Research data for five types of gland packings are reported. Relationships are shown with due regard for the number of loadings and the number of packing layers: relative deformation of the packing due to unit load, unit load on the packing due to its relative deformation, and compression and recovery modulus arising from relative deformation of the packing.Nowadays, gland packings made from heat-expanded graphite (HEG) are being increasingly used in global practice (in power, chemical, petrochemical, and oil and gas industry). This material has a low density and a relatively high elasticity, is resistant to many corrosive working media, and has a low friction coefficient and a high wear resistance.For calculating and designing gland seals with soft packing, it is essential to know the deformation characteristics of the HEG-based packings (coefficient of lateral pressure, shrinkage and recovery of the packings, friction coefficient, etc.).The coefficient of lateral pressure k is a ratio of unit loads on the packing in the radial q r and axial q z directions, i.e., k = q r /q z , and depends on many factors (material of the packing, its preliminary compaction, and axial unit load q z on the packing). It is determined only experimentally. In [1-3], the coefficient k was determined from the peripheral deformation of the outer surface of the chamber wall at a fixed axial load on the packing placed in the chamber. This deformation can be determined from the readings of the strain resistors attached to the wall [1] or of an elastic element in contact with the outer surface of the chamber wall [2,3]. The accuracy of k determination depends on the radial rigidity of the chamber wall (on the wall thickness): the greater the rigidity, more reliable the results. However, acceptable readings of the strain resistors or of the elastic element can be obtained only at a relatively low rigidity of the wall amenable to deformation. All k values obtained by this method are somewhat underestimated, and the degree of underestimation depends on the difference between the absolute rigidity (taken as absolute) and the actual radial rigidity of the wall of the gland chamber of the experimental unit.In all the referred works, the coefficient of lateral pressure was determined on the outer contour of the packing and the same value was taken for its inner contour.
It is shown that the mode of setting gasket between flanges significantly affects its axial pliability, which is a key flanged-joint calculation parameter. gasket has been studied for four modes of setting gasket between flanges: with primary compression (without lateral restraint), with one-sided internal restraint, with one-sided external restraint, and with volumetric (three-dimensional) compression. It is shown that the mode of setting gasket markedly affects the leak-tightness of the joint and the strength of its individual components. The described calculation procedure can be used to obtain the required data also for flanged joints with gasket made of materials that differ from fluoroplastic-4 in physicomechanical parameters.Calculation of detachable flanged joints for leak-tightness and strength is based on an assessment of the rigidity (pliability) of their components: flanges, fastening bolts, gasket, etc. The pliability values for the joint components are included in the calculating equations for the determination of the key parameters of the joint: diameter and number of fastening bolts, geometric dimensions of the flanges, force of gasket preloading, etc.[1]. The pliability of the bolts and flanges depends on their geometric parameters and the modulus of elasticity of the material, which, for these components, are taken as constant in the elastic stage of operation in the case of both loading (compression) and unloading (recovery) of the component. The deformation characteristics of the gasket with due account of its material depends, as a rule, on the magnitude and nature of loading (loading or unloading) and mode (conditions) of gasket setting between the flanges.Investigations were made on the axial pliability of an annular gasket from fluoroplastic-4 (polytetrafluoroethylene), also known as Teflon, set between the flanges with axial compression without restraining radial deformation, with one-sided internal restraint, with one-sided external restraint, and with volumetric (three-dimensional) compression. The investigation results [2] are plotted in Fig. 1. As evident from these plots, radial deformation under axial compression occurs essentially along the external contour of the annular gasket.The gasket is loaded with a unit compressing axial load q, under the action of which the gasket thickness diminishes, the outer radius r 2 increases, and the inner radius r 1 diminishes. However, the changes in these parameters differ owing to curvature of the gasket contour. Upon axial compression of the gasket tensile and compressive annular stresses appear in certain sections (across the gasket breadth). The gasket radius on which the annular stresses change sign ("neutral radius") [3]:
A conical joint is considered (flange variety) for joining parts of a pipeline. The main difficulty in the design is the need to provide difference in heights between the conical surfaces at the ends of the joined tubes and the conical surfaces in the seal, which is equal to the extent of compression of the insert in assembling the joint. The calculation is performed on the conical joint with reference element and packing, which is made from PTFE-4.A clamped connection ( Fig. 1) is used to join individual parts of a pipeline and by comparison with a flange joint (under otherwise equal conditions) involves less use of metal and less working effort in the assembly (particularly for points of difficult access). For example, for a pipeline with D y = 50 mm working at a pressure of 35 MPa the metal capacity of the clamped joint is less by a factor 6.9 than that of a standard flange one [1]. The relatively small volume in these joints in Russian equipment is explained by the absence of any necessary standard basis.The main difficulty in designing the joints consists in the need to provide a certain difference in heights of the conical surfaces of the end parts of the pipes and the conical surfaces in the joint (on the mean diameter), which should be equal to the magnitude ∆ of insert compression during the joint assembly. If the actual height difference is less than ∆, then the insert will not be loaded by the force providing the sealing. If on the other hand that difference is greater than ∆, the clamp will not be completely covered by the conical surfaces. To resolve this problem, it is proposed to design the joints in which the clamp is made from individual elements [2] or with a flexible force element [3].We consider the calculation of a clamp compound with sealing element (insert) made from PTFE-4. The cold PTFE-4 is mobile, and the insert is located in a closed volume and parallel to it there is a limiter for the axial deformation, whose axial rigidity considerably exceeds the axial rigidity of the insert [4,5]. The limiter on loading the insert during assembly of the joint provides for preservation of the given deformation of the insert during the increase of the sealing pressure to the working level.There is a necessary initial excess in the conical surfaces for the end parts of the tubes over the corresponding part of the clamp, which produces certain difficulty in assembling the joint. At the start of tensioning, the mounting bolts in the contact zone of the conical surfaces and the end parts of the tubes there are initial parts of the semicircle contacts, while the deviation of the median circles of the contact zone and the end parts of the joined tubes occurs in the middle part of the semicircle and is determined by the formula e * = ∆/2tanβ.
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