©　2017　Higher　Education　Press　and　Springer-Verlag　Berlin　Heidelberg　The　hypercompressor　is　one　of　the　core　facilities　in　low　density　polyethylene　production,　with　a　discharge　pressure　of　approximately　300　MPa.　A　packing　cup　is　the　basic　unit　of　cylinder　packing,　assembled　by　the　interference　fit　between　an　inner　cup　and　an　outer　cup.　Because　the　shrink-fitting　prestresses　the　packing　cup,　serious　design　is　needed　to　gain　a　favorable　stress　state,　for　example,　a　tri-axial　compressive　stress　state.　The　traditional　method　of　designing　the　interference　fit　value　for　packing　cups　depends　on　the　shrink-fit　theory　for　thickwalled　cylinder　subject　to　internal　and　external　pressure.　According　to　the　traditional　method,　critical　points　are　at　the　inner　radii　of　the　inner　and　external　cup.　In　this　study,　the　finite　element　method　(FEM)　has　been　implemented　to　determine　a　more　accurate　stress　level　of　packing　cups.　Different　critical　points　have　been　found　at　the　edge　of　lapped　sealing　surfaces　between　two　adjacent　packing　cups.　The　maximum　Von　Mises　equivalent　stress　in　a　packing　cup　increases　after　a　decline　with　the　rise　of　the　interference　fit　value.　The　maximum　equivalent　stress　initially　occurs　at　the　bore　of　the　inner　cup,　then　at　the　edge　of　lapped　mating　surfaces,　and　finally　at　the　bore　of　the　outer　cup,　as　the　interference　radius　increases.　The　traditional　method　neglects　the　influence　of　axial　preloading　on　the　interference　mating　pressure.　As　a　result,　it　predicts　a　lower　equivalent　stress　at　the　bore　of　the　external　cup.　A　higher　interference　fit　value　accepted　by　the　traditional　method　may　not　be　feasible　as　it　might　already　make　packing　cups　yield　at　the　edge　of　mating　surfaces　or　the　bore　of　the　external　cup.　Along　with　fatigue　analysis,　the　feasible　range　of　interference　fit　value　has　been　modified　by　utilizing　FEM.　The　modified　range　tends　to　be　narrower　and　safer　than　the　one　derived　from　the　traditional　method,　after　getting　rid　of　shrink-fit　values　that　could　result　in　yielding　in　a　real　packing　cup.