³⁺) determination, microbiological analysis in measuring the effectiveness of  a corrosion control and prevention technique.

1. Operational Data :

This includes pH, flow rate (velocity), pressure and temperature in measuring the effectiveness of a corrosion control and prevention technique.

 

1. iv) Fluid Electrochemistry

In fluid electrochemistry, potential measurement, potentiostatic and potentiodynamic measurements and A.C impendance are used in measuring the effectiveness of a corrosion control and prevention technique.

1.1.5. INHIBITORS

Inhibitors are often considered to be the first line of defense against corrosion.  NACE International states that an inhibitor is a substance which retards corrosion when added to an environment in small concentrations (Jones, 1988). Another generalization is that all inhibitors directly or indirectly coat or film the metal surface (Jones, 1988).  In a broader view many different substances can be called inhibitors:Organic film formers (eg:

Imidazolines/ amides, nitrogen heterocycles, fatty acid salts)  such as:

Scavengers (sulphites for oxygen or aldehydes for hydrogen sulfide)

1. Neutralizers ( simple amines) ii. Inorganic film formers ( phosphates or zinc/ calcium salts) iii.         Passivators ( chromates or nitrites) iv.     Bactericides (ex:  aldehydes or quats)

An inhibitor can be said to function by either adsorbing onto the surface of a metal, thereby producing a thick corrosion product, or by changing the corrosive environment (Nathan &

Bregman, 1973).  Generally, inhibitors function by doing the following:

1. Forming protective filming or scales ii. Slowing the corrosion rate by increasing/ decreasing the anodic/ cathodic reactions

 

iii.       Decreasing the diffusion rate of ions to the metal surface iv. Increasing the electrical resistance of the metal surface.

 

1.1.6        DRILLING FLUIDS

Drilling fluid is a circulating fluid used in drilling to perform any or all of the various functions required in drilling operations. It is the single most essential system in safe, efficient, and economic well drilling. The drilling fluid consists of a mixture of natural and synthetic compounds used for a variety of purposes, Fink (2011).

The challenges met during drilling operations in the petroleum industry have led to the formulation of different types of drilling fluids. Drilling muds are classified based on the continuous phase of the mud and they include;

1. Water Base Muds (WBM) – Also referred to as aqueous drilling fluid. It is basically 90–95 % of fresh water, salt or sea water and several dissolved substances meaning that water is the continuous phase here(Skalle, 2010; Devereux, 1999) . It is predominantly used in the industry due to its environmentally acceptable nature, and also because it is relatively cheap to operate with.
2. Oil Base Muds (OBM) – These muds have oil as their continuous phase, usually diesel oil, mineral oil or low toxicity mineral oil, and although they may pick up formation water, no additional water or brine is added. This is due to the fact that they contain wateremulsifying agents. This system which contains less than 5 % water has a number of advantages compared to WBM (Devereux, 1999).

 

 

1.2     Problem Statement

The corrosion of metal at the solid –liquid interphase is a major problem encountered in our society today.

Corrosion of metals in a corroding environment is practically unavoidable because metals are thermodynamically unstable in the environment.

1. Corrosion has over time proven a source of loss in drilling.
2. The use of corrosion inhibitors in mitigating the effect of corrosion in drilling remains expensive and yet environmentally unfriendly.

1.3        Objectives of Study

The main objective of this study is to use biomass inhibitor of plant origin as suitable substitutes to synthetic corrosion inhibitors used as additives to drilling fluid during oil drilling.

The specific objectives set out to achieve the aforementioned are as follows:

1. To ascertain the inhibition efficacy of a synthetic corrosion inhibitor commonly used as an additive to drilling fluid in a simulated drilling fluid.
2. To ascertain the inhibition efficacy of the ethanol extracts of chrysophyllum albidum leaves in a simulated drilling fluid.

• To investigate the effect of temperature on the corrosion rate and inhibition efficiencies of chrysophyllum albidum and synthetic corrosion inhibitor.

1. To determine some thermodynamic parameters from temperature studies involving the two inhibitors
2. To determine the possible mechanism of the inhibition process of the above stated inhibitors.

 

• Justification of Study

Plants extracts are organic inhibitors containing phytochemicals such as tannin, alkaloids, saponins and terpenoids with molecular & electronic structures similar to those of conventional corrosion inhibitors. The use of plant extracts as corrosion inhibitors pose immense benefits. Apart from minimizing cost, it has been proven to be more eco-friendly and generally less harmful to use. Furthermore these Organic inhibitors from natural products like other conventional inhibitors act by adsorbing on the metal surface to form an insoluble organic complex compound with the corroding specie hence reducing and

preventing its attack on the metal surface.

 

• Scope of Study

The scope of this study covers the assessment and comparison a synthetic corrosion inhibitor and an organic inhibitor of plant origin in the corrosion inhibition of mild steel in a simulated drilling fluid medium.  Weight loss and potentiodynamic polarization techniques are applied in this study to monitor inhibiting effectiveness of the selected corrosion inhibitors. Electrochemical method (potentiodynamic polarization technique) was also carried out to determine some corrosion kinetic parameters such as corrosion current density, I_corr, corrosion electrode potential, E_corr and to determine the type of inhibitor from the polarization curves. Temperature studies was also carried out to determine some thermodynamic parameters such as activation energy, Gibb’s free energy and change in enthalpy, hence, suggest the possible mechanism of  the adsorption process

 

ANTICORROSION PERFORMANCE OF CHRYSOPHYLLUM ALBIDUM AND A SYNTHETIC INHIBITOR IN SIMULATED DRILLING FLUID

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