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Cathodic Protection

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Yannick Pfisterer

on 5 March 2016

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Transcript of Cathodic Protection

Cathodic Protection
Degradación de Materiales. Ensayos no destructivos
by Yannick Pfisterer
Index
2. Significance
3. 2 Types of CP
4. Potentials
5. Anode Materials and Cathode Application
6. Electrolytes - Environment
7. Problems and Risks
8. Revision
and
Sources
1. Definition
Galvanic Cell
Cathode = Protected metal
Anode/Cathode/Electrolyte/Electric Curcuit
Chemical Reactions:
Ox.: Zn -> (Zn²+) + (2e-)
Red.: (2H+) + (2e-) -> H2
Ox. Reaction still occurs at Cathode
Methode to control corrosion on the metal surface by creating a galvanic cell
Galvanic/ Sacrificial
Cathodic Protection
Impressed Current
Cathodic Prodection
active
passive
anode is "sacrificed"
Direct Current required
Voltage of electric current
DC Power Source
Rectifier connected to local AC power source
other possibilities:
solar cells
windmills
thermoelectric current
changes in environment
=> custom manufactured
DC power source
Def: Work done in moving a particle of positiv charge from infinity to the responding point in n electric field
How the Potentials were determined:
Hydrogen is the Standard = 0 Volt
potential difference in galvanic cell between anode and cathode where determined
other potentials could be calculated
S/G Anode: difference have to be approx. 1 Volt
Galvanic/ Sacrificial
Anodes
Impressed-Current Anodes
Magnesium Anodes
conductive environment -> corrodes reliably
not suitable in salt water -> quicker corrosion
=> burried in soil to protect pipelines (in cloth sacks with bentonite clay)
=> also on offshore structures
- provide a quicker protection
Zinc Anodes
high weight
usable in salt/ fresh water
Al would passivate (react with environment)
=> ship´s hull -> easy replacement
=> Weight Bracelet on pipeline
Aluminum Anode
light weight
mostly used in alloys:
Al-Zinc-Mercury
Al-Zinc-Indium
Al-Zinc-Tin
Al does not passivate in saltwater if tin, antimony or mercury present
=> offshore structures
-> use of light weight
High-Silicon Cast Iron
Graphite Anodes
Mixed Metal Oxide Anodes
(Ceramic Anodes)
abrasion resistant and very robust
=> onshore applications strained by high weights
nagational lock in a river
=> onshore pipelines
-> with multiple anodes
low electrode-to-environment restistance
brittle nature -> must be handled carefully

newest product available
oxide coating/ ceramic bulks
exist in sheet-/mesh-/wire-form
stays in shape during lifespame
used in chlorine environment
=> Watertanks
=> Burried steel structures
=> Chlorine productions
environment represents the electrolyte within the CP structure
if it conducts badly it can cause malfunction in the CP
good cunductivity desired
near cathode: area becomes more basic -> mineral deposit at surface
extra protection
more soluble in cold water
coating must be resistant
=> offshore oil-/gas- platform not coated
difficulties measuring acurate voltages
change of environment
soil or freshwater:
-> copper/ copper sulfate
seawater
-> silver/ silver chloride
Hydrogen Embrittlment
Cathodic Disbonding
Cathodic Shielding
Production of Hydrogen at the cathode
can pass through crystalline steel structure
=> gas accumulates under surface
-> bubbles and cracks
around cathode more basic
coating might react with H+-Ions
disbonds from steel
accelerated by heat
dielectric coating of the steel blocks DC flow to steel
insufficient CP defense
=> metal loss due to
corrosive environment
Sources-Pictures1
Impressed-Current Anode:
http://upload.wikimedia.org/wikipedia/commons/1/16/GIC_cathodic_protec.jpg

Impressed-Current Anode2:
http://upload.wikimedia.org/wikipedia/commons/thumb/9/98/Cathodic_Protection_diagram.svg/2000px-Cathodic_Protection_diagram.svg.png

Sacrificial Anode:
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/section_23/06ebc176ac158067a2c4b8fdf423381a.jpg

Impressed-Current Anode3:
http://i.ytimg.com/vi/QYd9ENn1nP0/maxresdefault.jpg

Mainly used for:
http://www.ep-power.com/Images/Others/SolutionICCP.png

Corrosion on Pipelines:
http://www.puretechltd.com/blog/wp-content/uploads/2013/10/ExternalCorrosion_12.jpg

Pipeline Accident:
https://app.ntsb.gov/news/img/Sissonville.jpg
https://app.ntsb.gov/news/2014/140310.html
Sources-Pictures2
ICCP - Big Scale:
http://www.exoweld.co.za/App_Images/Editor/image/New%20images/Markets_applications/Illustrations/Large/Cathodic-Protection-(large).jpg

Zinc Anodes on Ships
http://www.marineprotection.co.nz/attachments/Image/Ahuriri_019_v2.jpg

Storage Tank - ICCP:
http://www.technoprotection.com/uploads/applications/technical-drawing-Aboveground-storage-tank-floor.png

Aluminum on platform:
http://upload.wikimedia.org/wikipedia/commons/f/f1/Anodes-on-jacket.jpg

Potential Chart:
http://www.engineeringtoolbox.com/electrode-potential-d_482.html

Potential Chart2:
http://www.corrosionist.com/Corros1.gif

Corrosion
http://www.hyperspacetravelagency.com/wp-content/uploads/rust.jpg

magnesium anode prepakage
http://4.bp.blogspot.com/-Ov66phGFOCk/TfjisB_RIII/AAAAAAAAAMA/IKRsl9NAzMI/s1600/magnesium%2Banode%2Bprepakage.jpg

Youtube: Cathodic Protection - Galvanic - Sacrificial
https://www.youtube.com /watch?v=RAlC75xG4qU

Youtube: Impressed Current Cathodic Protection
https://www.youtube.com /watch?v=QYd9ENn1nP0

Navigational Lock:
http://upload.wikimedia.org/wikipedia/commons/c/ca/Keiteleen_kanava.jpg
Sources
ASM Handbook Online
http://0-products.asminternational.org.fama.us.es/hbk/do/navigate?navOn=true&scope=EVERYTHING&anchor=&start=0&src=/content/V13a/D04/A25/index.htm
Wikipedia
http://en.wikipedia.org/wiki/Cathodic_protection
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