CORROSION AND CORROSION PROTECTION - · PDF fileCORROSION AND CORROSION PROTECTION ... NORSOK M-001 and ISO 21457 are valuable ... Aluminum alloys

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CORROSION AND CORROSION PROTECTION
A short introduction course
by Roy Johnsen, Professor NTNU

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WHO IS ROY?
Siv.ing. NTH 1979
Dr.ing. NTH 1984
Scientist SINTEF 1981-1985
Research Manager Statoil 1985-1991
Director CorrOcean 1991-2003
Professor Corrosion and Surface protection IPM/NTNU 2004 ->
Sabatical 2011/2012 Statoil Autumn 2011
Qatar Petroleum Spring 2012
Ifea "Materialvalg for instrumenter og ventiler", des. 2011 [email protected]

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GOALS FOR THIS LECTURE
I will try to explain to you: why corrosion can occur
why coupling between different metals can cause severe corrosion (=galvanic corrosion)
how reduce the probability of corrosion to initiate and grow
that stainless steel is not always stain less (rustfri)!

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Henningsvr- Lofoten October 2009

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Petronas Twin tower January 2010

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WEATHER WALL FROM THE EKOFISK FIELD Same material as for Petronas TwinTower

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Hardangerfjord Bruravik Brimnes July 2010
WHY?

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E6 Minnesund - Kollomoen

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COMMUNICATION BOUY
INFORMATION: Instrument buoy on 100 m
water depth
Concrete anchor on the seabed
Metal hook made from AISI 316 to fasten the anchor line
Design life time 10 years
Dilemma:
Shall I use a fiber rope or galvanized wires for
the anchor line?
SEABED
Concrete anchor
Metal hook
SEAWATER
Instrument buoy
Anchoring

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EXTREEME FAILURE CASES

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DIFFERENT TYPE OF FAILURES On Statoil operated installations 1997-2007
FATIGUE
31%
CORROSION
31%
WEAR
5%
HYDROGEN EMBRITTLEMENT
FABRICATION
BRITTLE FRACTURE
INSTALLATION 2%
LIQUID METAL EMBRITTLEMENT
CREEP
3%

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LITTERATURE

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WHAT IS NEEDED TO GET CORROSION STARTED
Metal + Water
CORROSION can occur

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HOW TO AVOID CORROSION?
Metal +
Water
CORROSION can occur
Remove the water and stop the corrosion

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-2 86420 141210 16
0
-1.2
-0.4
-0.8
1.6
1.2
0.8
0.4
2.0
-1.6
PASSIVITY
CORROSION
IMMUNITYCORROSION
*A
H2O/H2
O2/H2O
pH
E(V)
POURBAIX DIAGRAM Carbon steel
Does not say anything about the corrosion rate

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WATER BASED CORROSION
We need: Water present A metal with Anodic and Cathodic
reactions
Anodic reaction = Cathodic reaction
A: Fe => Fe2+ + 2e-
C: O2 + 2H2O + 4e- => 4OH-

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TYPES OF CORROSION
Uniform corrosion Galvanic corrosion Localized corrosion
Pitting corrosion Crevice corrosion Stress corrosion cracking
CO2/H2S corrosion Flow induced/erosion corrosion Corrosion fatigue Bacterial corrosion Wear Tribo-corrosion

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DIFFERENT CORROSION TYPES
Uniform corrosion
Galvanic corrosion
Crevice corrosion
Pitting corrosion

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Stress Corrosion Cracking
CO2-Corrosion
Erosion corrosion
Hydrogen Induced Stress Cracking
DIFFERENT CORROSION TYPES, cont.

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GALVANIC SERIES

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GALVANIC CORROSION
Two different metals in the same electrolyte and in metallic contact.
Corrosion rate depends on: Actual metals
Area ratio between the metals
A
A - noble B un-noble
A
Metall A Metall B

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GALVANIC CORROSION
ALWAYS VALID: Current from Un-noble metal IA = Current to noble metal IC
iA*AA = iC*AC
ia, ic = current densities (A/m2)
Metal A Un-noble
Metal B Noble
IA IC
I
NOT WANTED: Small un-noble alloy connected to a big noble alloy!

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USE THE GALVANIC SERIES!
Heat exchanger

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90/10 CuNi Titanium
Coating
HOW TO AVOID GALVANIC CORROSION? Always cote the noble metal!
If coating failure: iCuNi=iTi*ATi/ACuNi

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PREFERENTIAL WELD CORROSION
Base metal
Weld metal
Heat affected zone

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IMPORTANT FACTORS FOR CORROSION
Electrolyte composition
Temperature
Oxygen content
Chloride content
CO2 and/or H2S content
Oxidizing species (e.g. chlorine)
pH
Velocity
Content of solids (e.g. sand)

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HOW TO REDUCE THE PROBABILITY OF CORROSION?
Select a material that does not corrode in the actual environment (if possible)
Apply a coating
Cathodic protection
Change and/or modify the environment
Change the design

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MATERIAL SELECTION
NORSOK M-001 and ISO 21457 are valuable guideline documents
REMEMBER:
Quality control during supply/delivery is important NORSOK M-650
Material compability when connecting materials (i.e. galvanic corrosion)
Stainless steel is never stain less (rustfrie) if you exceed critical process parameters
Design parameters shall be followed in operation

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EXPERIENCE WITH AISI 316 In chloride containing environment
PIPE FOR SEAWATER TRANSPORT INSTRUMENT TUBING

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CORROSION PROTECTION through coating
PATER NOSTER - SWEDEN INSTALLATION IN THE NORTH SEA

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HOT DIP GALVANIZING (varmforsinking)

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TYPES OF COATING
We normally talk about three types of coating: 1. Metallic coatings
Electrolytic applied Chemical Welding Thermal spraying
2. Ceramic coatings Thermal sprayed Deposited
3. Organic coatings Rubber lining Polymer layers Paints
Thermal spraying
Overlay welding
Painting

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METALLIC COATINGS
Two classes of metallic coatings 1. The coating is more noble than the substrate
Cathodic coating
2. The coating is less noble Anodic coating
1 2 Nickel Zinc

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CATHODIC PROTECTION IN PRACTICE
Propeller to be protected
Wire to connect anode and object
Anode

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SACRIFICIAL ANODES
Aluminum alloys
Zinc alloys
Magnesium alloys (seldom)
Flush mounted
Stand off
Bracelet
Zinc anode after 4 years in use

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CORROSION AND CORROSION PROTECTION - · PDF fileCORROSION AND CORROSION PROTECTION ... NORSOK M-001 and ISO 21457 are valuable ... Aluminum alloys