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Pipe joining techniques for Phase 2 upgrades high-pressure systems -Summary report from CERN’s 18th of May 2018 workshopJEROME DAGUIN – PAOLO PETAGNA
T H AN KS T O : G E O R G V . , F R ITZ M . , A N TT I O . , K A R OL R . , B A R T V . , P A U L K . R . , P I E R R E D . , A L L E N Z . , P E TER R . , H A N S P . , C H I - MEN G L .
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Outline
CERN’s 1 day workshop
Context of Ph2 upgrades
Leak tightness and reliability
The joining techniques
◦ Brazing techniques
◦ Welding techniques
◦ Fittings
Conclusion
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CERN’s 1 day workshopPIPE JOINING TECHNIQUES FOR PHASE 2 UPGRADES HIGH-PRESSURE SYSTEMS
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CERN Workshop – 18th of May 2018
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https://indico.cern.ch/event/721360/overview
1 full day
8 talks
≈ 60 participants
Mailing list created (contact me if you want to be added)
“The workshop is intended as an informal and
open discussion on all the aspects of joining
techniques for CO2 cooling system piping,
including fittings, welded joints, brazed joints
and special connections involving electrical
breaking.”
Context of Ph2 upgrades
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The ATLAS iTK Ph2 upgrade
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Pixel outer barrel
Pixel inner systemPixel outer endcap
Strip barrel
Strip endcap
392 CLs
158 CLs
384 CLs
108 CLs
? CLs
>1000 cooling
loops
>10000 pipe
connections of all
types
The CMS TK Ph2 upgrade
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TBPS Flat/Tilted
109 CLs
TB2S
124 CLs
>600 cooling
loops
>10000 pipe
connections of all
types
TEDD
280 CLs
TBPX/TFPX
104 CLs
TEPX
32 CLs
Ph2 upgrades numbers
CMS TK + EC is around 500kW
ATLAS iTk is around 250 kW
CO2 at -35°C or below
PS= 130 bar
Ptest = 186 bar
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Leak tightness and reliability
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Leak tightness and reliability
No gas vessel (pipe, etc.) is absolutely leak tight
◦ And actually it does not need to be
The leak rate must be low enough that the required operating pressure is maintained and that the lost fluid is not doing any damage to the environment or incurs a large financial loss
All estimates must be seen in the context of the system size (number of joints)
For what we need r<10-4 mbar.l.s-1 (He) is entirely adequate
◦ Which is (relatively) easily achievable…
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Leak tightness and reliability
Reliability is the real challenging requirement we need to achieve in our systems!
◦ This is what:
◦ During installation costs money, time and nerves
◦ During operation costs acceptance
How do we quantify reliability ?
◦ By a failure rate
We need to establish
◦ What failure rate do we need ?
◦ How can we establish this performance for a given design/part ?
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Leak tightness and reliability
A verification for system larger than 10-100 fittings is beyond our means…
◦ Use industry standards connection techniques as much as possible
◦ They have much larger use statistics
◦ The problem is that for the tube dimensions we aim for, there is no industry standard – not even for brazing or welding
◦ In the qualification think carefully about the loads for which the joining technique needs to be qualified and perform control tests using these loads
◦ Include tests at increased stress level to find faults without the need of excessive statistics
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Pass/fail test sample size to demonstrate a failure rate of 1 in 10,000
Reminder:
PS=130 bar
Ptest on site = 1.44 x PS = 186 bar
Ptest in lab for qualifications = 2 x PS ? = 260 bar ?
Brazing techniques
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Soldering/BrazingJoining of two components with a brazing filler material (BFM), whose liquidus temperature is below the melting point/range of any joined component◦ No melting of the component material
Soldering of stainless steel/copper:◦ Typically used SnAg3.5 (ISO 9453 S-Sn96Ag4; Tliq = 221°C), Rm ≈ 25 MPa
Brazing at high temperature of stainless steel/copper:◦ Typically Ag-based filler metals, i.e. AWS BAg-7 (Tliq = 650°C), Rm ≈ 400 MPa
SolderingTl_FM < 450°C
BrazingTl_FM > 450°C
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Brazing techniques
Classified by heating technology:
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Brazing techniques – Manual brazingManual Brazing at Atmosphere
•Heat Sources: Flame Torch (Acetylene), Induction, (Plasma, Arc…)
•Working Temperature of common filler metals: 600-800°C• Steel/Stainless Steel, Copper Alloys: I.e. AgCuZnSn
(650°C)
•Application of flux necessary to remove surface oxides
•Brazing of tube fittings:• Lap joints (5-10 mm overlap, rule is min. 3x Wt)
• Gap clearance of joint 0.1-0.2 mm on diameter
• Manual process, individual qualification of personnel necessary
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Brazing of CMS Pixel Ph1 tubes in CERN EN/MME workshop
Brazing techniques – Manual brazingManual Brazing at Atmosphere
Preparation of components:• Cleaning/Etching (Surface treatment)
• Application of flux on brazed surfaces
• Assembly and possible inertion for tubes (Ar-flush inside) to avoid oxidation on the inner wall
• Brazing material normally applied as rods/wires
• Brazing with avoiding overheating (can change viscosity of filler, incrusting of flux)
Post treatment:• Cleaning/removal of flux from components. Mechanically and cleaning with detergent/warm water
(surface treatment)
Flux contains components as KF, Borates etc. -> corrosive!
• Visual inspection
Precautions:
• Ventilation of fumes (flux) which can condense on surrounding surfaces
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Brazing techniques – Vacuum brazing
General features of vacuum brazing
Assemblies brazed in vacuum chambers (10-2 mbar…10-7 mbar)
Parts have to be clean (outgassing, pollution) and principally oxide-free (wetting properties)
Heating performed by radiation, induction, (laser, microwave, EB..)
◦ Most common technology: vacuum furnaces with resistor heaters
Use of vacuum compatible filler-materials (no volatile components at corresponding brazing temperatures)
◦ Most common BFM for vacuum brazing:
◦ Silver-Copper alloys (780-950°C)
◦ Gold-Copper alloys (950-1050°C)
◦ Nickel-based alloys (1000-1200°C)
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Brazing techniques – Vacuum brazing
Advantages of vacuum brazing◦ No flux used/necessary
No residual fluxing agents have to be removed/cleaned after process, no risk of corrosion induced by remaining flux (mostly acids containing fluorides and/or chlorides)◦ Brazed parts stay clean and no oxidation
occurs during brazing processBesides flux has not to be removed, the surfaces stay clean and metallic (applications for UHV and RF-cavities)
Specifically for furnace brazing:◦ Low distortion of assembled pieces due to
homogeneously heated partsHigh precision assemblies maintain their geometry and alignment
Disadvantages of vacuum brazing◦ General high costs:
◦ Vacuum furnace equipment
◦ Only batch production possible
◦ Preparation of all assembly parts necessary (surface treatment)
◦ Vacuum grade filler materials more expensive
◦ Long brazing cycles (up to few days from cold to cold)
Specifically for furnace brazing:◦ Complete assembly has to be heated
Due to high brazing temperatures material properties will be influenced by the heat treatment (annealing, grain growth, diffusion/precipitation)
◦ Complex preparationFixed placement of filler material, fixed positioning of assembly parts has to be assured
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Brazing techniques – Vacuum brazing
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SS-copper transition
for dielectric
SS-SS direct brazing of
VCR-connector to capillary
ss-copper transition for
subsequent orbital welding
Brazing to ceramic
with Cu-sleeves
Assembly sequence:
1. Brazing copper sleeves to capillary/tube
2. Brazing of VCR-connector (with nut) or welding fitting
3. Final assembly with dielectrics
Usage of three different BFM with decreasing melting range
Inlets SS-capillaries (Øo1.6mm and Øo2mm)
Return copper pipes (Øo5mm)
Qualific
atio
n s
am
ple
s fo
r US
-inspectio
n
US-imaging of SS-Cu transition
Assembly of capillaries for CMS PIXEL Ph1 upgrade
Brazing techniques - Soldering
Soft soldering was used for the CMS Tracker Outer Barrel piping connections
◦ Single phase C6F14 cooling with max 6 bar
◦ Copper-Nickel pipes 2.2/2.0 and 2.5/2.3
◦ Joint sleeve in brass
◦ Soft solder from CERN store: Multicore SnPbAg 62/36/2 with core flux (ERSIN 362)
Final soldering was done in situ (≈50%)
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Tip of the soldering iron
machined to a concave
shape for increased
thermal contact area to
the pipe and the brass
pieceSoldering iron with fume extraction tip
Developments are on-going for soft-
soldering of SS pipes
Welding techniques
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NASA welding methodSelecting the right welding parameters for automatic welding
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The Low-Limit / High limit method is a good method to select the
nominal welding parameters and assure that possible fluctuations do
not bring the series welds out of spec.
Welding power
Not fully penetrated To much penetration Full penetration (all good welds)
Low limit weld High limit weldNominal limit weld
Weld
sa
mp
les
NASA welding methodCertification procedure
Each welding type is pre-qualified with weld samples◦ 5 Low limit welds, 5 nominal welds and 5 high limit welds.
◦ From each weld group the following tests are done to qualify the quality
◦ All visual inspection (in and outside), all should look similar
◦ 1 burst test (>4x design pressure)
◦ 1 longitudinal cut and microscopic analyses
◦ 3 samples for further research if needed
Production of a series of welds◦ 3 high, 3 low and 3 nominal pre welds samples.
◦ All process welds done at nominal settings
◦ 3 high, 3 low and 3 nominal post welds samples.
◦ The pre and post weld samples are send to NASA for inspection
◦ 1 burst, 1 microscopic and 1 spare for each type
◦ All process welds are inspected visually and compared with post and pre weld samples.
◦ Dye penetrant tests on process welds
Due to the automatic welding and the similarity of all welds, no further complex inspection of the welds is needed
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Welding techniques – Orbital welding
Orbital welding on SS or Ti is standard and “easy” down to 1/8” and 200µ/300µm Wt
Massively used in all systems in operation and under development
Requires careful alignment, good pipe preparation and Ar protection
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SWAGELOK M200 Orbital welder setup
@ Sheffield
CMS PIXEL Ph1 Supply manifoldLHCb VELO cooling blocks
Welding techniques – Orbital weldingOrbital welding below 200µm Wt is more tricky…◦ CMS Ph2: 2.5OD/150µm Wt Ti tubes
◦ ATLAS Ph2: 2.5OD/180µm Wt Ti tubes
Tube cutting, preparation and alignment extremely difficult for butt welding of thin wall tubes◦ Sleeve welding reduce difficulty
Machine stability at low current is essential for thin wall tubes welding◦ Such machines are not available OFF-the-shelves in industry
◦ Sheffield developed their own machine with VBC company
◦ Can weld down to 125µm Wt Ti tubes
◦ Argonne is proposing to add thickness welding a sleeve together with the tube
◦ Enables better alignment as well !
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Cross section through 2.5mm x 0.178mm wall
tube and sleeve fitting at welded joint area
Butt
weld
Sleeve
weld (filet)
vbc IP50
Fittings
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Fittings – VCR typesStainless steel fittings with metal seal◦ Can be re-used (almost) indefinitely – gasket need to be changed
◦ Extremely reliable
◦ Leak tight
Available for pipe sizes of 1/8”, 1/4”, 1/2”, 3/4” and 1”
Many suppliers on the market since couple of years◦ Swagelok, Rotarex, Hamlet, Fitok… and even Hikelok on ALIBABA !!!
Female nut silver plated to prevent galling when tightening
Don’t exist for tubes smaller than 1/8”◦ Drilling of blind glands + brazing allows for use with smaller pipes
Connection is quite bulky…
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Fittings – Custom design
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Laser-welding between
gland and tubing
Identical
glands
¼” hex male nut M5.5 x 0.9
threads
Aluminum gasket being captured
inside the male nut
¼” hex female nut with M5.5 x
0.9 threads
OD 2.2 mm, wall 0.1 mm
304L ss tubing
Enhanced version for Ph2 TBPX/TFPX
CMS PIXEL Ph1 FPIX design Fixed male nut induced torque transfer
to tube during tightening and self
untightening during
pressure/temperature cycles in the
assembly phase
CMS PIXEL Ph1 BPIX design
ATLAS IBL LAPP design
Electron Beam welds
Fittings – Custom design
Material choice and welding parameters are essential when designing such fittings
◦ Hot cracking issues in the development phase of the FPIX Ph1 fittings (See Stephanie T. talk in Bonn in 2016)
https://indico.cern.ch/event/469996/contributions/2148019/attachments/1277061/1895241/FPIX_Laser_Welding_Bonn_Forum_2016.pdf
Design is not as simple as a scale down of SWAGELOK VCR design…
◦ Small size induce new constraints (tightening torque, torque transfer…)
Since our sampling capacity is limited, testing and validation parameters should be much more constraining than operational parameters
◦ PS=130 bar
◦ Ptest on site = 1.44 x PS = 186 bar
◦ Ptest in lab for qualification = 2 x PS ? = 260 bar ?
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Fittings – Large sizes
Phase 2 plants will need up to 2” pipes◦ Anything above 1” cannot be done with VCR
Standard flanges available in DIN, ANSI or B10 dimensions◦ Outside diameter of flanges 184 – 216 mm for DN50
◦ Generally too big for our installations…
SAE flanges used for high pressure hydraulic up to 400 bar (6000 PSI)◦ O-ring replaced by CF copper gaskets
◦ Testing foreseen at CERN in the coming weeks
Compact flange option to be investigated◦ Described in the NORSOK standard
◦ Used in Oil and Gas industry
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Conclusions
We are about to build (very…) large systems with (very…) large number of connections of all types
Wide range of joining techniques available
◦ Make the good choice based on the detector constraints
◦ Take it into consideration in the early phase of the design
This is a bit more than just plumbing…
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