API X70 Pipeline Steel Research Articles

Experimental Investigation on Corrosion Behaviour of Heat-Treated API X70 Pipeline Steel

Experimental Investigation on Corrosion Behaviour of Heat-Treated API X70 Pipeline Steel

Coupled slow strain rate and acoustic emission tests for gaseous hydrogen embrittlement assessment of API X65 pipeline steel

Hydrogen embrittlement (HE) sensitivity of API X65 pipeline steel was evaluated in this study through the simultaneous application of slow strain rate tests (SSRT) and acoustic emission (AE) monitoring on hollow dog-bone samples. Exposure to hydrogen gas decreased the elongation to fracture percentage with a significant rise in embrittlement index for the higher pressure of 10 MPa. SEM images of the fracture surfaces demonstrated that the fracture mechanism changed from ductile to ductile–brittle under 1 MPa pressure, and to predominantly brittle with quasi-cleavage characteristic when testing under 10 MPa hydrogen gas. Classification of the AE events based on waveform analysis revealed a mainly shear mode fracture for 10 MPa nitrogen sample, while a dominant tensile mode fracture was identified for the hydrogen charged samples.

To Investigate the Effect of Heat Treatment on API X70 Pipeline Steel

To Investigate the Effect of Heat Treatment on API X70 Pipeline Steel

Imidazoline behavior as corrosion inhibitor in the electrochemical characterization of SCC behavior of an API X70 steel exposed to brine solution

Abstract The effect of concentration of an organic imidazoline as inhibitor on internal stress corrosion cracking (SCC) behavior of an API X70 pipeline steel exposed to a brine solution was studied. The SCC process using simultaneously the slow strain rate stress test (SSRT) and electrochemical measurements was performed. Fracture surface analysis and secondary cracking were observed through a scanning electron microscopy (SEM). According to SEM fractography and SSRT results, the steel showed high SCC susceptibility with a brittle fracture and several secondary cracks without addition of inhibitor, whereas the addition of inhibitor to brine solution was effective to increase the SCC resistance of steel at concentrations of inhibitor of 50 and 100 ppm. A further addition of concentration of inhibitor had a negative effect on the mechanical properties of the steel. Electrochemical measurements results are in accordance with the SCC susceptibility, indicating that corrosion inhibitor film suppressed the anodic and cathodic reactions increasing the resistance to SCC until concentration of 100 ppm. Further addition of inhibitor aggravated the localized corrosion due to local desorption of inhibitor molecules. The Hilbert–Huang transform (HHT) analysis revealed the contribution of different corrosion process contained in the electrochemical current noise (ECN) signals at several inhibitor concentrations.

Understanding the inhibitory mechanism and protection performance of avocado seed nanoparticle extract in API X65 steel corrosion in a 1M HCl acid environment

There is currently a high need for effective and nontoxic corrosion inhibitors in the acidising industrial process due to rising concern for human life and environmental sustainability. As a result, in this work the anticorrosive efficiency of avocado seed nanoparticle extract (ASN) in APIX65 pipeline steel corrosion was examined in 1M HCl medium through weight loss and the potentiodynamic polarisation approach. The inhibitor morphology, particle size, and elemental composition were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The SEM examination of the steel surface indicates a considerable difference, demonstrating that the inhibitor formed a protective barrier on the metal surface with heteroatom constituents from the inhibitor. The findings show a corresponding increase in inhibition efficiency as the inhibitor concentration increases, with the highest inhibitor efficiency found at 95.65% for 5 g of ASN in 1 M HCl solution. Regarding the electrochemical test, ASN performs as a mixed-type corrosion inhibitor. The weight loss test findings corroborated the electrochemical investigations, indicating that ASN had a high inhibitive effect on X65 steel in an acid medium. The ASN nanosize gives a huge surface area, resulting in increased reaction activity and the development of more shielding coatings. This study sheds light on the development of sustainable corrosion inhibitors for X65 steel.

A numerical study on the correlation of ductile crack extension in Ni-based clad pipe girth welds with circumferential surface cracks and clamped SE(T) specimens

This work describes a numerical investigation on the relationships between ductile crack extension in Ni-based clad pipe girth welds and an API X80 pipeline steel with circumferential surface cracks and SE(T) specimens under fixed grip conditions. A primary objective is to gain further insight and understanding of the effects of constraint on ductile tearing behavior in piping components with dissimilar girth welds and how well crack growth resistance curves measured using single edge notched tension fracture specimens correlate with ductile fracture behavior in circumferentially surface cracked pipes. The numerical description of CTOD−R curves employs a computational cell approach incorporating the Gurson–Tvergaard (GT) constitutive model to simulate ductile crack extension in the crack configurations analyzed. The numerical analyses consider predictions of ductile crack growth in 3-D models of circumferentially cracked pipes with varying crack depth over pipe thickness ratio, a/t, from measured J-resistance curves derived from fracture resistance testing of clamped SE(T) specimens. The analyses also focus on comparing predictions of ductile crack extension using two different definitions for the CTOD.

Correlation of Microstructure with Anisotropy of Low‐Temperature Toughness in Two API X70 Pipeline Steels

This study aims to investigate the correlation between the microstructures and the anisotropy of low‐temperature toughness for two high‐strength API X70 pipeline steels fabricated at different coiling temperatures. The microstructures are characterized using an optical microscope, a scanning electron microscope, and an electron backscattered diffraction analysis, with tensile and Charpy V‐notch impact tests also conducted on the steel specimens in various directions relative to the rolling direction. Some pearlites formed by a higher coiling temperature increase the ductile‐to‐brittle transition temperature (DBTT) by 38 °C in the T–L (transverse‐longitudinal) direction. On the other hand, the DBTT of the specimens with the T–L and L–T (longitudinal–transverse) directions (−106.6 and −109.3 °C, respectively) exhibits excellent low‐temperature toughness, but the specimen with the D–D (diagonal–diagonal) direction shows the highest DBTT (−65.2 °C). The resulting anisotropy in the low‐temperature toughness of the API X70 pipeline steel is discussed from the standpoint of an orientation distribution function analysis in this study. It is suggested the anisotropy of the low‐temperature toughness is mainly attributed to the texture components of RD (rolling direction) fibers originating from deformed austenite.

Experiment and simulation of high‐cycle corrosion fatigue damage evolution and corrosion pit tolerance analysis of crack nucleation

AbstractBased on the elasto‐plastic damage constitutive model, a continuum nonlinear damage evolution model for the high‐cycle corrosion fatigue of the API X65 pipeline steel is proposed. Firstly, a series of experiments are carried out to determine the corrosion fatigue damage parameters of X65 steel in the artificial seawater, then the corrosion fatigue damage model is used in the finite element (FE) analysis to predict the crack nucleation life of high‐cycle corrosion fatigue. In order to consider the influence of corrosion pit on the crack nucleation of corrosion fatigue, a user‐subroutine UMESHMOTION provided by the general software ABAQUS is used to construct a numerical model of damage evolution with the corrosion pit effect considered on the API X65 steel. Numerical results show that the numerical model considering the effect of damage and corrosion pit can better predict the crack nucleation life of the API X65 steel than that considering only the damage effect.

Failure analysis in API X70 pipeline steel in sour environment with an emphasis on fracture surfaces and crack propagation

The aim of this study is to investigate the fracture surfaces and crack propagation in an API X70 pipeline steel in acidic environment. To this purpose, as-received and electrochemically hydrogen-charged tensile specimens are subjected to tensile testing. Moreover, EBSD measurements were carried out on the cross section (RD-ND plane) in as-received and hydrogen-charged specimens. The results showed that hydrogen charging and strain rate of tensile testing were considered as two effective parameters in determining the type of fracture. Moreover, the fracture of the uncharged specimens was quite ductile and the strain rate had little effect on the fracture type. A direct correlation was found between type of fracture and the strain rate in hydrogen-charged specimens. With increasing strain rate, the fracture in hydrogen-charged specimens did not have enough time to initiate from inclusions and precipitates and connect to the main fracture surface. <001>∥ND oriented grains have the highest hydrogen atoms due to the largest interatomic space and the distortion energy accumulated at grain boundaries due to the lack of sufficient activated slip system. The variation of KAM distribution to higher values of hydrogen-charged specimen could be effectively associated to the formation of dislocation walls and dislocation tangles especially in the vicinity of bcc grain boundaries. The higher volume fraction of the grains with high Taylor factor data formed in the hydrogen-charged specimen were highly susceptible to plastic instability, enhancing the crack propagation.

Sensitivity to hydrogen induced cracking, and corrosion performance of an API X65 pipeline steel in H2S containing environment: influence of heat treatment and its subsequent microstructural changes

In this investigation, the effect of microstructural changes and phase equilibria on corrosion behavior and hydrogen induced cracking (HIC) sensitivity of an API X65 pipeline steel was studied. For this purpose, heat treatment was performed at 850 °C, 950 °C, 1050 °C and 1150 °C to engineer the desired microstructure of this pipeline steel. Then, the microstructural evolution was performed by optical microscopy, and Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Corrosion properties were evaluated in H2S environment by open circuit potential (OCP), Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). As well, HIC sensitivity of the API X65 pipeline steel was assessed by hydrogen charging of the cathode and immediately conducting the tensile test. Microscopy analyses showed that the microstructure of the steel is ferritic-pearlitic together with the islands of martensite/austenite constituents. Increasing the heat treatment temperature reduced the amount of pearlite and increased ferrite grain size. It also stabilized the ferrite content. Corrosion results indicated that no active layer was formed on the surface of this pipeline steel. Also, increasing the heat treatment temperature increased the corrosion resistance and reduced sensitivity to micro-galvanic localized corrosion. As well, results suggested that the sensitivity to HIC in the API X65 pipeline was substantially increased with increasing the amount of pearlite and reducing the amount of ferrite; i.e. at lower heat treatment temperature.

Evolution of microstructure and texture in pipeline steels at different TMCP procedures with regard to hydrogen induced cracking

SEM and EBSD techniques are used to evaluate hydrogen induced cracking susceptibility in API X70 pipeline steels produced by thermo-mechanical controlled process (TMCP) in laboratory scale. Based on the observations, there is no dominant texture in the specimens and the grains are randomly distributed. Different TMCP parameters and rolling processes generates different grain size, and grains are often elongated along the rolling direction. The results also show that cooling rate is another factor affecting the grain size. A high cooling rate does not allow the grains to grow. The reason for the transgranular type of cracking might be the strong grain boundaries in ambient temperatures which prevents the intergranular cracking. Based on experiments, the hydrogen environment does not have permanent effects on the mechanical properties of the investigated specimens. The electrochemical hydrogen charging experiment shows that the grain refinement improves the resistance to hydrogen embrittlement.

Ex Situ Examination of Matrix and Inclusions of API-X100 before and after Exposure to Bitumen at Elevated Temperature.

The corrosivity of bitumen at 60 and 120 °C was examined by exposing American Petroleum Institute (API) X100 (yield strength 100 ksi, 690 MPa) pipeline steel to bitumen in an autoclave for 30 days. Prior to the autoclave measurements, the inclusion types in the API-X100 pipeline steel were characterized by scanning electron microscopy (SEM), and four types of inclusions were identified, according to their elemental compositions. The four types of inclusions and the surrounding matrix were characterized by ex situ SEM before and after exposure to bitumen. The results show that no obvious corrosion occured at the inclusions or the matrix after exposure at 60 and 120 °C.

Effects of different cooling rates on the microstructure, crystallographic features, and hydrogen induced cracking of API X80 pipeline steel

Hydrogen-Induced Cracking (HIC) is a primary failure mechanism of pipeline-welded joints in the absence of external loading in the oil and gas exploration industries. Three different cooling rates after austenitization were used to simulate in the laboratory different regions of the heat-affected zone (HAZ) formed when welding an API X80 pipeline steel specially designed to enhance the HIC resistance. The samples were characterized with regard to microstructure and crystallography as well as HIC resistance. The HIC resistance test used NACE TM0284-2011 methodology. The microstructure and its homogeneity varied as a function of cooling rates. Samples containing inclusions and segregation zone from the segregation bands of specimens showed reduced HIC resistance, while specimens containing only acicular ferrite and granular bainite coupled with the absence of segregation zone showed significant improvement in HIC resistance. The best HIC resistance results came from samples presenting fine acicular ferrite consisting of fine interlocking plates, with divergent crystallographic orientations, preventing the formation of localized strain distribution inside the grain and at grain boundaries. It was also found that a large proportion of medium-angle boundaries prevent microcrack initiation and the transgranular mode of crack propagation.

Characterization of ductile fracture criterion for API X80 pipeline steel based on a phenomenological approach

Steel pipelines for oil/gas transportation might be subjected to large plastic strain under extreme loading conditions, which will lead to localized fracture. The damage mechanics model is a promising tool to perform most of the assessment analysis and evaluation at the simulation level. In this paper, a micro-based Gurson-Tvergarrd-Needleman (GTN) model and two recently proposed uncoupled fracture criteria, modified Mohr-Coulomb (MMC) criterion and extended Rice-Tracey (ERT) criterion are evaluated using API X80 steel. A comprehensive experimental study including five different notched specimens covering a wide range of stress triaxiality and lode dependence is conducted. Corresponding finite element models are established. A phenomenon-based hybrid numerical-experimental calibration method is used to determine the fracture parameter for these three models. Then the calibrated parameters are validated through notched tensile tests and compact tension (CT) tests. It is shown that the presented fracture criteria are in a good capability to characterize the ductile fracture behaviors of API X80 pipeline steel.

Experimental investigation on dissimilar weld between super duplex stainless steel 2507 and API X70 pipeline steel

This work investigates the microstructure and mechanical properties of 2507 super duplex stainless steel and API X70 high strength low alloy steel weld joint. This joint finds application in offshore hydrocarbon drilling riser and oil–gas pipelines. Coated shielded metal arc welding electrodes have been designed and extruded on 309L filler and their performance compared with a commercial austenitic electrode E309L. Filler 309L solidifies in ferrite-austenite (F-A) mode with a resultant microstructure comprising skeletal ferrites with austenite distributed in the interdendritic region. Results of tensile and impact tests indicate that weld fabricated with laboratory-developed electrodes has higher ductility and impact energy than the commercial electrode. The tensile strength and weld hardness of commercial electrodes are superior. The laboratory-made electrode’s microhardness is lower than the commercial electrodes, making the former less prone to failure. An alternative welding electrode coating composition has been suggested through this work and found to be performing satisfactorily and comparable to the commercially available electrodes.

Investigation of Fracture behaviour of API X70 Pipeline Steel

Oil and gas production has significantly increased over the years in order to meet future demands for oil and gas products, regardless of the unstable price being experienced by producing nations. The use of pipelines for the transportation of these products has been the globally recognized solution. These pipelines are fabricated by welding and their fracture properties depend on a number of factors which include temperature, particularly for pipelines operating in cold environment such as deeper water depths. Therefore, information of fracture behaviour of welded pipelines located in cold regions is therefore important for reliable design for service. In this paper, fracture behaviour of welded x70 pipeline steel was investigated using charpy v-notch specimens. Impact tests were carried out on weld and parent materials at temperatures -10°C, -20°C, -40°C, -60°C, -80°C, -100°C, -120°C, -160°C, 0°C, 10°C and 20°C. Results revealed that higher energy was absorbed in the weld than in parent materials regardless of the test temperature used. results implied that the fracture behaviour of the material could be significantly influenced by temperature, welding and the notch sensitivity of the materials.

Fracture properties and fatigue life assessment of API X70 pipeline steel under the effect of an environment containing hydrogen

A series of fracture toughness and fatigue crack growth rate tests were performed on the X70 pipeline steel base and weld metals under 10 MPa of a natural/hydrogen gas mixture with 1% H2 blends. It is observed that the 10 MPa gas mixture with 1% H2 causes a significant reduction in the fracture toughness in both metals. The fatigue crack growth rates are markedly accelerated under the gas mixtures with 1 % hydrogen blend compared with the tests performed in ambient air. The obtained fracture parameters serve as inputs for fatigue life assessment analyses under the effect of a hydrogen-containing environment. The observed design fatigue life depends strongly only on the environmental conditions. The design fatigue strength of the structural pipeline exposed to hydrogen is much shorter than that under ambient air owing to the decrease in fracture toughness properties and acceleration of the fatigue crack growth rate.

Effect of sulfate-reducing bacteria on corrosion of X80 pipeline steel under disbonded coating in a red soil solution

Effect of sulfate-reducing bacteria on the corrosion behaviors of API-X80 pipeline steel has been studied in crevices under simulated disbonded coatings in red soil solution. The results show that there are amounts of SRB in the crevice under the simulated disbonded coating in the red soil solution during the whole period of experiment. The electrochemical impedance spectroscopy shows that SRB can enhance the corrosion of the steel in the crevice under the simulated disbonded coating, and the thermodynamic analyses indicate that SRB can accelerate the corrosion of steel using not only sulfate but also ferric hydroxide as electron acceptors.

Three phase corrosion of pipeline steel: Size effects of deposited solids under water droplets and an oil diffusion barrier

Existing studies have examined either under deposit corrosion in bulk solutions or underoil droplet corrosion without deposits. Yet, neither of these scenarios represents the conditions existing within a diluted bitumen pipeline where underoil droplet corrosion occurs in tandem with under deposit corrosion. Herein, this industrially important 3-phase system – solid deposit, aqueous droplet, oil cover – is studied for the first time. In particular, the relationship between varying deposit particle size and underoil droplet corrosion is established. Scanning electron microscopy coupled with profilometry was used to monitor droplet corrosion over time for API-X100 pipeline steel covered with different sized silica particles underneath simulated diluted bitumen. A zero resistance ammeter was used to validate the observed corrosion from the immersion experiments. The data indicate that localized corrosion coupled with uniform corrosion occurred beneath the large (80% of the cumulative particle size distribution less than 540 µm) and small (80% of the cumulative particle size distribution less than 43 µm) silica covered underoil droplets on API-X100 pipeline steels after 24 h of exposure. The underoil droplet corrosion of silica covered steel has maximum localized penetration predominantly around the silica pile perimeter. With continued exposure, up to 240 h, the corrosion beneath the two sizes of silica continues to develop with a difference in rate. The maximum penetration rate (13.58±0.76 mm/year) of localized corrosion under the large silica particles was higher than that (10.02±0.87 mm/year) of the localized corrosion beneath the small silica particles.

Effect of Environmental Media on the Electrochemical Behavior of API X70 Pipeline Steel

This work investigates the corrosion behavior of X70 steel in different environments: sea sand, desert sand, mud and sea water. The principle of extracting solutions from these media consisted of mixing a soil material with distilled water, the mixture was agitated using an automatic agitator, which resulted in the extraction of solution. Potentiodynamic polarization and electrochemical impedance tests are used to characterize the samples in both media. The results show that the pipeline steel X70 has an excellent corrosion resistance in the sea sand solution, resulting in a low corrosion current density compared to other media. The impedance diagrams for both media are characterized by two capacitive loops, the first loop is attributed to charge transfer processes and the second loop is related to diffusion phenomena. The observation of corroded surfaces shows that the corrosion mechanism in different media is by pitting.