PACKING
Figure 4 : Sealing test cell details Figure 5 : Mechanical test cell details in Figure 1 , except for the gland flange mechanical integrity check where 2-bolt non-axisymmetric configurations are considered . Figure 2 shows the global calculation sequence . An “. xls ” spreadsheet has been developed to apply the calculation . The calculation process involves two major steps . 1 . Calculation of the required initial bolt load to fulfil the tightness criteria in all the situations ( assembly and operation ) and definition of the tightening range from the tool dispersion
2 . A check on the mechanical integrity of the bolt and the gland flange and check of packing friction level for an initial bolt force corresponding to the upper limit of the tightening range
fully transferred to the first ring in contact with the gland . A pure axial displacement is considered for the gland without any alignment problem . The mechanical model accounts for deformation and stiffness of the packing and the live loading-system . No deformation is considered for the gland , stuffing box or bolts . The bolt load variations between the assembly phase and operation conditions are calculated taking into account the differential axial thermal expansion in the packing assembly and the packing rings creep / relaxation behaviour . The use of a live-loading system can be introduced in this calculation .
Packing characterization
The following packing material parameters can be handled by the calculation model :
• For sealing behaviour : the required initial axial contact pressure on the packing top surface at tightening QA ( L ) and during operation Qsmin ( L ) to meet the tightness class L .
• For mechanical behaviour :
• The relaxation ( or creep ) coefficient
• The axial to radial load transmission coefficient
• The static friction coefficient at the stem / packing and housing / packing interface
Gland deformations ( bending ) are neglected , and the axial bolt load is assumed to be
Figure 6 : Mechanical test cell with heating element
Figure 7 : Leakage diagram ( reference A ) for 40 MPa initial load
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