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• The laser strain sensor was used to obtain accurate experimental data. • The actual working temperature and relaxation have profound effects on sealing performance of rubber. • The main failure mechanism caused by temperature and relaxation have been discussed. • Temperature safety factor and stress relaxation safety factor were put forward. In the last few decades, rubber seal elements have been extensively used in the oil and gas industry. However, mechanical properties of rubber decrease at high temperatures, and stress relaxation can lead to sealing performance degradation, even sealing element failure. Therefore, how high temperature and stress relaxation affect the sealing performance of rubber is an important issue in oil and gas production. According to the oilfield feedback information, hydrogenated nitrile butadiene rubber (HNBR) was chosen for sample tension test at different temperature (20 °C and 120 °C) and the stress relaxation tests at 120 °C. The constitutive model of rubber was fitted by the test data. At the setting pressure of 14 MPa, the influence of temperature and stress relaxation on the packer rubber seal system was investigated by finite element analysis (FEA) software. The results indicated that temperature and stress relaxation had an appreciable impact on the sealing performance of packer rubber seal system. The average contact stress at 120 °C between the rubber and the borehole wall, compared with the calculation results at 20 °C, decreased by more than 15% and the maximum contact stress decreased by 20%. Similarly, the average contact stress before the relaxation decreased by more than 35% after stress relaxation behavior at 120 °C. In addition, the maximum contact stress decreased by 50% due to the stress relaxation. Our experimental results and discussion enable us to provide some advice to improve the sealing performance of a packer seal system, and present a basic experimental and theoretical foundation for future research into the optimum design of a packer sealing system. [ABSTRACT FROM AUTHOR]

To apply thin films to tempered injection molds, an automatable sealing solution is necessary. The study investigates the required external clamping force for a sealing frame with O-ring, which is needed to enable leak-tight closure. The clamping of thin films for different hardness of elastomer O-rings and their compression were investigated in a tensile test machine. The important parameters for a low leakage of the sealing solution were identified by defined vacuum tests. The automation capability was assessed. The study revealed that high external clamping forces and low leakages are majorly dependent on high compression and high hardness of the O-ring. This results in a contact pressure, which is the primary criteria for the sealing performance of O-rings with a hardness of 15–75 Shore A. The results show that thin films made of thermoplastic polyester-ether tear in the tensile test at low compressions if the hardness of the O-ring exceeds 60 Shore A. Tearing occurs at lower compressions than needed for a sufficient sealing performance. Therefore, the choice of the O-ring and the dimension of the groove need to be based on the required sealing performance of the sealing frame and not on the fixture of thin films. • High hardness/compression and low diameter of O-ring result in gas-tightness. • Retaining force is determined by coupling's surface, O-ring, and its compression. • High depth of O-ring's groove can decrease forces at sufficient sealing performance. • Dimension of sealing frame should be based on sealing, not on fixture of thin films. [ABSTRACT FROM AUTHOR]

The performance of a bolted flange joint is characterized mainly by its "strength" and "sealing capability." Performance of bolted flange joints is mostly discussed under steady state loading with and without internal pressure loading. Present design codes do not address the effects of steady state and thermal transient loading on a joint's performance. The use of different gaskets affects the performance of a gasketed joint due to joint relaxation behavior. In this paper, the performance of the gasketed bolted flange joint is analyzed using detailed nonlinear finite element analysis, for two different gaskets - solid-plate and spiral-wound - when subjected to combined internal pressure and steady state thermal loading. [ABSTRACT FROM AUTHOR]

Abstract: Hydraulic cylinders are widely used as actuators for construction machines, airplanes and military machines. In the case of these devices, due to their use under severe environmental conditions, such as excessive water, SiO2 and dust seals which has a high packing ability and long service life have normally been required. These characteristics are largely influenced by the material and geometries of seals, such as the approach angle, the round radius of a lip edge and interference. Recently, many studies have been undertaken regarding material, so that many materials have been developed. But the concrete studies including the relationship between the geometry of seals and sealing ability and the optimal geometry design of seals to obtain superior sealing ability have hardly been performed yet. Therefore, in this study, we predicted the deformation behavior and contact pressure distribution of dust seals with the variation of geometry of a seal lip using finite element analysis. Also, we estimated the effect of each design variable on the sealing effect and presented the engineered value of design variables, not experienced ones. [Copyright &y& Elsevier]

Interface stresses and sealing performance of thin-wall box-shaped bolted flanged joints using silicone sealant under internal pressure and thermal conduction conditions are analyzed by the thermo-elastic finite element method. The flexible flanges were fastened by M8 bolts and nuts with an initial clamping force (bolt preload) after being joined with the silicone sealant. In the elastic and thermo-elastic Finite Element Method (FEM) calculations, the effects of the bolt pitch distance, flange rigidity and flange thickness were examined on the interface stress distributions. In addition, the effects of the linear thermal expansion coefficient and Young's modulus of the silicone sealant in the steady temperature state were also examined from a design standpoint. In the experiments, leakage pressure was measured when the silicone sealant was applied between an aluminum flexible flange with 1 mm thickness and an aluminum flange (body) with 10 mm thickness. Measurements of sealing performance with the silicone sealant and a sheet gasket were also conducted. In addition, strains in the joint in steady temperature states were also measured by strain gauges to understand the effect of the operative temperature on the sealing performance. The experimental results were found to be in fairly good agreement with the calculated results. From the results, it was found that the effect of the thermal conduction condition was greater than that of the internal pressure on both the interface stress distributions and the sealing performance. In addition, the sealing performance was found to be better in the joint with the silicone sealant than that with the sheet gasket. [ABSTRACT FROM AUTHOR]

This paper deals with a new seal system between flange joints without using a gasket. This gasketless flange includes a groove and an annular lip that is machined in one of the flange rings which when removed being in contact with the other flange to form a seal line when the flanges are assembled. In this study, firstly, fundamental dimensions are examined for unplasticized polyvinyl chloride (PVC-U JIS) to obtain the best sealing performance. Then, the effects of material difference and flange nominal size upon the sealing performance of the new gasketless flange are investigated for two types of materials, 0.25% carbon steel (S25C JIS) and PVC-U. It is found that the critical internal pressure at which leakage appears is mainly controlled by the maximum stress at the annular lip for each material even if the flange nominal sizes are different. The gasketless flange made by PVC-U shows the higher critical internal pressure compared with the case of S25C if the same clamping forces are applied. The effect of stress relaxation for PVC-U on the sealing performance is also considered. Then, it may be concluded that this PVC-U gasketless flange as well as S25C has good sealing performance. [Copyright &y& Elsevier]

Rubber is the key component of a compression packer, which directly affects the success or failure of seals. Presently, the contact stress between the rubber and borehole walls is used as the main evaluation criterion for the sealing ability of the rubber of the compression packer. However, this evaluation criterion is imperfect. This study establishes the sealing performance and reliability evaluation system of a compression packer at 120°C. Considering the influence of time and temperature on the mechanical characteristics of rubber materials, the international advanced test technology was used to complete the uniaxial, planar and biaxial tensile tests and stress relaxation test for hydrogenated nitrile butadiene rubber (HNBR) of a compression packer under high temperature. Next, the hyperelastic and viscoelastic constitutive models of rubber materials based on high-temperature test data were established. Comprehensive sealing performance and reliability evaluation system for the compression packer rubber with compression rate, linear pressure, surface pressure and sealing performance coefficient were proposed. The evaluation system tested the rubber's stress relaxation effect on the rubber's sealing performance. The establishment of the evaluation system improved the shortcomings of the current packer-sealing performance evaluation system and provided a theoretical basis for the design and optimisation of the key structure of the packer-sealing system. Besides, based on the evaluation system, a platform for automatic structure simulation analysis and optimisation design of packer sealing system was developed and successfully applied to the actual design and optimisation process of packer. The system can effectively predict the sealing ability of the packer and guide field applications of the packer.

• An encapsulation method of perovskite films by ultrashort pulse laser was proposed. • This encapsulation method does not require optical contact conditions. • The encapsulation effects of two different glass materials were compared. • The effectiveness of the encapsulation was verified by experiments. • This method provides a direction to solve the stability of perovskite solar cells. Perovskite solar cells (PSCs) are a promising application industry, but its stability is not very ideal at present. The bottleneck of the PSCs industrialization is that perovskite material is very sensitive to humidity, and it is easy to produce hydrolysis and failure. Therefore, it is necessary to develop an effective encapsulation method to achieve a better long-term stability. Ultrashort pulse laser glass welding technology is one of the effective encapsulation methods, but it is still difficult to be used in engineering due to the harsh conditions of optical contact. To solve these problems, a sealing welding method of perovskite films based on ultrashort pulse laser under the natural stacking conditions was proposed, the effectiveness of the sealing weld was verified by experiments, which provides support for the engineering application of perovskite solar cells, and also provides a possible direction for the application of ultrashort pulse laser glass welding technology. [ABSTRACT FROM AUTHOR]

The development of leakage and strength of a metallic bolted flange joint are investigated in this work. Finite element analyses in 2D and 3D have been developed using ANSYS to study a steel flange and bolt with an aluminium gasket. The pressure-penetration criterion (PPNC) in ANSYS has been used to model fluid leakage propagation between the flange and the gasket. Validation was performed with a benchmark test, using published study of a bolted metallic flange joint; the agreement between the results is excellent. Results showed that the finite element method using PPNC is a good method to study leakage behaviour compared to other methods, which are relatively time-consuming and expensive. The influence of the flange dimensions on the maximum stresses and leakage propagation has been investigated in this study. Furthermore, the agreement between the 3D and axisymmetric 2D FEA models is very good, so the latter can be used to save computational time. This study was undertaken as a preliminary to a larger project about bolted flange joints made of composite materials. [ABSTRACT FROM AUTHOR]

• The change of the canister surface temperature during the helium leak has been confirmed. • This phenomenon can be used for the leak monitoring. • The mechanism has clarified by the tests using a small canister model and the analysis. • In the small canister model, the air tests could nearly simulate the thermal-hydraulics phenomenon in the actual canister rather than the helium tests. In the long-term storage management of spent fuel, the sealing integrity of the canister is important for the concrete cask. Thus, stress corrosion cracking (SCC) countermeasures and helium leak monitoring have been attracting attention internationally. In the previous studies, we have confirmed that the canister surface temperature changed during a helium leak by using a full-scale cask model. Based on this temperature change, we have also proposed leak detection methods. However, for practical use of a leak detector, it was necessary to clarify a mechanism that the canister surface temperature changes during the leak. Here, the mechanism was clarified by performing leak tests using a 1/18-scale small canister model of an actual canister and analysis using a thermal–hydraulic general-purpose code. The relation between the internal pressure and the surface temperature of the canister was examined by using different type of internal gases and heat rates of the canister as parameters. [ABSTRACT FROM AUTHOR]

As the core component of a fracturing tool, a rubber packer plays a vital role during the well stimulation process. Its sealing performance significantly affects the fracturing effects. This study adopted a 3D multi-body contact nonlinear finite element analysis with the Mooney–Rivlin constitutive model to investigate the sealing performance of the hydrogenated nitrile butadiene rubber. The effects of key parameters such as the total thickness, sub-thickness, height, and rubber hardness on the sealing performance were systemically investigated. Numerical results indicated that maximum contact stress appeared around the rubber packer's upper part because of the combined effect of friction and axial compression. Besides, the numerical results were validated with theoretical and experimental results, in which the error between theoretical and numerical results was less than 7%, and that between the numerical results and experimental results was approximately 17.7%. Under the conditions considered, key parameters of rubber packer were optimized as a total thickness of 20 mm, a sub-thickness of 13 mm, a height of 70 mm, and a hardness of 70 International Rubber Hardness Degrees, in terms of the maximum contact stress and deformation displacement. The proposed numerical approaches could accurately predict rubber packer's deformation status, which consequently had technical guiding significance for the design of similar sealing components in various applications. Image 1 • Effect of key parameters on the sealing performance of HNBR packer was studied. • Maximum stress appeared at packer's upper part due to friction and compression. • Contact stress was distributed unevenly and varied along the contact length. • The Packer's middle part first contacted the casing and formed arcuate curvature. [ABSTRACT FROM AUTHOR]

• Proposes a kind of high-pressure sealed preventing shoulder protruding (HPS-PSP) structure packer. • The comparison between theory and experiment verifies the accuracy of the model calculation results. • The optimization analysis of the structural parameters of the packer rubber is carried out. • The HPS-PSP packer effectively solves solves the problem of shoulder convexity and low sealing pressure of the original structure. Shale gas is a kind of unconventional oil and gas resources that can be exploited in shale strata. According to the evaluation of oil and gas resources carried out by the ministry of land and resources of China, the geological resources of shallow shale gas with a depth of 4500 m are 122 trillion cubic meters. However, the overall geological conditions of shale gas in China are complex and the buried depth is too large. For deep shale gas wells with vertical depth of more than 3500 m, problems such as shoulder protruding, tearing, crushing and insufficient sealing performance of rubber tube are caused by high-pressure fracturing. Aiming at the above problems, proposes a high-pressure sealed preventing shoulder protruding (HPS-PSP) structure packer. Based on the deformation theory of rubber tube, the finite element calculation model of packer tube under the setting condition was established. The influence of the thickness of the prevent shoulder protruding ring and the height of the trapezoidal ring groove and the length of the trapezoidal upper base on the sealing performance of the rubber tube were analyzed. The results show that: The HPS-PSP packer can effectively solve the problems of protrusion of rubber tube shoulder and insufficient sealing performance, and the contact pressure increases by 60.1% compared with the conventional one. The research work provides a method to improve the sealing performance of packer rubber, which is of great significance to improve the applicability of packer in deep shale gas fracturing operation. [ABSTRACT FROM AUTHOR]

A collection pipeline is designed to connect the divertor with the cooling and the baking systems in HL-2M. The ConFlat flange 25 used as the connecter in the pipeline is one of the feasible schemes. According to the requirements of the leak rate, the helium leak detector is used to research on the vacuum sealing performance of the flanges with the heating rate of 35 °C/h, 50 °C/h, 65 °C/h, 80 °C/h and 95 °C/h. The results show whatever the heating rate is, the leak rate increases as the temperature rises. When the temperature rises from 250 °C to 350 °C, the leak rate increases very rapidly. Moreover, the faster the temperature rises, the greater the fluctuation of the leak rate is. And the influence of helium pressure in the pipeline on the leak rate is very small. When the initial torque applied on the bolts is10 N m, the maximum leak rate is 7 × 10−10 Pa m3/s in the first heating process but is greater than 1.0 × 10−6 Pa m3/s in the second heating process which exceeds the acceptable leak rate of 1.0 × 10−9 Pa m3/s. So if we don't pre-tighten the bolts again in the heating cycles, the initial torque must be larger than 10 N m. • The relationship between the vacuum sealing performance of the ConFlat flange 25 and the temperature is researched by experiments. • The relationship between the vacuum leak rate of the CF25 and the heating rates is researched by experiments. • The mechanism of the seal performance during baking process is researched by combining the numerical simulation and the experiment. [ABSTRACT FROM AUTHOR]

Oil and gas leakages represent the (functional) failure mode as a result of sealing failure of thread connections. With the expectation for more safer and efficient operations during the exploration and production phase of oil and gas fields, Oilfield Country Tubular Goods (OCTG) require the use of thread compounds (pipe dope) to lubricate tubular connections during installation, provision of high resistance to presence of galling and ascertain a consistent friction coefficient, thus importantly to improve the sealing performance of API standard connections or among other expectations. In the period of improvement and upturning procedures for thermal enhanced oil, high temperature fluids (around 300 °C) with the production wells having a lower production temperature.To characterize the long-term sealing performance of OCTG threaded connections, this paper presented the experimental comparative studies and, the effect of viscosity degradation of five different types of thread compounds for thread connections samples using a programmable digital rheometer device under influences of shear rate, temperature and different loading conditions. The experimental outcome shows a dramatical transformation of the tested five thread compound's viscosity and how their sealability performance is being compromised. In view of this, the tested samples showed that the reduced viscosity properties will impede the tubulars connection leak tightness and durability in most thermal well's development. Our results also revealed that particular samples do fail at low temperature condition (70 °C) as this may impinge on pipe connections behavior during the breakout operation. • Thread compound rheology is affected by temperature but also by the cyclic behavior of the shear rate • Thermal failure of a thread compound can be seen during a rate up rate down cycle • Thread compounds viscosity decreases logarithmic with shear rate • A novel rheological test method has been defined in this paper [ABSTRACT FROM AUTHOR]

In order to explore the dynamic characteristics of the mechanical seal under different fault degrees, this paper selected the upstream pumping mechanical seal as the object of study. The research established the rotating ring-fluid film-stationary ring 3D model, which was built to analyze the fault mechanism. To study extrusion fault mechanism and characteristics, different dynamic parameters were used in the analysis process. Theoretical analysis, numerical simulation, and comparison were conducted to study the relationship between the fault degree and dynamic characteristics. It is the first time to research the dynamic characteristics of mechanical seals in the specific extrusion fault. This paper proved feasibility and effectiveness of the new analysis method. The fluid film thickness and dynamic characteristics could reflect the degree of the extrusion fault. Results show that the fluid film pressure fluctuation tends to be more intensive under the serious extrusion fault condition. The extrusion fault is more likely to occur when the fluid film thickness is too large or too small. Results illustrate the opening force is affected with the fluid film lubrication status and seal extrusion fault degrees. The fluid film stiffness would not always increase with the rotating speed growth. The seal fault would occur with the increasing of rotating speeds, and the leakage growth fluctuations could reflect the fault degree. [ABSTRACT FROM AUTHOR]

• This helium leak detection method uses the temperatures of the bottom of the canister and air at an inlet. • The index temperature which had information of inside of the canister could be obtained with calculation. • In casks which has a flow channel accessible to the bottom of its canister, these methods are useful. The aging management of spent nuclear fuel has received increasing attention worldwide. The loss of containment by stress corrosion cracking (SCC) on the canister surface of the concrete cask has been concerned. However, a detector of a helium leak from the canister has not been installed. In light of further improvement of the safety, the containment of the concrete cask should be monitored on a steady basis as well as the metal cask. For development of the detector, we experimentally confirmed that when the internal pressure of the canister decreased, the temperature of the upper part of the canister decreased and the temperature of the bottom of the canister increased. Based on this phenomenon, we had proposed a method using the temperature difference between the top and bottom of the canister for leak detection. This method requires the temperatures at two points on the canister surface; however, it would be difficult to install a temperature sensor on the canister bottom in the case of an air flow channel with a complicated shape. Thus, we have been investigating an easier technique that the leak could be detected by temperature information only at one of the two points on the canister. A method using ambient temperature at the top of the canister has already been developed, and this paper introduced new detection methods using the temperatures of the bottom of the canister and air at its inlet. [ABSTRACT FROM AUTHOR]

The contact mechanics model of the metal lens-type sealing gasket is established on the basis of Hertz theory on the macroscopical scale in this paper. The relationship among sealing width, contact pressure, and preload is solved. Based on the structural characteristics of the subsea collet connector, the self-locking characteristics are analyzed to determine the gain coefficient of the sealing structure for the loading thrust. On the microscopic scale, the contact characteristics of the turning lens-type sealing gasket and the hub structure are analyzed by the equivalent replacement of the peak cut coefficient of the one-dimensional sinusoidal wave. The influence of different leakage forms on sealing performance is discussed from both radial and circumferential leakage, and the leakage rate of the lens-type sealing structure is calculated. The hydrostatic pressure experiment of the subsea collet connector with lens-type sealing gasket is carried out, and the correctness of the theoretical analysis is verified from the results of the pressure maintaining, sealing width measurement, and preload conversion. [ABSTRACT FROM AUTHOR]

In this paper, a pressure compensated sealing method is proposed to solve the problem that the piston rod seal does not have the sealing compensation capability after wear. The pressure compensation simulation and experimental research on piston rod seals with different degrees of wear were carried out. In the experimental study, the monitoring data was collected by fiber Bragg grating sensors, tension sensors, pressure sensors and displacement sensors, and the parameters that reflect the sealing performance and friction characteristics are extracted therefrom. The relationship between the compensation pressure and the parameters under different degrees of wear was analyzed. The results show that the pressure compensation sealing method can improve the sealing performance of the sealing ring. • A pressure compensation method is proposed to improve the sealing ability after the seal is worn. • The method was verified by piston rod seals with different degrees of wear. • Nine parameters were extracted from the data collected by the four sensors. • The pressure compensation seal has certain sealing compensation ability. • The relationship of the sealing performance and friction characteristics is revealed. [ABSTRACT FROM AUTHOR]

This work presents a gas-liquid miscible backflow pumping seal (G-LMBPHS) aimed to seal lubricating oil in a high-speed bearing chamber as presented in this paper. The sealing mechanism and performance of the G-LMBPHS are numerically investigated and validated experimentally with a visualization test device, and the theoretical results fundamentally accord with the experimental values. The results reveal that G-LMBPHS uses high pressure fluid generated by the hydrodynamic effect of the groove to prevent the leakage of lubricating oil. When the shearing action generated by the rotational speed completely cancels out or even exceeds the pressure, G-LMBPHS can achieve perfect sealing with no any leakage of the lubricating oil. And G-LMBPHS designed in this study will have wide applications in engineering. • G-LMBPHS is a new hydrodynamic seal designed for bearing chambers with high speed and oil-gas or oil mist lubrication. • G-L Reynolds equation is formed by equivalent density and viscosity of gas-liquid fluid, and results are verified by test. • The sealing mechanism is examined by analyzing the variation of the pressure distribution and streamlines. • With enough rotational speed, G-LMBPHS can achieve perfect sealing with no any leakage of the lubricating oil. [ABSTRACT FROM AUTHOR]

• Packer rubber thermal aging experiments were carried out and the setting model of packer rubber tube was established. • It was pointed out that the Yeoh model was more suitable for the material constitutive of the packer tube under high temperature conditions. • Analyzed the sealing performance and strength behavior of packer in high temperature condition. • Sensitivity analysis of packer rubber key parameters was carried out. With the exploration and development of high temperature oil and gas wells, high temperature working conditions have gradually become the new normal state of drilling and completion engineering. Due to the high temperature, the failure of the packer rubber seal and the crushing seriously affect the normal development of oil and gas fields. This paper, aiming at the seal failure of rubber tude at high temperature, the parameters of the constitutive model of rubber tude were studied through the rubber thermal aging experiments. And the finite element calculation model of the packer under the sitting condition was established. The effect of temperature load on the sealing performance and strength behavior of packer rubber was studied. The effect of key parameters of the rubber tube-casing gap δ , the dip angle α of the adjacent rubber tube contact surface and the initial setting load on the sealing performance of the packer under high temperature conditions were analyzed. The findings show that the Yeoh model is more suitable to describe the high temperature material constitutive structure of the packer tube; At high temperature, the larger the gap δ is, the worse the packer sealing performance is; While 12–24° for angle α , sealing performance is better; The suggested initial setting limit load for packer rubber tube safety seal is 68–76 kN. The research work in this paper is of great significance to the design of packer rubber tube structure and its adaptability to high temperature conditions. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate the sealing performance of self-etch adhesives (SEA) after smear layer deproteinization with chemo-mechanical caries removal agents (CRA) to enamel and dentin cavity walls in comparison with 6% NaOCl smear layer deproteinizing., Methods: Eighty extracted bovine incisors with tapered cylindrical cavities (2.5 mm upper diameter, 1.5 mm lower diameter, 2 mm depth) at the cemento-enamel junction were randomly divided into four pre-treatment groups; no treatment (control), Papacarie (papain enzyme-based CRA), Carisolv (NaOCl-based CRA), and 6% NaOCl. After pretreatment, G-Bond Plus (GBP, one-step SEA) or Clearfil SE Bond 2 (CSE, two-step SEA) was applied to the pre-treated cavity, and then filled with a flowable resin composite (Clearfil Majesty ES Flow). Gap formations at the enamel and dentin lateral walls, and on the dentin cavity floor were investigated using swept-source optical coherence tomography (SS-OCT) after 24-h water storage at 37 °C. Deproteinizing effects of the tested agents on smear layer-covered enamel and dentin were quantified by changes in the amide:phosphate ratio using ATR-FTIR analysis., Results: Papacarie significantly reduced gap formation with both self-etch adhesives at all locations, compared to the control group (p < 0.05). In contrast, increased gap formation was observed with Carisolv and NaOCl. In most groups, CSE exhibited significantly lower gap formation than GBP (p < 0.05). ATR-FTIR revealed a significant decrease in the amide:phosphate ratio for all the deproteinizing agents (p < 0.05)., Conclusions: Chemo-mechanical CRAs could effectively remove the organic phase of enamel and dentin smear layer. The papain enzyme-based gel Papacarie could improve the sealing performance of the self-etch adhesives to both enamel and dentin., Competing Interests: Declaration of Competing Interest The authors declare that there are no conflicts of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

End fittings are essential components in marine flexible pipe systems, performing the two main functions of connecting and sealing. To investigate the sealing principle and the influence of the temperature on the sealing performance, a hydraulic-thermal finite element (FE) model for the end fitting sealing structure was developed. The sealing mechanism of the end fitting was revealed by simulating the sealing behavior under the pressure penetration criteria. To investigate the effect of temperature, the sealing behavior of the sealing ring under different temperature fields was analyzed and discussed. The results showed that the contact pressure of path 1 (i.e., metal-to-polymer seal) was 31.7 MPa, which was much lower than that of path 2 (metal-to-metal seal) at 195.6 MPa. It was indicated that the sealing capacities were different for the two leak paths, and that the sealing performance of the metal-to-polymer interface had more complicated characteristics. Results also showed that the finite element analysis can be used in conjunction with pressure penetration criteria to evaluate the sealing capacity. According to the model, when the fluid pressures are 20 and 30 MPa, no leakage occurs in the sealing structure, while the sealing structure fails at the fluid pressure of 40 MPa. In addition, it was shown that temperature plays a significant role in the thermal deformation of a sealing structure under a temperature field and that an appropriately high temperature can increase the sealing capacity. [ABSTRACT FROM AUTHOR]

The VX gasket is an important part of the wellhead connector for a subsea Christmas tree. Optimization of the gasket's structure can improve the connector's sealing performance. In this paper, we develop an optimization approach for the VX gasket structure, taking into consideration working load randomness, based on the Kriging surrogate model-NSGA-II algorithm. To guarantee the simulation accuracy, a random finite element (R-FE) model of the connector's sealing structure was constructed to calculate the gasket's sealing performance under random working load conditions. The working load's randomness was simulated using the Gaussian distribution function. To improve the calculation efficiency of the sealing performance for individuals within the initial populations, Kriging surrogate models were constructed. These models accelerated the optimization speed, where the training sample was obtained using an experimental method design and the constructed R-FE model. The effectiveness of the presented approach was verified in the context of a subsea Christmas tree wellhead connector, which matched the 20'' casing head. The results indicated that the proposed method is effective for VX gasket structure optimization in subsea connectors, and that efficiency was significantly enhanced compared to the traditional FE method. [ABSTRACT FROM AUTHOR]