CALCULATION OF STRESSED-DEFORMED STATE OF THREE-LAYER PIPES OF SYMMETRIC AND ASYMMETRIC STRUCTURE

Objectives This article discusses the evaluation of the effectiveness of three-layer pipes of a symmetric and asymmetric structure. For this, the stress-strain state of three-layer pipes of different materials under the influence of internal pressure is investigated. Pipeline structures today occupy important positions in the infrastructures of many countries. Trunk structures affect the economy, industry. Every year, new safety requirements are added to the reliability indicators of these structures.Method The calculation is carried out by numerical methods, namely using the finite element method (FEM), implemented in the LIRA PC.Result The calculation of the pipes is performed, on the load from the transported medium, applied to the inner contour of the pipe. Moreover, for three-layer pipes of all variants, Nx tensile stresses along the generatrix, Ny ring tensile stresses and Txy shear stresses in the xy plane were determined. Isopoles of tensile and shear stresses are given.Conclusion The numerical results showed that the use of less deforming material as a material for the manufacture of asymmetric bearing layers leads to a redistribution of stresses in the bearing layers and aggregate, and this must be taken into account when designing three-layer pipes.

Research on Pipeline Damage Imaging Technology Based on Ultrasonic Guided Waves

Pipeline structures are important structural components that cannot be replaced in actual engineering applications. Damage to a pipeline structure will create substantial safety hazards and economic losses in a project. Therefore, it is extremely important to study damaged pipeline structures. In this paper, L(0,2) mode guided waves are used to identify, locate, and image single and double defects in straight pipe structures. For the case where there is a single defect in the straight pipe section, the influence of different excitation frequencies on the reflection coefficient of L(0,2) modal guided wave is studied, and the optimal excitation frequency of L(0,2) guided wave is 70 kHz when single damage is determined. For the case of double defects in the straight pipe section, the double-defect size, the distance between the defects, and the relative defect positions are studied, and the influence of the defect recognition effect is analyzed. The propagation path of the ultrasonic guided wave in the double-defect pipe section is analyzed. Finally, the effectiveness of the three-point axial positioning method and damage imaging method is verified by the single-defect tube segment ultrasonic guided wave flaw detection experiment.

Low-coherent fiber-optic interferometry for in situ monitoring the corrosion-induced expansion of pre-stressed concrete cylinder pipes

The corrosion-induced expansion of pre-stressed concrete cylinder pipes shapes a major determining factor in the durability of most pipeline systems. However, a structure extended in a very large span and accompanied by a slow corrosion-induced structural damage is still a challenge in practice. Here, a low-coherent fiber-optic interferometry is proposed for in situ measuring the corrosion-induced expansion by directly circling the sensing optical fiber on the outer surface of the pipe. Since the accuracy of the absolute deformation measurement by the low-coherent fiber-optic interferometry can reach 3–5 μm, we are able to improve the sensitivity by choosing the length of the sensing fiber. In the experiment, we employ 50-m sensing fiber; therefore, a resolution of about 0.1 microstrains had been approached. We chose 12 places along the pipeline as the corrosion-induced expansion monitoring points. On monitoring for about half a year, a non-uniform interface in structure, such as the repaired places, was found as a key factor of the corrosion-induced expansion development, which could be a reference for the further health care of the pipeline structures.

Numerical Simulations of Dynamic Pipeline-Vessel Response on a Deepwater S-Laying Vessel

The dynamic action induced on offshore pipelines by deepwater S-laying is significant, and directly determines how the pipeline structures are designed and installed. Existing research has not fully investigated the benefits of coupling models of pipeline and pipelaying vessel motions. Therefore, this paper presents a coupled time-domain numerical model for examining the effect of coupled dynamic reactions. The coupled model takes into account the motion of the pipelaying vessel, surface waves, ocean currents, wind forces, pipeline dynamics, and contact between the rollers and the pipeline. A proportional, integral, derivative (PID) controller was used for simulating the control of the pipelaying vessel. The hydrodynamic forces that the pipeline experiences were modeled using the Morison equation. The model was solved using Newmark’s method and verified using OrcaFlex software. The model was then used to analyze practical operations: the laying of a 22″ gas export pipeline on the seabed by the pipelaying vessel HYSY201 in the Pingbei-Huangyan gas fields in the East China Sea. The effects of coupled factors on pipelaying vessel motions and pipeline dynamics were approximated. These effects included configurations, axial tensions, and bending moments. The results show a significant connection between the dynamic responses of the pipelines and pipelaying vessel motions.