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