Tensile Deformation and Fracture Behavior of API-5L X70 Line Pipe Steel

Thermo-mechanical controlled processing (TMCP) is employed to obtain the required level of mechanical properties of contemporary HSLA steel plates utilized for gas and oil pipeline production. The strength and crack resistance of pipeline steels are mainly determined by its microstructure and crystallographic texture. In this study, the influence of the structural and textural states of industrially produced API-5L X70-X80 pipeline steels on tensile mechanical properties was analyzed. TMCP routes with different hot rolling temperatures and cooling rates were employed. The texture of steel was assessed using the Taylor factor, which was calculated based on electron backscatter diffraction (EBSD). The decrease in rolling temperature resulted in the sharper texture characterized by {001} planes banding (cleavage planes in the bcc lattice) parallel to rolling direction. The tensile deformation behavior at the stage of necking was determined by the crystallographic and morphological texture of the material and demonstrated significant anisotropy. Rupture of all investigated samples was accompanied by the development of splitting on the fracture surface. The splitting was localized in the rolling plane similar to the splitting in standard Charpy tests of pipeline steels.

The Microstructure and Mechanical Properties of Ferritic-Martensitic Steel EP-823 after High-Temperature Thermomechanical Treatment

The effect of high-temperature thermomechanical treatment (HTMT) with plastic deformation by rolling in austenitic region on the microstructure and mechanical properties of 12% chromium ferritic-martensitic steel EP-823 is investigated. The features of the grain and defect microstructure of steel are studied by Scanning Electron Microscopy with Electron Back-Scatter Diffraction (SEM EBSD) and Transmission Electron Microscopy (TEM). It is shown that HTMT leads to the formation of pancake structure with grains extended in the rolling direction and flattened in the rolling plane. The average sizes of martensitic packets and ferrite grains are approximately 1.5–2 times smaller compared to the corresponding values after traditional heat treatment (THT, which consists of normalization and tempering). The maximum grain size in the section parallel to the rolling plane increases up to more than 80 µm. HTMT leads to the formation of new sub-boundaries and a higher dislocation density. The fraction of low-angle misorientation boundaries reaches up to ≈68%, which exceeds the corresponding value after HTMT (55%). HTMT does not practically affect the carbide subsystem of steel. The mechanical properties are investigated by tensile tests in the temperature range 20–700 °C. It is shown that the values of the yield strength in this temperature range after HTMT increase relative to the corresponding values after THT. As a result of HTMT, the elongation decreases. A significant decrease is observed in the area of dynamic strain aging (DSA). The mechanisms of plastic deformation and strengthening of ferritic-martensitic steel under the high-temperature thermomechanical treatments are also discussed.

An Improved Dynamic Model of the Mecanum Wheel for Multibody Simulations

Mobile robots and autonomous guided vehicles have become an indispensable part of modern industrial environments and are used for a wide range of handling operations. To fully use the potential of mobile platforms, omnidirectional platforms are a good choice. A prominent and widely used variant in the industry are Mecanum wheels, which allow arbitrary movement in any direction in the plane. In most applications only the kinematics is considered, however, dynamic models that take the geometry of the rollers into account are still missing. In this paper two models for Mecanum wheels with different degrees of detail are derived. The detailed model considers the rollers as single bodies undergoing contact and friction with the rolling plane. As the wheel consists of multiple rollers, a complex contact situation with temporal overlapping and additional vibrations occurs. The simplified model reproduces the overall kinematics of the rollers with orthotropic friction and only one rigid body for the wheel, thereby being computationally more efficient. Both models are well suited to reproduce essential dynamic effects of a mobile robotic platform, which can not be described by the conventional kinematics model. We implement and compare both models with experimental results, showing the good performance of both models.

Grounding of Design and Technology Parameters of Combined Coulter Furrow Opener of Precision Seed Drill

A formation of a seedbed is an important step during seed sowing process. A quality of seedbed formation influences on seeds distribution along both a row and a depth and is triggering the opportunity to obtain early and even sprouts. The design of the furrow opener is the main element that has a direct impact on the qualitative formation of seedbed and technological parameters of coulter operation. During the research, there has been analyzed the modern construction of precision seed drills coulters and specified advantages and disadvantages of their operation. It has been established that the most advanced are coulters having a working section with a combined angle (sharp and obtuse) of entry into the soil. The attained results afforded to develop an improved design of the coulter furrow opener of the precision seed drill. There was brought forward a combined wedge furrow opener, the upper part of which has a working section with a sharp angle of entry into the soil, lower - and compactor, located in the rear part of the furrow opener, which forms seedbed has a working surface with an obtuse angle of entry into the soil. There were obtained analytical dependences targeted to determine the main structural and technological parameters of the operating elements of a combined coulter furrow opener which is used to seed cultivated crops: the angles of entry into the soil of the upper and lower part of the furrow opener, compactor in the rolling plane and the angle of tip of the furrow opener in the horizontal plane.

A Novel Test Design for Large Strain Uniaxial Reverse Loading of AZ31B Sheet Out of the Rolling Plane

Understanding a magnesium alloy sheet's response to load reversals is important to accurately simulate and optimize a component's manufacturing process. Through this research, the room temperature compression-tension and tension-compression experiments with strains up to ∼12% are performed on AZ31B-H24 sheet specimens along the normal direction of a 6.35 mm-thick sheet. Miniature specimens machined through thickness are tested using a novel setup designed for large strain reverse loading data generation where specimen size is limited. The reliability of the devised setup is verified by finite element simulation and by reproducing in-plane curves obtained via an anti-buckling fixture. A shot peening process involving prevailing through-thickness deformation is modeled and numerical results indicate that employing only in-plane properties of magnesium sheets for simulating such processes can lead to inaccurate predictions.

Остаточные напряжения в несущей ленте AISI 310S на этапе нанесения буферного слоя YSZ при изготовлении ВТСП-2 провода

Using neutron diffraction we determined internal residual stress in the stainless steel AISI 310S carrier tape with a thickness of 100 μm and a width of 4 mm after mechanical polishing and the ABAD deposition of the textured YSZ buffer layer. It is shown that mechanical polishing causes a slight distension of the tape in the rolling plane. After the deposition of the YSZ layer, uniform tensile stress of 70 MPa isotropic in the rolling plane was observed inside the tape. Calculations have shown that it results from relaxation of compressive stress acting on the surface of the tape in a layer several times thicker than the YSZ layer. It is assumed that the surface of the tape is plastically deformed during the YSZ deposition.

Separation Characteristics of an X65 Linepipe Steel From Laboratory-Scale to Full-Scale Fracture Tests

Separations are small fissures that form along the rolling-plane of some steels when sufficient stresses are created to open planes of weakness in the material. In the pipeline industry, separations have been observed on the fracture surfaces of tensile, Charpy, and drop-weight tear tests — the key tests for determining the fracture arrest capabilities of line pipe steels. When compared, the separation appearance between lab-scale tests and full-scale fracture test are noticeably dissimilar. Therefore, the influence separations have on the fracture behaviour may not clearly scale between lab-scale and full-scale tests. In this study, the separation severity of Charpy, DWTT, and full-fracture propagation test fracture surfaces was measured and compared. Two full-scale burst tests were carried out with pipes containing a CO2/N2 mixture. Fracture surfaces were observed along the length of the pipe and captured when the separation appearance changed. For each pipe section, the corresponding lab-scale test surfaces were compared. With the separations measured across all fracture faces, the separation appearance of the full-scale test surfaces did not provide the same values as the lab-scale tests. However, the lab-scale tests did capture the trend in separation severity for each pipe section. Only the lab-scale test surfaces showed a correlation in separation severity.

Исследование внутренних напряжений в несущей ленте-подложке из нержавеющей стали AISI 310S для ВТСП проводов второго поколения методом нейтронной стресс-дифрактометрии

The method of neutron stress diffractometry has been used to study a distribution of residual stresses in the stainless steel AISI 310S ribbon, of 100 μm thick and 4 mm wide, in three directions – along, across and perpendicular to rolling plane. The residual macro stresses averaged over the ribbon length of 40 cm are determined. The longitudinal, transverse and normal macro stresses are respectively –71±21 MPa, –31±16 MPa, and –11±16 MPa on one edge of the ribbon and +30±19 MPa, +64±16 MPa, and +30±16 MPa on the other edge. Such distribution of macro stresses compressing the ribbon on one edge and stretching it on the other edge is inherent for so-called crescent-shaped deformation of the ribbon – its bending in rolling plane along rolling direction. A correlation between the macro stresses magnitude and the micro stresses presence has been observed – the stronger macro stresses the higher concentration of micro stresses.

Stress Corrosion Cracks in Pipeline Steels

The demand for pipeline steels has increased in the last several decades since they were able to provide an immune and economical way to carry oil and natural gas over long distances. There are two important damage modes in pipeline steels including stress corrosion cracking (SCC) and hydrogen induced cracking (HIC). The SCC cracks are those cracks which are induced due to the combined effects of a corrosive environment and sustained tensile stress. The present review article is an attempt to highlight important factors affecting the SCC in pipeline steels. Based on a literature survey, it is concluded that many factors, such as microstructure of steel, residual stresses, chemical Composition of steel, applied load, alternating current (AC) current and texture, and grain boundary character affect the SCC crack initiation and propagation in pipeline steels. It is also found that crystallographic texture plays a key role in crack propagation. Grain boundaries associated with {111}//rolling plane, {110}//rolling plane, coincidence site lattice boundaries and low angle grain boundaries are recognized as crack resistant paths while grains with high angle grain boundaries provide easy path for the SCC intergranular crack propagation. Finally, the SCC resistance in pipeline steels is improved by modifying the microstructure of steel or controlling the texture and grain boundary character.

Effects of Different Parameters on Initiation and Propagation of Stress Corrosion Cracks in Pipeline Steels: A Review

The demand for pipeline steels has increased in the last several decades since they were able to provide an immune and economical way to carry oil and natural gas over long distances. There are two important damage modes in pipeline steels including stress corrosion cracking (SCC) and hydrogen induced cracking (HIC). The SCC cracks are those cracks which are induced due to the combined effects of a corrosive environment and sustained tensile stress. The present review article is an attempt to highlight important factors affecting the SCC in pipeline steels. Based on a literature survey, it is concluded that many factors, such as microstructure of steel, residual stresses, chemical composition of steel, applied load, alternating current (AC) current and texture, and grain boundary character affect the SCC crack initiation and propagation in pipeline steels. It is also found that crystallographic texture plays a key role in crack propagation. Grain boundaries associated with {111}∥rolling plane, {110}∥rolling plane, coincidence site lattice boundaries and low angle grain boundaries are recognized as crack resistant paths while grains with high angle grain boundaries provide easy path for the SCC intergranular crack propagation. Finally, the SCC resistance in pipeline steels is improved by modifying the microstructure of steel or controlling the texture and grain boundary character.