issues concerning the reliability of cryogenic system
DESCRIPTION
ISSUES CONCERNING THE RELIABILITY OF CRYOGENIC SYSTEM. Outline. From LEP2 to LHC LHC Cryogenics system architecture (redundancy) Reliability of sub-systems and components Maintenance policy and shut-down strategy Conclusions. Previous considerations. - PowerPoint PPT PresentationTRANSCRIPT
Chamonix XIV Jannuary 2005 M. Sanmarti/ AT-ACR 1
ISSUES CONCERNING THE RELIABILITY OF CRYOGENIC SYSTEM
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR2
Outline
From LEP2 to LHC
LHC Cryogenics system architecture (redundancy)
Reliability of sub-systems and components
Maintenance policy and shut-down strategy
Conclusions
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR3
Previous considerations
Most of the main cryogenic components have been extensively used at CERN
Considerations based on experience more than detailed failure risk analysis LEP2 and first LHC commissioning experience
Availability, failures & MTBF’s related to beam (LEP2) and beam commissioning (LHC)
Major or first order failures: ”something that breaks or something that does not work as expected“
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR4
LEP2 experience
Cryogenic system downtime rates from 1996 to 2000
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
1996 1997 1998 1999 2000
Dow
ntim
e ra
te [%
]
Cryo failures rate
Utility failures rateDe-icing
LEP impact
Cry
o U
pgra
de
More than 120.000 h cumulated running hours
Cryo impact < 1%
Recovery after utility failures downtime <2%
De-icing: reduced cooling capacity, time used for MD
Sub-system or Hardware commissioning
Beam commissioning…
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR5
Learning from LEP2
Components (impact on machine): Main components failures during commissioning or restart after SD Cryogenics downtime (not including utilities): < 1,0%
MTBF Cryo system 0.1 years, MTBF Cryoplant 0.4 years, MTTR 1-2 hours Cold boxes (MTBF years): instrumentation and turbines very reliable Compressor stations:
Mainly aging problems on instrumentation/piping (MTBF 0.5 years) Controls: dedicated and robust control system was almost transparent Distribution & RF cavities:
mainly beam related issues (heat load) affecting cooling capacity Access needed although no urgent intervention required (key components
in RA) Impurities (De-icing):
Gaseous impurities at warm turbines level (120 K & 90 K) Predictable: time used for MD or interventions
Maintenance: Extensive preventive maintenance campaign during SD periods Corrective: MTTR < 1-2 hours but amplified impact on machine (x7)
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR6
LEP 1500 I/O channels, 8 compressors, 7 turbines per point (4 points)
LHC 9000 I/O channels, 16 compressors, 20 turbines per point (5 points)
From LEP2 to LHC cryogenic system
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
LHC
4 x 12/18 kW @ 4.5 K
288 SC RF cavities
2 km @ 4.5 K
8 x 18 kW @ 4.5 K
8 x 2,4 kW @ 1.9 K
1’800 SC magnets
24 km @ 1.9 K
36‘000 tons @ 1.9 K
LEP2
75 tons @ 4.5 K
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR7
The LHC cryogenic architecture per point
2
3
4 5
6
7
811.8
Built-in redundancy
Weak point: 2-3
Warm CompressorStation
Upper Cold Box
Interconnection Box
Cold Box
Warm CompressorStation
Lower Cold Box
Distribution Line Distribution Line
Magnet Cryostats Magnet Cryostats
Cold Compressorbox
Warm CompressorStation
Cold Compressorbox
Warm CompressorStation
Shaft
Sur
face
Cav
ern
Tun
nel
LHC Sector (3.3 km) LHC Sector (3.3 km)
1.8 K Refrigeration Unit New 4.5 K Refrigerator Ex-LEP 4.5 K refrigerator 1.8 K Refrigeration Unit
DFBA DFBA
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR8
Major (sub-systems) failures
One 4.5K Ref. or one 1.8K unit out of
order:=>Low intensity OK
(beam commissioning OK)
Common parts (QUI-QRL-DFB), loss of isolation vacuum : => Total stop of the machine
BUT transition:
≈ 12 to 24 hours
Unlikely to occur during life-cycle, but possible!
QUI
QSRA
QSCA
QURC
QSCC
QRL
Sector
QURA
QSV
QSRB
QSCB
QURC
QSCC
QRL
Sector
DFB DFB DFB DFB
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR9
4.5 K & 1.8 K Refrigerators Instrumentation: high reliability and spares, MTTR~1-2h Warm compressors: no redundancy but spare capacity or connection
to adjacent refrigerators would allow degraded mode (low intensity): Oil piping: if spares, MTTR 1-2 days Motor/Compressor replacement??
Turbines: no spares at the moment, diagnosis + 5 h. intervention delay if spare available, otherwise degraded mode allows continuation of tests
Cold compressors: spares available, diagnosis + 5 hours delay, no degraded mode allowed
Impurities: Dryers (H2O), switchable adsorbers (Air, 80 K), single adsorber (H2, 20 K)
Vacuum (leaks): temporary solution until SD major intervention ACCESS constrains: underground and UX4, UX6, UX8 for QURC (1.8
K)
From the cooling capacity point of view such failures should not affect beam commissioning (spares, redundancy, adjacent refrigerator) but the operational constraints and the recovery time will increase
? Degraded modes could be a problem for scrubbing run
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR10
QUI (Interconnecting Box) Instrumentation:
Redundancy on control loop and QRL interfaces sensors Cryogenic valves (no redundancy): high MTBF Heater (warm up): redundancy but degraded mode, longer warm up
Vacuum (leaks): temporary solution until SD major intervention Impurities (Solid): possibility of clogging the QUI filter (line D) provoking a
stop of the cooling flow It would mainly happen during the cool down and the first few quenches It requires 1-2 days to replace the filter and reach again nominal
conditions
Filters in CFB (Magnets Test Bench) Shut Down 2004-2005
From the functionality point of view: The QUI assures the redundancy of the refrigerators Clogging of line D filter is the most likely failure to occur No redundancy for cryogenic valves of QRL interfaces Any intervention needs underground access: UX4, UX6 & UX8
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR11
QRL and Ring equipment I QRL
Instrumentation: Redundancy or degraded mode possible Most of Cryogenic valves are redundant (degraded mode):
• In situ exchange: up to 1 week intervention depending on valve position
Quench valves (cool-down/fill): no redundancy for filling (once/year), security redundancy
Beam screen: Clogging problems (small Ø pipe): beam screen temperature?? Loss of instrumentation (heater & temp., no redundancy):
No Temp. control, higher helium flow Problems during “scrubbing” run
DFB’s, Standalone magnets & DSL’s: Instrumentation:
HTS valves: easily repair HTS temperature: redundancy or other control options (valve
characteristics against current) Level gauges: redundancy or easily repairable (except for D2, D3) DFB: presentation by A. Perin this Workshop
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR12
QRL and Ring equipment II
Dipoles & Inner Triplets: Temperature sensors redundancy (needs electronics replacement) Other control options (opening valve characteristics, copy valve position of
adjacent cells) Level gauge bayonet heat exchanger: liquid in line B and possible magnet
temperature perturbation (operational issue not affecting pumping capacity but temperature control)
Isolation Vacuum: presentation by P. Cruikshank this Workshop
RF cavities: Instrumentation, valves as above Pressure stability and protection during quench/quench recovery (presentation by
S. Claudet)
From the functionality point of view: Reliability of primary components is high Replace (redundancy) possible or degraded modes: less control (temp.) and
higher helium consumption Any intervention needs access to the tunnel: radiation issues for IT??? (OK for BC)
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR13
LHC experience
New LHC 4.5 K cryoplant @ PM18 (2002-2004): No major gaseous impurities problems (solid impurities filters in
CFB, MTB) Availability about 99% (50% utilities/cryo) for 20000 cumulated
running hours with degraded modes or spare capacity
String2 experience (2002-2003): 98,5% availability over 4170 h (2002) & 98,6% availability over
1950 h (2003) Prototype/commissioning: mainly tuning, quench recuperation
and controls No major problems with instrumentation or beam screen circuit
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR14
0:00
6:00
12:00
18:00
24:00
30:00
36:00
42:00
48:00
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00
Utility failure [h]
Rec
over
y Ti
me
(CR
YO
OK
) [h]
LEP contractual performancesLEP 3.3kV Failures - 60'000 hours (98-00)LEP 400V Failures - 60'000 hours (98-00)LHC estimated performancesLHC Test String 2 mains failures - 5000 hours (01-02)LHC Test String 2 simulated utility stopLHC with degraded vacuum & leaking QRV
Utilities Failure Recovery (L. Serio @ Chamonix 2003)
Cryogenics is a recovery time amplifier
LEP contractual time recovery < 5.5 hours + 7*stop duration
LHC estimated time recovery < 6 hours + 3*stop duration
Controls :? Complete new control system (still design problems)? Ethernet dependent (control loops, PLC communication)
Recovery performances:× Recovery predictions have still to be validated for the
global system during hardware commissioning× Degraded modes will increase recovery time
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR15
Maintenance Policy
Existing maintenance plan to be upgraded (LEP), completed (new LHC installations) and everything to be implemented in CERN CAMMS
Based on preventive maintenance campaign during SD Baseline: 13 weeks for full maintenance campaign Issues arising: Safety valves (5000 u.) every 2 years inducing
corrective maintenance
Spare parts: first batch after commissioning using industrial method for criticity analysis, ~2,2% cryoplant cost (280kCHF for 4.5 K refrigerator) Assures MTTR of 1-2 hours No spare for turbines, warm compressors/motors…
Maintenance management: No CERN resources for execution Maintenance management needs to be reinforced and fully driven by
CERN Manpower management depending on SD scenarios
Presentation by T. Pettersson this Workshop
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR16
Shut Down Strategy (16 weeks from Chamonix’04)
Scenario 1: full maintenance & floating temperature (T~200 K) Keeps preventive/corrective ratio (LEP and present experience):
same availability rates Perturbations during cold check-out: corrective maintenance after SD Requires ELQA if T>80K (+ 5 weeks during MCO) Thermal cycling of components: helium leaks, welding stress…
Scenario 2: maintenance on 1 cryoplant/point keeping sectors “cold” Increases preventive/corrective ratio: reduce availability rates?? Lower risk of perturbations during cold check-out (after SD) No need of additional 5 weeks for ELQA No thermal cycling of components Not possible in sector 2-3
Utilities: driven by cooling water towers 4 weeks per LHC point (2 points in parallel): to be reviewed for
Scenario 2
In any case, warm up could be needed for ring components replacement (magnet, etc..)
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR17
Conclusions I In principle, the cryogenic system should have a very low impact
(except on sector 2-3) the beam commissioning because of: Redundancy of systems Available spare cooling capacity for low intensity beam Reliability of components and instrumentation
However, failure of sub-systems and components can not be ruled out completely and could result in few days delays to switch to redundant system or component and to adapt to new configuration
Worst failure would be the loss of insulation vacuum on the QUI or QRL as well as the refrigerator in point 2 or DFB’s for magnet powering
Most likely failure would be filters blockage on the QUI during or after the first cool down and magnets quench due to accumulation of impurities (consolidations under study)
Recovery time after major failure (utility or cryo) will be approximately 6 hours plus 3 times the stop length (15 times if bad vacuum/QRV leaks)
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR18
Conclusions II
The cryogenic sub-systems will be individually tested, but the overall cryogenics system will certainly require complex and extensive commissioning prior and during powering to validate the global and collective behavior and optimize operating modes
The availability or quench recovery performances of the cryogenic system:
could be reduced by additional heat loads or non conformities from commissioning
Depends on a correct Maintenance Management: it has already started and needs CERN dedicated resources!
Chamonix XIV Jannuary 2005 M. Sanmarti / AT-ACR19
Acknowledgements
Many thanks to: L. Serio S. Claudet G. Riddone R. Van Weelderen A. Perin P. Gomes Ph. Gayet N. Bangert
for their contribution to this presentation