Abstract The corrosive nature of seawater poses significant challenges to the design of gas cylinders in marine environments. Currently, TC4 titanium-alloy cylinders are predominantly used because of their resistance; however, they are costly and challenging to manufacture. To address this issue, this study proposes employing TC4 titanium alloy liner carbon fiber composite cylinders, which can reduce the manufacturing cost and processing difficulty while ensuring excellent protection against seawater corrosion and fatigue resistance. The fatigue life of the cylinders was predicted and analyzed using the finite element method, and a prototype was manufactured for verification. The results show that the composite layer can effectively share the stress load for the liner under the working pressure cycle, which increases the fatigue life of the titanium alloy liner carbon fiber composite cylinders and provides strong support for their application in marine engineering.

Abstract With increasing wellbore depth, the environmental conditions become progressively more severe, characterized by elevated temperatures and pressures. Consequently, the pressure variations within the well induced by Tubing Conveyed Perforation (TCP) operations exhibit a more pronounced intensity. These nonlinear pressure fluctuations generate significant impact loads at the bottom of the perforating gun, which can cause failure of the perforating tubing. A transient nonlinear pressure field model of perforation explosion was established based on hydraulic-mechanical coupling to effectively control the risk of accidents. The model considers the effects of several hundred perforation charges and their precise placement in relation to blind holes, thus taking into account the impact of shot density. As a result, the model more accurately reflects actual field conditions. The study investigated the evolution of nonlinear pressure fields at different positions of the entire tubing under perforation explosion and analyzed the influence of different factors on nonlinear pressure fluctuations at the bottom of the perforating gun. The results showed that the peak pressure of the perforation section was much higher than that of the tubing section and the rathole section, maintaining at approximately 200 MPa. The pressure wave attenuated to the initial wellbore pressure of about 80 MPa only seven meters away from the perforation section center. The peak pressure at the bottom of the perforating gun was positively correlated with the initial wellbore pressure, perforating fluid density, shot density, and quantity of explosive. These results provided guidance for the prediction of TCP wellbore nonlinear pressure fluctuation.

Abstract This paper studies the response of ELBOW31 and ELBOW31B element types under pure bending conditions, using shell and beam element models for benchmarking. Various model lengths are evaluated, showing that a model length of six pipe diameters exhibits a hardening effect when total strain exceeds 3.5%, though a strain up to 1% is deemed sufficient for pipeline design. The study examines the effects of ovality modes and boundary conditions such as NOWARP and NOOVAL on the bending response. ELBOW31 with one or two ovality modes yields accurate results, while additional ovality modes or zero ovality mode can lead to overprediction of the elastic bending moment capacity. The introduction of the NOWARP condition enhances the accuracy of the ELBOW31 model, while the NOOVAL condition alone produces unrealistic results. The simplified ELBOW31B model shows good agreement with the ELBOW31-NOWARP model but similarly overpredicts the bending moment when zero ovality mode is used. The study also finds that Poisson's ratio and model length have no significant impact on the bending response when no restrictions are applied. Additional analyses, as presented in Appendices A and B, highlight the importance of D/t ratios in pipeline performance. A D/t ratio of 20 offers a stiffer response with reduced ovalization, while a D/t ratio of 50 results in greater flexibility and increased ovalization. These findings provide valuable insights for the selection of element types, boundary conditions, and D/t ratios in robust pipeline design.

Abstract To study the factors affecting the sealing performance of a Y-shaped sealing ring at the stem of a 140-MPa cage throttle valve under -46°25C and 180°C operating conditions, uniaxial tensile tests were conducted on polytetrafluoroethylene (PTFE) and its modified materials. Finite element simulation software was then used to perform a simulation study of the Y-shaped sealing ring. The finite element simulation software was used to perform a sensitivity analysis on the five most critical parameters of the Y-shaped sealing ring and to perform dimensional optimization by using the multi-island genetic algorithm. The results show that compared with 25°C, under a 180°C condition, the contact stress at both ends of the sealing lip decreases when the valve stem moves upward . Under the condition of -46°C, the contact stress at the sealing lip increases when the valve stem goes down, the contact stress at both ends of the sealing lip decreases when the valve stem goes up; and the impact of the stem movement speed on the maximum value of the Y-shaped sealing ring contact stress is small.The design dimensions that have the greatest influence on the maximum von Mises stress and the maximum contact stress of the inner lip of the Y-seal during stem movement are the width and the tip height of the lip, respectively. The optimum values of the design variables are determined and the feasibility of the theoretical design is verified by testing.

Abstract Failure Assessment Diagrams (FADs) constitute a well-known structural integrity evaluation tool that allows structural components containing crack-like defects to be assessed through a simultaneous analysis of fracture and plastic-collapse processes. FADs are included in the most recognized structural integrity assessment procedures/standards, such as BS7910 and API 579/ASME FFS-1, and their use is generally limited to metallic components containing crack-like defects. On the other hand, structural responsibilities are being assumed by 3D printed composites, and particularly by those obtained through FFF (Fused Filament Fabrication), beyond their most extended use as prototyping materials. The resulting structural components may contain notch-type defects (e.g., grooves, corners, holes, etc.) that determine their corresponding structural integrity. Thus, it is necessary to define structural integrity assessment criteria for this kind of materials when containing any kind of stress risers, beyond crack-like defects. This work justifies the use of BS7910 Level 1 FAD, coupled with a notch correction derived from the Theory of Critical Distances (TCD), to analyze graphene-reinforced PLA plates subjected to pure tensile loading conditions and containing U- and V-notches. The results reveal that, for U- and V-notches, the assessment points representing the plates at failure are located within the FAD area corresponding to unsafe conditions, providing conservative evaluations with moderate safety margins. For plates containing circular holes, the proposed approach provides unsafe predictions.

Abstract In 2013, Atomic Energy of Canada Limited (now Canadian Nuclear Laboratories) experimentally measured the damping of a straight tube with a variety of tube supports to examine low-frequency damping. These tests were motivated by the discovery of severe tube damage caused by in-plane fluidelastic instability (FEI) in the U-bend regions of new replacement recirculating steam generators (SG). The measurements were intended to assess the applicability of existing design guidelines for estimating the support-related damping of a tube. In the tests, the damping ratios of a single steam generator tube were measured using both log-decrement and power-based methods. Noncontacting excitation and position-sensing techniques were employed to improve accuracy. Initial baseline tests explored configurations with no support and drilled-hole supports of different hole sizes, and these results were compared with previously published work. Subsequent tests were performed to measure damping of tube vibration parallel to flat-bar supports. Most of the tests were performed with the tube fully submerged in still water. The tests examined the effects of fluid (water or air), natural frequency, gap width, preload, and vibration normal to the bars. This paper describes the test apparatus, methods, and analysis techniques. A summary of the results is presented. The initial baseline results showed that the damping ratios measured without any supports and with a drilled-hole support were consistent with previously published data. However, the subsequent measurements showed that, contrary to a published design guideline, the anti-vibration bars resulted in no significant additional viscous or squeeze-film damping when the vibration was parallel to the bars. On the other hand, the results did show that anti-vibration bars could introduce significant in-plane Coulomb-type damping if there was sufficient tube-to-support preload or impacting.