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

Transcription

1 1 CORROSION AND CORROSION PROTECTION A short introduction course by Roy Johnsen, Professor NTNU

2 2 WHO IS ROY? Siv.ing. NTH 1979 Dr.ing. NTH 1984 Scientist SINTEF Research Manager Statoil Director CorrOcean Professor Corrosion and Surface protection IPM/NTNU > Sabatical 2011/2012 Statoil Autumn 2011 Qatar Petroleum Spring 2012

3 3 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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5 6 Henningsvær- Lofoten October 2009

6 7 Petronas Twin tower January 2010

7 8 WEATHER WALL FROM THE EKOFISK FIELD Same material as for Petronas TwinTower

8 9 WHY? Hardangerfjord Bruravik Brimnes July 2010

9 10 E6 Minnesund - Kollomoen

10 11 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? Instrument buoy Anchoring SEAWATER Metal hook Concrete anchor SEABED

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13 14 EXTREEME FAILURE CASES

14 15 DIFFERENT TYPE OF FAILURES On Statoil operated installations WEAR 5% HYDROGEN EMBRITTLEMENT CREEP 3% INSTALLATION 2% LIQUID METAL EMBRITTLEMENT CORROSION 31% FABRICATION BRITTLE FRACTURE FATIGUE 31%

15 17 LITTERATURE

16 18 WHAT IS NEEDED TO GET CORROSION STARTED Metal + Water CORROSION can occur

17 19 HOW TO AVOID CORROSION? Metal + Water CORROSION can occur Remove the water and stop the corrosion

18 20 POURBAIX DIAGRAM Carbon steel O2/H2O PASSIVITY 0.4 E(V) 0 CORROSION H2O/H IMMUNITY * A CORROSION ph Does not say anything about the corrosion rate

19 25 WATER BASED CORROSION We need: Water present A metal with Anodic and Cathodic reactions A: Fe => Fe e - C: O 2 + 2H 2 O + 4e - => 4OH - Anodic reaction = Cathodic reaction

20 27 TYPES OF CORROSION Uniform corrosion Galvanic corrosion Localized corrosion Pitting corrosion Crevice corrosion Stress corrosion cracking CO 2 /H 2 S corrosion Flow induced/erosion corrosion Corrosion fatigue Bacterial corrosion Wear Tribo-corrosion

21 28 DIFFERENT CORROSION TYPES Uniform corrosion Crevice corrosion Galvanic corrosion Pitting corrosion

22 29 DIFFERENT CORROSION TYPES, cont. Stress Corrosion Cracking Erosion corrosion CO 2 -Corrosion Hydrogen Induced Stress Cracking

23 30 GALVANIC SERIES

24 31 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 - noble A A B un-noble Metall A Metall B

25 32 GALVANIC CORROSION I Metal A Un-noble I A I C Metal B Noble ALWAYS VALID: Current from Un-noble metal I A = Current to noble metal I C i A *A A = i C *A C i a, i c = current densities (A/m 2 ) NOT WANTED: Small un-noble alloy connected to a big noble alloy!

26 34 USE THE GALVANIC SERIES! Heat exchanger

27 35 HOW TO AVOID GALVANIC CORROSION? Always cote the noble metal! 90/10 CuNi Titanium Coating If coating failure: i CuNi =i Ti *A Ti /A CuNi

28 36 PREFERENTIAL WELD CORROSION Base metal Weld metal Heat affected zone

29 38 IMPORTANT FACTORS FOR CORROSION Electrolyte composition Temperature Oxygen content Chloride content CO 2 and/or H 2 S content Oxidizing species (e.g. chlorine) ph Velocity Content of solids (e.g. sand)

30 39 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

31 40 MATERIAL SELECTION NORSOK M-001 and ISO 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

32 41 EXPERIENCE WITH AISI 316 In chloride containing environment PIPE FOR SEAWATER TRANSPORT INSTRUMENT TUBING

33 42 CORROSION PROTECTION through coating INSTALLATION IN THE NORTH SEA PATER NOSTER - SWEDEN

34 43 HOT DIP GALVANIZING (varmforsinking)

35 44 TYPES OF COATING We normally talk about three types of coating: 1. Metallic coatings Thermal spraying Electrolytic applied Chemical Welding Thermal spraying 2. Ceramic coatings Thermal sprayed Deposited 3. Organic coatings Rubber lining Polymer layers Overlay welding Paints Painting

36 45 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 Nickel 2 Zinc

37 49 CATHODIC PROTECTION IN PRACTICE Propeller to be protected Wire to connect anode and object Anode

38 50 SACRIFICIAL ANODES Aluminum alloys Flush mounted Zinc alloys Magnesium alloys (seldom) Stand off Bracelet Zinc anode after 4 years in use

39 51 CATHODIC PROTECTION Sacrificial anodes impressed current Sacrificial anodes and coating Impressed current and coating

40 52 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? SEAWATER SEABED Galvanized wire! Instrument buoy Anchoring Metal hook Concrete anchor

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43 55 SUBSEA CORROSION Corrosion no galvanic contact

44 56 WHAT ABOUT CORROSION ON INSTRUMENTS AND VALVES? Instrument sticks/thermo pockets have suffered from corrosion often due to wrong material used (AISI 316) or material combinations Corrosion of electronic boards in corrosive environment Coating often used on valves to improve corrosion/ wear resistance and friction optimization of coating selection and application method important What has been described is also valdid for instruments and valves.

45 57 GOALS FOR THIS LECTURE I will try to explain to you: why corrosion can occur why coupling between different metals can cause severe corrosion how the probability of corrosion to start can be reduced that stainless steel is not always stain less ( rustfri )!

46 58 QUESTIONS? Leak in a water pipe caused by the cold winter in Trondheim January 2010