EFFECT OF (STYRENE-VINYL ACETATE) COPOLYMERS AS HIGHLY WATER-REPELLENT FILM ON CORROSION PROTECTION OF CARBON STEEL PETROLEUM PIPELINES.

1. 1.     CONCLUSION.

Summarising the data presented above, we can conclude that,new hydrophobic coating of styrene vinyl acetate copolymer was synthesized by Emulsion Phase Inversion Concentration Polymerization as corrosion inhibitors. The research results revealed that: -

• The inhibition efficiency (IE %) increases with the increasing of the inhibitor concentration.
• Increasing the temperature from 298 °k to 333 °k leads to activate the coupons surface; thereby, the corrosion rate increases.
• Higher activation energy (Ea) indicates to higher resistance of the coated metal to corrosion.
• As the water contact angles of the coated coupons increases from 48.16 ^oto 98.64 ^o, the inhibition efficiency of the coated film by E3-copolymer increased from 82.45 % to 99.21%.
• The maximum inhibition efficiency of 99.21% was obtained by E3-copolymers using 300 ppm and at 298 °k.

EFFECT OF (STYRENE-VINYL ACETATE) COPOLYMERS AS HIGHLY WATER-REPELLENT FILM ON CORROSION PROTECTION OF CARBON STEEL PETROLEUM PIPELINES

^aAbd El-Azeim, A.; A.I.Hashem^b ;

M.R.Noor El-Din^c andR.E.Morsi^c

aKhalda Petroleum Company, Cairo, Egypt.

b Faculty of Science, AinShams University, Abassia, Cairo, Egypt.

c Egyptian Petroleum Research Institute(EPRI), 1AhmedEl-ZomorSt., NasrCity11727, Cairo, Egypt.

Key Words:hydrophobic, emulsion polymerization, copolymer, corrosion, inhibitor.

ABSTRACT

Corrosion is first and foremost a safety risk which has to be understood and managed.

In this study a highly water-repellent hydrophobic coating was synthetized to protect carbon steel petroleum pipelines from corrosion. To achieve this target, (styrene-vinyl acetate) denoted as P(St-VAc) (E1, E2 and E3) copolymers of different molecular weights and different monomer molar ratios were synthesized. The chemical structures of the prepared copolymers were elucidated by FT-IR, and ¹H-NMR spectroscopy. The molecular weights of the prepared copolymers were determined using GPC. The wettability of the prepared coating films and the value of Ra (arithmetic mean roughness)were measured via contact angle and confirmed by AFM techniques. Different factors affecting the efficiency of prepared materials in corrosion inhibition e.g. i) Concentration of the coating solution ii) Temperature iii) Activation energy iv) Contact angle; were studied.

1. 1.     INTRODUCTION

Crude oil and natural gas can carry various high-impurity products, which are inherently corrosive. The presence of corrosive media as carbon dioxide (CO₂), hydrogen sulfide (H₂S) and high salinity water (formation water) during the production and transportation of crude oil through the mild steel pipelines causes a corrosion problem in the transfer crude oil pipelines. Corrosion is a spontaneous process in nature and there is no one can stop it from happening. Most research is an attempt to reduce the rate of corrosion to the lowest possible rate (Noor El-Din et al., 2018).Therefore, the mitigation of corrosion requires effective materials to keep corrosion rates in control.To prevent the metal corrosion as possible, four methods known as corrosion prevention were used: metal selection and surface conditions, cathodic protection, corrosion inhibitors and coating (protective coating method).Coating method objective is to protect the metal surface by forming a water repellent coating film, that isolates the metallic surfaces from the aggressive corroded media as moisture, salts, acids etc. four types of coating agents were used to increase the corrosion protection of metal surface: solvent-based anticorrosion agents (drying method), water-based anticorrosion agents, corrosion-protective oils without solvent and dipping waxes. The concept of preparing surfaces that repel water creates huge opportunities in the area of corrosion inhibition for metals and alloys. Given their water repellency, superhydrophobic coatings form an important and successful method to slow down the breaking of the oxide layer of metals and thus prevent the metal surface underneath from further corrosion. Several works have been carried out in order to study the corrosion resistance of metals coated with superhydrophobic surfaces (Mavis, 2019).Wettability is controlled by: surface roughness, water droplet size and contact angle. A superhydrophobic surface is usually defined as one that repels water to such an extent that the water contact angles exceed 150° (Wang and Jiang, 2007) but it has also been less commonly adopted as 140° (Toes et al., 2002). Superhydrophobic surfaces were formed by successful combination of low surface energy and high surface roughness.Requirements of such polymeric coatings are much more stringent. They must adhere well to the substrate and must not chip easily or degrade from heat, moisture, salt, or chemicals. The most favorite method to prepare high molecular weight polymers and\or copolymers with water repellent character (hydrophobic character) is emulsion polymerization methods. The oil in water emulsion polymerization was classified to three types: macro-emulsion, micro-emulsion and mini-emulsion.

In this study, a copolymer based on styrene vinyl acetate at different proportions were synthesized for the preparation of hydrophobic coating film. The efficiency of the prepared material on the hydrophobicity of the coating film were studied as corrosion resistant materials.  (styrene-vinylacetate)denoted as P(St-VAc) copolymers of different molecular weights and different monomer molar ratios (50:50, 25:75 and 75:25 wt.,% donated E1, E2 and E3, respectively) as organic hydrophobic coated materials partwere synthesized. Different techniques e.g. FT-IR, ¹H-NMR spectroscopy and GPC, were used for characterization of the prepared copolymers. The corrosion inhibition efficiency of the coated carbon steel sheets was carried out by weight loss technique (Rotating Cage Test) (ASTM G170).The wettability of the prepared coating films and the value of Ra (arithmetic mean roughness), were measured via contact angle and confirmed by AFM techniques.

1. 2.     EXPERIMENTAL PROCEDURE

2.1.   Materials

The physicochemical characteristics of monomers, emulsifiers, solvents and their sources are illustrated in Table 1. The water used in all experiments was double distilled, deionized (DI-water) and filtered prior use. Produced water sample (formation water) provided by Qarun petroleum company-Western desert, Egypt is illustrated in Table 2.

Table 1: Physico-chemical characteristics of raw materials and their sources

* Hydrophile - lipophile Balance

Table 2: Qarun analysis water

2.2.  Preparation of poly (styrene-vinyl acetate) co-polymer P (St-VAc)

Oil-in-water nano-emulsion polymerization was performed using a new technique namely Emulsion Phase Inversion Concentration (EPIC) (Noor El-Din et al., 2017). (RHLB) value required to form a stable emulsion of PSt and P (St-VAc) copolymer laid in the range from 14.5 to 17.5. For optimum emulsification conditions, the blending ratio of emulsifiers: Brij 30 (Polyoxyethylene-4-lauryl ether) (E), Poloxamer 188 (2-(2-propoxypropoxy) ethanol) (P), and AOT (dioctyl sodium sulfosuccinate) (A) were adjusted and mixed at constant rotation of 600 rpm and 25^oC to form the mixed emulsifiers base (EB) to satisfy the appropriate RHLBvalue (Noor El-Din et. al., 2017).

The preparation of P(St-VAc) copolymer was performed in two steps as follows: -

2.2.1.      Preparation of stable emulsion of (St-VAc) monomers as oil base in water

 Into 1-liter three-necked round bottomed flask equipped with a condenser and magnetic stirrer was immersed in a thermostated bath held at 40°C, oil soluble phase of (St (20 ml, 0.17 mole) and VAc (39.9 ml, 0.43 mole)), triethylamine (8 g). EB mixed surfactants (0.5 wt. %, 3.647 g based on total weight of the reactants) were separately added to 300 ml of DI-water at 25^oC. The ingredient mixture was purged with N₂ gas for 30 minutes the ingredients mixture was stirred using magnetic stirrer at rotating speed of 700 rpm and temperature of 25±2^oC.

2.2.2.      Polymerization of (St-VAc) as oil base in water

After 1 hour from the obtained stable emulsion, ammonium persulfate (0.065 g) and sodium bisulfite (0.040 g) were simultaneously added to the pervious ingredients under the same conditions. Afterwards, the temperature of the reaction was raised to 65 ± 5^oC and it was kept for another hour (Xiaoyu et. al., 2000). The polymerization reaction was stopped, cooled, and the product was precipitated according to a procedure based on solubility trials in various solvents.

2.3.   Characterizations of poly (styrene-vinyl acetate) co-polymer P (St-VAc)

The chemical structure of P(St-VAc) copolymer (E1) was elucidated using a Nicolet FT-IR spectroscopy [Thermo Fisher Scientific (USA)].For further confirmation, the chemical was confirmed by Proton Nuclear Magnetic Resonance (¹H-NMR) spectra using a 300 MHz Varian NMR 300 spectrometer,average molecular masses and molecular mass distribution of E1, E2 and E3-copolymers were determined using Gel permeation chromatography (GPC),The morphology of polymer was acquired through scanning electron microscope (SEM), contact angles (CA) of the glasses surface coated by E3-copolymerwas determined using TheatOptical Tensiometer, the surface free energy of the prepared coating films was calculated utilizing the results of the contact angle measurements and Atomic Force Microscopy (AFM) was used to evaluate the surface topography, root mean square (RMS), surface roughness value, and roughness maps of the coated films (topographic height images). Furthermore, the variations of surface topography at different concentrations of E3-copolymer, was highlighted.

2.4.  

Fabrication of hydrophobic coating film on carbon steel sheets

Carbon steel samples (coupons) consisting of: 0.07 % C, 0.24 % Si, 1.35 % Mn, 0.017 % P, 0.045% Sn, and the remainder Fe (wt %) was used as the coated substrates. Each specimen of the used coupon was mechanically pretreated before testing by grinding using emery paper of grades 400, 600, 800 and 1,000. The carbon steel coupons were sequentially washed by acetone and distilled water. Finally, the coupons were dried using dissector. Different concentrations as 100, 200, and 300 ppm of aqueous suspended solution of E3-copolymer was utilized for corrosion inhibition measurements.

A stable hydrophobic films of E3-copolymer with thickness film sheet of 6 mm was fabricated using dip-coating method reported by Fleming et al. (Fleming and Zo, 2013). The treated carbon steel sheets having dimensions of 7.0 × 2.0 × 0.3 cm were used as substrate material for dip-coating. The fabrication of hydrophobic film was separately performed by immersing the treated sheets in the aqueous solution E3-copolymer using dip-coater to create a hydrophobic layer on the treated carbon steel sheets. Afterwards, the coated sheets were putted in DRIE-chamber (deep reactive ion etching) to form low surface energy film over the coated surface. The sheets were left inside the solution for 30 minutes. At this stage, a thin layer of E3-copolymerwas deposited on the sheet surface. The coated sheet was pulled from benzene solution in constant speed rate to avoid the coated layer from loss. Excess liquid was drained from the surface. The coated sheet was dried by exposing them to hot air.

2.4.1.      Assessment of the coated film performance(Rotating Cage (RC) Test)

The corrosion inhibition efficiency of the coated carbon steel sheets in terms of corrosion rate (mpy) was carried out by weight loss technique (Rotating Cage Test) (ASTM G170).under the same field operating condition. Field parameters for certain well (SQ- 11) as water analysis, well temperature and pressure were adjusted for simulation test via Rotating Cage Test. A known weight of four coupons (one blank (uncoated coupon) and three coated coupons) supported by polytetrafluroethylene (PTFE) disks were mounted at 55 mm apart on the rotatory rod. Holes were drilled in the top and bottom PTFE plates of the cage in order to increase the turbulence on the inside surface of the coupon. According to the crude oil gross production and field parameters of well (SQ-11), the corrosive media composed of hydrocarbons base and formation waterat a ratio of 25:75, respectively was transferred to the rotating cage. The test was performed at rotating speed of 200 rpm, 30^oC and 1 bar atmosphere. After 24 hours, the tested coupons were removed from the media, washed carefully with bi-distal water for three times. Sequentially they were rinsed with acetone, and then left to dry in desiccator. After complete drying, the coupons were weighted three times. The inhibition efficiency (IE, %) of the coated coupons was calculated as follows:

Whereas; W_o is initial weight of the coated cop coupons (mg) [prior to hanging]. W_i is the final weight of the coated coupons (mg) [after hanging in corrosive media].

1. 3.     RESULTS AND DISCUSSION

3.1.   FT-IR spectroscopic analysis of PSt and E1- copolymers

The chemical structures of the purified E1-copolymer was elucidated by FT-IR spectroscopy as demonstrated by Fig.1 a strong absorption band at υ=2922 cm^-1 is due to aliphatic C-H stretching vibration absorption bands. The absorption peak at υ=3025.76 cm^-1 corresponds to C-H of aromatic stretching vibration bands that belong to benzene ring. In-plane stretching vibration bands at υ=1600-1607.14, 1490.86 and 1473.69 cm^-1 corresponding to C=C of the benzene ring and out-of-plan vibration band at υ=755.08 cm^-1 represent the C-C stretching, and bending vibrations in the aromatic ring, respectively. These bands reflect the presence of styrene moiety in PSt polymer.Absorption peaks at υ of 1738 cm^-1 and 1237 cm^-1 appeared. These peaks are assigned to (C=O) and (C-O) groups of the vinyl acetate, respectively.On the other hand, the observation of absorption peak at υ of 3100-3390 (broad band) cm^-1 indicates the presence of (OH) group. The presence of hydroxyl group may be ascribed to the presence of trace amounts of moisture that resulted from the purification step.

Fig.1: FT-IR spectrum of E1-copolymer.

3.2.  

¹H-NMR spectroscopy analysis of E1-copolymer

¹H-NMR spectroscopy is considered as a confirmed technique to elucidate the chemical structure of PSt and E1-copolymer. Fig. 2 depict the ¹H-NMR spectra of E1-copolymer. The chemical shift (δ-) at 7.14 – 7.30 ppm indicates to the presence of aromatic ring (m, -C6H5). Also, the chemical shift (δ-) at 6.63 ppm is (triplet) assigned to (m, –CH-) group. The hydrogen proton for (s, -CH2-) appeared as doublet at (δ-) of 5.51 ppm. As shown in Fig.3.4, the chemical shift (δ-) of P(S-VAc) copolymers was assigned as follows: a) δ at 2.4 ppm for (s, -CH2), b) δ at 3.5 ppm for (s, -CH-OCO2CH3), and δ at 0.846 ppm for (s, -CH-OCO2CH3).

As a result, FT-IR and ¹H-NMR analyses confirmed that E1-copolymer are successfully synthesized through EPIC emulsion polymerization technique.

Fig. 2:¹H-NMR spectrum of E1-copolymer.

3.3.   Molecular weight, particle size and morphology properties of the coating sheets

The influence of initial monomer ratios on the resultant molecular weights is shown in Fig. 3. From the results obtained, it is noticed that the differentiation in the final P(St-VAc)’s molecular weights is mainly attributed to the percentage of styrene monomer in the initial monomer ratio. By increasing the styrene percentage in the initial monomer ratio, the molecular weight of the resultant P(St-VAc) copolymer increases gradually with an acceptable morphology profile of the coated film. Generally, using different monomer ratio of St and VAc produces different copolymers with variable physical properties. The morphology of the formed coated layer depends primarily on the ratio of styrene and vinyl acetate in the formed P(St-VAc) copolymer. Indeed, the performance of the polymeric coated film is mainly dependent on two factors as the elasticity and the hydrophobicity of coated film. Increasing the styrene percentage enhanced the hydrophobicity of the final copolymer. On the contrary, the presence of little amount of vinyl-acetate promotes the physical characters of the final copolymers as elasticity, adhesion force and transparency. This means that P(St-VAc) copolymer becomes more elastic in nature by decreasing the styrene content in the initial monomer ratio. From the results obtained as shown in Figs. 3, it is clear that the synthesis of P(St-VAc) copolymers (as general formula) with high molecular weight practically decreases with increasing the percentage of vinyl acetate. For instance, the maximum molecular weight of E3-copolymer as (Mw=278602 Da and Mn=57809 Da) was obtained by initial monomer molar ratio of (75:25 wt., %) for St and VAc, respectively. The opportunity of VAc to dissolve in oil phase found to be highat low temperature. Consequently, lowering the solubility of VAc monomer in the continuous phase enhances its solubilization in the organic phase (oil phase) and giving a higher volume fraction of hydrophobe in the monomer droplets (Schork et. al., 2005).

Fig. 3: The molecular weight (Mn, Mw, Mp and Mz) of E1-, E2- and E3- copolymers at 0.50 wt., % of EB and 25 ^oC.

3.4.   Morphological characterization of E3-copolymer

Surface wettability of the coated film

Contact angle (CA)and the surface free energy (SFE) are vastly important properties used to determine the efficiency of glass coating film as water-repellent glass. Indeed, the values of the resultant contact angles values are varied with the type of surface coating film, surface topography, and the surface tension between certain liquid and the solid substrate.

The water contact angles (CAs) of the investigated copolymers (E1, E2 and E3) listed in Table 3. It is noticed that the slipperiest surface was obtained by E1 with contact angle (θ) of 84.05 ± 1.61^o and asthe styrene content increases in E2 and E3 copolymers, the measured contact angle increases from 73.71± 0.24^o to 98.64 ± 0.27^o, respectively. Table 3also, illustrates the effect of the molecular weights, styrene percentage and droplet size on the resultant CAs for E1, E2 and E3- copolymers, respectively. As mentioned before, the molecular weights of the prepared copolymers increases as a result of increasing the styrene percentage in the resultant copolymer (Tan et. al., 1981). This means that the possibility of the coated copolymer to become more water repellent might be increased. Consequently, a high value of contact angle was obtained. Another explanation of increasing the value of CA is due to the droplet size of the resultant copolymer. From the obtained results, it is evident that decreasing the droplet size of the prepared copolymer from 82.76.99 to 79.45 nm resulted in increasing in the value of contact angle CA from 84.05 ± 1.61^o to98.64 ± 0.27^o, respectively. This may be attributed to increase in the folding and the roughness of the polymeric matrix surface. This folding may result from a significant increasing in the collision frequency of the dispersed droplets during the polymerization process (Fatemehet. al., 2005). However, a slight decrease in the droplet size (increasing the surface area of the formed droplets) of the resultant copolymers resulted in a noticeable improvement in the roughness of the polymer surface, therefore, the hydrophobicity character of the coated glass surface increases.

As listed in Table 3, the static contact angle (θ) of the polished carbon steel surface (uncoated carbon steel surface)  is changed from 48.16 ± 0.61° to 98.64 ± 0.61° for E3-copolymer. This may be referred to the hydrophilic nature of the used carbon steel coupons(Yilbas et al., 2017). This means that the hydrophobicity character of the coated surface is much better than that obtained by un-coated carbon surface. The presence of the various structures (amorphous and crystalline) of E3-copolymer causes a little roughness of the coated carbon steel surface. This may be attributed to the chemical structure, and the morphology character of E3-copolymer and formation of some entrapped air-pocket like structure on the surface.The presence of these gaps in the coated film improves the roughness structure of the coated surface leading to increase the contact angle of the coated film(Latthe et. al., 2010).

Table 3: Particle size, molecular weight, and contact angle of E1-, E2- and E3- copolymers

3.5.   Evaluation of the coated surface as corrosion resistance material

3.5.1.      Weight loss measurement

In dipping immersion method, a thin coating film is deposited in the immersed carbon steel sheets from the solution containing E3-coplymer. This method is considered as a highly effective method for fabrication of hydrophobic anticorrosive surface (She et. al., 2014). The most common benefit of using holder-coupons inside the petroleum pipelines is to determine the corrosion rate of the internal pipelines corrosion over the period of exposure. Corrosion resistance of the coating coupons was assessed by weight loss technique. The corrosion rate from the weight loss coupons is calculated as shown in the following eq.: -

Where, C: Constant equal to 143,700, W: Weight loss in gm., A: Surface area of the mild steel in cm², T: Time of exposure in hours, and D: Density of mild steel used in g\cm³. The carbon steel alloy used through this work is carbon steel, No.1018 with UNS code of G10180, density of 7.86 g\cm³ and CORRATER Multiplier of 1.00.

The inhibition efficiency (IE, wt., %) of the coated coupons is calculated as shown in the following eq.: -

Where; w_o, w are the weight losses of uncoated and coated coupons, respectively.

The result of weight loss, inhibition efficiency (IE, wt., %), and the values of corrosion rate (Cr) for coated and uncoated carbon steel (blank sample) coupons in brine water are listed in Table 2. To calculate the weight loss of the coated carbon steel coupons, the coupons were immersed in the corrosive media for 24 hours with continues stirring at 200 rpm and 30^oC (According to ASTM G170 standard method). Triplicate specimens were exposed to the same conditions and the average weight losses were calculated. The efficiency of the coated materials as anti-corrosive materials is affected by: i) Time of exposure of coupons to the corrosive media andii) The concentration of the coated solution used in coating coupons. The assessment of the coated material is described as follows: -

3.5.1.1.     Effect of time exposure of coated coupons

As shown in Fig. 4and Table 4, the weight loss of the coated coupons generally increases with increasing the time exposure from 0 to 24 days. From the results obtained in Fig. 4, it is noticed that the coated coupons with E3-coploymer at concentration of 100 ppm and 298 °K exhibits a minimal increases in weight losses. From Figure 4, it is clear that the weight loss gives a constant rate with the exposure time for the most parts of the experimental period. After 4 days of the experiment, a slightly increasing in the mean weight losses from 6.5 × 10^-4 to 9.7 × 10^-3g was observed with increasing the exposure time from 5 to 24 days, respectively. This may be due to increase in the dissolution of the carbon steel via the corrosion of iron under the continuous attack of brine water to the carbon surface. This means that the adhesion strength between the E3-coploymer thin-coated film and the surface of the carbon coupons begins to collapse. Therefore, the oxidation-reduction mechanism of the carbon steel was started, thus, the wear rate of the coated coupons increases (Asiful and El-Sayed, 2015). As shown in Table 4, the time duration of carbon steel exposed to the corrosive environment affects the corrosion rate value (k), mpy. The formation of a highly effective hydrophobic film on the surface of the tested coupon minimizes the corrosion rate to a minimum level as the time exposure of the coupons decrease (Hu et. al., 2015). By inspection of the data illustrated in Table 4, show that the corrosion rate of coated carbon coupons by E3-copolymer decreased from 163.1 to 48.6 mpy compared to the corrosion rate of blank sample. This means that the corrosion rate is mainly affected by the chemical structure and the topography of the coated materials.

Fig. 4: A plot of weight loss (g) vs. Time (day) for uncoated and coated coupons with E3-coploymer at concentration of 100 ppm and 298 °K.

3.5.1.2.            Concentration of the coated solution

Fig. 5show the inhibition efficiency (wt., %) of uncoated coupon (blank) and coated coupons by E3-coplymer at different concentrations of the coating material solution of 0, 100, 200 and 300 ppm, respectively at 298 °K. The influence of concentration of the coated solution on the corrosion rate (k) values of uncoated and coated carbon steel coupons by E3-copolymer in brine water as corrosive media was investigated and results are listed in Table 4 and illustrated by Fig. 5. From the results obtained in Table 4, it is obvious that the corrosion inhibition rate (k) decreases from 3.7 to 0.6 mpy as the concentration of the coated solution increased from 100 to 300 ppm, respectively. This may be attributed to the formation of compacted inhibiting hydrophobic film on the metal surface. Increasing the efficiency of the coated material enhances its effect on the water-repelling, thus, the inhibition efficiency of the coated layer against the corrosive media increases (Funke, 1986).

Fig. 5: Corrosion inhibition efficiency (IE, wt., %) - time curves of coated and uncoated carbon steel dissolution in brine water at different concentration and 298 °K.

Table 4: Inhibition efficiency, corrosion rate for uncoated and coated coupons using different coating materials at different concentration (ppm) and 30^oC

3.5.2.      Effect of temperature

The effect of increasing temperature on the corrosion rate (k) and the activation energy (Ea) values of uncoated and coated carbon steel by E3-copolymer at temperatures ranging from 298 to 333 °k was investigated as listed in Table 5 The comparison between (Ea) values for uncoated and coated carbon steel coupons gives some explanation about the adhesion mechanism of the coated layer on the coupon surface at different temperatures. The activation energy of the corrosion rate increases as the adsorption and the adhesion of the inhibited layer on the coupon surface decreases (Noor El-Din et. al., 2012). Arrhenius equation stated that the value of the corrosion rate (k), and Ea mainly depends on the applied temperature (Noor El-Din et. al., 2012). The activation energy values (Ea, kJ/mol) were mathematically calculated from Arrhenius equation (Marwa et. al., 2018): -

Where; k is the corrosion rate of the coated carbon steel coupons, R is universal gas constant (8.314 J mol^-1k^-1), T is absolute temperature, and b is a the pre-exponential factor depends on the coupons alloy type.  

The activation energy (Ea) value obtained by E3-copolymer was calculated (17.2kJ/mol). The high activation energy (Ea) as compared to uncoated coupon sheet may be attributed to the formation of strong adhesion inhibited layer over the carbon steel sheet (Ashish et. al., 2011).From equation, it is clear that the corrosion rate depends on Ea, T and b values. Increasing the temperature leads to activate the coupons surface, thereby, the corrosion rate increases. Higher activation energy (Ea) indicates a higher resistance of the coated coupons to corrosion (Nnabuk et. al., 2018). However, activation energies less than 80 kJ/mol supports the physical adsorption mechanism.

Table 5: Activation energy (Ea) and Corrosion rate (k), mdd of uncoated and coated carbon steel coupons at 0, 100 ppm, respectively and different temperature of 298, 313 and 333 °K

3.5.3.      Effect of contact angle on the corrosion performance

The effect of water contact angles for coated coupons film using E3- copolymer on the inhibition efficiency (IE, %) was studied and illustrated by Fig. 6. From Fig. 6, it is obvious that the tendency of the coated film to roll-off the water droplets from the coated film has a direct impact on the corrosion resistance efficiency of the coated coupons. As the water contact angles of the coated coupons increases from 65.01 to 101.37, the inhibition efficiency of the coated film by E3- copolymer increased from 82.45 to 93.07 %. This may be due to the ability of the underlining carbon steel surface to resist corrode. By applying of superhydrophobic coated material, the ability of the underlining carbon steel surface to corrosion resistance increases (Hassan et. al., 2017).

Fig. 6: Effect of coated and uncoated materials on the corrosion inhibition efficiency, and contact angle between water and carbon steel surface at 0 and 100 ppm and 298 °K, respectively

3.5.4.     Surface morphology study

In this study, the surface morphology of uncoated and coated carbon steel coupons surfaces was examined using microscopic examination and scanning electron microscope (SEM): -

3.5.4.1.      

Microscopic examination

This technique allows for assessing the damage of the coated coupons under certain conditions. The performance of coated coupons is strongly dependent on the amount and shape of the porosity in the coated materials after exposure to corrosive media at a constant temperature (Ismail and Nazihah, 2015). Uncoated and coated coupons with E3-copolymer immersed in the corrosive solution of the brine water to examine the top-surface morphology of them for weight loss technique at concentration of 300 ppm and temperature of 298 °K after 24 hours was performed. The metallographic examination of uncoated coupons in the absence and the presence of brine water are illustrated by Fig. 7(a, b). Fig.7(c) show the coated coupons by E3- copolymer at 300 ppm and 298 °K. As shown in Fig. 7 (a-c), different sizes of pours is observed over the coupons surface. These pours allow the coupons of the coated film to become a crack surface, thereby, the tendency of the coated coupons to corrosion attack was increased.  Furthermore, it is noticed that the morphology of the coated coupons by E3-copolymer showsgood anti-corrosion resistance for the synthetic water with smooth top-surface compared to that uncoated coupons. This may be attributed to the chemical composition of the coated materials. It is inferred that the coated coupons by E3-copolymer show effective resistance against corrosion attack in used pipelines.

Fig. 7: Microscopic examination of uncoated and coated carbon steel surface after weight losses examination at 300 ppm concentration, immersion time of 24 days in brine water solution and 298 °k.

3.5.4.2. Scanning Electron Microscopy (SEM)

The hydrophobicity of any coated film increases as the porosity, folding and wrinkles of the surface morphology increases (Pavel et. al., 2009). From Fig. 8 (c), it is clear that the surface morphology of E3- copolymer’s coated film shows a dense, folding and a highly wrinkles surface film. In addition, irregular porous networks in macro-scale through E3- copolymer matrix are observed. The wrinkles and the variation of macroporosity size that scattered through the coated film enhance the roughness degree of the coated surface, which in turn leads to increase the static contact angle. Also, increasing the roughness and the macroporosity of the coated film may lead to increase the possibility to trap the air inside the polymer network, consequently, increasing the repelling performance of the coated film (Nakajima et. al., 1999). With increasing the surface roughness of the coated film, the water contacts angle increased; subsequently_, the coated surface becomes more hydrophobic. The surface morphology of the uncoated (blank) and coated carbon steel coupons using E3- copolymer after 24 days immersion in brine water solution at 300 ppm, 298 °K, and magnification power of 700x are shown in Fig. 8 (a, b). From Fig. 8 (b), E3- copolymer was found to be close in the surface morphology to uncoated coupon (blank). This means that the coating shows agood corrosion resistance for carbon steel.This may be attributed to the chemical composition and the adhesionpower of the coated materials.

Fig. 8 (a, b): SEM images for a) Blank coupon, and coated coupon by b) E3-polymer at 300 ppm concentration, immersion time of 24 days in brine water solution, 298 °K and magnification power of 700x.

3.5.5.     Atomic force microscopy (AFM)

To get more information about the morphology of the metal coated film that plated by E3-copolymer the samples were subjected for further characterization by atomic force microscope (AFM) technique. The surface topography, root mean square (RMS), surface roughness value, and roughness maps of the coated glass surface by E3-copolymer.The influence of E3-copolymer on the coated surface topography and the RMS roughness value was computed by NanoScope software without calculus) is illustrated inFigs. 9.The result in Fig. 9 shows thatthesurface topography of the E3-copolymer coated film appears to be uniform, featureless, and coated surface with RMS value of 5.71 nm. From the data obtained in Fig. 9, it is evident E3-copolymer coating may cause a noticeable change in the coated film in terms of the hydrophobicity character and the surface roughness. This amendment increases the contact angle of the carbon steel coated film by E3- copolymer from48.16 ± 0.61^oto 98.64 ± 0.27^o

Fig. 9: 2D-, 3D- AFM topographies of the coated glass using E3-copolymer at concentration of 0 wt. %.

1. 4.     CONCLUSION.

Summarising the data presented above, we can conclude that,new hydrophobic coating of styrene vinyl acetate copolymer was synthesized by Emulsion Phase Inversion Concentration Polymerization as corrosion inhibitors. The research results revealed that: -

• The inhibition efficiency (IE %) increases with the increasing of the inhibitor concentration.
• Increasing the temperature from 298 °k to 333 °k leads to activate the coupons surface; thereby, the corrosion rate increases.
• Higher activation energy (Ea) indicates to higher resistance of the coated metal to corrosion.
• As the water contact angles of the coated coupons increases from 48.16 ^oto 98.64 ^o, the inhibition efficiency of the coated film by E3-copolymer increased from 82.45 % to 99.21%.
• The maximum inhibition efficiency of 99.21% was obtained by E3-copolymers using 300 ppm and at 298 °k.

REFERENCES

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تأثیر بولیمرات مشارکة من (الاستیرین وخلات الفینیل) کطلاءات شدید الکراهیة للمیاه على حمایة أنابیب النفط المصنوعة من الصلب الکربون من التآکل

¹أحمد عبد العظیم حسین – ²أحمد إسماعیل هاشم – ³محمود ریاض نور الدین – رانیا السید مرسی

¹ شرکة خالدة للبترول – القاهرة – مصر.

² کلیة العلوم – جامعة عین شمس – العباسیة – القاهرة – مصر.

³ معهد بحوث البترول – 1ش أحمد الزمر – مدینة نصر – القاهرة – مصر.

التآکل داخل منشآت صناعة الغاز والنفط یشکل خطر على السلامة والصحة المهنیة ولذا یستوجب فهمة وإدارته بفاعلیة. یتضمن هذا البحث إنتاج طلاء شدید الکراهیة للماء یستخدم لحمایة خطوط الانابیب المصنوعة من الحدید الصلب الکربونی من التآکل ولتحقیق هذا الهدف تم تشیید بعض البولیمرات المشارکة من الاستیرین وخلات الفینیل وتقییمها کمثبطات للتآکل. وقد تم توصیف المرکبات المحضرة باستخدام مجموعة متنوعة من التقنیات، وهی: (1)الأشعة تحت الحمراء ((FT-IR، (2) الرنین المغناطیسی (¹H-NMR)، (3) التحلیل الکروماتوجرافی لنفاذیة الجیل (GPC) (لتحدید الوزن الجزیئی)، (4) المسح المجهری الإلکترونیSEM) )، (5) قیاسات زاویة التلامس (CA)، (6) القوة الذریة المجهریة (AFM).  کما تمت دراسة کفاءة الترکیبات المحضرة کطلاءات شدیدة الکراهیة للماء ومثبطات للتآکل بدراسة العوامل المختلفة المؤثرة على تلک العملیة مثل 1) ترکیز محلول الطلاء 2) درجة الحرارة 3) طاقة التنشیط 4) زاویة التلامس.

الکلمات الدالة:شدید الکراهیة للماء، البولیمرات المشارکة، البلمرة فی المستحلبات، مثبطات التآکل.