FE calculations for the bolted helium vessel May 6th 2015 F. Carra, L. Dassa, N. Kuder

FE calculations for the bolted helium vessel Intro   Safety PS=1.8 bara (=0.8 barg) Vtot = 160 L Safety valve 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Intro Load cases Pre-tuning always present 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Intro Scheme 1 - Main model with bolts, highest preload 4 - analytic sub-model for bolts (according to VDI 2230 Part 2 5 - Simplified FEM model for sealing plate weld 2 - Cavity sub-model (linear) 6- analytic sub-model for welded bolt covers on flanges Not yet performed!!! Not yet performed!!! 8 - Main model with bolts, smallest preload 7 - analytic submodel for welded bolt covers on plates Strength assessment 3 - Cavity model Elasto- plastic 9 - Cavity model thermo- mechanical 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Baseline Model simplified win order to facilitate the FE analyses Thickness of the cavity reduced according to material removal during BCP 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Combining effect of bolt pretension, pressurization and pretuning Helium vessel Bolt 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 Loads and boundary conditions 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Stress Maximum stress: 110 MPa Max allowable stress: 187 MPa (Ti Grade 2) 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Deformation Maximum deformation: 0.62 mm 06/05/15 FE calculations for the bolted helium vessel

Stress Intensity: “preload + pressure + pretuning” Cavity Stress (1) 06/05/15 FE calculations for the bolted helium vessel

Cavity Stress from the submodel (1) 06/05/15 Stress Intensity: “preload + pressure + pretuning” -> sub-model Cavity Stress from the submodel (1) It is mandatory to split the total stress in : primary stress secondary stress 06/05/15 FE calculations for the bolted helium vessel

𝑃 𝑙 <1.5𝑓 -> no local stress 𝑃 𝑙 + 𝑃 𝑏 <1.5𝑓 ∆(𝑃+𝑄)<3𝑓 LINEARIZATION Cavity 𝑃 𝑚 <𝑓 𝑃 𝑙 <1.5𝑓 -> no local stress 𝑃 𝑙 + 𝑃 𝑏 <1.5𝑓 ∆(𝑃+𝑄)<3𝑓 Stress (2) Stress due to pressure (primary stress) Stress due to pre-tuning (secondary stress) not present 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Pressure ONLY Stress due to pre-tuning (secondary stress) not present ONLY primary stress Cavity Stress from the submodel (2) 06/05/15 FE calculations for the bolted helium vessel

Cavity 𝑃 𝑚 <𝑓 𝑃 𝑙 <1.5𝑓 𝑃 𝑙 + 𝑃 𝑏 <1.5𝑓 ∆ 𝑃+𝑄 <3𝑓 LINEARIZATION on primary stress (only pressure) Cavity Stress Linearization 𝑃 𝑚 <𝑓 𝑃 𝑙 <1.5𝑓 𝑃 𝑙 + 𝑃 𝑏 <1.5𝑓 ∆ 𝑃+𝑄 <3𝑓 Red: membrane stress Green: bending stress Blue: membrane + bending stress VERIFIED 06/05/15 FE calculations for the bolted helium vessel

Cavity Elastic-plastic analysis (1) 06/05/15 THIS IS NOT A STRENGHT ASSESSMENT. Analysis performed only to have an idea about the plastic behaviour Cavity Elastic-plastic analysis (1) Equivalent stress 06/05/15 FE calculations for the bolted helium vessel

Cavity Elastic-plastic analysis (2) 06/05/15 THIS IS NOT A STRENGHT ASSESSMENT. Analysis performed only to have an idea about the plastic behaviour Cavity Elastic-plastic analysis (2) Total principal structural strain 1: 0.00511 / -6.07e-06 Total principal structural strain 2: 0.000694 / -0.000378 Total principal structural strain 3: 3.6e-06 / -0.00519 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Cavity Buckling Load multiplier = 48 wrt to p = 0.18 MPa 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Weld seams for plates Model Welds modelled as the edge-face contacts. Contacts established after the bolt preload to prevent the weld prestressing. before preload direction of relative plate movement 06/05/15 FE calculations for the bolted helium vessel

Weld seams for plates Results from FEM 06/05/15 ANSYS reaction moments and forces attached to the 3D solid weld seam. Results from FEM 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Weld seams for plates Fixed surface Surface where the loads are applied Strength assessment in Ansys Maximum stress (linearized): 142 MPa (with raw and fine mesh) Max allowable stress: 187 MPa (Ti grade 2) 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Bolts Model Pressure 0.18 MPa Sliding δ δ Mb -Mb Bolt line Threaded hole ---- Fixed joints Washer imprinted face Frictionless contact Bolt modeling in ANSYS 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Bolts The geometry of the beam corresponding to the bolt has been derived from the VDI 2230 Part 2 Results form Ansys Applied preload: 3800 N For the maximum values of the bending moment and shear force from ANSYS: Warning: the shear load evaluated with simplified model is > 362 N A part of the pressure load is carried out by the weld seams. Max. axial force PA [N] 3955 Max. bending moment Mb [Nmm] 1648 Max. shear force T 245 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Bolts For the assembly conditions Minimum preload: 2280 N Maximum 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. VDI strength assessment Surface pressure Evaluated 97 MPa Maximum : ? (1340 for Ti Grade 5) For the operating conditions Axial stress σa [MPa] 276 Bending stress σb 129 Shear stress τ 107 Equivalent stress σeq 445 Safety factor k - 1.9 Minimum length of engagement Actual length: 9 mm Minimum length: 6.9 mm 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Bolts Open questions Washers: Yes? Not? Which type? Locking effect? Galling ->Which coating to prevent it?: Dioxide? Molykote? 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Weld seams for bolts cover 06/05/15 FE calculations for the bolted helium vessel

Bolts Contact between plates 06/05/15 The joints don’t open. Contact between plates to be improved (in some cases) 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Thermal effects 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Optimization The scope Promising results: we think we are able to reduce the weight by 30 kg without loosing in stiffness 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Future tests 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 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 06/05/15 FE calculations for the bolted helium vessel

FE calculations for the bolted helium vessel Tank RFD Similar strength assessment will be performed for the tank of the RFD cavity 06/05/15 FE calculations for the bolted helium vessel