Corrosion of BeCu and Vacuum
Setback in Fermilab Main Injector
P. Hurh, A. Chen*, B. Brown, L. Cooley, J. Hylen, L. Valerio
The Fourth Workshop of Operation of LArge Vacuum systems,
Taiwan
April 1-4, 2014
Outline
• Fermilab MI and Upgrade
2013 at MI30
• Vacuum Setback
– Startup problems
– Huge gas load
– Corroded Copper seal
– Corroded BeCu spring
– Be contamination?
• Hunting for causes
– RGA scans
– Bi-metal galvanization?
– Radiation induced?
– Moisture?
– Be tests
• Summary
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ANU Shutdown Details
Recycler Layout and Tasks
Key: WBS
Elements Removed
New Elements
Areas Affected
Stochastic Cooling Kickers
New Injection Area
Stochastic Cooling Pickups
Current Injection Area
Electron Cooling Insert
New Extraction Line
New RR30 Straight Current Extraction Area
New 53 MHz RF
MI 14 Building
(Off project)
MI 39 Building
(Off project)
New Abort Kickers
Proton
Direction
MI-308
By Cons Gattuso
Drawing of Pre/Post-ANU SD 309-308
309 308
307
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Main Injetor/Recycler
Photo of Post ANU SD
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Startup problems
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• Cables mis-labeled
• IP/PS mis-matched
• Control card failure
• IP faulty- 1st evidence of corrosion
Corrosion on copper parts in 300 l/s ion pump just US of
308DS Collimator
Ion pump was shorted
Corrosion product on gasket appeared “pasty” and wet soon after removal
Some reports of funny smells
Ion pump had some “debris” and, when wiped with alcohol, showed some brownish residue
Original pump cleaned, new feedthrough and re-installed
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Startup problems
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• Huge Gas load ( IP in 15 min. protection mode)
• 308 area has larger IPs but Higher pressure
• High He background during leak-checking
Accelerator in Commissioning
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• Commissioning degas a quite bit.
• Pressure in 308 still higher than normal startup
To meet schedule requirements, accelerator commissioning started despite high vacuum pressure
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Time to investigate the huge gas load
Key: WBS
Elements Removed
New Elements
Areas Affected
Proton
Direction
MI-308
Lambertson Repalcement
Photo of Post ANU SD( event map)
Section 1
Section 1 Section 2 Section 3
Section 3
Section 3
Smoking
Cut
White
Residue
Heat test
Stained
Pump
Corroded
Pump
Corroded
Spring
Corroded
Pirani (originally on
bottom)
Most DS cut of
ANU mods
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Corroded Al
seal
Corrosion(?) of 6”Aluminum seal at 308
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308 elliptical bellows
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308 bellows dissection
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MI Elliptical Bellows (2.09”x4.84”)
BeCu172 spring
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MI Elliptical Bellows
• BeCu spring used to keep RF fingers in good contact
• No corrosion found on the spares stored in shelf for
18+years
7.67g, Silver Coated
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BeCu 172(Alloy 25) Beryllium: 1.80 - 2.00% Cobalt+Nickel+Iron: .6 max. % Lead: .02 max. % Copper: Balance
~1g of weight loss
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Pirani Gauge Gasket
Note: Orientation of gauge was underneath the beam tube
in the original configuration, cross to 30 l/s Ion Pump.
On Beamtube
On Pirani gauge
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White residue at DS of 308 Collimator • Partially “stuck” • Was found TiO
by SEM EDS result
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“Smoking Cut” near BV309
• With Odor “diffusion pump oil with more of an exhaust or metal smell with it”
• Cutting was repeated on other similar tube, but no significant “smoking” observed, with odor of metal grinding
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“Smoking Cut” near BV309, (Saw)
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Swabs from the tube
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• Black can be graphite from coating inside kickers
• “Oily” is dissolvable in acetone
RGA CART
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RGA
• RGA scans taken before/after heating bellows
• Scan during the heating was not success since the pressure rise too fast (in seconds) to recorded before tripped
• Heating with “heat gun” too fast, more control is needed
64 is new
before
after 30 and 46 higher
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CU/BE SPRING UNKNOWN CONTAMINATION
Image of samples in the SEM
EDS
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25
Full field average of “Blue Powder”
• Did not pick up any Sulfur or Sodium or Potassium • Carbon could be from carbon tape used to mount powder specimen in SEM
chamber • SEM EDS analysis indicated: Cu, O, C, N • Note that EDS is unreliable for anything lower Z than 5 (including Be) • Donna noted that the powder was very “wet”, although that was not noted
when it was first observed (so very hygroscopic)
Name M. Mass color
CuO 79.5 black
Cu(OH)2 97.6 blue
CuCO3 123.6 Light blue
Cu(NO3)2 187.6 blue
Where were these from?
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• Consistent with Copper
(II)Hydroxide (O:Cu = 2)
with some Copper
Oxide (O:Cu = 1)
• Measured 61/39 = 1.56
SEM EDS results of “Blue Powder”
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Citranox (assisted) Bimetal galvanic Corrosion Test at NWA
• Test Objective
– Create corrosion through
galvanic potential (Cu gasket
to SS flange)
– Assisted by fluid film of 1%
Citranox (ultra-sonic cleaning
solution used on vacuum parts
in MI)
• Test Procedure
– SS chamber w/ cup of Citranox
sol’n with vent open to 70C
– Cooled to RT with vent closed
– Sit at RT for ? days
– Open and observe
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Citranox (assisted) Bimetal galvanic Corrosion Test at NWA
• Heat Up
– About 3 hours to temperature
– No fluid loss visible
– Condensation on cooler window
• Cool Down Start
– Window cooled fast
– Lots of condensation on window
– Hard to get view of SS inner walls
– Used Heat gun (on cool) and observed color change
– Cu gasket on window flange not obviously wet
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Citranox (assisted) Bimetal galvanic Corrosion Test at NWA
• After Cool Down
– Cooled to 18 C overnight
– Lots of condensation on
window
– Hard to see interior surfaces
• Heat gun on window
– Within seconds, window
cleared (except for very large
drop)
– Lots of condensation visible on
top 2/3 of chamber
– Lower third appears drier
– Some droplets on window
gasket?
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Citranox (assisted) Bimetal galvanic Corrosion Test at NWA
• What to do next?
– Let sit for 1 week, open,
inspect?
– Heat top, Cool bottom?
• So far, no sign of corrosion on
Copper gasket in Window
Flange
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More Corrosion Tests:
• 3 hydration corrosion tests – #7: Pure copper gasket sprayed with undiluted ammonia
– #8: Silver-coated copper gasket sprayed with undiluted ammonia
– #9: Silver-coated copper gasket dipped in 1% nitric
• All samples left to dry 24 October on watch glass
• Samples confirmed to be dry* 28 Oct. Watch glass
with samples then put into secondary container with
water and covered
Photographs taken 2 December
* “dry” may have been interpreted as a dry top surface
• Some corrosion is already evident
• Some moisture is visible where specimen and glass
touch, but the amount of moisture is smaller than that
observed on 2 December
6 November 2013 -
Tampa FL
30th Low Temperature - High Field Superconductor Workshop 32
Photo of #9 on 10/29/13
Hypothesis and Next Steps
• Dried nitric acid became re-activated with humidity
• 1% nitric residue corroded a large amount of material – Mass change will be measured
– Does the reaction terminate when all nitrate is consumed? If not, why not? Is it because nitrate catalyzes hydroxide formation?
• Liquid pooled either because: – Corrosion products are hygroscopic
– Some water was applied to the watch glass by mistake • We are repeating the experiment
• The liquid could be an effective electrolyte – We will measure pH and conductivity
– What happens if there is a SS counter-electrode?
• Residues have colors of expected salts – Black = silver nitrate, blue = copper nitrate or copper hydroxide
– We will perform EDS analyses
• But, 5% nitric spray on a silver coated small gasket was used in another test, but result varies.
6 November 2013 -
Tampa FL
30th Low Temperature - High Field Superconductor Workshop 33
Wet Chemistry Process?
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Copper
CuO
Cu(OH)2
CuCO3
Cu(NO3)2
…
Nitric
(starter)
Silver
(catalytic
)
H2O
(wet)
silver nitrate provides an intermediate species to catalyze the formation of copper hydroxide via copper nitrate. That is, silver nitrate plus water provides nitric acid to attack copper and form copper nitrate, but then copper nitrate plus more water forms copper hydroxide and returns the nitrate back to the silver. Hence, the major reactant is water, the major product is the bluish copper hydroxide, and the catalysts are trace nitric acid and silver.
Air Ionization by Radiation
• During beam operation, primary protons in the residual gas of
the vacuum space and secondary particle flux in the tunnel
air ionize the air, creating some amount of nitric acid, ozone,
and other compounds.
– 0.2 gram of nitric might be possible with 1e-7 torr for 7 years of
operation
• To a much lesser extent, the same can occur from residual
(gamma) radiation.
– order of 1 milligram of Nitric compounds. With atmospheric
pressure and 10R/hr
• Neither process would seem to create enough acid in the
vacuum space to react with 1 gram of copper or more.
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Moisture (permeation from roughing port)
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O-Ring permeation
O2 H2O N2 total
rate 1.7 40 0.233
P psi 3.1 0.34 11.5
D inch 3 3 3
Q 1.3 1.3 1.3
s 0.2 0.2 0.2
L 1e-8 std cc/s 13.8 35.6 7.0 56.5
24% 63% 12%
after one
year std cc 4.4 11.2 2.2 17.8
mg 6.2 9.0 2.8
total rate std.cc/s 5.6E-07
torr.l/s 4.2E-07
Flood
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Pumping Port is 9” from floor
Cons Gattuso
Beryllium Particulate
• It was realized on August 20, that the corrosion product from the BeCu spring (MI elliptical bellows) could have significant amounts of Be particulate. It was on the spring
• By the time ES&H was informed and the work was stopped (August 21), several more cuts into the system were performed.
• Work resumed under close supervision from ES&H with respirators (full-face or powered air purifying).
• Be test results indicated that a wipe sample of the blue corrosion product contained 350 micrograms of Be. Air samples of the 308 tunnel area and MI-60 drop area found no detectable Be.
• Currently any work on the MI vacuum system will be done under an HA which requires respirators and/or glove box and air sampling.
• Testing is currently underway to confirm this is a local phenomena associated with the 307-308 area
• Vigorous tests has been done for ES&H, No Be Contamination was found in other area or airborne
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Summary
• The exact cause(s) of the corrosion remain unknown, many
hypothesis, but not confirmed.
• However, We believe Nitric component and moisture play critical
roles, as well as silver. silver nitrate provides an intermediate
species to catalyze the formation of copper hydroxide via copper
nitrate.
• Lessons learned: – Keep vacuum tube under vacuum, or completely sealed. Active
pumping shall implement for long shutdown
– Monitoring measure shall apply, as QA
– Keep open communication across groups to reduce risk of mis-
matching
• What we missed anything? Your suggestions are appreciated!
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