In order to characterize the dynamic process of the crack growth in the weld of oil and gas pipelines, a mathematical model of fluid-solid-magnetic multifield coupling was constructed in this paper. Based on this model, the bidirectional fluid-solid coupling and unidirectional magnetic structure coupling caused by the weld deformation were achieved by dynamic application of the fluid permeation pressure, calculating the internal crack growth in the pipe weld, reconstructing the computational grid near the internal crack, and discussing the characteristics of the magnetic leakage field in the process of the internal crack growth in pipe weld. Thus, a fluid-solid-magnetic coupling algorithm for the internal crack growth in pipe welds considering fluid permeation pressure is established. According to the characteristics of the internal crack opening distance, internal crack growth length, crack tip energy release rate, peak values of magnetic induction intensity level, and vertical component, the process of the internal crack growth is measured. The results show that the fluid osmotic pressure accelerates the process of the internal crack growth and this algorithm can solve the problem of the characterization and evaluation of crack growth in pipe welds under fluid-solid-magnetic coupling action.
Based on fundamental theory of fracture mechanics and magnetic flux leakage using the virtual crack closure technique (VCCT) via the finite element modelling method, one type of magnetic-structural coupling algorithm which is suitable for single-and multi-crack growth will be proposed. Single-and multi-crack growth behaviour at different locations along circumferential and radial pipeline welds is also studied. After calculating crack incremental growth time with the above algorithm, the geometrical shape of cracks will be upgraded, the air mesh at the crack location is reconfigured. During expansion, automatic exertion of slight pressure increments of the load step, and crack growth calculation and magnetic field analysis will be also carried out iteratively. Six typical working conditions are applied as examples, of which the initial length lc is 2 mm. According to crack-opening distance, length of crack expansion, horizontal and vertical component peaks of magnetic induction intensity and other characteristic values describing crack growth, the damaged part and degree of damage to the pipeline weld was judged. Additionally, internal and external cracks, single and multiple pipeline cracks were also identified. The application of this algorithm can provide a theoretical basis for the research on crack growth of the pipeline weld.
In this report, jet pulse electrodeposition (JPED) was employed to deposit Ni–TiN nanocomposites on mild steel substrates. Effects of jet rate on cross-sectional composition distribution, microstructure, microhardness, and corrosion properties of the obtained nanocomposites were studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), microhardness testing, and electrochemistry. Results revealed the presence of high concentrations of Ni (54.7 at. %) and Ti (17.6 at. %) particles across throughout the thickness of composites prepared at 3 m/s. Nanocomposites prepared at 3 m/s exhibited uniform and smooth morphologies, with exiguous grains and an arithmetic mean roughness (Ra) of ∼23.61 nm. Also, nanocomposites prepared at 3 m/s showed smaller nickel grains than those obtained at 1 and 5 m/s. Icorr and Ecorr of Ni–TiN nanocomposites formed at 3 m/s were respectively minimum at 2.093 × 10−2 mA/cm2 and −0.462 V, confirming higher corrosion resistance. The microhardness values of Ni–TiN nanocomposites prepared at jet rates of 1, 3, and 5 m/s were respectively maximum at 751.5, 862.8, and 814.2 HV, respectively.
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