**2.2 Economic**

*Corrosion Inhibitors*

generated by the corrosion reaction [6].

corrosion is of paramount importance.

three main categories as shown in **Figure 1** [8].

**2. Impact of corrosion**

**2.1 Material and energy**

aspect of electrochemistry. Electrons will be flowing from certain areas of a metal surface to other areas through an electrolyte that is capable of conducting ions. This stems from the incredible tendency of metals to react electrochemically with water, oxygen, and other substances in the aqueous environment. In an electrochemical corrosion process, the anode is that area of the metal surface that is corroding due to the loss of electrons while the cathode is the area that consumes the electrons

Almost all of us are familiar with corrosion happening to metal structures, boats, steel pilings, household utensils, etc. Unfortunately, many of us are not aware of corrosion that is deteriorating the properties of underground water, oil, and gas pipelines crisscrossing our land or water pipes in the home where corrosion occurs mostly from the inside. Successful enterprises put in considerable efforts in controlling corrosion at the design stage and in the operational phase to avoid major corrosion failures, such as unscheduled shutdowns, fatalities, personal injuries, and environmental contamination in a modern business environment. However, even the best design is unable to foresee all conditions that can allow corrosion intruding into the life of a system [5]. Steel reinforced bar (rebar) can corrode in concrete without being noticed at all and can cause damage to buildings, bridges, parking structures, the collapse of electrical towers, failure of a section of highway, etc., resulting in a huge amount of repairing cost and threatening public safety [7]. This is why regular maintenance of the metallic components that are susceptible to

Even though the main reasons for considering corrosion are economic and ecological, losses due to corrosion or costs of corrosion can be actually divided into

The impact of corrosion on the equipment and its surrounding deserves a huge attention when it comes to designing an industry. Corrosion is considered to be one of the most challenging issues for most of the industrialized countries. Corrosion of tanks, piping, metal components of machines, bridges, ships, etc. can incur a massive material and economic losses upon a nation. Additionally, the safety of operating equipment, such as boilers, pressure vessels, metallic containers for toxic chemicals, bridges, turbine blades and rotors, automotive steering mechanisms, and airplane components can be threatened by corrosion failure [8]. Furthermore, the

**78**

**Figure 1.**

*Breakdown of corrosion costs.*

Economic losses are classified into two types: (i) direct losses and (ii) indirect losses. Replacing the corroded structures and machinery of their components, for instance, mufflers, condenser tubes, pipelines, metal roofing, including necessary labor, repainting structures to prevent rusting, maintenance cost of cathodic protection system for underground pipelines, replacement cost of millions of domestic hot-water tanks and automobile mufflers, extra cost of using corrosion-resistant metals and alloys, galvanizing or nickel plating of steel, addition of corrosion inhibitors to water, and dehumidifying cost of the metal equipment storage rooms contribute to the direct losses. While it is quite difficult to assess the indirect losses, they have still been reported to add several billion dollars to the direct losses. Indirect losses include sudden shutdown of plants, loss of water, gas, or oil through a corroded pipeline, loss of efficiency in the energy conversion systems imposed by corrosion processes, contamination of water and food products in metal piping and containers, and overdesign requiring equipment to be designed many times heavier than normal operating pressure or applied stress to extend their lifetime [8]. Uhlig made the first ever systematic study on the cost of corrosion in 1949 [11]. Uhlig's report estimated the annual cost of corrosion in the United States to be US\$ 5.5 billion or 2.1% of the 1949 gross national product (GNP). This study measured the total costs by summing the costs related to anti-corrosion materials and corrosioninduced maintenance and replacement handled by owners and operators (direct) as well as those related to users (indirect) [5, 12].

Corrosion cost studies using different methods, such as Uhlig method invented by Uhlig in 1949 [11], Hoar method invented by Hoar in 1971 [13], and economic input/output model devised by National Bureau of Standards (NBS) collaborating with Battelle Memorial Institute in 1978 [14] have been undertaken by several major economies, including Australia, China, Finland, Germany, India, Japan, Kuwait, the United Kingdom, and the United States [15]. A common observation of these studies was that the costs of corrosion ranged from approximately 1–5% of the GNP of each nation. The variation in the corrosion cost with respect to GNP was ascribed to the methodology used by each study and the specifics of each country [12].

A study done by National Association of Corrosion Engineers (NACE) as part of its International Measures of Prevention, Application, and Economics of Corrosion Technologies Study (IMPACT) revealed that the global cost of corrosion in 2013 was estimated to be US\$ 2.5 trillion which was equivalent to 3.4% of the global GDP in that year [15]. This study utilized the World Bank economic sector and GDP data to relate the cost of corrosion studies to a global cost of corrosion. In order to address the economic sectors across the world, the global economy was divided into economic regions with similar economies (according to World Bank). These were: United States, European Region, India, Arab World (defined by the World Bank), Russia, China, Japan, Four Asian Tigers plus Macau, and Rest of the World. However, the costs estimated typically do not include environmental consequences or individual safety. It is noteworthy that receiving additional funds for corrosion studies, or updated information on these studies, more detailed and accurate global costs can be assessed.

#### **2.3 Human life and safety**

Corrosion can take a toll more than imaginable in human life and safety. This destructive phenomenon has been overlooked as the main reason of many fatal accidents for reasons of liability or simply because the evidence disappeared in the catastrophic event. The Silver Bridge collapse is one of the most dangerous and discussed corrosion accidents [16]. On December 15, 1967, this bridge connecting Point Pleasant, West Virginia and Kanauga, Ohio suddenly collapsed into the Ohio River to claim 46 lives. Stress corrosion cracking (SCC) and corrosion fatigue were determined to be responsible for this disaster. The Bhopal accident that took place in Bhopal, India on the night of the December 2–3, 1984 is one of the worst industrial accidents in terms of the lives lost and injuries. An unfortunate seepage of water (500 liters) caused by the corrosion of pipelines, valves, and other safety equipment into a methylisocyanate (MIC) storage tank at Union Carbide India Limited caused the release of MIC and other toxic reaction products into the surrounding areas that killed 3000 people and injured an estimated 500,000 people [17]. Swimming Pool Roof Collapse is another infamous corrosion accident that took place in Uster, Switzerland in 1985. The roof of this swimming pool was supported by stainless steel rods that failed due to SCC and killed 12 people [18].

### **3. Techniques for corrosion measurement**

#### **3.1 Weight loss measurement**

Weight loss analysis is known to the simplest, most reliable, and longestablished method of assessing corrosion losses in plant and equipment. A sample of metal or alloy under experiment is weighed and then immersed into a corrosive solution, and later removed from the corrosive medium after a predetermined time interval. The metal specimen is then weighed again after cleaning all corrosion products. The corrosion rate, surface coverage (*θ*), and corrosion inhibition efficiency (*η*%) can be calculated using (Eqs. (1)–(3)):

$$\text{Corrosion rate} \left(\frac{mm}{year}\right) = \text{ } \textbf{8.76} \times \textbf{10}^3 \frac{m\_i - m\_f}{S\rho t} \tag{1}$$

$$\Theta\_{\circ} = \begin{array}{c c} \text{CR}\_{\circ} - \text{CR} \\ \text{CR}\_{\circ} \end{array} \tag{2}$$

**81**

*Green Corrosion Inhibitors*

*3.2.1 Tafel extrapolation*

(*η*%) based on (Eq. (5)):

Corrosion rate = *<sup>i</sup>*

equivalent weight in gram/equivalent, ρ is density in g/cm3

can be experimentally obtained from real polarization plots.

*3.2.3 Electrochemical impedance spectroscopy (EIS)*

%= *icorr*

without and with the inhibitor, respectively.

*3.2.2 Linear polarization resistance (LPR)*

*DOI: http://dx.doi.org/10.5772/intechopen.81376*

rate of corrosion and mechanism of corrosion protection [20]. Polarization methods are based on changing the current or potential on a sample under investigation and recording the corresponding potential or current change. This can be facilitated with the help of either a direct current (DC) or an alternating current (AC) source [5]. Some important and widely used techniques have been discussed briefly below.

Tafel curve is a current-potential plot that shows the anodic and cathodic reactions in the electrochemical cell. In this method, the potential of the working electrode (metal sample) varied over a range at a specific rate and the resulting response in current is recorded. The anodic and cathodic reactions that are taking place simultaneously produce a total current that is represented by a curved line. The linear portions of logarithmic Tafel plot are extrapolated to produce an intersection that generates a point that signifies an approximation of the corrosion current (*icorr*) and the corrosion potential (*Ecorr*). This *icorr* facilitates the calculation of the corrosion rate based on (Eq. (4)) and the corrosion inhibition efficiency

> *<sup>o</sup>* <sup>−</sup> *<sup>i</sup>* \_\_\_\_\_\_\_*corr icorr*

exposed to corrosive solution, *i°corr* and *icorr* are the corrosion currents in amperes

Because the linear polarization resistance (LPR) method is non-destructive [21], it has quick application and can be used in the field test through portable instrumentation [22], it is the most popular of the electrochemical techniques [23]. The principal of LPR is based upon introducing a small perturbative DC electrical signal to disturb the corrosion equilibrium on the surface of metal specimen. The response of the equilibrium to this perturbation is measured with respect to a reference half-cell [24]. The polarization resistance (*Rp*) of a material is known to be the Δ*E*/Δ*i* slope of a potential-current density curve at the free-corroding potential. The polarization resistance can be related to the corrosion current (*icorr*) using the Stern-Geary approximation in which the anodic (*ba*) and cathodic (*bc*) Tafel slopes

Electrochemical impedance spectroscopy (EIS) is a very powerful electrochemi-

cal technique that has wide applications in the evaluation of coatings in corrosion research. This technique provides valuable information about the corrosion protection imparted by an inhibitor. In this technique, an AC voltage (in the case of potentiostatic EIS) or current (in the case of galvanostatic EIS) is applied to the system under investigation to receive response in the form of AC current (voltage) or voltage (current) as a function of the frequency. This technique can be

where *K* is a constant that represents the units for the corrosion rate, *EW* is the

\_\_\_\_\_\_\_\_\_\_\_ *corr* × *K* × *EW*

<sup>ρ</sup> <sup>×</sup> *<sup>A</sup>* (4)

, *A* is the area in cm<sup>2</sup>

*<sup>o</sup>* × 100% (5)

$$
\eta \text{ } \% = \frac{\text{CR}\_o - \text{CR}}{\text{CR}\_o} \times \text{100} \text{\%} \tag{3}
$$

where *mi* is the weight of the metal sample in grams before immersion, *mf* is the weight of the metal sample in grams after immersion, *S* is the total area of metal in cm2 that has been exposed to corrosive solution, *ρ* is the density of metal sample in g/cm2 , *t* is the time in hours during which the sample was immersed, *CR*○ and *CR* represent the corrosion rates (in mmpy) without and with the inhibitor, respectively [19, 20].

#### **3.2 Polarization measurements**

Since corrosion is a phenomenon that involves electrochemistry, electrochemical-based corrosion measuring experiments provide valuable information about the

#### *Green Corrosion Inhibitors DOI: http://dx.doi.org/10.5772/intechopen.81376*

rate of corrosion and mechanism of corrosion protection [20]. Polarization methods are based on changing the current or potential on a sample under investigation and recording the corresponding potential or current change. This can be facilitated with the help of either a direct current (DC) or an alternating current (AC) source [5]. Some important and widely used techniques have been discussed briefly below.

### *3.2.1 Tafel extrapolation*

*Corrosion Inhibitors*

**2.3 Human life and safety**

Corrosion can take a toll more than imaginable in human life and safety. This destructive phenomenon has been overlooked as the main reason of many fatal accidents for reasons of liability or simply because the evidence disappeared in the catastrophic event. The Silver Bridge collapse is one of the most dangerous and discussed corrosion accidents [16]. On December 15, 1967, this bridge connecting Point Pleasant, West Virginia and Kanauga, Ohio suddenly collapsed into the Ohio River to claim 46 lives. Stress corrosion cracking (SCC) and corrosion fatigue were determined to be responsible for this disaster. The Bhopal accident that took place in Bhopal, India on the night of the December 2–3, 1984 is one of the worst industrial accidents in terms of the lives lost and injuries. An unfortunate seepage of water (500 liters) caused by the corrosion of pipelines, valves, and other safety equipment into a methylisocyanate (MIC) storage tank at Union Carbide India Limited caused the release of MIC and other toxic reaction products into the surrounding areas that killed 3000 people and injured an estimated 500,000 people [17]. Swimming Pool Roof Collapse is another infamous corrosion accident that took place in Uster, Switzerland in 1985. The roof of this swimming pool was supported by stainless

steel rods that failed due to SCC and killed 12 people [18].

Weight loss analysis is known to the simplest, most reliable, and longestablished method of assessing corrosion losses in plant and equipment. A sample of metal or alloy under experiment is weighed and then immersed into a corrosive solution, and later removed from the corrosive medium after a predetermined time interval. The metal specimen is then weighed again after cleaning all corrosion products. The corrosion rate, surface coverage (*θ*), and corrosion inhibition effi-

\_\_\_\_ *mm*

*CRo* − *CR CRo*

where *mi* is the weight of the metal sample in grams before immersion, *mf* is the weight of the metal sample in grams after immersion, *S* is the total area of metal in cm2 that has been exposed to corrosive solution, *ρ* is the density of metal sample in g/cm2

is the time in hours during which the sample was immersed, *CR*○ and *CR* represent the corrosion rates (in mmpy) without and with the inhibitor, respectively [19, 20].

Since corrosion is a phenomenon that involves electrochemistry, electrochemical-based corrosion measuring experiments provide valuable information about the

*year*) <sup>=</sup> 8.76 <sup>×</sup> <sup>10</sup><sup>3</sup> *mi* <sup>−</sup> *mf* \_\_\_\_\_\_

*CRo* − *CR CRo*

*<sup>S</sup><sup>t</sup>* (1)

× 100% (3)

(2)

, *t*

**3. Techniques for corrosion measurement**

ciency (*η*%) can be calculated using (Eqs. (1)–(3)):

θ = \_\_\_\_\_\_\_

η%= \_\_\_\_\_\_\_

**3.2 Polarization measurements**

Corrosion rate (

**3.1 Weight loss measurement**

**80**

Tafel curve is a current-potential plot that shows the anodic and cathodic reactions in the electrochemical cell. In this method, the potential of the working electrode (metal sample) varied over a range at a specific rate and the resulting response in current is recorded. The anodic and cathodic reactions that are taking place simultaneously produce a total current that is represented by a curved line. The linear portions of logarithmic Tafel plot are extrapolated to produce an intersection that generates a point that signifies an approximation of the corrosion current (*icorr*) and the corrosion potential (*Ecorr*). This *icorr* facilitates the calculation of the corrosion rate based on (Eq. (4)) and the corrosion inhibition efficiency (*η*%) based on (Eq. (5)):

$$\text{Corrosion rate} = \frac{i\_{\alpha rr} \times K \times EW}{\rho \times A} \tag{4}$$

$$
\eta \,\eta \,\%= \frac{i\_{corr}^o - i\_{corr}}{i\_{corr}^o} \times \mathbf{100}\,\% \,\tag{5}
$$

where *K* is a constant that represents the units for the corrosion rate, *EW* is the equivalent weight in gram/equivalent, ρ is density in g/cm3 , *A* is the area in cm<sup>2</sup> exposed to corrosive solution, *i°corr* and *icorr* are the corrosion currents in amperes without and with the inhibitor, respectively.

### *3.2.2 Linear polarization resistance (LPR)*

Because the linear polarization resistance (LPR) method is non-destructive [21], it has quick application and can be used in the field test through portable instrumentation [22], it is the most popular of the electrochemical techniques [23]. The principal of LPR is based upon introducing a small perturbative DC electrical signal to disturb the corrosion equilibrium on the surface of metal specimen. The response of the equilibrium to this perturbation is measured with respect to a reference half-cell [24]. The polarization resistance (*Rp*) of a material is known to be the Δ*E*/Δ*i* slope of a potential-current density curve at the free-corroding potential. The polarization resistance can be related to the corrosion current (*icorr*) using the Stern-Geary approximation in which the anodic (*ba*) and cathodic (*bc*) Tafel slopes can be experimentally obtained from real polarization plots.

#### *3.2.3 Electrochemical impedance spectroscopy (EIS)*

Electrochemical impedance spectroscopy (EIS) is a very powerful electrochemical technique that has wide applications in the evaluation of coatings in corrosion research. This technique provides valuable information about the corrosion protection imparted by an inhibitor. In this technique, an AC voltage (in the case of potentiostatic EIS) or current (in the case of galvanostatic EIS) is applied to the system under investigation to receive response in the form of AC current (voltage) or voltage (current) as a function of the frequency. This technique can be

performed in a 2- or 3-electrodes system with the help of a potentiostat-galvanostat and a frequency response analyzer (FRA) [25]. Usually, an AC voltage having small perturbations ranging from 5 to 10 mV is applied in the system over a range of frequencies typically starting from 100 kHz to 10 mHz. Based on the shape of the Nyquist plot produced by the experiment, the electrochemical cell containing the metal sample, adsorbed inhibitors, and the electrolyte medium is represented by an equivalent circuit that includes information about the solution resistance *Rs*, charge transfer resistance *Rct*, and the double layer capacitance *Cdl*. A large *Rct* value and decreasing *Cdl* values with increasing inhibitor concentrations indicate better corrosion protection [26].
