Showing 12 results for Api X65 Steel
Vahid Asghari, Naghdali Choupani, Mehdi Hanifi,
Volume 16, Issue 11 (1-2017)
Abstract
Structuralintegrity assessments of pipelines play a key role in the design and safe operation of pipeline systems. Gas pipelines currently experience internal transmission pressures up to 15 MPa in low ambient temperatures. Combination of high strength and good toughness is essential for the steels and welded joints used in pipelines. In this study, the KIC toughness has been determined for base metal and seam weld of a pipe of grade API X65, following the ASTM E1820 standard. The API X65 steel is the most commonly used pipe material in Iran highpressure gas transportation pipelines. The fracture toughness tests employed sidegrooved and fatigue precracked compact tension specimens, extracted from the original pipe, to determine the crack growth resistance curves based upon the unloading compliance method using the single specimen technique. From these, KIC values of 302 MPam1/2 and 262 MPam1/2 were obtained for base metal and seam weld, respectively. These results produce toughness data which serve to evaluate and compare crack growth resistance of base metal and seam weld metal and to determine the critical sizes of acceptable cracks in pipelines.
Ali-Akbar Majidi, Sayyed Hashemi,
Volume 17, Issue 11 (1-2018)
Abstract
Fractography of drop weight tear test (DWTT) specimens has received great attention by researchers in recent years due to the complex fracture surface of this test specimen. In this research, macroscopic characteristics of fracture surface of spiral seam weld in API X65 pipeline steel are investigated for the first time using chevron-notched DWTT specimensTest specimens were machined from an actual steel pipe of API X65 grade with an outside diameter of 1219mm and wall thickness of 14.3mm. Then chevron notch of 5.1, 10 and 15mm depth was placed in the center of each specimen and test samples were fractured under dynamic loading of 7m/s. Fractography of the fracture surface of test specimen with 5.1mm notch depth (as typical of test samples) showed that cleavage flat fracture initiated from the notch root (where stress intensity factor was high). Cleavage fracture changed immediately to ductile shear fracture, deviated to one side of specimen and grew extensively in heat affected zone, and finally terminated in base metal. Delaminations were observed in shear fracture area almost parallel to crack growth direction. After that, shear lips and inverse fracture appeared in hammer impacted area. By calculating the percent shear area from standard formulations, it was found that test specimen had above 95% shear area, and ductile fracture was the dominant fracture mode implying the fitness of tested steel for application in high-pressure gas transportation pipelines.
H. Hashemi , S.h. Hashemi,
Volume 19, Issue 7 (7-2019)
Abstract
The API X65 steel (with a minimum yield strength of 65ksi equivalent to 448MPa) is one of the most common types of pipe steels in the transportation of natural gas in Iran. By studying the ductile and brittle fracture areas at the fracture surface of this steel, we can show the quality of this type of steel. In the present study, macroscopic fracture surface characteristics in three-point bending test specimen are studied (based on the geometry and standard notch of drop-weight tear test specimen). Test specimens were machined from an actual steel pipe of API X65 grade with an external diameter of 1219 mm (48 inches) and wall thickness of 14.3 mm. Due to the quasi-static test conditions and speed of the machine's jaw (0.1 mm/s), the test was carried out on base metal specimens with machine chevron notch of 15, 10, and 5.1 mm depth, respectively, that was controlled with changing location. By applying the test load, cracking initiated from the notch root in each specimen and continued without crack specimen (ligament). At the end of the test, test specimens were cooled by liquid nitrogen and were broken in a brittle manner. In this paper, after investigation of the failure mode and the crack expansion in the standard specimen, investigation of macroscopic fracture surface characteristics was conducted by optical microscopy. By observing the fracture surface, different features such as thickness variation, shear regions (ductile fracture), cleavage fracture, shear lips, inverse fracture, and brittle fracture were studied. Having above 85% shear area, the ductile fracture of specimen was confirmed.
E. Fathi-Asgarabad, S.h. Hashemi,
Volume 20, Issue 5 (5-2020)
Abstract
One of the most important purposes of the drop weight tear test (DWTT) is to achieve the value of fracture energy for better evaluation of tested steel properties. In the present research, experimental and numerical measurement of fracture energy in drop weight tear test specimen with chevron notch on API X65 steel has been carried out. The purpose of the determination of this energy is to estimate the strength of material due to fracture. The test specimen was cut from an actual spiral seam welded steel pipe of API X65 grade with an outside diameter of 1219mm and wall thickness of 14.3mm and then it has been machined to standard size. Then chevron notch with a length of 5.1 was placed in the middle of the specimen and the specimen was fractured under dynamic loading with an initial impact velocity of 6.3m/s. The maximum force of 229kN and 225kN were achieved for experimental and numerical data, respectively by drawing force-displacement and energy-displacement curves. The fracture energy of the test sample for experimental and numerical data was obtained as 7085J and 6800J, respectively by evaluation of the area under the force-displacement curve. Based on the results of experimental curves, about %59 of fracture energy was used for crack propagation and the remaining was used for crack initiation and plastic deformation of test sample near anvils and striker regions. In the end, drawing a linear curve for fracture energy of specimen based on the hammer velocity showed that the slope of this curve could be a good criterion for estimating the energy loss and fracture behavior of the test specimen.
S.s. Mohitzadeh, S.h. Hashemi,
Volume 20, Issue 9 (9-2020)
Abstract
In this study investigated the effects of momentum variations on fracture energy in Charpy impact testing of API X65 steel by experimental and numerical methods. Experimental analysis was conducted in the various speed of impact about 3.50 to 5.72 m/s and impact energy varied about 450 to 1200 J. The experimental results showed that increase of about 63% in impact speed increased the fracture energy about 15%, because of material properties dependence on loading rate. Numeral studies were performed in two categories with ABAQUS software. First mass variation in constant velocity assumed standard quantity about 5.5 m/s in which impact energy varied about 300 to 1200 J and the second, velocity variation with constant mass assumed 50 kg that impact energy varied about 625 to 1600 J. The simulation results showed the variations in mass had not any effect in fracture energy and in all analyses, it was about 265 J. However, increasing the velocity variations with constant mass, caused a slight reduction of about 5% in the fracture energy. The reason for the difference between experimental and numerical results is the lack of consideration of the effect of strain rate on mechanical properties of tested steel in numerical analysis.
H. Hashemi, S.h. Hashemi,
Volume 20, Issue 9 (9-2020)
Abstract
Because of the inherent structure of welded pipelines, the seam weld can be a potential source for initiation and propagation of crack that can eventually lead to failure of the structure. Due to the critical conditions in the welding region, the investigation of failure energy in gas transportation pipeline is very important for engineers and line designers. In this paper, the three-point bending test (according to the standard specimen of drop-weight tear test) was performed quasi-statically on the seam weld pipe and base metal of spiral seam weld pipe of API X65 steel from which force diagrams were extracted. The presence of sudden load drops in the force-displacement diagram of the specimen in the weld indicated the inhomogeneous structure of the weld. The diagrams of force-displacement, yield and ultimate force, amount of steady crack growth and fracture energy of the metal and seam weld specimens including initiation and propagation energy of crack were investigated and compared. Also, the ratio of the force drop to the ultimate force at the same displacement rate was investigated. The results showed that in seam weld compared to the base metal specimen, the yield force was higher and the ultimate force, the amount of steady crack, initiation and propagation energy of crack were lower. In addition, the lower ratio of force to ultimate force (at the same displacement) in the base metal also indicated a high resistance of the base to the crack propagation.
M. Tazimi, S.h. Hashemi, S. Rahnama,
Volume 20, Issue 10 (10-2020)
Abstract
In this study for the first time, changes in the thickness of the fracture cross-section of the inhomogeneous sample (with horizontal weld seam) of the API X65 steel, using drop weight tear test specimen have been investigated experimentally. The fracture surface of the test specimen consisted of three zones of base metal, heat affected zone and weld metal with different microstructure and mechanical properties. The most thickness reduction was in the cleavage fracture area of the notch root. In the base metal zone, thickness changes were constant which indicated the stable crack growth in this area. In both heat affected zones before and after the weld zone, the thickness changed with a constant slope. Due to the high hardness and low fracture energy of the weld zone, the lowest percentage of thickness changes was in this zone. Thickness in the weld zone increased with a constant slope due to the stretching of the weld zone to the end of the crack growth path by the force caused by the change of fracture mode from tensile to shear. Also in the reverse fracture zone, due to the increased in compressive strain caused by impact of the hammer on the sample, the thickness increases with a significant slope and reached the maximum value.
Hamed Khosravi Khor, Sayyed Hashemi, Mahdi Raghebi,
Volume 20, Issue 12 (11-2020)
Abstract
The purpose of this paper is to experimentally investigate the natural frequencies of notched homogeneous and inhomogeneous specimen made from API X65 steel. The specimens cut from spiral welded pipe, tested on an equipped low blow drop weight tester with accelerometer. The tests were performed according to the API 5L standard. The homogeneous specimen was seamless and included only the base metal, while the inhomogeneous specimen included the weld seam and three zones of base metal, heat affected zone and weld. In the present study the specimens were subjected to hammer low blow in the middle without plastic deformation. The laboratory data (voltage-time) were transferred from time to frequency domain using Fourier transformation and the imposed oscillations were removed from the frequency signal by the Butterworth low pass filter. As the hammer drop height increased, the natural frequency in the specimens was almost constant. The natural frequency in the inhomogeneous specimen was less than the homogeneous specimen. Having information about the natural frequency, it is possible to prevent the destructive phenomenon of resonance in the main test (complete fracture of the specimen). Also, using the results of equipped low blow drop weight test and knowing the natural frequency, the dynamic stress intensity factor of the test specimen can be determined.
Mojtaba Shojaeddin, Sayyed Hashemi, Ali Akbar Majidi-Jirandehi,
Volume 22, Issue 6 (5-2022)
Abstract
To use higher capacities in Iran's energy transmission systems, API standardized pipes made of API X65 steel have been utilized (made of thermo-mechanically controlled rolling process, TMCR steels). The TMCR inherently increases the anisotropic properties of steel coils and plates used for pipe manufacturing. In addition, the production of helical welded pipe involves steps that can lead to different mechanical properties in different directions. The aim of the present study is to measure the orientation dependence of the Charpy fracture energy. Therefore, the effect of changing the angle of specimens relative to the rolling direction and also the effect of changing the notch orientation (three notch A, B and C in total) on the fracture energy in API X65 steel has been experimentally determined. The maximum change in the average Charpy fracture energy at different angles relative to the rolling direction is a maximum of 13% (in notch B), but the largest change in the average Charpy fracture energy between different notches is a maximum of 12.2% (at an angle of 0 °). As a result, the effect of changing the angle of the specimen relative to the rolling direction is greater than the effect of changing the notch orientation on the Charpy fracture energy. Also, at an angle of 67.5 degrees to the direction of rolling (equivalent to the diagonal direction (D-D)), the most fracture energy for all notches was obtained. To quantitatively compare the fracture energy changes in different notches, an index called anisotropy index has been presented
Mohammad Tavid, Sayyed Hashemi,
Volume 23, Issue 1 (12-2022)
Abstract
Fatigue failure is the most common type of failure in structures under oscillatory loading. Fatigue damage in steel gas pipelines is very important due to internal pressure fluctuation. A large part of pipelines in oil and gas industry of Iran are made of thermomechanical steel of grade API X65, made by spiral submerged arc welding. In this study, the stress-life curve and fatigue limit of the spiral weld seam of this steel are determined by fatigue tests. For this purpose, 20 test specimens (12 specimens used in the limited fatigue life zone and 8 specimens used to estimate fatigue strength) according to ISO 1143 standard. All test samples were cut from an actual spirally welded pipe with 1219mm outside diameter and 14.3 mm wall thickness and were tested on a completely reverse rotating-bending fatigue machine. Statistical analysis of the results was performed by considering the normal logarithmic distribution. Mean curve, confidence interval, and characteristic curve of the results were obtained in the finite fatigue life range using Basquin fatigue model according to ISO 12107 and ASTM E-739 standards. In the fatigue resistance range ISO 12107 standard was used. The mean endurance limit of the seam weld of the tested steel was 258.5 MPa which is located in the conventional range of 0.4 to 0.6 of the ultimate tensile strength of this steel.
Soroush Gholami Moghaddam, Sayyed Hashemi,
Volume 23, Issue 2 (1-2023)
Abstract
The critical Crack Tip Opening Angle (CTOAc) is considered as a convenient parameter to characterize the crack arrest toughness of natural gas pipeline. Load-displacement curve is a comprehensive reflection of geometry, mechanical property and fracture behavior of a loaded specimen, so it would be highly advantageous to deduce (CTOAc) from load-displacement curve directly. From force-displacement curves, maximum force of 209kN and 207kN were obtained for experimental and numerical data, respectively. In this article, a combination of load-displacement and deformation of the drop weight tear test specimen was used to calculate the critical crack tip opening angle. For this purpose, the simplified single-specimen test method was used. The (CTOAc) is dependent on the slope of the steady-state crack growth region and the plastic rotation factor. Firstly, based on the fact that load decreases linearly with the increment of displacement during steady-state crack growth, the slope of the experimental load-displacement curve of API X65 steel in the steady-state crack growth region was obtained as 21.583. Secondly, by modeling the drop weight tear test in Abaqus software and using two methods of mises stress and neutral axis, the plastic rotation factor was obtained as 0.5688 and 0.5651, respectively. Finally, these
parameters were used and the critical crack tip opening angle was determined as 12.00 and 12.08 degrees.
Mohammad Tavid, Sayyed Hashemi,
Volume 24, Issue 5 (4-2024)
Abstract
Thermomechanical steels are widely used in oil and gas pipelines due to their high toughness and high resitance against crak growth. A large part of the steel pipelines used in the oil and gas industry in Iran is made of API X65 steel. The fluctuations of internal gas pressure in steel pipes can cause fatigue failure and lead to gas leakage and explosion. So, the control of damage initiation and structural integrity of gas pipelines is of great importance. In this study, the S-N curve and the fatigue strength of the base metal of the API X65 steel were estimated by performing fatigue tests. For this purpose, 24 and 25 test specimens along the seam weld in the coil transverse direction, and perpendicular to the seam weld along the coil rolling direction were prepared according to ISO 1143 standard, respectively. All test samples were cut from an spirally welded pipe with 1219mm outside diameter and 14.3mm wall thickness and were tested on a completely reverse rotating-bending fatigue machine. Statistical analysis of the results was performed by considering the normal logarithmic distribution. The mean curve, characteristic curve, and confidence interval of the results were obtained both in the finite fatigue life range and in the fatigue resistance. The mean endurance limit of the base metal perpendicular to and parallel to the seam seam were 305 and 291 MPa, respectively which were in the range of 0.4 to 0.6 of material tensile strength and above the seam weld endurance limit (258 MPa).
