API 5L X65 Research Articles

Assessment of corroded API 5L X52 pipe elbow using a modified failure assessment diagram

Pipe elbows (bends) are considered critical pressurized components in the piping systems and pipelines due to their stress intensification and the effect of bend curvature. They are prone and hence more exposed to different corrosion failure modes than straight pipes. Late detection of such elbow damages can lead to different dangerous and emergency situations which cause environmental disasters, pollution, substantial consumer losses and a serious threat to human life. A comprehensive safety and reliability assessment of pipe elbows, including usage of prediction models, can provide significant increases in the service life of pipelines. It is well known that the limit pressure is an important parameter to assess the piping integrity. In this paper, the integrity assessment of damaged pipeline elbows made of API 5L X52 steel was done within the framework of numerical modeling using the finite element method (FEM) and finite element analysis (FEA). The evaluation of numerically FEM modeled limit pressure in the corroded elbow containing a rectangular parallelepiped-shaped corrosion defect with rounded corners at the intrados section was done and compared to different codes for calculating limit pressure. Moreover, the area with the corrosion defects with different relative defect depth to wall thickness ratios was FEM modeled at the intrados section of the pipe elbow where the highest hoop stress exists. The results showed that the codes for straight pipes could not be applied for the pipe elbows due to the significantly higher error in the obtained limit pressure value compared with numerically FEM obtained results. However, the results for modified codes, adapted for the pipe elbow case using the Goodall formula for calculation of the hoop stress in pipe elbows with defects are pretty consistent with the numerical FEA results. The notch failure assessment diagram (NFAD) was also used for the straight pipe and pipe bends with different corrosion defect depth ratios, while the obtained critical defect depth ratios further highlighted the criticality of pipe elbows as an essential pipeline component.

Burst capacity and development of interaction rules for pipelines considering radial interacting corrosion defects

Pipelines failures during its service life caused by the impact of multiple corrosion defects are most probable to occur, which may induce severe consequences as compared to single defect acting alone. Interaction rules were developed for multiple defects in the longitudinal and circumferential directions previously, but the knowledge on two or more defects aligned radially is still not well understood. This paper aims at investigating new interacting limits when corrosion defects are acting both on the internal and external wall, separated by a radial spacing, SR. The studies were carried out using burst test experiments as well as numerical modelling using pipe specimens of type API 5L X42. Six colonies of radial interacting corrosion defect arrangements were tested. The paper investigates the effects of the radial interaction by means of radial limit, SRLim. It was found that increasing the defect depths of internal and external defects would highly reduce the failure pressure, Pmultiple. Depending on the orientations of the multiple defects acting radially, the failure pressure may be less or more than the case of single defect, Psingle. Thus, the failure pressure ratio of Pmultiple/Psingle should be used as a measure, with any values larger than 0.99 depict no interaction taken place among those multiple defects. From the six colonies, only two colonies showed the significance of radial interactions. The paper then suggests that when radial interaction does not presence, multiple corrosion defects acting radially may then be treated as single defect.

Through-Thickness Inhomogeneity of Texture, Microstructure, and Mechanical Properties After Rough and Finish Rolling Treatments in Hot-Rolled API 5L X70 Pipeline Steel

The development of inhomogeneity in the microstructure, texture, and mechanical property in hot-rolled (API) 5L X70 pipeline steel after rough and finish thermomechanical control processing has been investigated by experimental measurements. Our investigations revealed that the rough rolling stage produced mostly large and coarse ferrite grains across the thickness, while the finish rolling stage led to a rather refined small-grained microstructure. EBSD investigations confirmed that after the rough rolling stage, recovered and deformed grains dominated the quarter and mid-thickness compared to the surface. Investigation of the finish rolled steel showed that in comparison with the quarter and mid-thickness sections of the plate, the surface section mostly consists of deformed grains. The texture components obtained from x-ray measurement showed that after rough and finish processing stages, the {001} , {110} , {123} , {112} , and {001} components were observed to be present. However, inhomogeneity of texture was observed at different depths of the rolled steel, such that in comparison with the surface, volume fractions of texture and intensities of the desired γ-fiber texture were seen to be highest at the mid- and quarter-thickness sections after both rolling stages. The room-temperature tensile stress–strain curves showed that the highest yield strength was observed for samples obtained from the near-surface section, while samples obtained from the mid-thickness section showed the highest elongation during tensile deformation. Overall, the final stage processing was observed to refine the final microstructure of the steel, thus improving the strength of the steel.

Hydrogen embrittlement of API 5L X65 pipeline steel in CO2 containing low H2S concentration environment

The basic corrosion mechanisms in CO2 environments are widely investigated and reported by scientific community. However, cracking failure mechanisms in CO2 environment or in environments where CO2 coexist with other gases need a better understanding. Cracking susceptibility of API 5L X65 in pure CO2 was recently reported and the basic mechanism was attributed to hydrogen embrittlement. The influence of hydrogen permeation and the detrimental effect of cathodic polarisation support the assumption of hydrogen embrittlement as the determining factor for the loss of plasticity and strength. The loss of strength of an API 5L X65 steel when CO2 and H2S coexist in the same environment is the focus of the present work. Hydrogen embrittlement (HE) and hydrogen induced cracking (HIC) of pipeline steels are failures modes expected to occur in CO2 with traces of H2S environments. The present work aims to approach the performance in laboratory of an API 5L X65 steel in CO2 with traces of H2S environment (slightly sour), using as baseline the performance of the material in pure CO2 environment (sweet), already reported. Hydrogen permeation and Slow Strain Rate Tests (SSRT) were carried out in CO2 environment containing low concentration of H2S. It was observed that traces of H2S in CO2 environment promote much more intense hydrogen permeation, much higher than in purely CO2 environment. Loss of ductility was also much more severe than in CO2 environment, with and without the influence of cathodic polarisation. Hydrogen generation enhancement promoted by traces of H2S in solution, corresponding to an average content of 21 ppm in solution, had a heavy effect on hydrogen embrittlement of the steel, confirmed by the lower ratio of reduction in area (RRA) and time to fracture in comparison with sweet service conditions.

Fracture assessment of pipeline girth weld at low temperature

The results of long-distance oil and gas pipeline failure analysis are important to the industry in order to maintain the reliability and safety of them. Seam welding in these pipes is done with good accuracy at place of work, while girth welding is carried out in the installation site and usually causes the main failure problem. Therefore, the most vulnerable and crucial part of these pipes is the girth welding. Investigating the fracture behavior of girth weld in high-pressure gas pipeline systems at low temperatures is important because these products are hazardous and may lead to explosion, leading to economic losses and environmental pollution. In the present study, the fracture behavior of girth-welded API 5L X65 natural gas transportation pipes was experimentally investigated at low temperatures. The fracture parameters were obtained using Arcan fixture in which all of the in-plane modes including pure tensile mode to pure shear mode can be created by altering the loading angle from 0° to 90°. Finite element analysis was also conducted by ABAQUS finite element software in order to determine geometrical coefficients which are required in calculating the fracture toughness. Results revealed that by decreasing the temperature and increasing the mode II loading contribution, the fracture toughness values were also decreased.

A Study of Fatigue Crack Growth Rate in Steels in Relation to Crack-Tip Plastic Deformation and Fracture. Part 2. Parametric Relation between Fatigue Crack Growth and Plastic Strains

The first part of this study presented low-cycle fatigue and cyclic fracture toughness test methods for 10GN2MFA steel at 20 and 270°C, experimental results to construct kinetic fatigue fracture diagrams and to determine low-cycle plastic strain and fracture characteristics. Here, those results are estimated as to the application of cyclic plasticity to describe the fatigue crack growth rate. The cyclic strain-hardening coefficient and the Paris–Erdogan equation exponent for ferrite-pearlite steels are shown, to be closely related as well as the intersection point of the diagram in the range of high crack growth rates was defined. The parameters of the above relation and coordinates of the intersection point were determined for the steels of this class. In the latter case, the optimization methods were used to find the minimum sum of squares of residual functions. Based on the correlation between the cyclic strain-hardening coefficient and Paris–Erdogan equation exponent, the conclusion was drawn of the lower boundary value of this characteristic predicted for an ideal elastoplastic material (zero cyclic strain-hardening coefficient), to be equal to 1.0. As also follows, other classes of the materials (and other cycle asymmetries) can exhibit similar relations in the form of rays coming from the point (0; 1.0) at a corresponding experimental slope to the coordinate axes. From the common intersection point of the diagram (Gurney point) and their slopes to the axes for ferrite-pearlite steels, the procedure was advanced to construct the linear section of the diagram based on the results of low-cycle fatigue tests with plotting the stress amplitude vs. plastic strain amplitude curve. The procedure was approved on 10GN2MFA steel at 20 and 270°C and SAE-1020 and API5L X60 steels taken from the literature. In view of data scattering for cyclic fracture toughness test results, the estimation of the linear diagram sections is quite adequate, and the procedure of their construction is appropriate and can be extended to other classes of the materials and stress ratios.

Experimental and finite element analysis of a damaged API5L X52 pipeline with longitudinal crack repaired by adhesively bonded metallic patch

An alternative of repairment by means of Lord DC-80 adhesive and metallic patch on two API5L-X52 pipes steel with 10 mm in thickness, 122 mm outside diameter and 750 mm length, which were damaged by mechanically longitudinal crack with 5 mm depth is presented. Repaired pipes were submitted to pressure testing (0.68–9.8 MPa) and 3D-FEM was used to calculate the Von Mises stress and strain. Results indicated that measured strain was smaller than the allowed strain, then no yielding occurred. Pressure tests revealed that leakage occurred at 9.8 MPa, where seals failed but not the pipe or repaired assembly. FEM results showed that the adhesive served to join the steel patch and pipeline, which operated as a component that lead to lower stresses regarding to the internal pressure in pipeline. The Von Mises stress values increased with the increment of pressure resulting that for 9.8 MPa, the greatest stress was reached at both edges of the API-X52 piping, followed by metallic patch and finally, the adhesive with the lowest values. Cracked pipelines within the analyzed dimension sizes did not present integrity problems and it did not fail. This kind of repairment could be safely used for pipes that present external defects.

Experimental and theoretical study on the corrosion inhibition of API 5L X52 steel in acid media by a new quinazoline derivative

For the first time, the synthesis, characterization, and electrochemical assessment as corrosion inhibitor of steel API 5L X52 immersed in 0.5 M HCl of the molecule 2-bromo-6(2′,6′-dichlorophenyl) dihydrobenzo [4, 5] imidazo [1,2c] quinazoline, 2Br2′,6′diClDHBIQz is reported. To evaluate the corrosion inhibition efficiency, IE, of this synthesized compound the following were assessed: inhibitor concentration, temperature, hydrodynamic conditions and steel exposure time to the corrosive medium. At 25 °C, EIS indicated the IE increased to 92.7% having added 15 ppm (0.03 mM) concentration, remaining practically constant (91.9 ± 0.78) % in the whole electrode angular speeds range considered; IE values higher than 85%, were attained even after 280 h acid exposure in stagnant conditions. SEM and AFM images revealed the steel-protective capacity of 2Br2′,6′diClDHBIQz while XPS analysis proved its presence onto the steel surfaces. The theoretical results are in complete agreement with the experimental XPS analyses.

Correction to: Fatigue Behavior of Welded API 5L X70 Steel Used in Pipelines

Correction to: Fatigue Behavior of Welded API 5L X70 Steel Used in Pipelines

Bacterial community analysis of biofilm on API 5LX carbon steel in an oil reservoir environment.

This study aimed to characterize the biofilm microbial community that causes corrosion of API 5LX carbon steel. API 5LX carbon steel coupons were incubated with raw produced water collected from two oil reservoir stations or filter-sterilized produced water. Biofilm 16S rRNA amplicon sequencing revealed that the bacterial community present in the biofilm was dominated by Proteobacteria, including Marinobacter hydrocarbonoclaustics and Marinobacter alkaliphilus. Electrochemical analysis such as impedance and polarization results indicated that Proteobacteria biofilm accelerated corrosion by ~ twofold (2.1 ± 0.61mm/years) or ~ fourfold (~ 3.7 ± 0.42mm/years) when compared to the control treatment (0.95 ± 0.1mm/years). Scanning electron and atomic force microscopy revealed the presence of a thick biofilm and pitting corrosion. X-ray diffraction revealed higher amounts of the corrosion products Fe2O3, γ-FeOOH, and α-FeOOH, and confirmed that the microbial biofilm strongly oxidized the iron and contributed to the acceleration of corrosion of carbon metal API 5LX.

Effect of Accelerated Cooling Rate and Finish Rolling Temperature on the Occurrence of Arrowhead Markings in Drop-Weight Tear Test of API 5LX70 Linepipe Nb–V–Ti Steel Plate

Four Nb–V–Ti steel plates of API 5LX70 linepipe were produced with changing accelerated cooling rate and finish rolling temperature using thermomechanical controlled process. The changes in ductile fracture surface, brittle fracture surfaces, including initial cleavage fracture and inverse fracture, arrowhead marking surfaces, and delamination were investigated using drop-weight tear test at temperatures of 0 °C and − 10 °C. Based on the drop-weight tear test results, an increase in the accelerated cooling rate, resulting in an increase in the volume fraction of quasi polygonal ferrite, fine polygonal ferrite, and granular ferrite microstructures, increased the percentage of ductile fracture surface and decreased the percentage of brittle fracture surfaces. Moreover, a reduction in the finish rolling temperature led to similar changes in the ductile fracture surface and brittle fracture surfaces due to an increase in the volume fraction of aciculae ferrite. Arrowhead markings surfaces, caused by the presence of banded structures, their percentage was reduced by increasing the accelerated cooling rate and decreasing the finish rolling temperature at the temperature of 0 °C. Furthermore, as the accelerated cooling rate increased, the number, length, thickness, and depth of delaminations were reduced at temperatures of 0 °C and − 10 °C.

A COMPARISON OF DIFFERENT NUMERICAL APPROACHES FOR FSW WELDS OF API 5L - X80 STEEL

This contribution offers a study for two numerical approaches of FSW joints for the API 5L-X80 steel. The first one, a pure thermal model, takes into consideration the preponderant frictional force of the tool being in contact with the workpiece. The second model is a computational fluid dynamic approach, which involves determining experimental values for physical constants and observing its influence in viscous dissipation and strain rates of the material. Temperature and thermal history from the FSW processing were recorded and analyzed. The acquired data was provided from two different heat input conditions. In cases of previewing tool or workpiece local temperature, the pure thermal model is a sufficient suitable approach. Conversely, the CFD model frequently requires huge amounts of information, regarding physical constants and experimental variables, becoming a delicate task for its construction. The pure thermal model was able to offer unequivocal temperature results without the need for large experimental data acquisition. This approach was considered to be finer employed when one aims to forecast temperatures in regions proximate to the welding line. The natural complexity associated with FSW processing suggests there are enormous quantities of experimental factors to be considered for the numerical modeling of high-temperature materials. Also, the CFD approach offers distinct results, which might be crucial for understanding the full aspects of experimental variables. A coupled numerical approach with both models is suggested to fully represent the thermophysical aspects of FSW processing.

Finite element modeling of HIC propagation in pipeline steel with regard to experimental observations

In this research, hydrogen induced cracking (HIC) phenomenon in pipeline steel has been investigated by finite element modeling (FEM) with the help of experimental observations. Abaqus software has been utilized to model the crack. To this, first an API 5L X70 pipeline steel was electrochemically charged by hydrogen for 8 h to create different types of HIC cracks. Then, SEM was used to observe different types of hydrogen cracks. Based on the observations, most of HIC cracks were observed at the center of cross section where center segregation of some elements occurred. The results showed that HIC cracks propagated in stepwise, sinusoidal, straight and disordered manner. Moreover, HIC crack nucleated from a point with high stress concentration factor which was between non-metallic inclusion or void and metal matrix. The initiated micro-cracks from two neighbor inclusions link together to form a long HIC crack. Based on the experimental observations and FEM modeling, it was concluded that the driving force for the HIC crack propagation is the presence of hydrogen at the crack tip after it is initiated. Crack tip usually acts as a very small void and the combination of hydrogen atoms makes a high pressure which propel the crack forward. Moreover, the HIC crack propagation path was predicted by fracture mechanics approach showing that the J-integral had its maximum amount when the HIC crack tended to propagate horizontally.

External surface cracked offshore steel pipes reinforced with composite repair system subjected to cyclic bending: An experimental investigation

In this paper, we experimentally studied the external surface crack growth in steel pipes reinforced with Composite System Repaired (CRS). CRS reinforced surface cracked API 5L X65 pipes were tested, containing three initial notch sizes and four reinforcement schemes. During the tests, the crack growth results, as well as the strain on the external mid-bottom composite laminate around the cracked area, and the vertical deflection of the specimens were recorded. The results showed that within the surface crack growth stage, the composite laminates were adequately bonded on the steel substrate, which significantly decreased the crack growth rate and prolonged the residual fatigue life. In addition, CRS reinforcement has increased the stiffness of the surface cracked pipes. Through the analysis on applying different reinforcement schemes, we indicated that increasing the amount of composite layers evidently facilitated the reinforcement effectiveness, while increasing the bond length did not; and the inversely diagonal wrapping pattern performance less effective.

Enhanced corrosion inhibition of carbon steel in HCl solution by a newly synthesized hydrazone derivative: Mechanism exploration from electrochemical, XPS, and computational studies

The corrosion inhibition properties of a synthesized hydrazone derivative namely, 1-(4-isopropyl phenyl) -2- (2,4-dinitrophenyl) (HYD (iso)) on API 5L-X60 carbon steel (CS) in 1.0 M HCl solution were evaluated by chemical, electrochemical, X-ray photoelectron spectroscopy (XPS) and theoretical studies. The obtained results revealed that the tested compound acted as a good corrosion inhibitor with inhibition efficiency of 96.32% at a concentration of 5 × 10−3 M. The polarization technique indicated that the HYD (iso) belonged to mixed-type inhibitors, preventing simultaneously anodic and cathodic reactions. The binding between the HYD (iso)'s molecule and CS surface follows a Langmuir adsorption type model and its inhibition mechanism is assisted by physical and chemical interactions. Scanning electron microscope (SEM) and contact angle analyses were performed to examine the surface morphology of inhibited and uninhibited samples. Additionally, theoretical studies using Density Functional Theory (DFT) and molecular dynamics (MD) simulation were performed to explore the most reactive sites of the hydrazone molecule and its adsorption mechanism.

Effect of Cooling Rate and Finish Rolling Temperature on Structure and Strength of API 5LX70 Linepipe Steel Plate

The present study has investigated the effect of changes in accelerated cooling (ACC) and finish rolling temperature (FRT) on the mechanical properties of high-strength low-alloy (HSLA) Nb-V-Ti steel plate of non-sour API 5LX70 linepipe during the thermomechanical controlled process (TMCP). Tensile test results showed that increasing ACC or reducing FRT enhanced yield and tensile strengths of the subject steel, which was also confirmed by the Vickers hardness test. Microstructure examinations demonstrated that increasing ACC and reducing FRT resulted in a lower volume fraction and a finer size of pearlite. Moreover, an increase in the ACC enhanced the formation of granular ferrite (GF) and fine polygonal ferrite (FPF), while a decrease in the FRT mostly affected the formation of acicular ferrite (AF). In all microstructures, banded structures and particles with a size of approximately 6 μm were observed due to segregation during solidification, where changing the parameters did not affect their formations.

Comparative Study of Microstructure and Mechanical Properties of X80 SAW Welds Prepared Using Different Wires and Heat Inputs

The present work investigated the effect of weld composition and welding heat input on the microstructure and mechanical properties of two submerged arc welded (SAW) joints of API 5L-X80 pipeline steel. The weld metals were joined by two welding consumables (one is rich in C, Ni, Cr, Mo) under different welding heat inputs (20-22 and 34-36 kJ/cm for single-wire and triple-wire processes, respectively). The triple-wire welding procedure with less C, Ni, Cr, Mo alloy contents favors the formation of acicular ferrite (AF), whereas single-wire welding procedure with increased C, Ni, Cr, Mo contents promotes the formation of lath bainite (LB). Nanoindentation is used to evaluate the property of different microstructures. The hardness of lath bainite (LB), granular bainite (GB) and acicular ferrite (AF) is 8.0 GPa, 5.8 GPa and 3.0 GPa, respectively. The Charpy impact energy of weld metal with triple-wire welding procedure (136-165 J) is much greater than that with single-wire welding procedure (15-44 J) at − 45 °C. Larger cleavage facet size is observed in the fracture surface of single-wire weld metal. A computational procedure is developed to understand the temperature fields during the triple-wire welding. Combining the experiments and numerical simulation, simple models to predict the microstructure evolution through the weld thickness are established.

Study on inner corrosion behavior of high strength product oil pipelines

Pipeline transportation is one of the five major modes of transportation. Inner corrosion problems in product oil pipelines are widespread but have not received attention, and high strength product oil pipelines are rarely used in China. In this paper, morphology and composition analysis and electrochemical methods were used to study the corrosion behaviors and characteristics of API 5L X65, X70 and X80 steel product oil pipelines. The feasibility of using high strength product oil pipelines in the transportation environment of product oil under the condition of inner corrosion is discussed, and the support for the safe operation of product oil pipelines is provided. The research results show that X80 pipeline steel has advantages over X65 and X70 pipeline steel. In the simulated liquid system of sediments in product oil pipeline, as the immersion time increases, the corrosion rate of X65, X70 and X80 pipeline steels shows a trend from high to low. Morphological analysis and electrochemical analysis showed that X80 pipeline steel showed better performance and adaptability to the environment, and its aerobic corrosion reaction was slower than that of X65 and X70 pipeline steel. X-ray photoelectron spectroscopy (XPS) results show that the three pipeline steels have the same corrosion mechanism, and all of them form Fe2O3, FeOOH, FeCO3, and FeS. The corrosion process is similar but the speed is different. This is attributed to the more corrosion-resistant trace elements in the X80 pipeline steel composition and the structure more compact. The application of high strength API 5L X80 steel in the product oil pipeline is still in its infancy, and it will be more practical to accelerate the development of API 5L X80 steel to make it more applicable to the construction of product oil pipelines.

Burst capacity of pipe under corrosion defects and repaired with thermosetting liner

This paper aims at providing insights on the use of thermosetting liner for the repair of offshore pipelines exposed to corrosion and leakage. The work which covers both experimental and numerical approaches were aspired due to the high cost of repair for pipelines, limitations of thermoplastic material and limited study of reinforced thermosetting liner. The experiment involves a destruction test called the burst test, carried out on an API 5L X42 carbon steel pipe under four case studies, namely (i) intact pipe, (ii) pipe with corrosion defect, (iii) pipe with corrosion defect and repaired with thermosetting liner and (iv) pipe with leakage and repaired with thermosetting liner. The numerical simulation was developed to first validate the experimental results and later to optimize the design of the thermosetting liner in terms of the number of layers required to restore the original strength of the pipe. The burst test shows an improvement in 23% of the burst capacity for the pipe with corrosion defects, after being repaired with a three-layer thermosetting liner. The parametric studies conducted showed that with an addition of thermosetting layers, the burst capacity improves by an average of 1.85 MPa. In conclusions, the improvement in strength can be further increased with increasing thickness of the thermosetting liner. The thermosetting liner was also determined to fail first inside the host pipe.

Investigation of the hydrogen induced cracking behaviour of API 5L X65 pipeline steel

The effect of microstructural features on the hydrogen induced cracking (HIC) susceptibility of two API 5L X65 pipeline steels were investigated by cathodic charging, hydrogen permeation and hydrogen microprint experiments. Microstructural evaluation after hydrogen charging revealed cracks at the mid-thickness (segregation zone) of both plates. However, more severe cracks were observed in the plate with higher dislocation density and residual stresses. The plate with lower plastic strain and more {111}-oriented grains had less severe cracks. Inclusions found along the crack path, comprising of Si-enriched oxides and carbides contributed to the initiation and propagation of cracks. The variation of the trapping behaviour and hydrogen diffusion through the plates were examined. The results confirmed that a higher ratio of reversible to irreversible traps contributes to increasing HIC severity in steels. Additionally, hydrogen transport through the steels was most prominent along the grain boundaries, indicating the importance of grain boundary character to HIC.