Maintenance of the LHC cryogenic system during the first · Maintenance of the LHC cryogenic system during the ... Cryo-Ops 2014 Maintenance of the LHC cryogenic system during the

Page 2 O. Pirotte, Cryo-Ops 2014 Maintenance of the LHC cryogenic system during the first long shutdown

Maintenance of the LHC cryogenic system during the first

long shutdown

O. Pirotte on behalf of the CERN cryogenic group 6th International Workshop on Cryogenics Operations

STFC Daresbury Laboratory, United Kingdom November 10-12, 2014


Content

• Introduction and context

• Preparation : planning, organisation, maintenance tasks

• Major overhauling

• Compressors, motors, oil pumps

• Statistics

• Filtering elements

• Requalification of pressure vessels

• Conclusion


INTRODUCTION LHC physics run 1 started end of 2009 (cryo installations from 2008)

Change of operation/maintenance sequence : • LEP : 9 months operation + 3 months shutdown • LHC : 3-4 years continuous operation (incl. 4 or 5 technical

stops of 1 week + one month Xmas stop per year) + 18 months Long Shutdown

Stop = no beams for physics, but cryogenic installations must remain in full operational mode (He inventory)

First long shutdown was expected in 2012 -> postponed mid 2013

Long Shutdown 1 (LS1)


PLANNING

Master planning defined by LS1 general coordination Planning based on the main consolidation works in the LHC tunnel (magnet splices): sequence of tasks starting from sector 5-6 and running clockwise

LS1 Master Planning : sequence of sectors

18 months for maintenance tasks


ORGANISATION & SCHEDULING

Basic principle for the schedule of the maintenance for a cryogenic plant

Week 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

Lock outDismountingTransportMajor overhaulingTransportRe-installationCommissioningCryo TuningFlushingCooling

Equipment available

Major overhauling Max 12 weeks

8 weeks Maintenance tasks

Identification of windows where cryogenic plants can be stopped and maintained


MAINTENANCE TASK LIST Identification of maintenance tasks and maintenance plans • Compressors (warm / cold) • Oil pumps • Motors • Filtering components (adsorbers, separators, coalescers, gas/oil/water filters) • Heat exchangers • Instrumentation (sensors, transmitters, …) • Valves, safety valves, bursting disks • Vacuum system components • Requalification of pressure equipment • Repairs (corrective: QRL, HX in cold box, …) CMMS, generation of

maintenance plans / category of equipment

> 5000 work orders MS Project planning

Major overhauling of (warm) rotating machines


Major overhauling

15734

24198 22642

29896

44104

33846 38983

52000

Jun-2009QSCB-8-CP3

Roller bearing(failure)

VMY536aH

Dec-2010QSCB-4-CP6

Roller bearing(breakdown)VMY536aH

Feb-2011QSCA-2-CP8 /

M08Balancing piston/ plain bearing

S93

Jun-2011QSCB-8-CP7

Roller bearing(breakdown)VMY536aH

Dec-2011QSCB-8-CP6

Plain bearings(wear)

VMY536aH

Feb-2012QSCB-4-CP7

Damaged rotorVMY536aH

Nov-2012QSCA-8-M08Plain bearing

(wear)Stal S93

Mai-2013ANRS

Roller bearing(breakdown)

Kaeser

Breakdown of 2 high stage Aerzen compressors (Dec 2010, Jun 2011) ⇒ Set up of an enhanced vibration monitoring system and of a plan to

modify the oil injection pipe to the balancing piston ⇒ Identification of bearings issues ⇒ Xmas stop 2011 : preventive replacement of bearings and balancing

piston for all high stage Aerzen ⇒ Identification of two issues : excessive wear for one plain bearing + one

damaged rotor

Main events during LHC physics run 1


PREDICTIVE MAINTENANCE DURING RUN 1

QSCB-8-CP6

QSCB-4-CP7

SKF analysis confirmed roller bearing issues detected (vibration monitoring)

Roller bearings of Aerzen high stage compressors


MAJOR OVERHAULING

Criterion for major overhauling :

- End of LHC physics run 2 : 2018 - Compressors : ~40’000 h max - Motors : max according to maintenance plan

LHC screw compressors before LS1

Manufacturer Qty Major overhauling recommendation

Aerzen 20 20'000 h Stal 37 40'000 h Kaeser 9 40'000 h Mycom 4 20'000 h Howden 4 4 years of operation

LHC motors before LS1

Type Voltage Power Qty Maintenance plan Major overhauling

Ball bearings 3.3 kV - 13 61

30'000 h Plain bearings 40'000 h Ball bearings (oil pumps) 400 V > 10 kW 27 30'000 h

≤ 10 kW 29 Replacement (new)


Motor-compressor systems of the LHC cryogenic installations sent for major overhauling

Point 1 Point 1.8 / Point 2 Point 4 Point 5

ATLAS SR

LHCB

LHCA

LHCB

CMS

M

ATLAS ANRS LHCCB

LHCCA LHCCA

LHCCB

ATLAS MR

Legend Total : 77 motor-compressor systems

C

CP1

M

C

CP2

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP6

M

C

CP7

M

C

CP1

M

C

CP2

M

C

M

C

CP5

M

C

CP6

CP3

M

C

M

C

CP1

M

C

CP2

M

C

M

C

CP7

M

C

CP8

CP3

M

C

CP4

M

C

M

C

M

C

CP1

CP2

M

C

CP1

M

C

CP2

M

C

CP1

M

C

CP5 CP6

CP4

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP4

M

C

CP7

M

C

CP8

M

C

CP9

M

C

CPA

M

C

CP1-2

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP6

M

C

CP7

LHCA

M

C

CP1

M

C

CP3

M

C

CP2

M

C

CP4

Point 6

LHCB

LHCCA

LHCCB

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP4

M

C

CP7

M

C

CP8

M

C

CP9

M

C

CPA

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP6

M

C

CP7

LHCA LHCA

M

C

M

C

CP2

M

C

M

C

CP7

M

C

CP8

CP3

M

C

CP4

M

C

M

C

CP5 CP6CP1

Point 8

LHCB

LHCCA

LHCCB

M

C

CP1-2

M

C

CP1

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP6

M

C

CP7

CP2

M

C

CP1

M

C

CP2

M

C

CP1

M

C

M

C

CP1-2

New motor-compressor systemsMajor overhaulingNo major overhauling

MAJOR OVERHAULING OF

55 Compressors 63 Motors 3.3kV


OIL PUMP

400V ELEC. MOTOR

OIL PUMPS

KRAL

MYCOM Oil pump motors (400V) Major overhauling : 26

Replacement (< 10kW): 26


CriticalityPumpmanufacturer

Compressoror system Maintenance plan In operation Spare

Major overhauled

StalS87S89

Manufacturer :5'000 hStandard : 8'000 hMajor overhaul : 24'000 h

22

11

22

8'000 h /24'000 h

StalS73S75

Manufacturer :5'000 hStandard : 8'000 hMajor overhaul : 24'000 h

98

44

45

24'000 h

No redundancyNext to compressor (electrical motor)

IMOS93 BoosterS93 High stage

Standard : 16'000 hMajor overhaul : 24'000 h

104

44

3 24'000 h

Sytems without redundant pump

Desmi LHCA Booster 1/1Hig stage 1/1

Standard : 8'000 hMajor overhaul : 24'000 h

22

22

24'000 h8'000 h

Kral LHCBBooster : 1 / 3High stage : 2 / 3

Major overhaul : 40'000 h1212

33

3 40'000 h

Kral CMSBooster : 1 / 2High stage : 1 / 2

Major overhaul : 40'000 h22

11

40'000 h

Mayekawa-Mycom

Compressor : 1 / 2 Major overhaul : 40'000 h 2 1 1 40'000 h

Allweiler Compressor : 1 / 3Standard : 16'000 hMajor overhaul : 24'000 h

3 1 2 40'000 h

Sytems withredundant pump(s)

No redundancyIntegrated in compressor

LHC Oil pumps before LS1 Newperiodicity

Oil pumps sorted according to criticality criteria (damage, process) Update of the maintenance taking into account :

• Vibration monitoring for all oil pumps • Spare are available • Results of major overhauling of samples achieved during LS1

*SKF bearing : 40’000 h

*


MAJOR OVERHUAL OF KRAL OIL PUMP

Major overhaul of a KRAL pump (> 40'000 running hours). − Pump generally in good condition; − No sign of wear identified on the screws; − Some significant wear marks on the inlet site,

probably caused by particles.


Preventive Maintenance • Complete cleaning, and dismounting of all the

compressor parts; • Control and measurements of functional clearances

during dismounting and before re-assembly of the compressor;

• Control and measurements of rotor alignment; • Inspection of all parts including rotors, slide valve,

housing, balancing piston, shaft and seats of seals; • Inspection and replacement of all bearings • Inspection and replacement of shaft seals; • Replacement of all gaskets and O-rings; • Re-painting of the compressor and parts; • Helium leak tightness test; • Conditioning with dry nitrogen; • Packing for transport to CERN, including a new set of

assembly gaskets; • Major overhaul report

Corrective Maintenance Polishing and/or grinding • of rotors (profile); • of slide-valve; Reconditioning • of bearing seats; • of shaft seal seat; • of shaft coupling seat; • drive end surface Re-machining • of rotor housing; • of slide valve bore; • of hydraulic cylinder ;

MAINTENANCE TASKS

STATOR: • Polishing the outside of the carcass • Cleaning, sandblasting and painting of interior

mechanical parts • Reconditioning of the terminals and boxes • Polishing all the connections • Replacement of all the seals on the terminals boxes • Spray with a varnish anti flash on the windings and in

the terminal boxes. • Report with pictures

ROTOR: • Control and balancing of the rotor if necessary • Spray with a varnish anti flash COOLER and fans (if existing): • Inspection and verification of the cooler. • Inspection and verification of the fans. • Decalcification, cleaning and rinsing of the water circuits. • Pressure test of the cooler circuits • Drying in a ventilated oven • Painting

Exchange • of piston rod; • of oil pump (Stal); • of balancing sleeve; • of balancing piston; • of slide valve (oversize); • of slide valve support; Consolidation; • of shaft seal holder (S93); • of clamping unit.


ALLOCATION OF MAINTENANCE COSTS

CP #

Over- hauled

Contractual revision period at contractor’s

premises

Major overhaul time (Average )

Allocation of costs

Preventive maintenance

Corrective maintenance

5 co

ntra

cts

Stal 24 12 weeks per batch of seven/eight compressors

11 weeks per batch of seven/eight compressors 88 % 12 %

Aerzen 17 8 + 4 weeks per batch of five compressor

8 weeks per batch of five compressors 78 % 22 %

Howden 4 6 weeks per compressor 4 weeks per compressor 97% 3%

Kaeser 6 6 weeks per batch of two compressors

12 weeks per batch of two compressors

(corrective maintenance) 86% 14%

Mycom 3 6 weeks per compressor 4 weeks per compressor 96% 4%

MOTOR #

Over- Hauled

% of the contract

Allocation of costs

Preventive maintenance

Corrective maintenance

3.3 kV 63 86 % 73 % 27 %

400 V 26 8 % 72 % 28 %

400 V exchange 26 6 % 100 % -

Total LHC major overhauling Allocation of costs

Motors 13%

Compressors 87%


ORGANISATION – FOLLOW-UP

~1 year


MAINTENANCE COSTS : STAL S70’s

78%

22%

S73

Preventive maintenance costCorrective maintenance cost

73%

27% S75


Model (overhaul) Asset Meter Unit Last overhaul Allocation of

corrective costs

S73-26A (4/9)

QCCV-STAB15 36666 18202 33% QCCV-STAB01 38902 12100 17% QCCV-STAH03 63459 30480 23% QCCV-STAH04 63618 30721 27%

Model (overhaul) Asset Meter Unit Last overhaul Allocation of

corrective costs

S75-26A (6/8)

QCCV-STAB16 42172 21838 16% QCCV-STAB17 45162 21320 12% QCCV-STAB18 47319 20560 14% QCCV-STAB03 58283 18829 24% QCCV-STAB02 59382 12100 22% QCCV-STAB04 62295 21624 13%


Model (overhaul) Asset Meter Unit Last

overhaul Allocation of

corrective costs

S87-26A (2/2)

S89-26A (2/2)

QCCV-STAH10 27522 11512 0,0%

QCCV-STAH09 29202 11958 0,0%

QCCV-STAH06 43635 12016 88%

QCCV-STAH05 45758 13591 12%



corrective costs

S93-26A (10/17)

QCCV-STAB10 30334 12009 13% QCCV-STAB20 43215 12130 5% QCCV-STAB19 44340 12432 5% QCCV-STAH11 48434 19594 15% QCCV-STAB05 53544 12064 12% QCCV-STAB06 54790 11913 10% QCCV-STAB09 57958 21746 13% QCCV-STAB08 62272 31155 1% QCCV-STAH01 64799 30304 22% QCCV-STAB07 65103 31791 9%

MAINTENANCE COSTS : STAL S80’s & S93

98%

2% S87 & S89


95%

5% S93



MAINTENANCE COSTS : AERZEN

82%

18% VMY536aM

Preventive maintenance cost

Corrective maintenance cost

75%

25% VMY536aH




corrective costs

VMY536aM (8/9)

QCCV-AERB05 42163 11% QCCV-AERB08 44575 11% QCCV-AERB07 46286 11% QCCV-AERB04 46769 23% QCCV-AERB11 49444 10% QCCV-AERB10 55208 36812 10% QCCV-AERB01 72868 37907 12% QCCV-AERB02 80920 39354 12%



corrective costs

VMY536aH (9/14)

QCCV-AERH10 17396 4% QCCV-AERB06 38599 14% QCCV-AERB09 41880 6% QCCV-AERH06 42471 28% QCCV-AERB12 44239 4% QCCV-AERH05 46710 6% QCCV-AERB03 78596 39203 4% QCCV-AERH02 81382 39619 6% QCCV-AERH01 83991 40593 6%


MAINTENANCE COSTS

97%

3%

Preventive Corrective

HOWDEN COMPRESSORS

Model Asset Meter Unit Allocation of corrective costs

WLVIH321 QCCV-HOW003 29,502 100%

WLV321 QCCV-HOW001 45,962

WLVIH321 QCCV-HOW004 47,794

WLV204 QCCV-HOW002 48,858

86%

14%


KAESER

96%

4%


MYCOM

Model (overhaul) Model Average

running hours Allocation of

corrective costs

KAESER (6/8) HSDV760 37'000 14 %

MYCOM (3/4)

HE4025SSC-LBL 37'000 4 %

HOWDEN


Maintenance costs vs model of compressor

0%10%20%30%40%50%60%70%80%90%

100%

Average correctivemaintenance costPreventive maintenancecost per compressor

* Double stage compressor type


COSTS vs TYPE OF CORRECTIVE TASK

STAL


LS 1 : major overhaul of LHC cryo compressors

HOWDEN : damaged rotor and casing

Wear of slide valve of STAL QCCV-STAB16 (P8) (remachining – oversize)

Scratches on KAESER rotors (QSCCB-4) Coming most probably from insufficient

lubrication -> 6 new rotor pairs


LS 1 : major overhaul of LHC cryo compressors

Capacity slide valve and support P6

Damaged plain bearing seat (QSCB-4-CP1-VMYaM)

AERZEN

Balancing piston (magnetic particles)


LS 1 : major overhaul of LHC cryo compressors Mayekawa - MYCOM

Rotor casing is in very good condition

Thrust bearings : normal wear Male rotor has damage on the position from the gear coupling

Damage on gear coupling from high stage

Bearing head is in good condition


MOTORS : allocation of corrective tasks

020406080

19 13

76

13 12.5 5

52

23 37.5

60

- 19% of QSCA motors with damaged coupling - 60% of QSCB motors with damaged coupling - 13% of shaft needed to be repaired (chroming) - 76% of polishing / grinding (normal wear) - 13% of plain bearing seats exchanged (too much damaged) - 12.5% of brass oil ring were exchanged - 5% of seals were exchanged - 52% of terminals were exchanged - 23% of motor needed a balance task - 37.5% of 400V motors were exchanged


LS 1 : major overhaul of LHC motors

Damaged terminals

Plain bearing

Shaft & coupling

issues


Recommissioning of motor-compressor systems of the LHC cryogenic installations after LS1 major overhauling. Vibration measurements according to VDI-3836 (compressors) & ISO-10816 (motors)

Point 1 Point 1.8 / Point 2 Point 4 Point 5

ATLAS SR

LHCB

LHCA

LHCB

CMS

M

ATLAS ANRS LHCCB

LHCCA LHCCA

LHCCB

ATLAS MR

Legend Total : 77 motor-compressor systems

C

CP1

M

C

CP2

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP6

M

C

CP7

M

C

CP1

M

C

CP2

M

C

M

C

CP5

M

C

CP6

CP3

M

C

M

C

CP1

M

C

CP2

M

C

M

C

CP7

M

C

CP8

CP3

M

C

CP4

M

C

M

C

M

C

CP1

CP2

M

C

CP1

M

C

CP2

M

C

CP1

M

C

CP5 CP6

CP4

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP4

M

C

CP7

M

C

CP8

M

C

CP9

M

C

CPA

M

C

CP1-2

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP6

M

C

CP7

LHCA

M

C

CP1

M

C

CP3

M

C

CP2

M

C

CP4

Point 6

LHCB

LHCCA

LHCCB

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP4

M

C

CP7

M

C

CP8

M

C

CP9

M

C

CPA

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP6

M

C

CP7

LHCA LHCA

M

C

M

C

CP2

M

C

M

C

CP7

M

C

CP8

CP3

M

C

CP4

M

C

M

C

CP5 CP6CP1

Point 8

LHCB

LHCCA

LHCCB

M

C

CP1-2

M

C

CP1

M

C

CP1

M

C

CP2

M

C

CP3

M

C

CP6

M

C

CP7

CP2

M

C

CP1

M

C

CP2

M

C

CP1

M

C

M

C

CP1-2

Nominal Noncompliant (balancing issues)No major overhaul


ELEC - INSTRUMENTATION 288 Valves

2000 Sensors 3500 Transmitters

320 Relays

VACUUM

200 Pumps 235 Gauges

29 Gate Valves

METHOD & COORDINATION

> 5000 Work Orders, CMMS,

Spare parts, Maintenance Plans, Plannings

Source: SERCO

LS1 MAINTENANCE OF CRYOGENIC INSTALLATIONS

MECHANICS MAJOR OVERHAULING

55 Screw Compressors 26 Oil Pumps 116 Motors

~75% of LHC

MECHANICS

2000 Safety valves 94 inspections of separator/coalescer

& 613 cartridges replaced 12 adsorbers (22 t of charcoal)

28 chemical cleaning ~ 6700 joints used


FILTERING ELEMENTS • Adsorbers (# > 50)

• @ room temperature (# > 20) (24’000 h) • LS1 New charcoal (pellets 4 mm – ref 208EA), except MR

ATLAS (PTFE coating) • Update the emptying/filling procedure : pumping out with

addition of water (dust ), manual filling or vacuum method

• @ cryogenic temperature (# > 30) (-) -> inspection of filters

• Coalescers (# >100) (removable or welded) • Oil separator (24’000 h) (with or without cartridge) • Oil separator with cartridges (16’000h) (24'000 if ΔP monitoring)

• Filters (# > 1000) (24’000 h)

• Various fluids : air, water, oil, gas process (He, N, Ar) • room and cryogenic temperatures -> inspection + corrective if necessary, except oil filters (systematic replacement/cleaning)


Coalescers (#100)

QSCA-2-2F167

QSCCB-4-S171

QSCB-4-7F160 QSCA-8-7F167


Filters (# 1000)

QSRB-18-4F210

QSCB-8

QSKA-2 QSRB-6-3F220


REQUALIFICATION OF PRESSURE VESSELS

• Acoustic Emission Test (AET) is an official and recognized pneumatic requalification method (many EN documents)

• Requalification pressure : "10% above the maximum operating pressure within the last operating period"

• CERN buffers inventory : 58 x 250 m3 + 68 x 80 m3 • Purchase of a piston compressor station (requalification process can be done

independently from operation)


CONCLUSION • The first shutdown of the LHC was a huge task • First time realized at CERN with 4 years of continuous operation

followed by 18 months shutdown maintenance plans revised accordingly

• Enormous work of inventory, data collection, method and procedure setting up to be recorded now in CMMS (->LS2) !

• Statistics and lessons have been presented, but some analyses are still on going (e.g. oil analyses)

• Preventive maintenance based on integrated running hours • In addition : predictive maintenance based on periodic vibration

monitoring and oil analysis • One year of preparation is a minimum : CMMS configuration,

maintenance plans, planning, contracts, …


Additional slides


Equipment Destination Mode of transport Quatity of transports Mycom Belgium Road 2 Trucks - not full (6500kg/compressor) Stal Sweden Road-Ferry 5 Trucks - 1 full (3500kg/compressor) Howden Scotland Road-Ferry 1 Truck - not full (4000kg/compressor) Kaeser Germany Road 3 Trucks - not full (1500kg/compressor) Aerzen Germany Road 4 Trucks - not full (4000kg/compressor) IHI Japan Road-Air 1 Transport not full (4 wooden boxes) S2M France Road 1 Trucks - not full (100kg/compressor) Motors Italy Road 13 Trucks - 8 full Total : 29 Trucks - 9 full

LS1 Logistics

CRG-ME LS1 : Compressor Remounting – Improvement of the alignment process

CRG-ME GM / 03-Apr-2014

• Configuration of the database (naming, dimensions)

• Taking into account of thermal growth • Taking into account of dynamic tolerances

Alignment at "cold"

Verification at "warm

"


Vibration measurements

Bearing datas stored in analyser settings

M1H Motor FS horizontalM1P Motor FS horizontal PVM1V Motor FS verticalM1A Motor FS axial

M2H Motor DS horizontalM2P Motor DS horizontal PVM2V Motor DS verticalM2A Motor DS axial

E1H Compressor male DS horizontalE1P Compressor male DS horizontal PVE1V Compressor male DS verticalE1A Compressor male DS axial

E2H Compressor male FS horizontalE2P Compressor male FS horizontal PVE2V Compressor male FS verticalE2A Compressor male FS axial

E3H Compressor female DS horizontalE3P Compressor female DS horizont.PVE3V Compressor female DS verticalE3A Compressor female DS axial

E4H Compressor female FS horizontalE4P Compressor female FS horizont.PVE4V Compressor female FS verticalE4A Compressor female FS axial

Measuring points

Tri-Axe Sensor

Machinery Health Analyser


Vibration analysis AMS suite – Machinery Health Manager

CMMS : Reporting & Statistics

Fault statistics for the motor-compressor sets and the oil pumps in operation

CRG-ME & WOs management / 16-May-2014


Equipment vibration monitoring Key for Equipment condition normal / unproblematic

to be observed

Point 18 to pay attention

LHCB / LHCCB critical / acions recommended

ID Mon

itorin

g Sc

hedu

le

Prov

. mon

i Sc

hedu

le

Janu

ary

Febr

uary

Mar

ch

April

May

June

July

Augu

st

Sept

embe

r

Oct

ober

Nov

embe

r

Dece

mbe

r

WO Description Type

Prio

rity

LHCB

QSCB-18-CP1 60

QSCB-18-CP2 60

QSCB-18-CP3 60 30 Wear - Increased internal play in male & female rotor, decreased

QSCB-18-CP6 60

QSCB-18-CP7 60

Scheduled Measurements 5 5 5 5 5 5 1 5 1

Measured Units 5 5 5 5 5 5 1 5 5 0 0 0

%-Completed 1 1 1 1 1 1 1 1 5 0 0 0

36

113%

32

Measures / Work Orders

LHCB

QSCB-18-CP1

QSCB-18-CP2

QSCB-18-CP3 18874787 Internal play OB M

QSCB-18-CP6

QSCB-18-CP7

WO's created 1 0 0 0 0 0 0 0 0 0 0 01


6R3.CV998 (RM S34)

Valves @ cryogenic temperature

QUICC-8-7CV760


Leak on refrigerator cold boxes

During LS1, 5 heat exchangers were repaired in 4 cold boxes

Documents

Maintenance of the LHC cryogenic system during the first · Maintenance of the LHC cryogenic system during the ... Cryo-Ops 2014 Maintenance of the LHC cryogenic system during the