Corrosion in Water Systems -

“A case of corrosion in accelerator cooling water

systems: the Daphne Wiggler magnet”

Luigi PellegrinoAccelerator Division

Desy, April 20, 2004 Luigi Pellegrino 2

Our Lab in Frascati (Roma)


Daφne: the Main Rings


COPPER CORROSION IN DEMINERALIZED WATER

In the accelerator cooling systems the copper corrosion in demineralized water is unavoidable but can be limited;The corrosion rate depends on conductivity, dissolved O2 and CO2, pH, temperature, flow velocity, imposed electrical potential difference, galvanic potential difference (different metallurgy).


Corrosion vs pH and O2

From: E. Maughan, “Case study-copper based coolig water system”, MEDSI 2002.


Water treatment(what we know we should do)

Conductivity and other parameters control by 1. polishing on line and 2. controlled make up;Limiting the oxigen inlet by closing the water circuit (sealed or inert gas cushion);Taking advantage by O2 pumping away with inert gas flow;Monitoring of parameters with continuous data acquisition;Vacuum deaeration;UV hygienization.


In addition:

Avoid stops and unnecessary opening of circuits;Avoid dead leg in circuitry;Avoid different metallurgy;Check any possible depression in the piping; Check unwanted electric potential difference.


Typical cooling schematic

MAKE-UP

POLISHING ON-LINE

N2

T


WATER TREATMENT

³

³

MAKE-UP

POLISHING ON LINE

PROCESS TANK


Nytrogen pressurization

TO THE PROCESS

HYDRAULIC GUARD

N2

5 kPa


Typical parameters values

Conductivity < 0.2 µS/cmDissolved oxigen <20 ppb 6.8 < pH < 7.2

But here follows an example of what happens when they are far away from their best....


Wiggler magnet cooling distribution


....an uncomfortable workplace!


Electric and hydraulic connections

A series of 4 Wiggler, each one made by 10 poles in series (5 upper and 5 lower), each pole is a series of 5 coils.All the 50 coils are an hydraulic parallel. The inlet water is at 32°C, the outlet reaches 65°C. Except coils, made of OFHC copper, and EPDM rubber hoses, all other components are in AISI 304L ss.


Manifold-coil connection

copper coil ID 4mm

S.Steel manifold

Rubber hose ID 6 mm

S.Steel spigot ID 4 mmWater flow


Zoom again to the internal of rubber hose between the manifold spigot and the coil end.Here is a section enlargement, ID 4 to 6 and again to 4mm, as a little “chamber”.


The failure historySolid pebbles (D>5 mm) formed in the “chambers” inside the rubber and there moved back and forth, obstructing sometime the flow in one or more coils.Therefore the coils heated until safety thermal device switched and shutted down the whole chain of four wiggler magnets (~1 MW electric power).After a while, the pebble moved, the flow went right and we was not able to find the cause of the failure!Only once a persistent obstruction permitted us to catch the problem and start finding a solution.


The causesThe relatively high conductivity, the relevant dissolved oxigen contents of cooling water and the high electric potential of some coils with respect to the grounded piping yield the production of copper oxides and their migration according to potential difference.Actually we found a coal-black powder in several circuit points.Probably sulphide-reducing bacteria cathalized the agglomeration process, starting on the lips of the inlet copper spigots, in a slower flow region.The deposits growed until detached and continued growing, probably without leaving the “chamber”. At the end its dimensions (>5mm) were greater than the spigots throat: at least the final growing phase was surely in the place where we found the pebbles.


Growth of the copper oxide pebble

WATER


The analysis (collaboration with “Centro Sviluppo Materiali” di Pomezia)

Analyzed water at inlet and return of magnets circuit, before and after the polishing system (conductivity, O2 contents, pH, dissolved metals);Checked the surface of pieces of copper conductor with some months of operating life (micrographia, “energy dispersion” X-ray surface analysis);Analyzed the pebble and the powder (SEM microscopy with EDS spectrometer).


Analysis results (sample taken before and after the polishing)

0.533.17.650.23.89after8133.57.860.53.85before

sample 3

0.931.57.650.34.30after7832.57.40.54.35before

sample 2

4237.870.312.40after9223.17.550.812.50before

microg/l°CmicroS/cmmg/lsample 1

Cutemp.pHconductivityO2


The copper oxide pebble


Copper oxide powder


EDS analysis of the powder


The corrective actions

We modified the polishing circuit and its location in the plant, to assure a continuus treatment of the whole water mass with the proper flow in the mixed bed bottles, and added new instruments and a datalogger;The N2 cushion system was reviewed and frequently checked;The whole plant pressurization scheme was reviewed, to ensure a positive pressure everywhere.


Typical water quality recovery from a maintenance stop of a week

CONDUCTIVITY AFTER A MAINTENANCE STOP (24-11-03)

0

0.5

1

1.5

2

2.5

12.00 0.00 12.00 0.00 12.00 0.00 12.00 0.00

TIME

CO

ND

UC

TIVI

TY (m

icro

S/cm

)


Another failure case...

Septum magnet coil

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Corrosion in Water Systems -