Seal Components Research Articles

Modeling Geochemical Stability of Cement Formulations for use as Shaft Liner and Sealing Components at Yucca Mountain(1)

ABSTRACTThe geochemical modeling codes EQ3NR/EQ6 were used to model the interaction of cementitious materials with ground water from the Yucca Mountain proposed nuclear waste repository site in Nevada. This paper presents a preliminary estimate of the compositional changes caused by these interactions in the ground water and in the cement-based compounds proposed for use as sealing and shaft liner materials at the Yucca Mountain site.

Responses of γ-aminobutyrate receptor from rat brain: Similarity of different preparation methods; muscimol induced desensitization and chloride exchange

Chloride-36 exchange into three different membrane vesicle preparations from rat brain homogenate was followed. The different preparations all contained the same sealed vesicular components characterized by their rates of chloride exchange. The GABA-mediated 36Cl- exchange in all the preparations occurred in two phases shown to be mediated by two distinguishable receptors present in the activity ratio of 5:1 as previously described (Cash, D.J., Subbarao, K. 1987. Biochemistry 26:7556, 7562). Reported differences do not result from differences in the membrane preparations used or from the use of a GABA-mimetic instead of GABA, but from experimental differences. The preparations compared were made with mild or vigorous homogenization and with different extents of purification from solutes or membrane components: (i) a synaptoneurosome preparation, (ii) a Ficoll gradient preparation, and (iii) a washed P2 preparation. In each preparation the same four populations of membrane vesicles were characterized by their 36Cl- influx rates: (i) a major population (40-50%) (tau 1/2 = 1.4 min), (ii) a slower exchanging major population (40-55%) (tau 1/2 = 24 min), (iii) a minor population (5-12%) containing active GABA receptor and having the GABA-independent permeability of the slower exchanging population, and (iv) a very small exchange (approximately 2%) (tau 1/2 approximately 0.2 sec). The GABA-independent 36Cl- exchange processes were kinetically first order. The relative quantities of the different vesicle populations varied slightly with the preparation and purification technique. The identity of these components, observed in the different preparations, was attributed to the vesicle formation being dependent on the morphology and properties of the membrane rather than the preparation method. The soluble brain extract was GABA-mimetic with the two observed receptors, causing channel opening and desensitization. But little washing of the membrane was required to observe the function of both receptors. Muscimol was GABA-mimetic with both receptors. With muscimol, channel opening occurred at 2.6-fold lower concentrations while desensitization was unaltered relative to GABA. This is additional evidence that these responses are mediated by different pairs of binding sites. The dependence of desensitization rate on muscimol concentration indicated that there are two binding sites mediating desensitization, as described with GABA.

A New Approach to the Development of Fire-Resistant Wellhead Equipment

Summary A testing procedure has been developed that considers the response of the total wellhead system (vs. individual seal components) to fire conditions. This paper details the mechanics and results of this program for tests to 2,000°F [1100°C] flame at pressures of 3,750 psi [25.9 MPa]. Significant behavioral differences were observed during the development and testing of specially designed fixtures incorporating metal-to-metal seals for the tubing head, tubing hanger, and lower master valve. As a result, more stringent design criteria evolved for the sealing technology and structural integrity of the wellhead, because it became apparent that solving sealing and material problems in one sealing area or component invariably created new problems in other locations. Highest priority was given to seal development because it seemed to be the most critical area of concern. It was concluded that meaningful tests could be conducted only when several related seals were allowed to interact in response to fire conditions. Tubing, annulus, and connector seals were considered appropriate seals for wellheads.

An Experimental and Theoretical Study of Pressure and Thermal Distortions in a Mechanical Seal

Distortions of mechanical face seal components have a significant effect on the seal performance. The finite element method is often employed to analyze complex seal sections; however, experimental verification is needed. In this paper, a technique for measuring pressure and thermal distortion of seal components is demonstrated for the first time in a production-type seal under normal running conditions. The technique uses capacitance probes which measure the fluid film geometry directly. The seal components have also been numerically analyzed for pressure and thermal distortion by the boundary integral element (BIE) method and the results are correlated with experimental measurements. While seals may be designed to be insensitive to the sealant pressure, the thermal distortion is shown to be very significant. The mechanisms and the effect of boundary conditions on thermal rotation are discussed. The BIE method is a rapid technique, which from an integral part of a modular seal design system and has been applied to seals now in successful service.

Thermocracking of a mechanical face seal

A microscopic examination and an analytical study were carried out to determine why and how thermocracking occurs in the mating ring of a mechanical face seal and what can be done to avoid this mode of seal failure. The particular face seal studied was a shaft seal with a mating ring made from a cobalt-based superalloy. The microscopic examination yielded a better understanding of the initiation and propagation of thermocracks in the metallic seal ring and of the role played by second phase particles in thermocracking. An analysis of surface temperatures and stresses in the seal, using finite element techniques, showed that the dominant stresses in the seal components are thermal stresses. A thermocracking mechanism is proposed which agrees well with all microscopic observations. Suggestions are made of steps that could be taken to alleviate the thermocracking problem and guidance is offered for the choice of future seal materials.

Instrumentation Requirements for Geologic Repository Sealing Systems

Schematic designs have been developed for shaft, tunnel and borehole seals for a HLW repository in bedded salt. General instrumentation requirements for penetration sealing are related to repository development schedules, to the types of test for which instruments are required, to preliminary test concepts, and to the various factors which must be taken into account in evaluating instruments. In developing instrumentation specifications emphasis will be given to methods used for investigating the nature of the disturbed zone created by excavation of a penetration, and to instruments required for in situ testing of seal components.

A sputtered zirconia primer for improved thermal shock resistance of plasma-sprayed ceramic turbine seals

Considerable success has been achieved in the development of plasma-sprayed Y 2O 3-stabilized ZrO 2 (YSZ) ceramic turbine blade tip seal components. The YSZ layers are quite thick (0.040–0.090 in) in comparison with typical thermal barrier coating layers applied to airfoils, which are more effectively cooled than the seal. The service potential of seal components with such thick ceramic layers are cyclic thermal shock limited. The most usual failure mode is ceramic layer delamination at or very near the interface between the plasma-sprayed YSZ layer and the Ni-Cr-Al- Y bondcoat. Deposition of a thin r.f.-sputtered YSZ primer to the bondcoat before deposition of the thick plasma-sprayed YSZ layer has been found to reduce laminar cracking in cyclic thermal shock testing. The cyclic thermal shock life of one ceramic seal design was increased by a factor of 5–6 when the sputtered YSZ primer was incorporated. A model based on thermal response of plasma-sprayed YSZ particles impinging on the bondcoat surface with and without the sputtered YSZ primer provides a basis for understanding the function of the primer.

Two‐dimensional shape optimal design

AbstractThis paper treats shape optimal design of two‐dimensional structures. Sensitivity of cost and constraint functions to changes in the shape of the structure are obtained by applying theorems from the calculus of variations and by using consistent first‐order approximations of functions arising in an optimal design problem. A generalized steepest descent algorithm is presented for determination of the optimum shape. The method is applied to a load carrying shear plate that models a component of the high pressure seal in a gun launched high velocity projectile.

Thermal Deformation in a Mechanical Face Seal

In this paper, the mechanical and thermal deformations of the seal components are analyzed, and the role they play in the failure of face seals is discussed. To obtain the thermal deformation, the heat generated between the sealing surfaces is estimated. The temperatures fields and the deformations for both the seal and mating rings are solved numerically. While mechanical deformation is found to be small, the thermal deformation is shown to be very, significant. This thermal deformation could distort the originally flat sealing surfaces convex along a diameter with an amplitude of 2 μm for the seal ring and of 0.75 μm for the seat. The distortion is even larger when the seal runs dry. Thermal deformation promotes seal face wear at the inner diameter and must be minimized. Presented at the 30th Annual Meeting in Atlanta, Georgia, May 5–8, 1975

Nature, causes, and prevention of labyrinth air seal failures

This paper is devoted to the problems of labyrinth air seals where radially extending teeth are carried by rotating components. In view of the possibility of resonance, determination of the natural nodal frequencies of seal components and supporting structure by analysis, tests, or both is of vital importance in the design and development procedure. Construction of Campbell frequency diagrams is a basic requirement to assure adequate frequency mistuning margin against vibration and fatigue failures caused by rubs. Aerodynamic disturbing forces have also excited flexural vibration and fatigue failure of seals. A w/R stability criterion has proven effective in evaluating the hazard of aeroelastic vibration due to pressure drop across multi-tooth seals. Acoustic oscillations in the annular chamber into which the seal discharges have coupled with the corresponding natural nodal flexural vibration of seal components, which increases nodal flexural vibration of seal components, and increases the hazard of vibration and fatigue failure. Transient thermal instability may occur if the heat generated during rub causes the inner component to grow at a faster rate than outer. Seals must have compatible thermal expansions to maintain close clearances even when engine operating transients are rapid. The design and application of severed damper sleeves and ring to rotor components are effective in protecting air seals and the cylindrical walls of annular chambers aft of seals against flexural vibration and fatigue failures excited by aerodynamic disturbing forces. Since acoustically coupled oscillations persist over relatively long distances and thus involve additional components, severed damper sleeves have proven effective in protecting these thin-walled components excited by aerodynamic disturbing forces.

Performance and acceptance of respirator facial seals.

Three respirator full face masks with different paripheral seal designs (flat, inner flap, and pneumatic) were modified to permit study of the facial seal component. Twelve subjects participated in the study. Each subject completed a three-hour test session on each mask. The first half of each session was devoted to a study of leakage at five seating forces; the second half of the session was devoted to a comfort study of the same mask under the same five seating forces. To test for the differences in' leakage for a given seating force a uranine aerosol test was used to challenge the integrity of the facial seal and permit quantitative measurement of percent leakage. Differences in apparent seating force (and therefore comfort) between the three facial seal designs were studied utilizing a psycho-physical technique. A suggested physiological correlate of comfort, galvanic skin potential, was also measured during the second half of the session. Significant differences were noted in the performance of one o...

507. Measurement of gas-leakage in sealed components: R. T. Lovelock, Proc. Symp. Soc. Environ. Engrs., (1), 1963, 47–50

507. Measurement of gas-leakage in sealed components: R. T. Lovelock, Proc. Symp. Soc. Environ. Engrs., (1), 1963, 47–50

Detection and measurement of leaks in hermetically sealed electrical components using krypton 85

Two methods of using the radioactive gas krypton 85 for leak detection are described. In the first, components to be tested are immersed in the gas, after which they are removed and individually monitored for radioactive content. Application of the method to detection of leaks in transistor encapsulations is discussed. Correlation has been obtained between leak rate and time for subsequent electrical failure.The second method of using krypton 85 is to insert a small quantity into each component before the final seal is made. Leak rates are then measured by collecting gas which leaks out and assaying it with a scintillation counter. This technique is illustrated by tests carried out on a hermetically-sealed pressure switch. The method is compared with the helium mass spectrometer, and it is concluded that using krypton 85 is just as sensitive, cheaper and more reliable.

A practical solution to the arcing problem at high altitudes

Malfunctioning of ballistic missile guidance equipment due to arcing at high altitudes is discussed in the light of a reconsideration of original design evaluation test techniques. Corrective methods are developed for the existing equipment resulting in sealed components to entrap ground atmosphere during flight. As an additional measure, partial encapsulation processes are used to exclude air from critical areas where voltage, terminal spacing and altitude could combine to cause electrical breakdown.

A method of leak testing hermetically sealed components utilizing radioactive gas

A method of leak testing hermetically sealed components such as transistors, relays, frequency standard crystals, small munitions, etc., utilizing a chemically inert radioactive gas (krypton-85) is described. A leak rate formula based on poiseuille's law is developed and the limitations in measurement imposed by the range of validity of this formula and of the random nature of radioactive decay is discussed. Means for differentiating between radioactive gas which has leaked inside the part being tested and gas absorbed on its surface is presented. A logarithmic rate unit called the leak index is proposed. A brief description of industrial equipment for accomplishing leak rate measurements along with precautions to assure full safety in its operation is given.

Leak detection practice with particular reference to the hydrogen palladium method

the principles of leak detection are discussed with specific reference to the Pirani and palladium-barrier ionisation gauges, as used to detect hydrogen applied externally as a test gas. Plant based on these techniques, with the detector in the backing space and other refinements, are described. The testing of single or multiple vessels based on this type of plant is discussed in detail with special reference to applications outside the vacuum field. The problem of leak testing completely sealed components is also discussed. The paper concludes with a consideration of calibrated reference leaks, for a quantitative assessment of the leakage rate, when testing to a specification.

Hermetically sealed components for industrial control

Today many different types of components are available in hermetically sealed units. These, though initially expensive, may prove worthy, because components last longer, maintenance is easier, and the parts are relatively tamperproof.

Triodes for very short waves—oscillators

Section 1 of the paper deals with the excitation of triode oscillators. The limitations of conventional circuits are discussed and it is shown that the progress in the design of oscillators for very short waves has been mainly due to the reduction of electron transit time and the reduction in the inductance and h.f. resistance of the leads to the electrodes.The electron transit time has been reduced in two ways, (a) by the use of very small inter-electrode spacings—in some types the grid-cathode spacing is between 0.08 mm and 0.1 mm, and (b) by increasing the space current density—values as high as 5 amp/cm2 have been employed under pulse conditions.Electrode-lead inductance has been reduced considerably by the use of disc seals and other forms of glass-metal joints, whereby the valve becomes an integral part of the circuit.In general, h.f. oscillators and amplifiers have two adjustable circuit elements, one electrode being common to the two circuits, and another being earthed. Five types of circuit have been used, but the most important are(a) Common-anode earthed-anode using a CV52, VT90, NT99, CV55 or CV240 valve.(b) Common-grid earthed-anode using a CV90, CV153 or CV273 valve.(c) Common-grid earthed-grid using a CV16, CV53, CV88, CV257 or CV288 valve.(a) and (b) have been the most commonly used for oscillators, and (c) for amplifiers.Section 2 describes the evolution of transmitting triodes for radar, and of local oscillators for reception. Most of the valves are of metalglass construction, and several types are described to illustrate the new techniques employed. The anode usually forms the metal component of the glass-metal seal, giving low inductance and good cooling. The grid is mounted directly either on a disc seal or on a copper thimble. The electrode seals are designed so that the valve can be plugged directly into a coaxial-line circuit.Oxide-coated cathodes are used in all the later designs, including transmitting valves operating at a pulsed anode voltage of 15 kV and a peak input of 500 kW.Some typical valves are the common-anode transmitting valve NT99—a pair giving 200 kW at 600 Mc/s, the common-grid transmitting valve CV288—a pair giving 100 kW at 1000 Mc/s, the common-grid receiving valve CV273—giving 4 to 5 watts at 1 000 Mc/s and 0.5 watt at 3000 Mc/s.Section 3 summarizes some of the problems associated with testing and specifications.