Calculation and analysis of the first interface micro-gaps of the thermal production wells

Heavy oil is an important oil resource. The main development method is thermal exploitation—steam stimulation. Drastic variation in temperature will result in thermally induced micro-gaps in the first interface during steam stimulation. The existence of micro-gaps will cause steam channeling in the hole and difficulty in engineering logging interpretation. According to the stress of casing string of thermal production wells and thermal injection model, the mechanical model of casing string of thermal production wells is divided into four intervals for further analysis, including the wellhead movement extension interval, the extension and compression movement interval between low-temperature zones, the packer movement interval, and the extension and compression movement interval between perforation sections. For different casing string intervals, two types of mathematical models of first interface micro-gap width are established. In order to comprehensively evaluate the micro-gaps, the mathematical model comprehensively evaluating cement sheath micro-gaps is established through superposition and geometric mean of two models. The models can be used to calculate the first interface micro-gap width of different intervals. In addition, the tri-strata axial symmetric finite element model of first interface with micro-gap is established, and the variation in temperature field, stress field, and width of micro-gap interval of wellbore is analyzed, which provides the theoretical basis for evaluation of micro-gaps.

Arbitrary Lagrangian–Eulerian simulations of highly electrically charged micro-droplet Coulomb explosion deformation pathways

Numerical simulation results of the Coulomb explosion pathways of cooled water and heated glycol droplets electrically charged to the critical Rayleigh limit are presented, calculated using an axi-symmetric finite element scheme previously used for the same problem [Radcliffe A. J., Non-conforming finite elements for axisymmetric charged droplet deformation dynamics and Coulomb explosions, Int. J. Num. Meth. Fluids 71:249–268, (2013), doi:10.1002/fld.3667.] which has been adapted to use arbitrary Lagrangian–Eulerian (ALE) methods and a novel tip reconstruction technique in order to greatly improve its accuracy in matching available experimental data.

Investigation of the Mandrel’s Stress States and Wear Conditions during Tube Hot Extrusion of IN690 Superalloy

A 2D axi-symmetric finite element model for tube hot extrusion process has been established by consideration of the billet transfer, glass lubrication, constitutive equation of IN690 superalloy and modified Archard wear model. The influence of extrusion process parameters on the stress state and wear conditions of the mandrel surface has been investigated. The results show that under the optimal extrusion process parameters of the extrusion speed of 250 mm/s, the friction factor of 0.05 and the billet preheating temperature of 1250 ̊C, the mandrel can be reused 200 times when it is fixed and 500 times when it moves with the ram.

Bolt Preload Reduction of Pipe Flange Connections After Plant Shutdown

When pipe flange connections clamped with sheet gaskets are subjected to thermal load, the bolt preloads that tighten a pair of pipe flanges tend to decrease. It has been studied in the previous paper why and how the bolt preloads decrease, in which the loading and unloading curves of sheet gaskets at elevated temperature are expressed by means of simple equations. Meanwhile, it is also known that the bolt preloads are likely to decrease when the plant is shut down. In this paper, a numerical procedure, which can predict the amounts of bolt preload reduction occurred in the shutdown process, is proposed using axi-symmetric finite element method (FEM). The analytical objects are pipe flange connections tightened with aramid sheet gaskets. In the finite element formulation, stress-strain curves of the gaskets after plant shutdown are approximated by simple curves, considering that the hysteresis appeared in the curves is considerably small, comparing to that between the loading and unloading curves in the running condition. It is shown that the bolt preloads are decreased by as much as from 40% to 50% of those in the running condition. The validity of the proposed numerical method is confirmed by comparing the numerical results of the bolt preload reduction to experimental ones.

Assessment of Lower Regions of Pressure Vessels Subjected to Corrosion Wall Thinning

Pressure vessels are common components of plant currently in operation within the nuclear industry and elsewhere. Their assessment and maintenance is of paramount importance to the integrity and safe working of the plant. Often these pressure vessels contain highly corrosive substances, which over time, cause deterioration in the integrity of the vessel. Current codes and standards such as BS7910, API579 and FITNET provide guidance on the assessment of cylinders and pipes with localised and general corrosion, but to date, no such guidance is available for complete vessels, where the corrosion occurs in the lower region of the vessel, e.g. where the base of a vessel is connected to the vessel wall. This paper investigates the resistance to plastic collapse, from internal pressure loading, of flat based cylindrical pressure vessels, where the base and wall thicknesses are considerably different due to corrosion damage. A ‘First Estimate’ or conservative lower bound collapse pressure solution for such vessels is described. The solution has been derived using axi-symmetric finite element models with varying degrees of general corrosion thinning.