Stuffing-box Seals Research Articles

FORECASTING EMERGENCY SITUATIONS AND THE DEVELOPMENT OF ACCIDENTS IN THE STORAGE OF LIQUEFIED HYDROCARBON GASES

In recent years, there have been fundamental changes in the industry due to a change in the structure the use of primary energy resources. For most the developed countries of the world, one the components of changes in industry was the emergence and constant increase in the share of chemical, fire and explosive technologies and industries using liquefied gases, primarily hydrocarbons – propane, butane, ethylene, butylene, propylene and others.
 The aim of the work is to analyze possible emergency situations at the storage facilities of liquefied hydrocarbon gases and predict possible scenarios for the development of accidents in the places of their storage, as well as develop recommendations for the prevention of these dangerous situations.
 The main reason for the leakage of the tank is mechanical or corrosive wear, as well as errors of operating and maintenance personnel. Other reasons (pressure exceeding critical values, accidents at neighboring blocks, natural factors, etc.) that can lead to a leakage of the storage facility with liquefied gases are less likely, but they cannot be completely excluded. A salvo leak a large amount of vapors liquefied petroleum gases is unlikely due to the underground location of the tanks.
 Considering the reasons for the violation of the tightness the pipeline with liquefied hydrocarbon gases, it should be noted that a large pressure value is not created in the pipeline during its operation, which can lead to a violation of the tightness the pipeline along the pipe body. Therefore, the most probable violation of the tightness the pipeline as a result the departure of technological parameters beyond the critical values ​​should be considered a violation the tightness of flange connections and stuffing box seals of valves. Violation of the tightness the pipeline due to corrosive wear is most likely as a result of external factors affecting the pipeline (atmospheric phenomena). It is impossible to predict the extent of the leakage and their location.
 Thus, a detailed analysis the causes of the occurrence were carried out and a probable scenario the development of accidents at the storage of liquefied hydrocarbon gases was considered. A logical diagram of the occurrence and development of accidents has been built. Recommendations have been developed for the prevention of emergency situations at storage facilities of liquefied hydrocarbon gases and the actions of employees in case their occurrence.

Physical Model and Calculation of Face Packing Seals

Increasing the reliability and service life of dynamic-pump shaft seals is the most important requirement for their creation. The most common type of seals is still traditional stuffing box seals, which are controlled leakage assemblies that are periodically restored during operation. A radical change in the design of standard stuffing box seals is the transition to face packing seals with a constant pressure against the packing. It is shown that face packing seals can successfully combine the advantages of mechanical face seals and the simplicity and relatively low cost of traditional stuffing box seals. Mechanical face seals, in which one of the packing rings is replaced by a stuffing box packing, have advantages that significantly expand the application of traditional stuffing box seals. A scheme and a physical model of the face packing seal operation are described. During the operation of the seal, the packing is pushed away from the mating metal surface by the pressure of the medium. In this case, a confusor gap is formed, the length of which is proportional to the ratio of the sealed pressure to the pre-compression pressure of the packing. The calculation of the distribution of the hydrostatic pressure and gap along the radius of the face joint of the seal is presented. The irregularity of the contact pressure along the radius, caused by the pressing out of the packing by the sealed inlet pressure, causes premature wear of the overloaded areas of contact surfaces. Expressions are proposed for estimating friction power losses in face packing seals. It is shown that these losses are significantly lower in comparison with the power losses in traditional stuffing box seals. Assessment of the thermal state of face packing seals has been carried out. An expression has been obtained for determining the flow rate that provides the average contact-surface temperature not exceeding the permissible value. Our studies have shown that the load factor of face packing seals, in contrast to mechanical face seals, must be close to unity. The obtained dependencies make it possible to calculate face packing seals at their design stage.

Анализ энергетических характеристик безмасляного спирального вакуумного насоса

This paper presents an analysis of the indicator power of an oil-free scroll vacuum pump based on the indicator diagrams obtained through high-speed pressure sensors. These values are compared with the results of calculations using a mathematical model of the pump working process. It is shown that the divergence of the calculated results and experimental values does not exceed 4%, which confirms the adequacy of the developed mathematical model. The total power of the scroll pump exceeds the indicator power by more than 2 times due to the friction losses between the face seals and disks of the reciprocal scroll elements, friction losses in the stuffing box seals and rolling bearings, as well as due to the coefficient of efficiency of the motor. The influence of the radial clearance between the scroll elements on the power consumption is considered. It is shown that at low pressures nearing the ultimate pressure, the power increases with the increased clearance, while at inlet pressures exceeding 40 kPa it decreases. The performed analysis can be used for selecting the optimal geometrical parameters of the scroll elements and increasing power efficiency of the pump depending on specific operating conditions.

Design Improvement of Stuffing Box Seals of Centrifugal Pump Shafts, Based on the Study of the Sealing Mechanism Physical Model

Design Improvement of Stuffing Box Seals of Centrifugal Pump Shafts, Based on the Study of the Sealing Mechanism Physical Model

Determination of mechanical characteristics of stuffing box packings

The resource of stuffing box seal is determined not only by the unit design and by the conditions of its operation, but also essentially depends on the correct choice of stuffing box packing. Not one of stuffing box packing manufacturers does not provide data on mechanical properties. Therefore, in this paper the results of experimental investigations on determining the mechanical properties of packings are presented. The obtaining mechanical characteristics allow to clarify existing methods of calculation and to increase sealing and durability of stuffing box packing seals.

CONSTRUCTION DEVELOPMENT AND BASING OF QUICK- DETACHABLECAPS APPLICATION IN HIGH CAPACITY GAS FILTERS

Erection of high capacity gas regulator stations gains more large scales nowadays. In this case gas cleaning from mechanical contaminants accomplished by filters with welded steel body, equipped with removable cap for periodic disassembly and cleaning of air filter unit аnd consisted of flange with elliptical bottom added to it. For example, for FGS-SN-500 filter with 1,2 MPa operating pressure and capacity of 150 000m 3 /h, cap mass more than 350 kg complicates considerably its disassembly and re- input setting, that are accomplished only by using the special load lifting technique built in filter construction. General duration of disassembly for removable cap of FGS-SN-500 filter, according to the data of gas distribution organization takes 1,5 hour and for re-input setting is 2,5 hours. General duration of disassembling and re-input setting of removable cap is 4, 0 hours correspondingly. At that time disassembly of air filter unit, compressed air purging and solvent washing or using washing means take no more than 1, 3 hour (in case of need). For lowering metal capacity and long duration of disassembly and re-input setting there was offered the construction of quick-detachable cap. In contrast to the existing analogue the cap is completely arranged in the inner volume of the body, it has sealed stuffing box that use rubber molding ring which can provide necessary level of pressurization for five years that is up to standard date of their replacement for new ones, efficient connection of removing cap and body without bolted joints using. The suggested construction for gas cutting off from the filter exit by quick-detachable cap with stuffing box seal by rubber molding ring comparing with existing analogues of FGS-SN-500 type permits to decrease the cap mass 1,6 times according to lowering of its outer diameter; to reduce duration of disassembly operation and re-input setting three times; to diminish the quantity of sealing gasket replacement 3,1 times; to diminish the quantity of sealing gasket replacement during the filter service life.

Compensation of Temperature Strain of the Elements of Detachable Joints

Breakdown of air tightness due to a variation in load is possible in detachable airtight joints as the temperature of their constituent elements varies. Methods of assuring the constancy of the load independently of any variation in temperature for the flange connection and a stuffing box seal with soft stuffing and calculations of the parameters necessary to achieve this objective are presented.

Evaluation of the Airtightness of a Frontal Stuffing Box Gland and the Friction of Its Sealing Elements

Results are presented for studies conducted on the airtightness of a frontal stuffing-box seal with four sealing elements. Losses of the frictional capacity of the stuffing-box packing are determined. Feasibility of effective use of frontal stuffing-box seals for rotating shafts is indicated. Recommendations are given for selection of the packing material, proceeding from values of the coefficient of friction and penetrability factor.

Conditions for Reliable Long Service by Stuffing-Box Seals

Conditions for Reliable Long Service by Stuffing-Box Seals

A theoretical analysis of the lateral pressure coefficients in a soft-packed stuffing-box seal

This paper represents a theoretical analysis concerning the relationship of the lateral pressure coefficients K i (between packing and stem) and K 0 (between packing and housing) in a soft-packed stuffing-box seal, with the result of K i K 0 = μ 0 μ i 1+ 2t d 4d+3t 4d+5t The theoretical values are consistent with the results of the experiment by W. Ochonski, K. Hayashis and K. Hirasata, and one of the authors.

Stuffing box seal having braided packings…

Stuffing box seal having braided packings…

Determination of required conditions for nonleakage of valve stuffing-box seals

Determination of required conditions for nonleakage of valve stuffing-box seals

Analysis of axial and radial stress distribution in packing in stuffing-box seals taking account of stress relaxation.

An analytical approach to determine the axial and radial stress distribution in packing in stuffing-box seals is presented taking account of stress relaxation by means of a viscoelastic model. Radial-to-axial stress ratio and friction coefficient of the asbestos and graphite packing rings were experimentally determined, and they were found to be constant over time under the stress relaxation condition. Change of stress distribution with time in asbestos/graphite packing in stuffing-box seals is investigated by comparing the analytical results with the corresponding experimental results. The stress in packing decreases rapidly just after gland tightening and gradually decreases further with time, and it reaches an asymptotic value. The stress relaxation is reduced by repeated operation of gland tightening. This analytical model can simulate such behavior of packing as observed in actual packing installation.

Stress relaxation of gland packings and its modeling.

Tightening pressure of gland packings decreases with time owing to stress relaxation of the packings. In the first step toward the analytical prediction of the stress relaxation in real tightening operation of gland packings in stuffing-box seals, the relaxation behavior of gland packings is examined both bxperimentally and theoretically. Stress relaxation tests were conducted on kland packings of asbestos and graphite. A viscoelastic model is presbnted for a dbscription of the stress relaxation of packings. This model can simulate satisfactorily the stress response of packings, especially in repeated tightening operation.

Radial stress distribution and friction forces in a soft-packed stuffing-box seal

This paper presents a theoretical analysis and experimental results concerning distribution of radial (contact) stresses at the packing-stem and the packing-housing interfaces, deformation of the packing in the mounted condition (the stationary stem, without pressure of the medium) and friction forces in the operating condition (the reciprocating stem, with pressure of the medium) in a soft-packed stuffing-box seal. The derived formulae and experimentally determined material parameters for plaited PTFE-impregnated asbestos packing can be used in the design of soft gland packings, particularly industrial fittings such as valves and gate valves.

Calculation of stuffing box seals having an expanding chamber

Calculation of stuffing box seals having an expanding chamber

Procedure for design calculation of cantilevered shafts in equipment with mixing devices

The design calculation procedure set forth in this article is based on a solution of the problem described in [1 ]; this procedure is suitable for the design of cantilevered shafts of constant or variable section, with any number of mixing devices. In calculating a constant-section shaft, the following are given (see also Fig. 1): N is the maximum power used by the shaft, in W; w is the working angular velocity of the shaft, in rad/sec; n is a standardizing factor accounting for the viscosity and density of the medium being mixed; p is the density of the shaft material, in kg/mS; E is the modulus of elasticity of the shaft material, in N/m2; e is the eccentricity of the center of equivalent mass of the shaft with the mixing devices, in m; l is the length of the supported part of the shaft, in m; L is the length of the overhung part of the shaft, in m; x is the distance to the stuffing box from the start of the overhung part of the shaft, in m; M i are the masses of the mixing devices, in kg (here i = 1, 2, 3 ..... s, where s is the number of mixing devices on the shaft); ~i are the distances to the centers of gravity of the masses M i from the start of the overhung part of the shaft, in m; I i are the moments of inertia of the masses Mi, in kg-m2; era is the allowable stress for the shaft material, in N/m2; 5 is the allowable runout (wobble) of the shaft, in m; Wa is the allowable deflection of the shaft at the location of the stuffing box, in m; ,~a is the allowable angle of twist of the shaft per meter of length, in rad/min; ,~a is the allowable angle of rotation of the shaft sections at the locations of the bearings, in rad. According to RTM [Guideline Technical Material] 145-66 [2], at the sites of the stuffing-box seals, the allowable shaft deflection should be within the limits 0.5-10-4- < wa -< 10 -4 m, the allowable angles of rotation of the shaft sections with radial bearings being ,~a = 0.01 rad, and for spherical bearings Sa = 0.05 rad. According to the data given in [3], the allowable twist angle per meter of shaft length Ca = 4.36. 10 -3 rad /m.

Rotating Disk Apparatus for Reaction Rate Studies in Corrosive Liquid Environments

This paper describes the design and use of a rotating disk apparatus for studying reactions between fluids and solid surfaces. The apparatus is capable of operation in extremely corrosive liquid environments under controlled pressures and temperatures up to 70 atm and 150°C. The design includes a unique magnetic drive assembly that allows the disk to be rotated in the high pressure reactor vessel without the need of a stuffing box seal. All parts that contact corrosive fluids are fabricated from Hastelloy alloys and Teflon. A special feature of the reactor vessel is its ready conversion to a high pressure visual cell.

Performance of a Modified Packed-Gland Seal

An experimental investigation of the mechanics of hydrodynamic lubrication and heat generation and dissipation of packed-gland rotary shaft seals was performed on a somewhat novel design. The design differs from conventional stuffing-box seals in that the packing was inverted so that it rotated with the shaft. It was also skewed so as to enhance heat transfer and lubrication. Further, the gland was loaded hydraulically so that the axial pressure applied to the packing was readily controllable. These modifications proved to be successful in that much improved stability of operation was obtained through lowered coefficients of friction (with water as the sealed fluid) and interface temperature which prolonged seal life without serious detriment to leakage. Some rheological data on Teflon-asbestos packing is presented as well as kinetic coefficients of friction. Motion picture frame photographic sequences of the packing interface showing packing deterioration and lubricant film cavitation are included also.

Sealing Characteristics of Stuffing-Box Seals for Rotating Shafts

There are two distinct modes of operation of a stuffing-box seal. One mode occurs when the axial pressures produced in the packing by tightening the gland-bush are greater than the sealed fluid pressure and the other when they are less. Under the former conditions the fluid pressure distribution is an exponential function of the packed length and the frictional torque increases rapidly with this quantity. With high fluid pressures, however, the relation between fluid pressure and packed length is no longer exponential and most of the fluid pressure drop occurs over the last 10 per cent of the packed length. In addition very little increase in frictional torque occurs when the packed length is increased. Theoretical expressions have been derived for pressure distribution and friction torque and good agreement has been obtained between these and experimental results.