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Types of Corrosion in the Offshore Environment
Published in Karan Sotoodeh, Coating Application for Piping, Valves and Actuators in Offshore Oil and Gas Industry, 2023
The diffusion of the hydrogen into the grain boundaries causes material failure according to two mechanisms and theories; the first is called hydrogen embrittlement local plasticity (HELP) and the second is hydrogen enhancement de-cohesion (HEDC). According to HELP theory, hydrogen atoms are diffused into the void spaces between metal grains and bond together there. The atomic hydrogen causes dislocation in specific metal grains and plastic deformation, which eventually causes a crack in the material. Plastic deformation refers to permanent change in the shape of a material. In HEDC theory, hydrogen enlarges the atoms and molecules, which can then be fractured more easily by the application of stress. According to hydrogen cracking or embrittlement theory, materials with fine grins are at a lower risk of hydrogen attack compared to metals with coarse grains. One proven fact is that the susceptibility of a material to HISC corrosion is higher when the grains are perpendicular to the stress.
Mechanical Properties of Metals and Alloys
Published in Yip-Wah Chung, Monica Kapoor, Introduction to Materials Science and Engineering, 2022
At sufficiently small strains, the deformation is elastic, i.e., the specimen dimension returns to its original value upon removal of the applied stress. For most materials under these conditions of elastic deformation, stress is proportional to strain, as shown in Figure 4.2b. The slope of the straight line is known as the elastic or Young’s modulus E, i.e., E = σ/ε for small ε.
Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Pressure is the force applied per unit area on a body. Stress is the force acting per unit cross-sectional area on a body, tending to cause its deformation. Strain is the ratio of change in dimension of a body (e.g., change in length) to its original dimension (original length). The ratio of stress applied to a material to the strain induced in it is called the elastic modulus (E) of the material.
Microstructure, mechanical properties and corrosion fatigue behaviour of biodegradable Mg–Zn–Y–Nd alloy prepared by double extrusion
Published in Corrosion Engineering, Science and Technology, 2021
Jinming Wang, Jun Wang, Qinyuan Fu, Kun Sheng, Mengyao Liu, Yufeng Sun, Di Mei, Yage Kou, Shijie Zhu, Shaokang Guan
Tensile tests were conducted on an MTS machine (Bionix 370.2) with a tensile rate of 0.5 mm min−1 at ambient temperature. The dog-bone samples with the gauge length of 20 mm and the diameter of 5 mm were used in the tests (Figure 2). The stress corresponding to 0.2% plastic deformation is taken as the yield strength. After tensile tests, the fractured surfaces were observed using a scanning electron microscope (SEM; FEI Quanta 200). Vickers hardness (HV) tests were performed using a microhardness tester (HXD-1000TMSC/LCD) with a load of 200 g and a dwell time of 10 s. The bulk samples with the length of 10 mm, the width of 8 mm and the height of 8 mm were used in the tests, and the values of HV were shown using the average of ten points randomly selected on the surface of samples.
One-dimensional analytical model for thermo-hydro-mechanical coupling behaviour of hydrates overlying layer during gas production
Published in Marine Georesources & Geotechnology, 2021
Bin Zhu, Songqing Yang, Lujun Wang, Deqiong Kong
Figure 11 shows the influence of F on the variation of compression throughout the 20 production cycles. When pore pressure load applies only, the total soil expansion is nearly zero at the end of 20 cycles (see Figure 11(b)). This phenomenon is mainly due to a fast accumulation and dissipation cycle of EPP (see Figure 8(b,d)). Deformation develops and recovers in an elastic body. However, when thermal load is applied, the overlying layer shows considerable expansive deformation over time (see Figure 11(a)). It shows that temperature load is the dominant factor to determine the expansion of soil layer. In the first 10 cycles (t < 1200 h), the overall expansion of the overlying layer increases with the decrease in F. When F is equals to 0.08, the expansion during the last 10 cycles (t > 1200 h) tends to diminish, and the soil expansion tends to stabilize. With greater permeability, the accumulation rate of thermal-induced pore pressure is close to the dissipation rate so that the expansion rate is somewhat alleviated. To sum up, during the gas production stage, the accumulation rate of EPP in the overlying layer is greater than the dissipation rate. Thus, the EPP accumulation was mainly induced by gas hydrate dissociation, whereas the expansion was mainly caused by the temperature load in the huff-and-puff processes.
Special issue on ‘coupled dynamic analysis of floating structures with concept technologies: current status and emerging future trends’
Published in Ships and Offshore Structures, 2019
R. Sharma, S. K. Bhattacharyya, Tae-wan Kim
Fourth article is: Deformation and stress distribution of floating collar of net cage in steady current by Yun-Peng Zhao, Xiao-Dong Bai, Guo-Hai Dong and Chun-Wei Bi. Stress expresses the internal forces that the neighbouring particles of a material exert on each other when a force is applied. Similarly, the strain is the measure of the deformation. In this paper, the authors present a numerical model to investigate the deformations and stress distribution of floating pipes of fish cage subjected to the flow. They use a combinatorial approach that combines the FEM with hydrodynamic model. The presented model is validated through comparison with the data obtained from corresponding physical model tests and the results show fair agreement. On this paper, we note that there is an important but relatively unexplored area of the fishing crafts, nets and cages; and these are to be studied at high craft’s speed, current speed and different weather conditions. More studies on these structures will allow the design and development of efficient crafts, nets and cages and these will serve a large fishing community improving their lives and livelihood.