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

Chamonix, 3rd February 2009

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...

2

PTQVQV QV QVQV SVSV

Cold-massVacuum vesselLine ECold support postWarm JackCompensator/BellowsVacuum barrier

Q D D QD D D QD D D QD D D QD

Present configuration of pressure relief devices in standard

arcs

50m 50m100m

Quench valves on cold mass circuit (QV):• 3 QV, DN50 each, open on quench trigger; CM pressure ≤ 20 bars

PTQVQV QV QVQV SVSV

Cold-massVacuum vesselLine ECold support postWarm JackCompensator/BellowsVacuum barrier

Q D D QD D D QD D D QD D D QD

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 cell

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

3

Existing pressure relief device

Mounted on SSS

Pressure Forces on SSS with vacuum barrier

Vacuum barrier jack

2/3 load directly to vessel

1/3 load through support post

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

Q23 Q25Q24 Q26

PTQVQV QV QVQV SVSV

Q D D QD D D QD D D QD D D QD

Q27214 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 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

0

2000

4000

6000

8000

10000

12000

11:18:35

11:18:40

11:18:45

11:18:50

11:18:55

11:19:00

11:19:05

11:19:10

11:19:15

11:19:20

11:19:25

11:19:30

11:19:35

11:19:40Time

Curr

ent (

A)

0

5

10

15

20

25

P H

e ve

ssel

(bar

), P

beam

(mba

r), P

insu

latio

n (b

ar)

Ins Vac A19R3

Ins Vac A23R3

Ins Vac A27R3

I DCCT

I dump 3

I dump 4

P CM Q19-21.R3

P CM Q23-25.R3

P CM Q27-29.R3

Vac beam 23R3.R

Vac beam 23R3.B

Vac beam 31R3.R

Vac beam 31R3.B

G. De Rijk

7

Pressure estimate from elasto-plastic deformation of interconnect bellows

1055mm DR=20mm

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

A.Perin

95 105 115 125 135 145 155 165 175 185 1950

2.5

5

7.5

10

12.5

15

17.5

20

22.5

25

0

10

20

30

40

mfcor The

TimeTe

mp

era

ture

(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 kg

Estimated mass flow

100 120 140 160 1800

5

10

15

20

0

10

20

30

40

PQ25 Thelium Time( )

Time

Input Data

Pre

ss

ure

(b

ar)

Time (s)

Recorded data (cold mass)

Ma

ss

flo

w (

kg

/s)

Tem

pe

ratu

re (

K)

Time (s)

Temperature P4_34:LQOAA_25R3_TT821 Temperature P4_34:LQOAA_25R3_TT821

9

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

Maximum Credible Incident (MCI)

MCI scenario

• 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 ?

11

12

Possible MCI arc damage ?

MCI ?

Sect.3-4 incident

L.Tavian

13

Maximum flow for MCI

• 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)

L.Tavian

14

Overpressure estimates

2 kg/s

20 kg/s

40 kg/s

1

6

11

16

21

0 20 40 60 80 100 120

Vac

encl

osur

e P

[bar

]

Vac enclosure He T [K]L.Tavian

(MCI)

(sect.3-4)

(initial estimate)

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

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

BPM DN100

BPM DN100

Vac.inst. DN100

cryo.inst. DN63

17

Use of ports

Layout drawing LHCLSVI_0020

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

Use as pressure relief ports

18

The strategyReplacing 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”

BPM DN100

Vac. Equip. DN100Cryo.inst. DN63

Use of instrumentation ports should be temporary, until warming up of sectors

19

Pressure relief spring

Patrick ColyWim MaanPaul CruikshankCedric Garion

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)

Testing of a prototype

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

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

PTQVQV QV QVQV SVSV

Q D D QD D D QD D D QD D D QD

SV SVSV SV SV

22

Overpressure in vacuum vessel

2 kg/s

20 kg/s

40 kg/s

DP1

1.5

2

2.5

3

3.5

4

0 20 40 60 80 100 120

Vac

encl

osur

e P

[bar

]

Vac enclosure He T [K]

2.8

3.3

L.Tavian

(MCI)

(sect.3-4)

(initial estimate)

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: a. Evidence in sect.3-4 of floor breaking at p<1.5-1.87 bars (120-150 kN is limit of studs)

b. 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 under external pressure of Plug In Module bellows risk of breaking

beam vacuum

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

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

PTQVQV QV QVQV SVSV

Q D D QD D D QD D D QD D D QD

SV SV SV SV SV SV SV SV SV SV SV SV SV SV SV SV SV

27

Overpressure in vacuum vessel

2 kg/s20 kg/s

40 kg/s

DP

1

1.1

1.2

1.3

1.4

1.5

1.6

0 20 40 60 80 100 120

Vac

encl

osur

e P

[bar

]

Vac enclosure He T [K]

1.22

1.3

OK, well below 1.5 bars design pressure L.Tavian

(MCI)

(sect.3-4)

(initial estimate)

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Additional ports: 1 DN200 on every dipole

Courtesy of TRenaglia

• 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

29

Relief device: detailed view

Courtesy of T. Renaglia

• 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

30

Trials and qualifications

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)

Geometrical check during welding

• W5: Production of 20 pre-series valves at CERN• W5: Training and qualification of the three intervention

teams (Dubna, S-107, S-108)

Max.internal T 130°C, 40°C on MLI

Thermographic picture

M.Karppinen

31

Provisional Installation ScheduleTotal Sector

1-2Sector

3-4Sector

5-6Sector

6-7Remarks

W6 9 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

M.Karppinen

32

Special cases (1/2)

2 kg/s

20 kg/s

40 kg/s

11.21.41.61.8

22.22.4

0 20 40 60 80 100 120

Vac

encl

osur

e P

[bar

]

Vac enclosure He T [K]

6 DN200 + 4 DN100

L.Tavian

• Mid-arc vacuum sub-sectors: – ½ length insulation vacuum sub-sector (~100 m)– 6 dipoles only 6 DN200 relief devices– 2 SSS 4 DN100

1.8

2.1

>1.8 bars needs a 2nd DN200 device on dipoles

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

2 kg/s

20 kg/s

40 kg/s

11.11.21.31.41.51.61.7

0 20 40 60 80 100 120

Vac

encl

osur

e P

[bar

]

Vac enclosure He T [K]

8 DN200 + 8 DN100

1.4

1.52

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

L.Tavian

34

Still pending...

Study of overpressure for:• Standalone cryo-magnets in LSS• Triplets

35

Radial conductance (area)(passage from cold mass to vacuum vessel)

Impedance:• Aluminum shielding• MLIConductance:• Thermal shield slots

– At support posts (for thermal contractions)– At vacuum barriers– At Instrumentation Feedthroughs and diode

PTQVQV QV QVQV SVSV

Q D D QD D D QD D D QD D D QD

100 cm21000 cm2

1000 cm21000 cm2

128 cm2 128 cm2 128 cm2 450 cm21000 cm2

1000 cm21000 cm2 1000 cm2

1000 cm21000 cm2 1000 cm2

1000 cm21000 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

36

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)

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

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

Column buckling due to internal pressure

Beam screen bellows

Internal buckling pressure: ~ 3.5 bars

External buckling pressure: ~ 4 bars

Plug In module bellowsColumn 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?

Thank you for your attention

Supporting slides

43

• 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

44

Forces on free flange

BPM cablesN, Nm - negligible

Instrumentation cables eg cryo, vac, BPM (except Q7,9 11)

< 10 N,< 1 Nm

Flange weight11 N

Atmospheric Forcedp 1 bar = 1000 N

Existing clampingforce to limiter

~ 3000 N

Proposed springloaded clamping

10-20% of dp 1 bar ~ 100–200 N

DN100 ISO-K

Welded flange

Free flange

45

Spring Design

-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 40

5

10

15

20

25

30

35

40

45

50

Thickness: 0.8mm; sy=550MPa

Displacement [mm]

Fo

rce

pe

r fi

ng

er

[N]

clamping force at o-ring

removal force

Max tolerance

Min tolerance

o-ring max

type qty nominal removal dp 1 bar

fingers clamping force

(N) (N) (N)

DN63 6 102 168 509

DN100 8 136 224 991

DN200 16 272 448 3594