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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.

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).

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.

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

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.

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.