Comparison of Leakage Performance in Three Types of Gas Annular Seals Operating at a High Temperature (300°C)

Adequate sealing in rotating machinery reduces secondary leakage and results in more efficient and stable systems. Labyrinth seals are most common, although brush seals are popular in specialized applications. The hybrid brush seal (HBS) is a novel design that adds to the bristle brush matrix a number of cantilever pads that rest on the rotor surface. Upon shaft rotation the pads lift due to the generation of a hydrodynamic gas film, and the brushes effectively seal an upstream pressure. Hence, the HBS has no wear and no local thermal distortion effects. This article presents measurements of leakage versus pressure differential obtained in a three-tooth labyrinth, a conventional brush seal, and a hybrid brush seal for operation at high temperature (300°C) and with shaft surface speeds to 26 m/s. The measurements demonstrate that the HBS leaks ～ 31% less than a standard brush seal and is significantly better (～ 68%) than a similarly sized labyrinth seal. As temperature increases, the labyrinth seal leakage decreases because its clearance changes due to the thermal growth of the components. The HBS, on the other hand, shows leakage that is nearly insensitive to air inlet temperature. The measurements demonstrate HBS as a reliable seal technology for use in gas turbines, for example.     

Tribological Evaluation of an Al2O3-SiO2 Ceramic Fiber Candidate for High Temperature Sliding Seals

A test program to determine the relative slitting durability of an alumina-silica candidate ceramic fiber for high temperature sliding seal applications is described. Pin-on-disk tests were used to evaluate the potential seal material by sliding a tow or bundle of the candidate ceramic fiber against a superalloy test disk. Friction was measured during the tests and fiber wear, indicated h the extent of fibers broken in the tow or bundle, was measured at the end of each test. Test variables studied included ambient temperature from 25° to 900°C, loads from 1.3 to 21.2 N, and sliding velocities from 0.025 to 0.25 m/sec. In addition, the effects of fiber diameter and elastic modulus on friction and wear were measured. Thin gold films deposited on the superalloy disk surface were evaluated in an effort to reduce friction and wear of the fibers.

In most cases, wear increased with test temperature. Friction ranged from 0.36 at 500°C and low velocity (0.025 miser) to over 1.1 at 900°C and high velocity (0.25 m/sec). The gold films resulted in satisfactory lubrication of the fibers at 25°C. At elevated temperatures diffusion of substrate elements degraded the films. These results indicate that the alumina-silica (Al₂O₃SiO₂) fiber is a good candidate material system for high temperature sliding seal applications. More work is needed to reduce friction.     

高温油泵机械密封的改造

为防止2#蒸馏装置高温油泵单端面非集装式机械密封一旦泄漏引发的火灾事故发生,对高温油泵机械密封从密封型式、密封布置方式、密封材质、密封辅助冲洗方案等方面进行了改造,实现了机械密封安全保护及运转状态的实时监控,并对运行中出现的问题提出了解决的措施和建议。     

The Detection and Characterization of Blisters On Carbon-Graphite Mechanical Seal Faces

Blisters that develop on carbon-graphite mechanical seal faces are irregularities in surface topography that result in poor sealing performance and a high incidence of catastrophic failure. On first inspection, a blister is a burnished area that is slightly elevated above the surrounding seal surface. In this study, the topography of several hundred blisters was examined with interference microscopy. The shape of the burnished area is typically elliptical or cylindrical. The leading edge against the direction of rotation of the mating seal ring extends abruptly upward from the surrounding seal surface. The trailing surface gradually merges into the parent seal face. Most blisters have a maximum height of 0.25 μm to 0.75 μm (10 μ-in to 30 μ-in).     

Experimental Investigations and Field Applications of Oil-Film-Lubricated Mechanical Face Seals with Spiral Grooves

The oil-film-lubricated mechanical face seal described here is a hydrodynamically lubricated, noncontacting, mechanical face seal with zero leakage. On the basis of systematic theoretical analyses, research on design methods, and experimental investigations, many field applications have been made. The experimental investigations include test rig development; long-time high-speed running tests; frequent start-up and shut-down tests; measurements of the seal leakage, face temperature, and characteristics of the self-circulating screw pump; observation, measurement, and solution of interface wear, and so on. Until now, this new seal design has been successfully applied in more than 40 high-speed turbocompressors in the oil refinery and petrochemical industries, achieving zero leakage and long operation. These seals are all designed with different face spiral-groove patterns, structure arrangements, and supporting systems.     

A Condition Monitor For Liquid Lubricated Mechanical Seals

A recently developed condition monitor for liquid lubricated mechanical seals utilizes actively generated ultrasonic shear waves to determine conditions at the sealing interface. A shear wave transducer is mounted on the backside of the non-rotating seal face, and generates waves that propagate toward the sealing interface. The amplitude of the reflected waves indicates whether or not face contact occurs and, if there is contact, the severity of contact. Thus, this monitor is suitable for use with both non-contacting and partially contacting seals. Laboratory tests on a commercial, unbalanced seal demonstrate the effectiveness of the approach.     

Theoretical Analyses and Field Applications of Gas-Film Lubricated Mechanical Face Seals with Herringbone Spiral Grooves

The gas-film-lubricated mechanical face seal is a combined hydrodynamic and hydrostatic seal with positive leakage. Up to now, it has been widely accepted by end, users and builders of high-speed turbo compressors. The groove technology on the sealing face of the seat is one of the core technologies of dry gas seals. This article presents a patented herringbone spiral-grooved gas seal. Its one-dimensional analytical solution and two-dimensional numerical solution methods for the gas-film pressure distribution on the sealing face are presented. Up to now, more than 200 gas seals adopting this groove technology have been applied successfully in high-speed turbo compressors that deal with dangerous process gas in the oil refinery and petrochemical industries. The theoretical analyses and field applications show that gas seals with herringbone spiral grooves are advanced and practicable.     

Effect of temperature on the magnetic abrasive finishing process of Mg alloy bars

Experiments were conducted to evaluate the effect of temperature during magnetic abrasive finishing of Mg alloy bars. A magnetic abrasive finishing process is an unconventional finishing technique that has been used to achieve high-quality surfaces with dimensional accuracy. In this study, a Mg alloy bar, which is widely used in automobiles, aircraft, IT, and the defense industry, was chosen as a cylindrical workpiece. The workpiece was then finished with a magnetic abrasive finishing process at three different temperatures, i.e., a cryogenic temperature, room temperature, and high temperature. In the cryogenic temperature condition, liquid nitrogen and argon gas were used as the cryogenic cooling gases in the finishing process; the results from this treatment were compared with those obtained at room temperature and high temperature conditions. At the room temperature condition, the finishing process of the cylindrical workpiece was performed at 24 °C. To carry out the high temperature condition, a hot air dryer was used to maintain a finishing temperature of 112 °C. The experimental results show that the room and cryogenic temperatures could yield excellent performance in terms of the surface roughness. However, in terms of the removal weight and change in diameter, the high temperature condition was found to be superior. In the present research, the improvements of the surface roughness (Ra) at room temperature (24 °C) and cryogenic temperature (-120 °C) conditions were 84.21 % and 55 %, respectively.

     

Investigation of the mechanical behavior of a flexible solid metal seal for a cryogenic butterfly valve

Seat tightness at the fully shut position should be a consideration in the development of a butterfly valve for use in a liquefied natural gas (LNG) vessel. A flexible solid metal seal offers sufficient tightness of the butterfly valve and meets the specifications for cryogenic temperature. In the present study, characteristics for a cryogenic butterfly valve, such as the flow coefficient and the pressure loss coefficient, were estimated by numerical fluid analysis carried out to simulate 3-D flow and to study performance as it was affected by the opening angles of the valve disc. A design criterion to ensure the seat tightness of the butterfly valve at the fully shut position was proposed, in which the contact pressure between the metal seal and the valve disc would be compared with the fluid pressure. Numerical structural analysis showed that the contact pressure can be calculated by simulation of the frictional contact behavior on the surface of the metal seal and the valve disc. As a result, an adequate flexibility of the metal seal and the valve disc was required in order to accomplish a contact pressure that would be high enough to satisfy the seat tightness requirement. Under cryogenic temperature, thermal shrinkage caused the metal seal to adhere closely to the valve disc periphery at both sides and raised the contact pressure to a relatively high value, though there was no contact across a small area at the center position, which is susceptible to leakage. An additional displacement of the metal seal and the valve disc appeared at an operating fluid pressure of 6.9 bar and produced sufficient contact pressure at the no-contact area. This was verified by experimental leakage tests performed at room and cryogenic temperatures.     

Parametric Study of Spiral Groove Gas Face Seals

A finite element analysis for the isothermal flow in spiral groove gas face seals is detailed along with a successive approximation method for the iterative solution of the nonlinear Reynolds equation. Zeroth- and first-order pressure fields are calculated for evaluation of the seal opening force and leakage and the axial stiffness and damping force coefficients, respectively. A parametric study shows the static and dynamic force behavior of a baseline SGFS operating with a large pressure ratio. The recommended geometric parameters presented ensure large static stiffness and damping force coefficients while still allowing for low seal leakage rates. A reduction in the power loss and a significant increase in the seal static stiffness coefficient are unique features of thin seal dams.     

Finger Seal Solid Modeling Design and Some Solid/Fluid Interaction Considerations

The technology of shaft compliant seals was revolutionized when brush seals first replaced the labyrinth seals at many locations along compressor and turbine shafts. Finger seals present a compliant seal alternative to brush seals and through their geometric configuration bring about the added potential of hydrodynamic lifting and thus non-contacting operational features. Their manufacturing costs are well below those of brush seals and their potential lifting capability, by eliminating the wear factor, increases considerably their life span while making them a preferred embodiment to brush seals. The fingers' compliance allows both axial and radial adjustment to rotor excursions without damage to the integrity or performance of the seal. The work to be presented here concerns design development through numerical simulation of the motion of an assembly of two high pressure (HP) and one low pressure (LP) fingers arranged axially in a staggered configuration and subject to an axial pressure drop. This combination of fingers represents the smallest repetitive basic elemental cell component of a Finger Seal (FS). The numerical 3-D results presented herein were obtained using customized commercial packages. The solid models using ALGOR as the computational engine study the deformations and stresses of the finger(s) and its/their lifting capabilities. The integrated numerical approach coupling the hydrodynamic fluid model (Navier-Stokes based) to the solid fingers deformation and motion (CFD-ACE+ and FEMSTRESS) allows calibration of the floating and sealing capabilities of the FS at the same time. The entire study is aimed at generating reliable design procedures for the parametric design of a finger seal.     

Simulation of the Effects of a Plunge Ground Rod on Hydraulic Rod Seal Behavior

A numerical analysis of a reciprocating hydraulic rod seal with a plunge ground rod has been performed. It consists of coupled fluid mechanics, contact mechanics, and deformation analyses. The fluid mechanics analysis consists of a finite volume solution of the Reynolds equation. The deformation is computed with a finite element analysis. The contact of the seal asperities with the rod utilizes the Greenwood-Williamson model and the rod surface geometry is treated deterministically. The fluid transport, friction force, contact pressure distribution, and fluid pressure distribution in the sealing zone have been computed for a polyurethane U-cup seal and for a step seal with a polytetrafluoroethylene (PTFE) sealing element and a nitrile energizer. These have been compared with the results for a smooth rod.     

核辐射屏蔽密封解决方案及金属波纹管的性能分析

提出了核辐射屏蔽密封的解决方案,讨论了摇动式金属波纹管屏蔽密封技术的原理和可行性。利用有限元分析软件建立了结构中金属波纹管的有限元模型,得出了运转状况下波纹管中的应力分布,分析了波纹管影响密封结构性能的因素。     

机械密封的功率消耗试验及测量方法

随着机械密封应用的普及、机械密封的失效已成为石油化工等部门的回转机械（离心泵等）工作不可靠的重要因素,机械密封的端面摩擦不但直接消耗能源,而且,因端面摩擦过度而引起的密封失效泄漏所造成的损失则更大。本文在试验的基础上,研究了机械密封消耗的构成,介绍机械密封摩擦功率的测量方法,对机械密封不同工况不功率消耗的变化进行了分析,提出了降低机械密封功率消耗和改善密封功能,提高机械密封的工作可靠性的途径。     

Automatic Feedback Control of Mechanical Gas Face Seals via Clearance Control

A new analytical approach is presented for designing controllers to regulate the axial clearance of a coned-face flexibly mounted stator mechanical gas face seal. The seal axial clearance is controlled by regulating the back-pressure force acting on the stator. The controllers are systematically designed using a completely analytical seal system model in which the linearized gas film stiffness and damping properties are represented by a constitutive model. An algorithm based on this model is derived to calculate the critical axial clearance where the seal is marginally stable, and a stable reference axial clearance is chosen. Proportional and proportional-plus-integral controllers are designed and analytically studied in terms of closed-loop stability and speed of response using the system model. The controllers are verified using a full numerical simulation (including nonlinear effects) of the mechanical gas face seal system, and the results demonstrate the effectiveness of both controllers to maintain the reference axial clearance.     

Effect of Impeller Geometry,Rotational Speed,and Fluid Properties on Seal Chamber Flow

Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) are used to measure the three components of the flow velocity in the seal chamber of a mechanical pusher seal at three shaft rotational speeds of 1000, 1800, and 3600 rpm. The flow details in the narrow gap region between the rotor and the stator are also measured. The Taylor numbers corresponding to the three rotational speeds with water and a lightweight heat transfer mineral oil used as process fluids varied between 1.087 × 10⁷ and 9.48 × 10¹⁰. A smaller size impeller with diameter 12.7 cm compared with 25.4 cm diameter impeller used in previous works, was used in this research. Large differences are observed between flow structures in the seal chamber flow for oil and water. The effect of impeller size and the location of balance holes on the seal chamber flow for water at rotational speed of 1800 rpm is presented     

Mechanical behavior and sealing performance of metal sealing system in roller cone bits

Metal sealing system is used frequently in the dynamic rotary seal of downhole tools of petroleum, natural gas and mining. Mechanical behavior and sealing performance of the metal sealing system in roller cone bit were analyzed in this paper. Influences of pressure difference, compression ratio, fluid pressure, angle and thermal load on the metal sealing system’s mechanical behavior and seal performance were studied. The results show that the effect of pressure difference should be considered under fluid pressure. The von Mises stress concentrates on the inside of O-rings under the influence of compression ratio. The low-stress area appears on the inside of O-rings under the effect of fluid pressure. The high-stress concentration area of metal sealing surface appears on the surface of metal rings under different angles. Sealing performance, compression ratio, fluid pressure and angle have the same change trend. Thermal load is not a single impact on the stress distribution and deformation, but together with fluid pressure affects the sealing performance. The dynamic O-ring more easily fails than the static O-ring. Those results can provide a new direction for the structural optimization of metal sealing system in roller cone bits.

     

Effect of Shaft Microcavity Patterns for Flow and Friction Control on Radial Lip Seal Performance–A Feasibility Study

It has been shown that deterministic microfeatures on the shaft of a radial lip seal impact seal behavior. This work seeks to determine whether it is feasible to control lubricant pumping direction and enhance pump rate with microcavities. The effect of nickel film triangular cavity orientation on seal performance, in particular the flow direction, the pumping rate, and the friction torque, is investigated experimentally. Cavity shape, area fraction, and depth are held constant while cavity orientation is varied. The oil drop test results are compared to those for conventional seals; i.e., plain stainless steel shafts and shafts with an electroplated nickel surface but no micro-cavities. It was found that shafts with surface texture designs can control the pumping direction and increase the sealing capability via enhanced pump rates by up to eight times that of stainless steel shafts. Preferential orientations pumped oil toward the wider end, or base, of the triangular cavities while patterns in neutral, or nonpreferential, orientations were found to reverse pump. The presence of microcavities reduced the friction torque by as much as 51% when pumping and in all cases reduced the operating temperatures. In some cases, the microcavities also reduced the friction torque 8–13% when the seal was operating in a starved condition.     

A Transient Dynamic Analysis of Mechanical Seals Including Asperity Contact and Face Deformation

Face seals are typically designed to be in contact at standstill. However, as speed and pressure build up, the seal faces deform from their factory flat conditions because of viscous and dry friction heating, as well as mechanical and centrifugal effects. It is imperative that such deformations form a converging gap for radial flow to ensure stable operation and to promote favorable dynamic tracking between stator and rotor. A numerical simulation is presented for the transient response of a face seal that is subjected to forcing misalignments while speeds and pressures are ramped up and down. Asperity contact forces and transient face deformation caused by viscous heating are included. A new closed-form solution is obtained for the elastoplastic contact model, which allows seamless transition between contacting and noncontacting modes of operation. The model is then used to calculate face contact forces that occur predominantly during startup and shutdown. The viscous heating model shows that the time-dependent deformation (coning) is hereditary and that it lags behind the instantaneous heat generation. The dynamic analysis provides a numerical solution for the seal motion in axial and angular modes. The eventual build up of hydrostatic pressure and coning during startup generates opening forces and moments that separate the seal faces, resulting in noncontacting operation. The reverse occurs during shutdown; however, because of the thermal time constant a seal may continue to leak even after it returns to standstill. The analysis and simulation results compare very well with a closed-form solution that predicts a critical speed of separation of contacting seals.     

硅橡胶与金属黏附效应的产生与影响分析

为探讨橡胶密封件与金属法兰之间的黏附效应产生的原因及黏附效应对密封的影响,根据硅橡胶密封结构的使用特点,设计硅橡胶密封圈与金属法兰在不同温度、不同时间下的黏附实验.通过硅橡胶密封圈与防锈铝合金和2种不锈钢材料的对比实验发现,硅橡胶密封圈与不锈钢金属法兰易发生黏附,与防锈铝合金金属法兰不易发生黏附.通过对金属法兰表面接触...