API 5L X65 Research Articles

Simulation of Cooling Curves of the Heat Affected Zones of API 5L X80 Steel of Welds Made by Flux Core Arc Welding Self Protecting

The simulation of cooling curves of the heat affected zones (HAZ) of API 5L X80 steel was based on the cooling rates of welds made by the process named FCAW-S (Flux Core Arc Welding Self-Protecting). The specimens were analyzed by macroscopy, light microscopy (LM) and scanning electronic microscopy (SEM) to investigate the effects of cooling conditions on the tensile test and Vickers hardness. A thermo-mechanical simulator showed be able to reproduce the different thermodynamics conditions of points in the HAZ and allowed the reproduction of the thermal cycle obtained by welds were applied to the specimens of API 5l X80 steel. The values of the yield strength, ultimate strength and hardness found in the specimens were lower than those presented by the material as received.

Thermo-mechanic and Microstructural Analysis of an Underwater Welding Joint

Abstract The aim of this research is to present a comparative analysis between theoretical and experimental thermal fields as well as a microstructural behaviour and residual stresses applying multiple weld beads in the joint of two API 5L X52 pipe sections. The thermal field, microstructural and residual stresses were numerically modelled through the finite element method (FEM) and compared to experimentally. The simulation conditions used in the FEM analysis were similar considerations to the underwater welding conditions. The finite element analysis was carried out, first by a non-linear transient thermal analysis for obtaining the global temperature history generated during the underwater welding process. Subsequently, a microstructural behaviour was determined using the temperatures distribution obtained in the pipe material by calculating the structural transformations of the material during the welding process, and finally a stress analysis was developed using the temperatures obtained from the thermal analysis. It was found that this simulation method can be used efficiently to determinate with accuracy the optimum welding parameters of this kind of weld applications.

Strategies for corrosion inhibition of slurry pipelines prior to commissioning

A practice used to prevent corrosion in buried slurry pipelines is the hibernation of pipelines with an aqueous solution containing corrosion inhibitors before beginning the mining operation. The aim of this work is to evaluate the corrosion resistance of API 5L X70 steel used in the slurry pipelines in hibernation solution containing sodium sulphite, sodium hydroxide and glutaraldehyde in a synthetic river water. The electrochemical techniques used are the Tafel analysis and electrochemical impedance spectroscopy. The synergistic effect of the components of hibernation solution on the corrosion resistance of the API 5L X70 steel was evaluated. A lower corrosion resistance was obtained for the API steel in aqueous solution of sodium sulphite, and in solution of sodium sulphite with glutaraldehyde. The hibernation solution was efficient in inhibiting steel corrosion but the highest corrosion inhibition efficiency was obtained with the glutaraldehyde aqueous solution.

Evaluation of the Simultaneous Effects of Sulfate Reducing Bacteria, Soil Type and Moisture Content on Corrosion Behavior of Buried Carbon Steel API 5L X65

Evaluation of the Simultaneous Effects of Sulfate Reducing Bacteria, Soil Type and Moisture Content on Corrosion Behavior of Buried Carbon Steel API 5L X65

Soil Stresses on Carbon Steel Pipe Undergoing Uplift

This paper presents a three-dimensional numerical study to evaluate the variations in stresses in the soil mass surrounding a carbon steel pipe class API 5L X60 submitted to uplift due to ground elevation. Analyses were carried out for soil relative density, pipe stiffness and surficial surcharge loading. Results have shown that stress variations due to uplift are lower for looser backfill soils and flexible pipes. Stress variations in pipe invert are meaningful in the vicinity of the region between stable and unstable soil masses.

Assessment of Ductile-to-Brittle Transition Behavior of Localized Microstructural Regions in a Friction-Stir Welded X80 Pipeline Steel with Miniaturized Charpy V-Notch Testing

Friction-stir welding (FSW) is an alternative welding process for pipelines. This technology offers sound welds, good repeatability, and excellent mechanical properties. However, it is of paramount importance to determine the toughness of the welds at low temperatures in order to establish the limits of this technology. Ductile-to-brittle transition curves were generated in the present study by using a small-scale instrumented Charpy machine and miniaturized V-notch specimens (Kleinstprobe, KLST); notches were located in base metal, heat-affected, stirred, and hard zones within a FSW joint of API-5L X80 Pipeline Steel. Specimens were tested at temperatures between 77 K (−196 °C) and 298 K (25 °C). Based on the results obtained, the transition temperatures for the base material and heat-affected zone were below 173 K (−100 °C); conversely, for the stirred and hard zones, it was located around 213 K (−60 °C). Fracture surfaces were characterized and showed a ductile fracture mechanism at high impact energies and a mixture of ductile and brittle mechanisms at low impact energies.

The Effect of Temperature and Acid Gas Loading on Corrosion Behavior of API 5L X52 Carbon Steel in Amine Unit

The effect of temperature and H2S concentration on amine corrosion of API 5L X52 carbon steel in a CO2-saturated 25 wt.% diethanolamine solution was investigated via electrochemical techniques. It was found that increase in temperature from 25 to 80 °C resulted in severe increase in corrosion rate from 0.88 to 16.24 mpy due to increase in degradation rate of amine. Also, it was concluded that increase in H2S concentration led to increase in corrosion rate because of formation of more heat stable amine salts. The effect of temperature on corrosion rate was more significant than acid gas loading.

Numerical Evaluation of Temperature Field and Residual Stresses in an API 5L X80 Steel Welded Joint Using the Finite Element Method

Metallic materials undergo many metallurgical changes when subjected to welding thermal cycles, and these changes have a considerable influence on the thermo-mechanical properties of welded structures. One method for evaluating the welding thermal cycle variables, while still in the project phase, would be simulation using computational methods. This paper presents an evaluation of the temperature field and residual stresses in a multipass weld of API 5L X80 steel, which is extensively used in oil and gas industry, using the Finite Element Method (FEM). In the simulation, the following complex phenomena were considered: the variation in physical and mechanical properties of the material as a function of the temperature, welding speed and convection and radiation mechanisms. Additionally, in order to characterize a multipass weld using the Gas Tungsten Arc Welding process for the root pass and the Shielded Metal Arc Welding process for the filling passes, the analytical heat source proposed by Goldak and Chakravarti was used. In addition, we were able to analyze the influence of the mesh refinement in the simulation results. The findings indicated a significant variation of about 50% in the peak temperature values. Furthermore, changes were observed in terms of the level and profile of the welded joint residual stresses when more than one welding pass was considered.

Effect of pre-crack in the fracture properties of steel pipes used in oil type API 5L X70

In this work, we studied the impact resistance of the weld metal of a steel API 5L X70, assessing the influence of geometry and dimensions of the specimen fracture toughness. Curves resistance to crack propagation ductile (J–R) following the methodology “Single Specimen” together with the variation of the elastically generated by the crack initiation (CMOD) providing a load versus displacement/length graph for crack (ASTM E1820-05). Tests were conducted on samples according to the standard SE(T) to surface cracks (a/W = 0.2) and deep (a/W = 0.5) and the ratios W/B = 1.0 and 2.5, keeping the plane strain. The results show that regardless of initial crack dimension, no significant differences were observed in the curves J–R, confirming the similarity of the curves for W/B = 1.0 for any a/W. However, most of the samples showed anomalous ductile crack growth, generating high plane stress along the sides of the notches. Samples tested according to the J–R curve showed no cracks of encapsulating, and the values of the crack length a i and a f are very close to those obtained by the elastic flexibility variation method. Since delamination influenced the properties of impact for increased efforts to crack propagation, mainly by microstructural conditions of the samples.

The Role of Porosity and Surface Morphology of Calcium Carbonate Deposits on the Corrosion Behavior of Unprotected API 5L X52 Rotating Disk Electrodes in Artificial Seawater

The role of porosity of calcium carbonate deposits on the corrosion performance of API 5L X52 steel was investigated by chronoamperometry, Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscope/Energy Dispersive Spectroscopy and X-Ray Diffraction. EIS analysis showed that calculation of the area under Bode phase diagrams in high frequency domain is the best electrochemical approach for porosity percentage estimation. Applied potential has the most significant influence on porosity percentages. The least amount of porosity can be obtained by an interactive process at less negative potentials and more rotation speeds, i.e. −1.0 VSCE and 600 rpm resulting in a uniform and compact layer of aragonite crystals.

Corrosion behaviour of polycrystalline Nb2O5 thin films and its size effects

This study examines the effect of film thickness ranging from 230 to 404 nm on the corrosion resistance of Nb2O5 thin films grown by chemical solution deposition. The films were characterized to obtain the relationships between the deposition parameters and the most relevant physical properties (structural, surface morphology and corrosion resistance). From X-ray diffraction and XPS analyses we can conclude that the films were stoichiometric Nb2O5 and crystalline. The internal strain and morphology of the film changes as the number of layers increases indicating a thickness dependent grain size. The surface roughness, corrosion resistance were also affected by the film thickness. Electrochemical impedance spectroscopy (EIS) shows that the thicker film have higher passive and charge transfer resistance than the control samples. These results coating layer of Nb2O5 improves the corrosion resistance on an API 5L X80 steel alloy due to the formation of a film on the surface.

Corrosion Resistance of API5L X52 Carbon Steel in Sulfide Polluted Environments

In the present work, the corrosion behavior of base and welded API5L X-52 carbon steel coupons in synthetic ground water solution NS-4 was studied. Subsequently, the morphology and composition of the corrosion product deposits were determined using scanning electron microscopy (SEM). Based on weight loss as well as Tafel’s measurements, increasing the sulfide ions content above 0.4 mM, had an inhibition effect on the corrosion behavior of carbon steel. According to EDAX analyses, increasing of sulfide concentration from 0.4 to 4 mM Na2S, the Fe/S ratio decreased from 12.02 at 0.4 mM to 2.6 at 4 mM Na2S.

Optimización de los Parámetros de Soldadura por Arco Sumergido en Acero HSLA: una Aplicación para Manufactura de Tuberías de Conducción de Hidrocarburos

Resumen El acero HSLA (High Strength Low Alloy) API 5L X70 es utilizado para fabricación de tuberías para transporte de hidrocarburos. La construcción de tuberías de este material involucra alta cantidad de soldadura, donde los parámetros empleados influyen directamente en las estructuras metalúrgicas y en las propiedades mecánicas del mismo cuando soldado. Así, para estudiar el impacto de los parámetros de soldadura por arco sumergido en la resistencia mecánica y dureza de la Zona Afectada por el Calor (ZAC), fue llevado a cabo un diseño central compuesto que totalizó 17 pruebas. Las variables de entrada fueron corriente, voltaje y velocidad de avance; como variables de salida se consideró resistencia a la tensión y dureza Vickers de la ZAC. Para tal estudio fue utilizado el proceso de soldadura por arco sumergido, pruebas de tensión y pruebas de dureza Vickers. Se utilizó la metodología de superficie de respuesta para el modelado y la optimización fue realizada utilizando algoritmos genéticos y la gráfica de frente de Pareto. Fueron obtenidas 16 combinaciones de parámetros con la optimización, de las cuales fue escogida una para validar los modelos. Con los resultados fue posible establecer modelos matemáticos empíricos satisfactorios para las variables de respuesta.

Fusion-bonded epoxy composite coatings on chemically functionalized API steel surfaces for potential deep-water petroleum exploration

Corrosion of oil and gas pipelines significantly reduces the service life of the pipelines, thus increasing costs, and more seriously, it can cause catastrophic environmental accidents. More recently, the exploitation of oil in ultra-deep seawater fields is facing new technological challenges in material selection owing to the extreme production conditions. Thus, the development of organic coatings as protective layers for steel pipelines is of crucial importance against highly corrosive environments. In this work, fusion bonded epoxy (FBE) coatings were deposited onto chemically functionalized carbon steel surfaces with organosilanes to investigate the potential applications in protection against corrosion and degradation in harsh marine environments. Carbon-steel API 5L X42 (American Petroleum Institute Standard grade) was chemically functionalized with two organosilanes, 3-APTES [(3-Aminopropyl)triethoxysilane], and 3-GPTMS [(3-Glycidyloxypropyl)trimethoxysilane], followed by the deposition of FBE composite coatings. The systems were extensively characterized with respect to each component as well as the steel-coating interface. The contact angle measurements and Fourier transform infrared spectroscopy (FTIR) results clearly indicated that the steel surface was effectively modified by the functional amine and glycidyl silane groups, leading to the formation of interfacial covalent bonds with increased hydrophobicity compared to bare steel surfaces. In addition, the morphological and chemical characterizations of FBE by scanning electron microscopy, atomic force microscopy, X-ray diffraction, and FTIR showed that it is composed of an epoxy-based organic matrix of bisphenol-A diglycidyl ether (DGEBA) reinforced with uniformly dispersed inorganic phases of calcium silicates and TiO2 particles. Moreover, the chemical functionalization of the steel surfaces with amino and glycidyl silanes significantly altered the interfacial forces with the FBE coatings, resulting in higher adhesion strength for 3-APTES-modified steel compared to 3-GPTMS-steel; however, both mostly showed cohesive rupture mode in the FBE component.

Microstructural evolution in friction stir welded API 5L-X52 steel

3 Abstract: Welded API-5L steel pipes have been extensively used in the oil industry. One of the major parameters affecting the mechanical properties is the grain size, which is altered with the joining method. In this paper microstructural evolution in the friction stir welded API 5L-X52 steel pipes has been investigated.Specimens were cut from a 2mm thick API 5L-X52 steel pipe. The steel sheets were then joined by friction stir welding process; at a linear speed of 100 mm/min. The tool rotational speed was varied from 400 to 800 rpm. Samples were then evaluated using tensile test, metallographic and hardness measurements. Microstructural investigations revealed the stir zone, heat affected zone and thermo mechanically affected zones. Heat input in the stir zone led to the formation of elongated austenite grains which were transformed to fine ferrite and pearlite grains and widmanstatten ferrite in certain regions. Plastic deformation and recrystallization enhanced the hardness and tensile strength as well as toughness of the welded joint in the API 5L-X52 steel.

Comparison of Mono- to Diphosphate Ester Ratio in Inhibitor Formulations for Mitigation of Under Deposit Corrosion

Mitigation of localized under deposit corrosion (UDC) in upstream oil and gas pipelines is an important research topic for both industry and academia. In a research program to better define the various inhibitor components that provide mitigation of UDC, this initial research investigates the effect of varied ratios of mono- to dinonylphenol phosphate esters (PE) by testing a set of specifically formulated inhibitors. Inhibitors with three mono- to di-PE ratios were tested in the presence and absence of 2-mercaptoethanol (ME). Using two 1.25 in (3.18 cm) diameter API 5L X65 pipeline steel samples and 250 μm silica sand, UDC testing was conducted for 28 d in a CO2 saturated solution at 70°C and 1 bar (100 kPa) total pressure. Analysis has shown that localized corrosion (pit penetration rate) increased for ME-free nonylphenol PE as the concentrations of di-PEs and mono-PEs approached equivalency. The nonylphenol PE inhibitor with a 50:50 mono- to di-PE ratio at 100 ppm concentration failed to protect the surface of the sample under the individual sand grains. Even the base product inhibitor package with no PE provided better mitigation under these test conditions than the 50:50 mono- to dinonylphenol PE. However, it was observed that the addition of ME provided a dramatic improvement in the mitigation of UDC for each mono- to di-PE ratio of the nonylphenol PE tested. From this research, it is seen that the mono- to di- PE ratio is important to consider when developing corrosion inhibitors containing PEs.

Evaluation of ductile tearing for API-5L X70 pipeline grade steel using SENT specimens

Pipelines in harsh environments may be subjected to large deformations. Classic stress-based design needs to be complemented with strain-based design. An important parameter in the design is the crack growth resistance. SENT testing (Single Edge Notch Tension) allows to determine the so-called material’s tearing resistance curve. Very recently the first standard on SENT testing, BS 8571:2014, has been published. SENT testing is however still subject to extensive research and different approaches with respect to eg. notch placement, crack extension measurement and analysis exist. In this paper two methods for calculating crack extension based on the unloading compliance procedure are used and compared, proving that they show little difference. This is performed on an API-5L X70 steel grade and this for different configurations, namely an inner diameter notch and a through thickness notch. The results showed little difference between the different configurations, although the inner diameter showed higher crack growth resistance. Furthermore, the results are compared to visual observations of the fracture surfaces and a hardness map. The fracture surfaces corresponded to the obtained resistance curves. However, no real correlation between the hardness map and the other results could be seen.

Inhibition effect of flavonoid extract of <i>Euphorbia guyoniana</i> on the corrosion of mild steel in H<sub>2</sub>SO<sub>4</sub> medium

The influence of flavonoids extracts of three parts of Euphorbia Guyoniana towards the corrosion of type API 5L X52 steel in 15% H 2 SO 4 has been evaluated by weight loss method and polarization technique. The results showed that extracts are a good inhibitors for API 5L X52 steel in this medium. The corrosion inhibition efficiency increases on increasing plant extracts concentration. The inhibition is attributed to the adsorption of the surface of the metal. Potentiodynamic polarization results revealed that the studied inhibitors behave as a mixed type. Keywords: API 5L X52 steel, corrosion inhibition, sulphuric acid, Euphorbia Guyoniana, flavonoids extract

Hydrogen failure sensitivity of A516-Gr70 and API 5L-X70 steels in sour environments

Purpose – This paper aims to clarify the corrosion behavior of two famous structural steels in sour environment. These steels have a vast application in oil and gas industries. The study aims to find the effect of different concentrations of sour solution on the origin of crack in these steels. Design/methodology/approach – After preparation of specimens, different sour solutions were made using the synthetic brine (according to National Association of Corrosion Engineers [NACE], Technical Committee Report 1D182) and various amounts of Na2S.9H2O and CH3COOH. The polarization test was done by Potansiostat apparatus model Zahner-IM6 at two temperatures, 25°C and 50°C. The corrosion current densities were obtained from the polarization curves. Finally, the corrosion products and hydrogen-induced cracking (HIC) were investigated by Tescan Vega II XMU scanning electron microscope (SEM) linked to a Rontec energy-dispersive X-ray spectroscopy (EDS) system. Findings – API 5L-X70 steel showed smaller corrosion current values than A516-Gr70 steel. The HIC cracks propagated parallel to the surface of A516-Gr70 steel in three solutions and confirmed the inappropriateness of this steel for sour environment applications. Originality/value – This paper studies the effect of sour environment on the behavior of two famous industrial steels at two temperatures by new method.

Fracture toughness assessment at different temperatures and regions within a friction stirred API 5L X80 steel welded plates

Friction stir welding (FSW) is a promising candidate for use in pipeline steels because it offers high productivity and sound welded joints. This study presents a fracture toughness assessment of FSW-welded two-pass butt joints, different regions within the joints and tests temperatures (25°C, −15°C, −20°C, −35°C, −40°C) were used. Base plates of API-X80 steel 12mm thick were FSW-welded using two different pass sequences, coincident and alternate directions. The results presented consistently high toughness values down to −20°C for all the assessed notches, which indicates that FSW may be suitable for general pipelines steels applications in that range of temperatures.