Insulation vacuum and beam vacuum - PowerPoint Presentation

Slide1

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

Chamonix, 3rd February 2009

Content:Insulation vacuum:Present overpressure release schemeEvidence from sect.3-4 incidentMaximum Credible Incident (MCI)New overpressure release schemefor sectors remaining coldfor warmed up sectorsBeam vacuum overpressure releaseSummary

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...

1Slide2

Present configuration of pressure relief devices in standard arcs

50m50m100mQuench valves on cold mass circuit (QV): 3 QV, DN50 each, open on quench trigger; CM pressure ≤ 20 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 release from 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 cellCryostats:

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 2Slide3

Existing pressure relief device

Mounted on SSS 3Slide4

Pressure Forces on SSS with vacuum barrier

Vacuum barrier

jack

2/3 load directly to vessel

1/3 load through support post

Forces

Δ

p =

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

! Slide5

Sect.3-4 incident: Ins.Vac.overpressureQ23Q25

Q24Q26Q27

214 m

(DN90) (DN90)Collateral damage observed in sect.3-4:Primary damage (direct effect of pressure/flow):3 SSS with vac. barrier uprooted and longitudinally displacedFloor break at jack fixations, but also studs brokenMLI damage, sootBellows damage (CM and beam vacuum lines)

 Avoidable by limiting pressure rise and improved ground fixationSecondary 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

5Slide6

Development of pressuresG. De Rijk

6Slide7

Pressure estimate from elasto-plastic deformation of interconnect bellows

1055mm DR=20mm1016 mm

Assumptions: Elastic-plastic material, yield stress= 275MPa, 2D FE model with large displacements

Proportional loading Pressure to have DR ~20mm = 7 barsC.Garion7Slide8

Helium mass-flow rateA.Perin

Temperature (K)Hypothesis: Helium temperature given by sensor P4_34:LQOAA_25R3_TT821All 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 kgEstimated mass flow

Pressure (bar)Time (s)

Recorded data (cold mass)Mass flow (kg/s)Temperature (K)Time (s)Temperature P4_34:LQOAA_25R3_TT821Temperature P4_34:LQOAA_25R3_TT8218Slide9

Evidence in sect.3-4

Other cases: floor broke AND studs  F> 120-150 kN ? Q28 3R: weak floor broke, not studs  F < 120-150 kN

9Slide10

Maximum Credible Incident (MCI)Slide11

MCI scenarioIn 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 ?11Slide12

Possible MCI arc damage ?

MCI ?Sect.3-4 incident

L.Tavian12Slide13

Maximum flow for MCIThe 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 valueBurning 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)L.Tavian13Slide14

Overpressure estimatesL.Tavian

(MCI)(sect.3-4)(initial estimate)

14Slide15

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”Slide16

Existing ports: all on SSS

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 portsBPM DN100BPM DN100Vac.inst. DN100cryo.inst. DN6316Slide17

Use of portsLayout drawing LHCLSVI_0020

214 m8 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

Use as pressure relief ports

17Slide18

The strategyReplacing clamps with spring-loaded clamps (so-called “pressure relief springs”)

Port acts as an additional relief deviceBlow-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”

BPM DN100Vac. Equip. DN100Cryo.inst. DN63Use of instrumentation ports should be temporary, until warming up of sectors

18Slide19

Pressure relief spring Patrick Coly

Wim MaanPaul CruikshankCedric GarionMain 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)Testing of a prototype

Prototype

19Slide20

Status of relief springsProcurement:Relief springs for 432 DN63, 1870 DN100, 1232 DN200 (plus spares)Offer this weekValidate DN63,100, 200 with small pre-series (geometry, installation, opening tests)

Still to define: Flange retention systemProtection measures to avoid hazardous opening (stepping on, hitting…)Safety approval: on-going discussions with GSInstallation: could start from wk 13Input P.Cruikshank20Slide21

Cold sectors, new (temporary) relief schemeKeep existing 2 DN90 relief devicesMount relief springs on 5 DN100 vac. flangesMount relief springs on 8 DN100 BPM flangesMount relief springs on 4 DN63 cryo.instr. flanges

 Cross section increase: x 10

SV

SVSV

SV

SV

21Slide22

Overpressure in vacuum vessel

2.83.3L.Tavian

(MCI)(sect.3-4)

(initial estimate)22Slide23

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!23Slide24

Consequence of pressure above 1.5 bars (2/2)3 bars<P<4 bars:Strenght of Vacuum Barriers/Support Posts/Jack fixations becomes marginalIf 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 fixationsP~ 4 barsStability under external pressure of Plug In Module bellows risk of breaking beam vacuum

24Slide25

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 upSlide26

New overpressure relief schemeKeep existing 2 DN90 relief devicesMount relief springs on 4 DN100 blank flangesAdd 12 DN200 new relief devices (1 per dipole) Cross section increase: x 33

SV

SV

SV

SVSV

SV

SV

SV

SV

SV

SV

SV

SV

SV

SV

SV

SV

26Slide27

Overpressure in vacuum vessel

1.221.3OK, well below 1.5 bars design pressure L.Tavian

(MCI)

(sect.3-4)(initial estimate)27Slide28

Additional ports: 1 DN200 on every dipoleCourtesy of TRenaglia

DN200, reasonable upper limit for safe millingTop position is best for safety (personnel, H/W), and for gravity sealing of coverInterconnection 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 28Slide29

Relief device: detailed viewCourtesy of T. Renaglia

External weld for safety (limited risk of burning MLI) and ease Thick tube for weld quality, and limited distortion of sealing surfaceSt.steel top cover, with O-ring sealingSelf-weight sealing, but spring clamps can be mounted if necessary29Slide30

Trials and qualifications

Trials and qualification stepsW2: 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)

Geometrical check during welding

W5: Production of 20 pre-series valves at CERNW5: Training and qualification of the three intervention teams (Dubna, S-107, S-108)Max.internal T 130°C, 40°C on MLI Thermographic picture30

M.KarppinenSlide31

Provisional Installation Schedule

TotalSector 1-2

Sector 3-4

Sector 5-6Sector 6-7Remarks

W69

9

Surface

W7

69

20

20

20

Tunnel

W8

159

30

30

30

W9

249

30

30

30

W10

339

30

30

30

W11

429

30

30

30

W12

472

14

5

14

10

W13

562

90

W14

616

54

SUM

154

154

154

154

Contract

DUBNA

S-107

S-108

ALL

31

M.KarppinenSlide32

Special cases (1/2)6 DN200 + 4 DN100

L.TavianMid-arc vacuum sub-sectors: ½ length insulation vacuum sub-sector (~100 m)6 dipoles  only 6 DN200 relief devices2 SSS  4 DN100

1.8

2.1>1.8 bars  needs a 2nd DN200 device on dipoles 32Slide33

Special cases (2/2)DS zones: 20% shorter insulation vacuum sub-sector (~170 m)8 dipoles  only 8 DN200 relief devices4 SSS (Q11-Q8), [5 around Pt.3-7 (Q7)]  ~ 8 DN100

8 DN200 + 8 DN100

1.41.52

Marginal, >1.5 bars, if T>80K  proposed adding 2nd DN200 on dipoles L.Tavian33Slide34

Still pending...Study of overpressure for:Standalone cryo-magnets in LSSTriplets

34Slide35

Radial conductance (area)(passage from cold mass to vacuum vessel)Impedance:Aluminum shielding

MLIConductance:Thermal shield slotsAt support posts (for thermal contractions)At vacuum barriersAt Instrumentation Feedthroughs and diode 100 cm2

1000

cm21000 cm21000 cm2128 cm2128 cm2128 cm2450 cm2

1000 cm21000 cm21000 cm2

1000

cm2

1000

cm2

1000

cm2

1000

cm2

1000

cm2

1000

cm2

TOTAL per vacuum

sub

-

sector

:

12900

cm2

~

100

times

area of

present

over-pressure

valves

~ 10 times

area of

new

overpressure

scheme

for cold

sectors

~

3

times

area of

new

overpressure

scheme

for warm

sectors

Transversal conductance

is

not the «

bottleneck

», if MLI

does

not

restrict

passage

35Slide36

MLI obstruction in sect.3-4

Suction/ripping/clogging through over-pressure valve …yes some clogging at valves, but… full-open DN solution will

be less sensitive

No evidence in sect.3-4 event of full blanket blown apart (Velcro™ fixation holds)36Slide37

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 tubesWill additional burst disk at intermediate positions help?Depends on the ratio of impedance between beem tube and burst disk discharge manifoldUp 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)

37Slide38

Evidence in sect.3-4ruptured disk

- Internal buckling pressure: ~ 5 bars (relative)- External buckling pressure: ~ 2 bars (not critical: small in plane squirm mode), local critical mode: ~ 9 bars Column buckling due to internal pressureBeam screen bellowsInternal buckling pressure: ~ 3.5 barsExternal buckling pressure: ~ 4 bars

Plug In module bellows

Column buckling due to internal pressureC.Garion38Slide39

Summary (1/2)Evidence from sect.3-4 and MCI:Estimated overpressure in sect.3-4 

~7 barsEstimated helium flow rate  ~20 kg/s (peak), x10 times initial estimateCollateral 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 pressureCompliance with new safety regulations ?Input for task forces on safety and risk analysisReinforced ground fixations for SSS with vacuum barriers are being studiedFurther testing of support posts and vacuum barriers to assess next structural limit39Slide40

Summary (2/2)Warm sectors, final solution with additional pressure relief devicesAdd 1 DN200 port per dipole (with or without relief springs)

Use of DN100 ports with relief springs, except instrumentation onesPressure for MCI remains within 1.5 bars design pressureFunctional 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 barsPending: study of standalones and triplets

Beam insulation vacuum: work still in progressPossibility of adding overpressure devices (burst disks) every 50 m if useful

Other issues: valves?40Slide41

Thank you for your attentionSlide42

Supporting slidesSlide43

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 eg cable 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.

Pressure Relief Springs

43Slide44

Forces on free flange

BPM cablesN, Nm - negligibleInstrumentation cables eg cryo, vac, BPM (except Q7,9 11)< 10 N,< 1 Nm

Flange weight11 NAtmospheric Forcedp 1 bar = 1000 N

Existing clampingforce to limiter ~ 3000 NProposed springloaded clamping10-20% of dp 1 bar ~ 100–200 NDN100 ISO-KWelded flange

Free flange44Slide45

Spring Design

removal forceMax toleranceMin tolerance  

o-ring

max typeqtynominal removaldp 1 bar 

fingersclampingforce 

(N)

(N)

(N)

DN63

6

102

168

509

DN100

8

136

224

991

DN200

16

272

448

3594

45