FE calculations for the bolted helium vesselMay 6th 2015
F. Carra, L. Dassa, N. Kuder
FE calculations for the bolted helium vessel 206/05/15
IntroSafety
Safety valve
● PS=1.8 bara (=0.8 barg)
● Vtot = 160 L
IntroLoad cases
Pre-tuning always present
06/05/15 FE calculations for the bolted helium vessel 3
IntroScheme1 - Main model
with bolts, highest preload
2 - Cavity sub-model (linear)
7 - analytic submodel for welded bolt covers on plates
6- analytic sub-model for welded bolt covers on flanges
4 - analytic sub-model for bolts (according to VDI 2230 Part 2
5 - Simplified FEM model for sealing plate weld
8 - Main model with bolts, smallest preload
3 - Cavity model Elasto-plastic
Strength assessment
9 - Cavity model thermo-mechanical
Not yet performed!!!
Not yet performed!!!
FE calculations for the bolted helium vessel 406/05/15
Helium vesselBaseline
Model simplified win order to facilitate the FE analysesThickness of the cavity reduced according to material removal during BCP
FE calculations for the bolted helium vessel 506/05/15
Combining effect of bolt pretension, pressurization and pretuningBolt pretension 3800 N
Gravity 9806.6 mm/s2
0.2 mm
Pressure 0.18 MPa
Thermal expansion 0.2 mm
Fixed support
Scale x100
Cavity submodel
Helium vesselLoads and boundary
conditions
FE calculations for the bolted helium vessel 606/05/15
Helium vesselStress
Maximum stress: 110 MPaMax allowable stress: 187 MPa (Ti Grade 2)
FE calculations for the bolted helium vessel 706/05/15
Helium vesselDeformation
Maximum deformation: 0.62 mm
FE calculations for the bolted helium vessel 806/05/15
CavityStress (1)
Stress Intensity: “preload + pressure + pretuning”
FE calculations for the bolted helium vessel 906/05/15
CavityStress from the submodel (1)
FE calculations for the bolted helium vessel 10
Stress Intensity: “preload + pressure + pretuning” -> sub-model
It is mandatory to split the total stress in :
• primary stress
• secondary stress
06/05/15
Stress due to pressure (primary stress)
-> no local stress
LINEARIZATION CavityStress (2)
Stress due to pre-tuning (secondary stress) not present
FE calculations for the bolted helium vessel 1106/05/15
CavityStress from the submodel (2)
Pressure ONLYStress due to pre-tuning (secondary stress) not presentONLY primary stress
FE calculations for the bolted helium vessel 1206/05/15
CavityStress Linearization
LINEARIZATION on primary stress (only pressure)
FE calculations for the bolted helium vessel
• Red: membrane stress• Green: bending stress• Blue: membrane + bending stress VERIFIED
06/05/15
CavityElastic-plastic analysis (1)
THIS IS NOT A STRENGHT ASSESSMENT.Analysis performed only to have an idea about the plastic
behaviour
Equivalent stress
FE calculations for the bolted helium vessel 1406/05/15
CavityElastic-plastic analysis (2)
THIS IS NOT A STRENGHT ASSESSMENT.Analysis performed only to have an idea about the plastic behaviour
Total principal structural strain 1: 0.00511 / -6.07e-06Total principal structural strain 2: 0.000694 / -0.000378Total principal structural strain 3: 3.6e-06 / -0.00519
FE calculations for the bolted helium vessel 1506/05/15
CavityBuckling
Load multiplier = 48 wrt to p = 0.18 MPa
FE calculations for the bolted helium vessel 1606/05/15
before preload
direction of relative plate movement
Welds modelled as the edge-face contacts. Contacts established after the bolt preload to prevent the weld prestressing.
Weld seams for platesModel
FE calculations for the bolted helium vessel 1706/05/15
Weld seams for platesANSYS reaction moments and forces attached to the 3D solid weld seam.
Results from FEM
FE calculations for the bolted helium vessel 1806/05/15
Fixed surface
Surface where the loads are applied
Weld seams for platesStrength assessment in Ansys
Maximum stress (linearized): 142 MPa (with raw and fine mesh)Max allowable stress: 187 MPa (Ti grade 2)
FE calculations for the bolted helium vessel 1906/05/15
BoltsModel
δ
Mb
-Mb
Sliding
δ
Pressure 0.18 MPa
Bolt line
Threaded hole
---- Fixed jointsWasher imprinted face
Frictionless contact
Bolt modeling in ANSYS
FE calculations for the bolted helium vessel 2006/05/15
Bolts
For the maximum values of the bending moment and shear force from ANSYS:
Results form Ansys
Max. axial force PA [N] 3955
Max. bending moment
Mb [Nmm] 1648
Max. shear force T [N] 245
Applied preload: 3800 N
Warning: the shear load evaluated with simplified model is > 362 N A part of the pressure load is carried out by the weld seams.
The geometry of the beam corresponding to the bolt has been derived from the VDI 2230 Part 2
FE calculations for the bolted helium vessel 2106/05/15
BoltsVDI strength assessment
Axial stress σa [MPa] 276
Bending stress σb [MPa] 129
Shear stress τ [MPa] 107
Equivalent stress σeq [MPa] 445
Safety factor k - 1.9
For the operating conditions
For the assembly conditions
Minimum preload: 2280 NMaximum preload: 3800 N(60% of scattering allowed)
Utilization factor: 45% (usually around 80%)Assembly Permitted Preload: 4490 N
Warning: Procedure for preload definition could be modified since it seems that the preload required is even lower.
Minimum length of engagement• Actual length: 9 mm• Minimum length: 6.9 mm
Surface pressure• Evaluated 97 MPa• Maximum : ? (1340 for Ti Grade 5)
FE calculations for the bolted helium vessel 2206/05/15
FE calculations for the bolted helium vessel 23
BoltsOpen questions
Washers:• Yes? Not?• Which type?• Locking effect?
Galling ->Which coating to prevent it?:• Dioxide?• Molykote?
06/05/15
Weld seams for bolts cover
FE calculations for the bolted helium vessel 2406/05/15
BoltsContact between plates
The joints don’t open.
Contact between plates to be improved (in some cases)
FE calculations for the bolted helium vessel 2506/05/15
FE calculations for the bolted helium vessel 26
Thermal effects
06/05/15
OptimizationThe scope
Promising results: we think we are able to reduce the weight by 30 kg without loosing in stiffness
FE calculations for the bolted helium vessel 2706/05/15
Future tests
Test are planned for:
• Friction between titanium threads and between bolt head and plate
• Traction test on bolts at room T and at 2 K• Shear behaviour of the bolts at room T and at 2 K• Friction between Titanium plates at room T and at 2 K• Test of a dummy vessel• Coatings on bolts
Cavity calculation will be performed again in order to verify the not clarified points:• with higher preload on bolts• with friction
Very conservative hypothesis:• No friction between plates (-> all the shear load carry out by the
bolts)• Pressure (1.8 bara) due to the vacuum failure considered as
permanent load on the cavity • Very low preload on the bolts
FE calculations for the bolted helium vessel 2806/05/15
Tank RFD
Similar strength assessment will be performed for the tank of the RFD cavity
FE calculations for the bolted helium vessel 2906/05/15
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