Insulation vacuum and beam vacuum overpressure release

1. Insulation vacuum and beam vacuum overpressure release V.Parma ,TE-MSC, with contributions from: V.Baglin, P.Cruikshank, M.Karppinen, C.Garion, A.Perin, L.Tavian, R.Veness • Content: • Insulation vacuum: • Present overpressure release scheme • Evidence from sect.3-4 incident • Maximum Credible Incident (MCI) • New overpressure release scheme • for sectors remaining cold • for warmed up sectors • Beam vacuum overpressure release • Summary • Acknowledgements (EN,TE,GS): S.Atieh, J.P.Brachet, P.Coly, M.Duret, B.Delille, G.Favre, N.Kos, T.Renaglia, J.C.Perez, J.M.Geisser, M.Polini, and many others... Chamonix, 3rd February 2009

2. Present configuration of pressure relief devices in standard arcs 50m 100m 50m • Quench valves on cold mass circuit (QV): • 3 QV, DN50 each, open on quench trigger; CM pressure ≤ 20 bars • Cryostats: • Vacuum vessel, interconnect sleeve bellows: not a pressure vessels according to European Directives (provided Δp≤0.5 bars). Design pressure: 1 bars external; 1.5 bars internal • Vacuum Barrier. Is a pressure vessel. Design pressure: 1.5 bars; Test pressure: 1.87 bars • Insulation vacuum pressure relief devices (SV): • Designed to keep internal pressure ≤ 1.5 bars, for a helium release with mass flow ≤ 2 kg/s (helium releasefrom cold mass to insulation vacuum without electrical arc) • 2 spring-loaded valve devices, DN90 each, 100m spaced • Opening at Δp= 70 mbar, full open at Δp= 140 mbars, •  Experimentally validation on QRL test cell

3. Existing pressure relief device Mounted on SSS

4. Pressure Forces on SSS with vacuum barrier jack Vacuum barrier 1/3 load through support post 2/3 load directly to vessel • Forces • Δp = 1.5 bars across vac. Barrier  120 kN(40 kN through support post, 80 kN through Vacuum Barrier) • 120 kN taken by 1 jack fixed to ground • Strength limits: • Support post. Load capacity up to 80 kN (Eq.to 3 bars) without collapsing (but additional testing needed to confirm value) • Vacuum barrier: 1.5 bars design pressure, (tested to 1.87 bars). Buckling safety factor ~3,  strength limit: ~ 4.5 bars (but testing mandatory to confirm value) • Note: if support post collapses, Vacuum Barrier collapses, but not necessarily viceversa!

5. Sect.3-4 incident: Ins.Vac.overpressure (DN90) (DN90) Q27 Q23 Q24 Q25 Q26 214 m • Collateral damage observed in sect.3-4: • Primary damage (direct effect of pressure/flow): • 3 SSS with vac. barrier uprooted and longitudinally displaced • Floor break at jack fixations, but also studs broken • MLI damage, soot • Bellows damage (CM and beam vacuum lines) •  Avoidable by limiting pressure rise and improved ground fixation • Secondary damage (consequence of SSS displacements): • ”Tug of War” effect . Damage to chain of interconnects/dipoles • Break of dipole support posts and cold masses longitudinal displacement in vessel • 1 SSS without vac.barrier uprooted and longitudinally displaced • Secondary arcs in damaged interconnects • Additional MLI damage and soot propagation to adjacent vacuum subsectors •  Avoidable if primary damage avoided

6. Development of pressures G. De Rijk

7. Pressure estimate from elasto-plastic deformation of interconnect bellows  DR=20mm 1055mm 1016 mm • Assumptions: • Elastic-plastic material, yield stress= 275MPa, • 2D FE model with large displacements • Proportional loading  Pressure to have DR ~20mm = 7 bars C.Garion

8. Helium mass-flow rate Estimated mass flow Recordeddata (cold mass) Temperature P4_34:LQOAA_25R3_TT821 Temperature P4_34:LQOAA_25R3_TT821 Temperature (K) Temperature (K) Mass flow (kg/s) Pressure (bar) Time (s) Time (s) Hypothesis: Heliumtemperaturegiven by sensor P4_34:LQOAA_25R3_TT821 All helium discharged through 1 hole. No plug major failure. Constant hydraulic diameter 54 mm Total mass of helium = 214 m x 0.026 m3/m x 147.8 kg/m3 = 822 kg A.Perin

9. Evidence in sect.3-4 Q28 3R: weak floor broke, not studs F < 120-150 kN Other cases: floor broke AND studs  F> 120-150 kN ?

10. Maximum Credible Incident (MCI)

11. MCI scenario 11 • In the sect.3-4 incident, the electrical arc has burnt the M3 pipe, the E line (partially), the V2 line and the V1 line (partially). • Could an electrical arc at a higher current burn also the M1 and/or the M2 line simultaneously ? With additional arcs on MQ bus-bar ? • In case it occurs, the mass-flow discharged to the vacuum enclosure could increase by a factor 3 (~ 60 kg/s). What about He temperature in vacuum enclosure ?

12. Possible MCI arc damage ? MCI ? Sect.3-4 incident L.Tavian

13. Maximum flow for MCI L.Tavian • The pressure evolution of the cold-mass allows to assess the overall mass flow (Sect.3-4:average ~15 kg/s, peak ~20 kg/s) • But we know from visual inspection that additional holes (secondary arcs) has been created by mechanical rupture of an interconnect. • What is the part of the total mass-flow due to this mechanical rupture ? If not negligible, mass flow of peak ~20 kg/s is a conservative value • Burning of 3 M lines will create a free opened section of 6 x 32 = 192 cm2. • But the free section available in the cold mass is about 2 x 60 = 120 cm2.  consequently, this section will limit the maximum flow to two times the flow produced by the sect.3-4 incident (~40 kg/s)

14. Overpressure estimates (MCI) (sect.3-4) (initial estimate) L.Tavian

15. What can we do on cold sectors without warming them up?(sect.2-3, 4-5, 7-8 and 8-1) “Making the best use of existing ports”

16. Existing ports: all on SSS Vac.inst. DN100 cryo.inst. DN63 BPM DN100 BPM DN100 • Every SSS: 5 ports • 4 DN100 ports (2 for vac. equip., 2 for BPM cable feedthrough) • 1 DN63 port (for cryogenic instrumentation feedthrough) • Every standard vacuum sub-sector: 4 SSS, i.e. 20 ports: • 16 DN 100 ports • 4 DN63 ports

17. Use of ports 214 m • 8 DN 100 ports for insulation vacuum equipment: • 2 for safety relief devices (VVRSH) • 2 pumpout ports (VFKBH) • 1 by-pass pumping group (VPGFA) • 1 gauge cross (VAZAA) • 2 blank flanges (VFKBH) • 8 DN100 ports (not shown in layout) for BPM cable feedthroughs (2 x SSS) • 4 DN63 ports (not shown in layout) for cryogenic inst Layout drawing LHCLSVI_0020 Use as pressure relief ports

18. The strategy Replacing clamps with spring-loaded clamps (so-called “pressure relief springs”) Port acts as an additional relief device Blow-off flange, effective full-open area (unlike present valves) General reluctance for safety reasons in applying to instrum.ports: opening by tripping over, BPM on tunnel passage side “pressure relief springs” Vac. Equip. DN100 Cryo.inst. DN63 BPM DN100 Use of instrumentation ports should be temporary, until warming up of sectors

19. Pressure relief spring Prototype • Main Functions: • Provide leak tightness at initial pumpdown from atm. pressure < 1 mbarl/s. • Opening pressure < 0.5 bar Δp • Provide adequate sealing • Avoid opening due to external forces (e.g. instr.cable forces) Patrick Coly WimMaan Paul Cruikshank Cedric Garion Testing of a prototype

20. Status of relief springs • Procurement: • Relief springs for 432 DN63, 1870 DN100, 1232 DN200 (plus spares) • Offer this week • Validate DN63,100, 200 with small pre-series (geometry, installation, opening tests) • Still to define: • Flange retention system • Protection measures to avoid hazardous opening (stepping on, hitting…) • Safety approval: on-going discussions with GS • Installation: could start from wk 13 Input P.Cruikshank

21. SV SV SV SV SV Cold sectors, new (temporary) relief scheme • Keep existing 2 DN90 relief devices • Mount relief springs on 5 DN100 vac. flanges • Mount relief springs on 8 DN100 BPM flanges • Mount relief springs on 4 DN63 cryo.instr. flanges  Cross section increase: x 10

22. Overpressure in vacuum vessel (MCI) 3.3 2.8 (sect.3-4) (initial estimate) L.Tavian

23. Consequence of pressure above 1.5 bars (1/2) P> 1.5 bars (ΔP>0.5 bars): • According to European Directives (EN13458), vacuum enclosure is a pressure vessel  to be treated accordingly. Safety implications being discussed with GS (B.Delille) 1.5 bars< P < 3 bars: • Risk of breaking floor and jack fixations • Improve jack fixations to floor (see next talk by O.Capatina): under a load equivalent to 3 bars (240 kN), no collapsing allowed (but damage and plastic deformations acceptable). Why up to 3 bars? Because at 3 bars support posts become critical. Important: • Evidence in sect.3-4 of floor breaking at p<1.5-1.87 bars (120-150 kN is limit of studs) • Jack fixations in tunnel tested up to 1 bars (120 kN) only, during vacuum commisionning (atm./vacuum on vacuum barriers) installation when Vacuum Barriers. Not tested at 1.5 bars •  Floor strenght should be checked too!

24. Consequence of pressure above 1.5 bars (2/2) 3 bars<P<4 bars: • Strenght of Vacuum Barriers/Support Posts/Jack fixations becomes marginal • If Support Post collapses, Cold Mass moves and collapses Vacuum Barrier similar chain of events as for sect.3-4, BUT pressure relief from opening of interconnect bellows may not occur, consequences could be more severe than in sect.3-4. Assess the upper limit above 3 bars: rupture testing of supports/VB/jacks fixations P~ 4 bars • Stability underexternal pressure of Plug In Module bellows risk of breaking beam vacuum

25. New overpressure relief scheme “Adding extra relief devices”To be implemented now on sect.1-2, 3-4, 5-6 and 6-7, and later on remaining sect. when warmed up

26. SV SV SV SV SV SV SV SV SV SV SV SV SV SV SV SV SV New overpressure relief scheme • Keep existing 2 DN90 relief devices • Mount relief springs on 4 DN100 blank flanges • Add 12 DN200 new relief devices (1 per dipole)  Cross section increase: x 33

27. Overpressure in vacuum vessel (MCI) 1.3 1.22 (sect.3-4) (initial estimate) OK, well below 1.5 bars design pressure L.Tavian

28. Additional ports: 1 DN200 on every dipole DN200, reasonable upper limit for safe milling Top position is best for safety (personnel, H/W), and for gravity sealing of cover Interconnection sleeve opened for removal of chips and protection of MLI (prevent fire hazard) Left position is best for flow conductance through thermal shield (large openings) Cross cut on MLI of thermal shield to help prevent plugging Courtesy of TRenaglia

29. Relief device: detailed view External weld for safety (limited risk of burning MLI) and ease Thick tube for weld quality, and limited distortion of sealing surface St.steel top cover, with O-ring sealing Self-weight sealing, but spring clamps can be mounted if necessary Courtesy of T. Renaglia

30. Trials and qualifications Thermographic picture Max.internal T 130°C, 40°C on MLI Geometrical check during welding Trials and qualification steps • W2: Final Design, Material order, 3 off trial nozzles, 1 off cutting tool (ø217.5) • W3-4: Welding trial 1 (DMOS in SMA18), Welding trial 2 (QMOS in SMA18 with APAVE), Welding trial 3 (SMI2:MB3118, complete valve and leak tests) • W5: Production of 20 pre-series valves at CERN • W5: Training and qualification of the three intervention teams (Dubna, S-107, S-108) M.Karppinen

31. Provisional Installation Schedule M.Karppinen

32. Special cases (1/2) • Mid-arc vacuum sub-sectors: • ½ length insulation vacuum sub-sector (~100 m) • 6 dipoles  only 6 DN200 relief devices • 2 SSS  4 DN100 6 DN200 + 4 DN100 2.1 1.8 >1.8 bars  needs a 2nd DN200 device on dipoles L.Tavian

33. Special cases (2/2) • DS zones: • 20% shorter insulation vacuum sub-sector (~170 m) • 8 dipoles  only 8 DN200 relief devices • 4 SSS (Q11-Q8), [5 around Pt.3-7 (Q7)]  ~ 8 DN100 8 DN200 + 8 DN100 1.52 1.4 L.Tavian Marginal, >1.5 bars, if T>80K  proposed adding 2nd DN200 on dipoles

34. Still pending... Study of overpressure for: • Standalone cryo-magnets in LSS • Triplets

35. 128 cm2 100 cm2 128 cm2 450 cm2 128 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 1000 cm2 Radial conductance (area)(passage from cold mass to vacuum vessel) Impedance: • Aluminum shielding • MLI Conductance: • Thermal shield slots • At support posts (for thermal contractions) • At vacuum barriers • At Instrumentation Feedthroughs and diode • TOTAL per vacuum sub-sector: 12900 cm2 • ~ 100 times area of presentover-pressure valves • ~ 10 times area of new overpressurescheme for cold sectors • ~ 3 times area of new overpressurescheme for warm sectors • Transversal conductance is not the «bottleneck», if MLI does not restrict passage

36. MLI obstruction in sect.3-4 Suction/ripping/clogging through over-pressure valve • …yessomecloggingat valves, but… • full-open DN solution willbeless sensitive • No evidence in sect.3-4 event of full blanket • blownapart (Velcro™ fixation holds)

37. Beam vacuum overpressure(work in progress byTE-VSC) • Present protection scheme: • Rupture disks at arc extremities (mounted on SSS Q8) • Damage in sect.3-4 (direct consequence of overpressure) • Pressurized beam tubes (rupture of 1 burst disk) • Buckling of beam vacuum bellows (could be secondary damage) • Net transport of pollution along beam tubes • Will additional burst disk at intermediate positions help? • Depends on the ratio of impedance between beem tube and burst disk discharge manifold • Up to what distance does a P of 3 bars die away to vanishingly low values?  Work is in progress (R.Veness) • If found technically valuable, burst disk can be added at any time (?) at every SSS (ports available with vacuum valves) • Approx.cost for all machine ~ 750 kCHF (J.M.Jimenez) • Delivery schedulefor large series: 8-10 weeks (P.Cruikshank)

38. Evidence in sect.3-4 Beam screen bellows Column buckling due to internal pressure ruptured disk - Internal buckling pressure: ~ 5 bars (relative) - External buckling pressure: ~ 2 bars (not critical: small in plane squirm mode), local critical mode: ~ 9 bars Internal buckling pressure: ~ 3.5 bars External buckling pressure: ~ 4 bars Plug In module bellows Column buckling due to internal pressure C.Garion

39. Summary (1/2) Evidence from sect.3-4 and MCI: • Estimated overpressure in sect.3-4 ~7 bars • Estimated helium flow rate  ~20 kg/s (peak), x10 times initial estimate • Collateral damage due high pressure build-up (insufficient pressure relief devices), uprooting of ground fixations of SSS with vacuum barriers, “tug of war” • New MCI suggests helium flow rate  ~40 kg/s (peak), x2 times sect.3-4 estimate New overpressure release schemes for MCI (ECR in preparation) Cold sectors, temporary solution with pressure relief springs: • Pressure for MCI still high (~3 bars), and above 1.5 bars design pressure • Compliance with new safety regulations ? • Input for task forces on safety and risk analysis • Reinforced ground fixations for SSS with vacuum barriers are being studied • Further testing of support posts and vacuum barriers to assess next structural limit

40. Summary (2/2) Warm sectors, final solution with additional pressure relief devices • Add 1 DN200 port per dipole (with or without relief springs) • Use of DN100 ports with relief springs, except instrumentation ones • Pressure for MCI remains within 1.5 bars design pressure • Functional testing of new overpressure scheme: reduced scale test set-up? Special cases: • Mid sector and DS sub-sectors require 2 DN200 per dipole to keep pressure below 1.5 bars • Pending: study of standalones and triplets Beam insulation vacuum: work still in progress • Possibility of adding overpressure devices (burst disks) every 50 m if useful • Other issues: valves?

41. Thank you for your attention

42. Supporting slides

43. Pressure Relief Springs • Recall of existing clamp functions: • Provide leak tightness at initial pumpdown from atmospheric pressure < 1 mbarl/s. • Provide leak tightness under nominal vacuum conditions < 1 E-7 mbarl/s. • Avoid accidental opening due to external forces: • Permanent forces eg cables, gravity, • Punctual activities egcable pulling, climbing on cryostat, equipment handling, tunnel transport, etc. • Provide adequate sealing forces/contact surface to overcome joint non-conformities: • Flange flatness and form, seal geometry, seal imperfections, scratches, contamination, seal deterioration.

44. Forces on free flange Instrumentation cables egcryo, vac, BPM (except Q7,9 11) < 10 N, < 1 Nm Atmospheric Force dp1 bar = 1000 N Flange weight 11 N Existing clamping force to limiter ~ 3000 N Proposed spring loaded clamping 10-20% of dp 1 bar ~ 100–200 N Free flange Welded flange BPM cables N, Nm - negligible DN100 ISO-K

45. Spring Design removal force Max tolerance Min tolerance