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Underground pipelines used for oil, gas and water distribution in Saudi Arabia and gulf region are estimated more than 33000 km in length with a range of diameters from 8 and 80 inch. Most of these pipelines are buried in different types of corrosive soil conditions and in most cases an external coating is employed along with cathodic protection (CP). Most of the existing pipelines are over 30 years old now and this is the stage to carry out rehabilitation projects for life extension of this aging infrastructure. The selection of the suitable coating systems for the rehabilitation projects is a very complicated process as it requires in depth understanding the coating/environments interactions in that particular environment along with application challenges. This paper discusses in detail the different types of external underground pipeline coating types and their selection criteria for rehabilitation projects along with recent trends and future recommendations.

Graphene has shown excellent corrosion protection of copper (Cu). The corrosion protection of Cu is governed by the characteristics of the deposited graphene and Cu surface morphology underneath. In this work, graphene films (1-2, 4-5 layers) were deposited on Cu using a chemical vapor deposition by changing hydrogen (H2) concentration during the annealing stage. The chemical structure and surface microstructural features of graphene/Cu were inspected by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The electrochemical corrosion performance of graphene/Cu was studied in 0.5 M sodium chloride solution using potentiodynamic polarization and electrochemical impedance spectroscopic measurements. The 1-2 layers of graphene and rough Cu surface were obtained for low H2 concentrations (0 and 2.5%), whereas high H2 concentrations, 20 and 50%, resulted in a smooth Cu surface and 4-5 layers of graphene. Our results showed that Cu with a smooth surface and multilayer graphene film exhibited the best corrosion resistance against electrochemical degradation. Tafel analysis revealed that Cu with 4-5 layers of graphene coating corroded nearly three orders of magnitude slower than the annealed Cu, without graphene coating. The results of this study can be useful for several applications where Cu is in close contact with salt species.

The electrochemical properties of three Ni-free duplex stainless steel alloys, designed in-house, were investigated in chloride (0.2M NaCl) solution at room temperature. The corrosion performance was measured in terms of pitting potential (Epit), passive current density (ip), polarization resistance (Rp) and susceptibility to metastable pitting. The results obtained showed that alloy 2 (Fe–16Cr–5Mn–1Mo–1Si–1Cu–0.22N) exhibited the highest corrosion resistance (highest Epit, lowest ip, highest Rp and lowest metastable pitting susceptibility) among the designed alloys. Alloy 2 was also found to be free of any secondary phase precipitations (sigma phase, Cr nitrides, chi phase) when aged at 600–900 °C for 3–50 h owing to its optimized composition.

The hydrodynamic corrosion inhibitive performance of two imidazole derivatives 2-ethyl-4-methylimidazole and 1-benzylimidazole was investigated on API X65 steel in 1.0 M HCl solution. Structural features of the molecules derived from density functional theory (DFT) calculations at B3LYP/6-31G(d.p) showed that 1-benzylimidazole possess high electron density due to $$\pi $$ network which lies flat on the surface and tends to form a stronger interaction with the metal. The addition of the inhibitor molecules in 1 M HCl solution shifted the corrosion potential $$({E}_{\mathrm{corr}})$$ in the noble direction. Tafel polarization and electrochemical impedance spectroscopy (EIS) experiments performed at 0–1500 rpm and 50–500 ppm of inhibitor concentration revealed that the corrosion rate was increased with an increase in rotation speed in the absence of inhibitor molecules. However, upon the addition of the inhibitor molecules in the solution minimized the corrosion rate with an efficiency of 82% in the case of 1-benzylimidazole at 500 ppm and 500 rpm electrode rotation. It was concluded that simple imidazole molecules could serve as corrosion inhibitors under extreme hydrodynamic conditions.

Erosion causes substantial damage in many industrial equipment such as pump components, valves, elbows, and plugged tees. In most cases, erosion is coupled with corrosion, resulting in major financial loss (nearly 3.4% of the global gross domestic product) as evidenced in oil and gas industries. In most cases, the erosion occurs in a submerged water medium. In this paper, erosion characteristics of stainless steel 316 were investigated computationally in a water-submerged jet impingement setup. The erosion profiles and patterns were obtained for various parameters over ranges of inlet velocities (3 to 16 m/s), nozzle diameters (5 to 10 mm), nozzle–target distances (5 to 20 mm), nozzle shapes (circular, elliptical, square, and rectangular), impingement angles (60° to 90°), and particle sizes (50 to 300 µm). The range of Reynolds number studied based on nozzle diameters is 21,000–120,000. The Eulerian–Lagrangian approach was used for flow field prediction and particle tracking considering one-way coupling for the particle–fluid interaction. The Finnie erosion model was implemented in ANSYS-Fluent 19.2 and used for erosion prediction. The computational model was validated against experimental data and the distributions of the erosion depth as well as the locations of the of maximum and minimum erosion points are well matched. As expected, the results indicate an increase in loss of material thickness with increasing jet velocity. Increasing the nozzle diameter caused a reduction in the maximum depth of eroded material due to decreasing the particle impact density. At a fixed fluid inlet velocity, the maximum thickness loss increases as the separation distance between the nozzle outlet and target increases, aspect ratio of nozzle shape decreases, and impingement angle increases. The erosion patterns showed that the region of substantial thickness loss increases as nozzle size/stand-off height increases and as particle size decreases. In addition, increasing the aspect ratio and impingement angle creates skewed erosion patterns.

Most oil and gas production wells have plenty of corrosive species present along with solid particles. In such production environments, CO2 gas can dissolve in free phase water and form carbonic acid (H2CO3). This carbonic acid, along with fluid flow and with/without solid particles (sand or other entrained particles), can result in unpredictable severe localized CO2 corrosion and/or erosion&ndash, corrosion (EC). So, in this work, the CO2 EC performance of API 5L X-65 carbon steel, a commonly used material in many oil and gas piping infrastructure, was investigated. A recirculating flow loop was used to perform these studies at three different CO2 concentrations (pH values of 4.5, 5.0, and 5.5), two impingement velocities (8 and 16 m/s), three impingement angles (15&deg, 45&deg, and 90&deg, ), and with/without 2000 ppm sand particles for a duration of 3 h in 0.2 M NaCl solution at room temperature. Corrosion products were characterized using FE-SEM, EDS, and XRD. The CO2 EC rates were found to decrease with an increase in the pH value due to the increased availability of H+ ions. The highest CO2 erosion&ndash, corrosion rates were observed at a 45&deg, impingement angle in the presence of solid particles under all conditions. It was also observed that a change in pH value influenced the morphology and corrosion resistance of the corrosion scales.

Duplex stainless steels (DSSs) exhibit excellent corrosion resistance and are being used in a variety of industrial applications. Reducing/eliminating the amount of nickel in such alloys will contribute significantly to its economic viability. Moreover, a well-established wear behavior for these alloys is also an essential development in most of their applications. Hence, in this work, the Taguchi technique was effectively implemented to investigate the effect of operating factors such as sliding speed and applied load on the wear behavior of different compositions of nickel-free DSSs. It was observed that the composition had a higher contribution of 33.66% to the wear rate (WR) and the contribution of the sliding speed to the coefficient of friction (COF) was found to be 68.17%. With a good agreement, a regression model was also developed to predict the WR and COF within a certain range of factors. Wear tests have also shown that the developed nickel-free DSS is a promising candidate in terms of wear resistance as compared to austenitic stainless steels (ASS).

Laser gas assisted surface treatment of steel 309 is carried out and the characteristics of the resulting surface are analyzed using the analytical tools. Scanning electron and 3-D optical microscopes are used to assess the morphological and metallurgical changes in the laser treated layer. Energy spectroscopy and X-ray diffraction are carried out to determine the elemental composition and compounds formed on the laser treated surface. The friction coefficient of the laser treated surface is measured using the micro-tribometer and compared to that of the as received surface. The corrosion resistance of the laser treated and as received surfaces is measured incorporating the electrochemical tests. It is found that laser treatment results in a dense layer and formation of nitride compounds at the surface. This enhances the microhardness at the laser treated surface. The friction coefficient attains lower values at the laser treated surface than that corresponding to the as received surface. The corrosion rate of the surface reduces significantly after the laser treatment process, which can be attributed to the passive layer at the surface via formation of a dense layer and nitride compounds in the surface vicinity. In addition, the number of pit sites decreased for the laser treated surface than that of as received surface.

Iron based alloys Fe (82−x) -Cr 18 -Si x (x = 0, 1, 2, 3) wt% were developed by mechanical alloying (MA). Phase evolution studies on the milled powders were conducted using X-ray diffraction (XRD) and field emission transmission electron microscopy (FE-TEM). Scanning electron microscope (SEM) was used to carry out morphological investigations. Results showed an initial solid solution formation at 5 h of milling and with continued milling to 35 h, an amorphous phase was formed. The amorphous phase was mechanically crystallized to α-phase at 85 h and 100 h of milling for Fe (82−x) -Cr 18 -Si x (x = 0) and Fe (82−x) -Cr 18 -Si x (x = 1, 2, 3) wt% alloys respectively. Both the lattice parameter and crystallite size were decreased with an increase in Si content of the alloys. With continued milling, micro-strain was increased and crystallite size of the alloys was decreased.

Spark plasma sintering (SPS) process parameters were optimized in terms of densification, microhardness and corrosion resistance to develop a nano-structured Fe-18Cr-2Si ferritic alloy. The powders were mechanically alloyed (MA) in a planetary ball mill and subsequently SPS was carried out under different processing conditions. Powders and sintered samples were characterized using X-Ray Diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD phase evolution studies on ball milled powders confirmed the formation of a crystallized alloy after 100 h milling. XRD of sintered alloy confirmed the development of a nano-structured ferritic alloy with a crystallite size in the range of 20–40 nm. Maximum densification of 96.0%, Vickers hardness of 710 HV and pitting potential (E pit = − 430 mV SCE ) was achieved at a sintering temperature of 1100 °C, for 15 min holding time, at 50 °C/min of heating rate and at an applied pressure of 60 MPa.

Laser treatment of an aluminum composite surface was carried out to improve tribological properties and corrosion resistance at the surface. The workpiece consists of 15% SiC and pure aluminum, and it is produced by hot pressing. The characteristics of the laser-treated surface were examined using optical and scanning electron microscopes, energy dispersive spectroscopy, X-ray diffraction, a micro-tribometer, and a potentiostat. Laser treatment was carried out by following a spiral scanning track at the surface. This provides a self-annealing effect of the lately formed laser tracks on the initially formed tracks while lowering the cooling rates at the surface. It was found that laser-treated surfaces are free from asperities such as large-scale cracks and voids. Laser treatment improves the hardness of the surface because of the dense layer formation in the surface region. The friction coefficient of the laser-treated surface attains lower values than that corresponding to the untreated surface. Laser treatment improves the corrosion resistance of the surface.

Erosion corrosion performance of API 5L-X65 carbon steel was investigated at three different impingement velocities (3, 6 &amp, 12 m/s), five different angles (15, 30, 45, 60, &amp, 90&deg, ), and with/without solid particles (average particle size of 314 &micro, m). The experiments were conducted in 0.2 M NaCl solution at room temperature for a duration of 24 h and the results showed that the maximum erosion corrosion rate was observed at 45&deg, irrespective of the velocity. The highest erosion corrosion rate at 45&deg, was due to the balance between the shear and normal impact stress at this angle. Ploughing, deep craters, and micro-forging/plastic deformation were found to be the main erosion corrosion mechanisms. The maximum wear scar depth measured using optical profilometery was found to be 51 &micro, m (average) at an impingement angle of 45&deg

Purpose – The purpose of this paper is to investigate the corrosion resistance of high velocity oxy-fuel (HVOF)-sprayed Diamalloy 2002 coating on carbon steel. The coating microstructure is examined in line with the corrosion resistance. Design/methodology/approach – HVOF spraying of coating is achieved, and the coating response to electrolytic solution is measured experimentally in terms of corrosion resistance. Findings – HVOF coating improves the corrosion resistance of the substrate such that the corrosion rate of the substrate is 7.1 mpy and the coating results in 4.5 mpy. However, presence of deep pit sites at the surface suggests the occurrence of preferential corrosion around the splat boundaries. In addition, closely spaced surface texture peaks act as crevice corrosion centers at the surface while initiating the formation of deep pit sites. Research limitations/implications – This study is limited by experimental investigations. In future, it may be extended to include model studies. Practical implications – The findings of this study are very useful for those working in the coating industry. However, HVOF coating is limited to high temperature protection in harsh environments. Social implications – It is useful for the power industry, particularly for gas turbines. Originality/value – It is an original work and describes the corrosion resistance of the coating surface. It is found that the coating improved the corrosion resistance of the steel surface.

Purpose – The purpose of the present study is to report the results of the laser treatment of high-strength low-alloy (HSLA) steel surface and corrosion response of the treated surface that was carried out. Metallurgical and morphological changes in the laser-treated layer are also examined. Laser treatment of the alloy surface improves the surface properties; however, development of high thermal stress field in the treated layer can exceed the yielding limit of the alloy lowers, particularly, the corrosion resistance of the resulting surface. Design/methodology/approach – Pre-prepared workpiece surfaces are laser-treated and electrochemically tested in an electrolytic solution. Corrosion rate of the resulting surface is analyzed and pit sites are examined. Findings – It is found that the presence of nitride compounds and fine grains acts like as a self-protective layer at the laser-treated surface while lowering the corrosion resistance. Consequently, laser gas-assisted treatment provides a positive effect on the corrosion properties of the treated surface through lowering the corrosion current. The pits are shallow and do not form a regular pattern at the workpiece surface. The secondary pitting is prevented by the protective layer formed at the laser-treated surface. Research limitations/implications – The study can be extended to include laser treatment including the hard particles, such as carbides, at the surface. However, this extension is left to another study. Practical implications – Laser treatment can be used for protection of surfaces from wear and corrosive environments. The findings of this study give insight into the improvement of the surface characteristics for this purpose. It serves to industry for the practical solution of the surface protection from corrosive environments. Social implications – The researchers and scientists working in the area get the benefit from the outcome of this work. Originality/value – It is an original work and gives insight into the enhancement of the corrosion resistance of HSLA steel after the laser treatment process.

Laser treatment of pre-prepared titanium alloy surface is carried out and electrochemical response of the treated surface is analyzed. B4C particles are located in a carbon film at the workpiece surface prior to the laser treatment process. Morphological and metallurgical changes are examined in the laser treated layer using analytical tools. Potentiodynamic tests are carried out to assess the corrosion rate of the treated surface. It is found that the laser treated surface is free from large-scale asperities such as large size cracks and cavities. Laser treatment significantly improved the corrosion resistance of the surface. The presence of B4C particles contributes to microhardness enhancement at the treated surface; however, the particles do not demonstrate any adverse effect on the corrosion resistance of the surface.

In this paper, the erosion behavior of commonly used stainless steels (AISI 310S, AISI 316), carbon steel (AISI 1020), and Aluminum 6060 were experimentally investigated. The effect of hardness on erosion rates and on the morphologies of eroded surfaces has been evaluated. The experiments were carried out using an air jet erosion tester and utilizing angular alumina as erodent with 50 lm particle size. The samples were tested at six different impact angles (15 ,3 0 ,4 5 ,6 0 ,7 5, and 90) using three different impact velocities (30, 60, and 100 m/s). The eroded surfaces were analyzed using a scanning electron microscope (SEM) for the evaluation of material degradation. The erosion rates were found to increase with the increase of the alloy bulk hardness and Aluminum 6060 showed maximum erosion resistance. For all specimens, the erosion rates were found to increase with the increase of impact velocity and the maximum erosion rate was found to occur between 15 and 30 impact angles. The obtained results were found to correlate very well with Oka et al. (Wear, 259:95–101, 2005) erosion model.

Laser gas assisted treatment of AISI H12 tool steel surface is carried out and the electrochemical response of the laser treated surface is investigated. Morphological and metallurgical changes in the treated layer are examined using a scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. Potentiodynamic polarization tests are carried out for untreated and laser treated specimen in 0.2 M NaCl solution at room temperature. It is found that the laser treated AISI H12 workpiece surfaces exhibit higher corrosion resistance as compared to untreated specimen as confirmed by lower corrosion rate, higher pitting potential, and lower passive current density.

Effect of copper on the defect density of Fe–20Cr–xCu (x = 0, 4) stainless steel alloys was investigated in deaerated pH 8·5 borate buffer solution at room temperature using Mott–Schottky analysis. Mott–Schottky analysis revealed that the addition of copper increased the acceptor density (NA, VCr−3), i.e. decreased the Cr+3 content of the passive film. Also the donor densities, shallow donor (ND1, VO+2) and deep donor (ND2, VCr+6), of the passive films formed were increased. XPS analysis confirmed the decrease in Cr content and enrichment of copper in the passive film of Cu containing alloys, which ultimately dictated their lower corrosion resistance, i.e. decreased film protectiveness and stability.

Effects of Cu on the polarization behavior of Fe-20Cr-xCu (x = 0, 2, 4 wt%) were examined in deaerated 0.1 M sulfuric acid (H2SO4) solution. In the active region, corrosion resistance of the alloys is improved with Cu content as a result of the enrichment of Cu on the surface of the alloys that occurs by the preferential dissolution of Fe. In the passive region, the effects of Cu on the passivation behavior of the alloys was dependent on the applied potential. At potentials active to −100 mV vs. saturated calomel electrode (SCE), the passivity of the alloys is improved with Cu content, which is confirmed by the increase in passivation rate with a decrease in oxidation tendency. In contrast, above −100 mVSCE, where the oxidation reaction of Cu+ to Cu2+ occurs, the passivity of the alloys was degraded significantly with Cu content, as confirmed by the increase in passive current density as well as the significant decrease in passivation rate. The deleterious effects of Cu on the passivation behavior of Fe-20Cr-xCu (x = 0, 2, 4 wt%) decreased at potentials noble to 500 mVSCE, primarily as a result of the significant decrease in Cu content in passive film and hence of the decrease in the oxidation reaction of Cu+ to Cu2+.

Effects of Cu on the stability of passive film formed on Fe–20Cr–xCu (x = 0, 2, 4 wt.%) alloys in deaerated 0.1 M H2SO4 solution were examined by potential decay test, X-ray photoelectron spectroscopy, and the Mott–Schottky analysis. The potential decay curves of Fe–20Cr–xCu (x = 0, 2, 4 wt.%) alloys passivated for 1 h at 400 mVSCE exhibited a 1st stage-potential decay to a potential of approximately −300 mVSCE. Especially, the stability of passive film decreased with an increase in Cu content, suggesting that the film formed on the Cu-containing alloys was less stable than that of Fe–20Cr alloy. The rapid potential decrease in the Cu-containing alloys was primarily due to the Cu-dissolution from the film, which increased the defect density of the passive film and hence decreased its stability. After the 1st stage-potential decay, Fe–20Cr alloy exhibited the 2nd stage-potential decay to −654 mVSCE or to an active state in 9000 s. However, the 2nd stage-potential decay did not occur in the Cu-containing alloys because of the Cu enrichment on the surface of the alloy. The Cu enrichment in the Cu containing alloys decreased the defect density in the film, and hence increased the stability of the passive film.

HVOF coating of Inconel 625 powder on carbon steel is carried out. Laser melting of the resulting coating is realized to improve coating structural integrity. Morphological and microstructural changes are examined in the coating prior and after laser treatment process using scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction (XRD). The residual stress developed is measured on the surface vicinity of the laser-treated coating using the XRD technique. The corrosion resistance of the laser-treated and untreated coating surfaces is measured, incorporating the potentiodynamic tests in 0.5 M NaCl aqueous solution. It is found that laser treatment reduces the pores and produces cellular structures with different sizes and orientations in the coating. Laser-controlled melting improves the corrosion resistance of the coating surface.

A new high Mn–Ni free (duplex stainless steel) DSS containing 18Cr–6Mn–1Mo–0.2N has been developed by examining the effects of manganese on the corrosion and mechanical properties of high Mn SSs containing 18Cr–4 ∼ 11Mn–0 ∼ 2Ni–0 ∼ 1Mo–0.2N. The alloy with 45% ferrite is found to be an optimum alloy with much higher mechanical strength and similar corrosion resistance compared with those of standard SS304. In addition, the alloy was free of precipitation of sigma phase and Cr-nitride when exposed to high temperatures due primarily to relatively low contents of Cr, N and Mo. With an increase in Mn content, the resistance to pitting and metastable pitting corrosion of high Mn DSS decreased since the number of (Mn, Cr) oxides, acting as preferential sites of pitting, increased with the Mn content.

Laser gas assisted treatment of dual matrix structured cast iron surface is carried out and the corrosion response of the surface is examined. A carbon film containing 15% SiC particles and remaining 85% carbon are formed at the workpiece surface prior to the laser treatment process. The formation of carbon film enhances the absorption of the incident laser beam and accommodates uniformly the SiC particles at the workpiece surface. Nitrogen at high pressure is used as an assisting gas during the laser treatment process. Metallurgical and morphological changes in the laser treated layer are examined using a scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. Electrochemical tests are carried out to measure the corrosion response of the laser treated and untreated workpiece surfaces. It is found that laser treatment results in a dense layer consisting of fine grains, partially dissolved SiC, and nitrogen compounds in the treated region, which improves corrosion resistance of the laser treated workpiece surface. © 2014 Elsevier Ltd.

Effect of silicon on the defect density of Fe–20Cr–xSi (x = 0, 1, 2) stainless steel alloys was investigated in deaerated pH 8.5 borate buffer solution at room temperature using Mott-Schottky analysis. Results showed that silicon was incorporated/dissolved in the passive film of Fe–20Cr–xSi (x = 0, 1, 2) alloys. Mott-Schottky analysis revealed that the addition of silicon decreased the acceptor density (NA ,V Cr −3 ), i.e., increased the Cr +3 content of the passive film. Also the donor densities, shallow donor (ND1 ,V O +2 )a nd deep donor (ND2 ,V Cr +6 ), of the passive films formed were decreased. XPS analysis confirmed the presence of Si in the passive film of Si containing alloys. This enriched silicon along with higher Cr +3 concentration of the passive film, dictated its enhanced

Effects of Si on the repassivation kinetics and stress corrosion cracking (SCC) of alloy 304Si were examined by a scratch electrode technique and slow strain rate test in chloride solutions and compared with those of other stainless steels (SSs), 304 and 316L. Repassivation kinetics of these alloys and Fe-20Cr-xSi (x = 0-2) alloy were analyzed in terms of the current density, i(t), flowing from the scratch as a function of the charge density, q(t), that has flowed from the scratch. Passive film initially nucleated and grew according to the place exchange model, and then grew according to a high-field ion-conduction model in which log i(t) has a linear relationship with 1/q(t) with a slope of cBV. The repassivation rate of Fe-20Cr-xSi (x = 0-2) alloys, evaluated by the cBV value, increased with an increase in Si content. Furthermore, repassivation rate decreased on the order of 304Si, 316L, and 304. The resistance to SCC of the SSs (304Si, 304, and 316L) measured in 35 wt % MgCl 2 solution at 120°C was in good agreement with those predicted based on the repassivation kinetics. The beneficial effects of Si on SCC of 304Si SS appears to be associated with the enrichment of Si in the passive film.

Effects of Mn on the localized corrosion, repassivation kinetics, and stress corrosion cracking (SCC) of high Mn-N stainless steels (SSs) were examined in chloride solutions and compared with those of type 304 SS. The resistance to pitting corrosion of high Mn-N SSs decreased with an increase in Mn content at the expense of Ni. Repassivation kinetics of the high Mn-N SSs was analyzed by the relationship between the current density i(t) and the charge density q(t) that has flown from the scratch; passive film initially nucleated according to the place exchange model and then grew according to the high-field ion conduction model in which log i(t) vs 1/q(t) has a linear relationship with a slope (cBV). The repassivation rate of the alloys, analyzed by the (cBV) value, was decreased with an increase in the Mn content. The resistance to SCC of the alloys measured in 25% MgCl 2 was in good agreement with that predicted, based on their repassivation rate. The deleterious effects of Mn on the localized and stress corrosion of the alloys appear to be associated with an increase in number and size of nonmetallic inclusions such as (Mn, Cr) oxides with Mn content.