Stress & Buckling FEA – Powder Decanter to ASME Section VIII Code

FEA Model of Decanter
FEA Model of Decanter
(FEA) Stress Intensities in Decanter
FEA Stress Intensities in Decanter

 

Stress and Buckling (FEA) Analysis on a Powder Decanter, which is used to Transfer Microcomposite Materials from one Reactor to Another. The buckling analysis was performed in accordance with ASME Boiler and Pressure Vessel Code Section VIII, Division 1.

The 14 gage (0.0781 inches) thick stainless steel decanter is supported by four 5/8-inch diameter bolts, and is subjected to external pressure (vacuum load) and product weight.

Material Properties

The decanter is manufactured from 304 stainless steel. The bolts used were specified as 316 stainless steel. The material properties used in the analysis are:
Young’s Modulus: 28.3 x 106 psi
Yield Strength: 30 ksi
Tensile Strength: 70 ksi

Four different load cases of the decanter were evaluated:

  • Bolt preload only
  • Bolt preload + deadweight
  • Bolt preload + deadweight + external pressure (vacuum)
  • Bolt preload + deadweight + external pressure + product load

Allowable Stresses

Stresses in the decanter were determined using finite element analysis, rather than hand calculations. Allowable stresses for the decanter were therefore taken from Section VIII, Division 2 of the ASME Code, which governs design by analysis. The allowable linearized stress intensity for SA240 Type 304 stainless steel is 20 ksi at areas away from local discontinuities, and 30 ksi at locations of local discontinuities.

The allowable stress for 316 stainless steel bolts are not in the ASME Code. However, the allowable stresses in the ASME Code are determined by taking the minimum of two-thirds times the yield strength of the material, and one-third of the ultimate strength of the material. Using this method, the allowable stress for the 316 stainless steel bolts is 20 ksi.

Buckling Analysis

The buckling evaluation of the Gen II Powder Decanter was performed in accordance with Section VIII, Division 1, of the 2001 ASME Boiler and Pressure Vessel Code using the computer program CodeCalc. The cylindrical, cone, and head portions of the decanter were evaluated for buckling due to an external (vacuum) pressure of 15 psig and found to be acceptable. The required minimum thicknesses for the small cylinder, cone, large cylinder, and head are 0.0191 inches, 0.0412 inches, 0.0412 inches, and 0.0625 inches respectively. All of these values are less than the nominal thickness of 0.0781 inches.

Stress Analysis

The stress analysis was performed using ANSYS finite element software, using ten-node structural tetrahedral solid elements. For other features, such as the bolts, two-node beam elements were modelled. The model had approximately 99,000 nodes and 53,000 elements. Various loading conditions (bolt preload, deadweight, and vacuum pressure) were used to verify the structural integrity of the vessel. The deadweight of the decanter was taken into account by applying an acceleration to the decanter equal to gravity in the z-direction. An external (vacuum) pressure of 15.0 psig was applied to the inside surfaces of the decanter.

Conclusions

The evaluation showed the Gen II Powder Decanter to be acceptable for vacuum and product load conditions with respect to deformation, stresses, and buckling. The deformations of the decanter when subjected to loading were negligible and all of the stresses were shown to be well below the allowable stress. The nominal thickness of the decanter was also shown to be sufficient to prevent buckling due to vacuum loading.

 

O’Donnell Consulting Engineers Performs Design and (Thermal, Stress & Buckling) Analysis to ASME Code for Clients in Industries Including Energy, Mining and Petrochemical.

(412) 835-5007

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