Marine Corrosion and Cathodic Protection

Cover
Half Title
Title Page
Copyright Page
Dedication
Table of Contents
Preface
Acknowledgements
Author
Units, abbreviations and symbols
Cathodic protection codes
1 The marine corrosion of steel
1.1 The corrosion of steel in seawater
1.1.1 How much do we know?
1.1.2 Why does steel corrode?
1.1.3 How does corrosion happen?
1.1.3.1 A definition
1.1.3.2 A school corrosion experiment
1.1.3.3 Some electrochemistry
1.1.3.4 Aerated seawater
1.1.3.5 Deaerated seawater
1.1.4 What doesn’t the basic science tell us?
1.2 Corrosion rates
1.2.1 Laboratory tests
1.2.1.1 Weight loss tests
1.2.1.2 The importance of the “Blank” weight loss measurements
1.2.1.3 Limitations of laboratory testing
1.2.2 Seawater immersion tests
1.2.2.1 Effect of temperature
1.2.2.2 Effect of water depth
1.2.3 Information from existing structures
1.2.3.1 Shipwrecks
1.2.3.2 Harbour piling
1.2.3.3 Seabed burial
1.2.3.4 Intertidal and splash zones
1.2.4 How do we use corrosion rate information?
1.3 The microbiological dimension
1.3.1 Clean seawater
1.3.2 Slightly polluted seawater
1.3.3 Heavily polluted seawater and sediments
1.3.3.1 Sulfate reducing micro-organisms
1.3.3.2 MIC mechanisms
1.3.3.3 MIC morphology and rates
1.4 The forms of corrosion
1.4.1 General corrosion
1.4.2 Galvanic corrosion
1.4.2.1 Classic example
1.4.2.2 Why does it happen?
1.4.2.3 What are the risk factors?
1.4.3 Pitting
1.4.4 Crevice corrosion
1.4.5 Fatigue and corrosion fatigue
1.4.6 Other forms of corrosion
References
2 Cathodic protection basics
2.1 A theoretical experiment
2.1.1 Removing electrons
2.1.2 Adding electrons
2.2 A simple model
2.2.1 How does cathodic protection work?
2.2.2 Implementation
2.3 The two views of current flow
2.4 Potential
2.4.1 What do we mean by “Potential”?
2.4.2 How do we measure the potential?
2.4.2.1 The problem
2.4.2.2 The solution
2.4.3 Potential measurement
2.4.4 What is the potential needed for protection?
2.5 Current
2.5.1 Bare steel
2.5.2 Coated steel
2.6 Power sources for CP
2.6.1 Davy’s work
2.6.2 Sacrificial anodes
2.6.3 Impressed current
2.6.4 Sacrificial anodes versus impressed current
2.6.4.1 Sacrificial anodes: advantages
2.6.4.2 Sacrificial anodes: disadvantages
2.6.4.3 Impressed current: advantages
2.6.4.4 Impressed current: disadvantages
2.6.4.5 Selecting between sacrificial anodes and ICCP
2.6.5 Hybrid systems
2.7 What does CP achieve?
2.8 Where do we go from here?
References
3 Designing according to the codes
3.1 Do we need CP?
3.2 Who does the CP design?
3.2.1 In the land of the blind
3.2.2 Who is the “Expert”?
3.2.3 Certification of competence
3.2.3.1 Is it needed?
3.2.3.2 NACE
3.2.3.3 ISO 15257
3.3 The basis of design
3.3.1 System life
3.3.2 Environmental parameters
3.3.3 Coating
3.3.4 Sacrificial versus impressed current?
3.3.5 Which codes?
3.3.6 Cathode parameters
3.3.6.1 Protection potential
3.3.6.2 The protection current density
3.3.7 Anode parameters
3.3.7.1 General
3.3.7.2 Operating potential
3.3.7.3 Charge availability
3.3.7.4 Utilisation factor
3.4 The design process
3.4.1 Overview
3.4.2 Calculating the cathodic current demand
3.4.2.1 Interfaces
3.4.2.2 Uncoated zones
3.4.2.3 Coated zones
3.4.2.4 Additional current demands
3.4.3 Minimum anode mass
3.4.4 Anode output
3.4.4.1 General
3.4.4.2 Estimating anode resistance
3.4.5 Anode optimisation
3.5 Example calculations
3.5.1 Case 1 – uncoated structure
3.5.1.1 Life
3.5.1.2 Structure and area
3.5.1.3 Current densities
3.5.1.4 Current demand
3.5.1.5 Minimum anode weight
3.5.1.6 Anode selection
3.5.2 Case 2 – coated structure
3.5.2.1 Scope of CP design
3.5.2.2 Design parameters
3.5.2.3 Calculations
3.6 Anode locations
3.7 Anode manufacture and installation
3.8 Limitations of the codes
3.8.1 Can we use other codes?
3.8.2 What if the codes gets it wrong?
3.8.3 Where the codes are silent
4 Thermodynamics
4.1 Introduction
4.1.1 In the chemistry laboratory
4.1.2 In the real world
4.2 The science of thermodynamics
4.2.1 Background
4.2.2 Heat and mechanical energy
4.2.2.1 Parameters
4.2.2.2 The laws
4.2.3 Chemical thermodynamics
4.2.4 Application to corrosion
4.3 Electrode potential
4.3.1 The reversible electrode
4.3.2 The Nernst equation
4.4 E – pH diagrams
4.4.1 The hydrogen electrode
4.4.2 The oxygen electrode
4.4.3 The metal and its corrosion products
4.4.4 The metal-water system
4.4.4.1 Zinc
4.4.4.2 Copper
4.4.4.3 Gold
4.4.4.4 Iron
4.4.5 Limitations of E–pH diagrams
4.4.5.1 Pure metals
4.4.5.2 Pure water
4.4.5.3 Thermodynamic basis
4.5 CP and thermodynamics
4.5.1 Immunity
4.5.2 Passivity
References
5 Electrode kinetics
5.1 Reversible electrodes
5.2 Electrochemical experiments
5.2.1 Some terminology
5.2.1.1 Electrodes, electrolytes, anodes, cathodes and half-cells
5.2.1.2 Potential
5.2.1.3 Polarisation
5.2.1.4 Overpotential and overvoltage
5.2.2 Galvanostatic polarisation
5.2.3 Potentiostatic polarisation
5.2.3.1 The potentiostat
5.2.3.2 Plotting polarisation curves
5.3 Obtaining polarisation curves
5.3.1 The experiments
5.3.2 Tafel behaviour
5.4 Analysing polarisation curves
5.4.1 Fitting theory to data
5.4.2 The concept of activation control
5.4.2.1 Activation energy
5.4.3 The Butler-Volmer equation
5.4.4 Tafel extrapolation
5.4.4.1 Exchange current density
5.4.5 Polarisation curves and polarisation diagrams
5.4.6 Departures from Tafel behaviour
5.5 Non-reversible electrodes
5.5.1 The mixed potential electrode
5.6 Corrosion in seawater
5.6.1 Oxygen-free seawater
5.6.2 Aerated seawater
5.7 Electrode kinetics and CP
5.7.1 General
5.7.2 The theory
5.7.3 Implications for CP
References
6 Protection potential – carbon steel
6.1 Introduction
6.2 What does CP need to achieve?
6.3 What do the codes say?
6.3.1 Aerated seawater
6.3.2 Anaerobic environments
6.3.3 Elevated temperature
6.4 Aerobic environments: The –800 mV criterion
6.4.1 Theoretical considerations
6.4.1.1 Thermodynamics: immunity
6.4.1.2 Thermodynamics: passivity
6.4.1.3 Electrode kinetics
6.4.2 Laboratory testing
6.4.2.1 The predictions
6.4.2.2 The results
6.4.2.3 Evaluation of the evidence
6.4.3 Practical experience
6.4.4 Implications
6.5 Anaerobic environments: The –900 mV criterion
6.5.1 The codes
6.5.1.1 British standards institution
6.5.1.2 European and ISO standards
6.5.1.3 NACE
6.5.1.4 DNV
6.5.2 Theoretical considerations
6.5.2.1 Thermodynamics
6.5.2.2 Electrode kinetics
6.5.3 Laboratory investigations
6.5.4 Field test data
6.5.4.1 Onshore pipelines
6.5.4.2 Offshore pipelines
6.6 The effect of temperature
6.6.1 What the codes say
6.6.2 The theory
6.6.3 Laboratory testing
6.6.4 Field experience
6.7 Excessively negative potentials
6.8 Optimum potentials
6.9 Potential distribution
References
7 Current and polarisation
7.1 What we need to know
7.2 What the codes advise
7.2.1 Current densities for seawater (offshore)
7.2.2 Current densities for seawater (near-shore)
7.2.3 Current densities for seabed burial
7.3 The problem with the codes
7.4 Laboratory testing: clean steel
7.5 Calcareous deposits
7.5.1 The chemistry
7.5.2 Importance
7.5.2.1 Benefits
7.5.2.2 Possible drawbacks
7.5.3 Laboratory investigations
7.5.3.1 Deposit growth
7.5.3.2 Deposit thickness
7.5.3.3 Factors affecting deposit growth
7.6 Site testing
7.6.1 The limitations of the laboratory
7.6.1.1 The microbiological dimension
7.6.1.2 Modes of polarisation
7.6.2 In-situ measurements
7.6.2.1 Monitoring of existing structures
7.7 Site experience
7.7.1 South China Sea
7.7.2 Middle East – operator 1
7.7.2.1 The requirement
7.7.2.2 Approach adopted
7.7.2.3 Example of analysis – structure A
7.7.2.4 Results of analyses – structures B - D
7.7.2.5 Application to other structures
7.7.3 Middle East – operator 2
7.8 Deeper waters
7.8.1 Codes
7.8.2 The theory
7.8.3 Laboratory testing
7.8.4 Site testing
7.8.5 The future
7.9 S-curves
7.10 The slope parameter
7.10.1 What is it?
7.10.2 Slope parameter versus “cookbook”
7.10.2.1 Two perspectives
7.10.2.2 SP0176
7.11 The rate of polarisation
References
8 Corrosion resistant alloys
8.1 Why consider CRAs?
8.2 Passivity
8.2.1 What do we mean by passivity?
8.2.2 Thermodynamics
8.2.3 Electrode kinetics
8.2.4 Passivity breakdown
8.2.4.1 Nature of the passive film
8.2.4.2 Pitting
8.2.4.3 Crevice corrosion
8.2.4.4 Stress corrosion cracking
8.3 Stainless steels
8.3.1 Corrosion resistance
8.3.1.1 Passivity
8.3.1.2 Passivity breakdown
8.3.2 Designations
8.3.3 Grades used offshore
8.3.3.1 Allotropes
8.3.3.2 Ferritic stainless steels
8.3.3.3 Austenitic stainless steels
8.3.3.4 Duplex stainless steels
8.3.3.5 Superduplex
8.3.3.6 Martensitic and supermartensitic
8.3.3.7 Some stainless steels used subsea
8.4 High nickel alloys
8.5 Copper alloys
8.6 Aluminium alloys
8.6.1 Alloy types
8.6.2 Corrosion threats and mitigation
8.7 CP of corrosion resistant alloys
8.7.1 Protection potential
8.7.1.1 Theory and practice
8.7.1.2 The codes
8.7.2 Protection current densities
8.8 Summary
References
9 Underwater coatings
9.1 Introduction
9.2 Some polymer basics
9.2.1 Polymerisation
9.2.2 Linear polymers
9.2.2.1 Polymers and copolymers
9.2.2.2 Flexibility
9.2.3 3-Dimensonal polymers
9.2.3.1 Cross-linking
9.2.3.2 Epoxies
9.2.4 Elastomers
9.3 Coatings and CP
9.3.1 Do coatings benefit CP?
9.3.2 Does CP benefit coatings?
9.3.3 Coating systems
9.4 Surface preparation
9.5 Coating system selection
9.5.1 Fixed steel structures
9.5.1.1 Early paints
9.5.1.2 Current systems
9.5.2 Ships and floating installations
9.5.2.1 External hulls
9.5.2.2 Ballast spaces
9.5.3 Submarine pipelines
9.5.3.1 Factory applied coating systems
9.5.3.2 Field joint coatings
9.6 Cathodic disbondment
9.6.1 Characteristics
9.6.2 Corrosion threats under disbonded coatings
9.6.2.1 Onshore pipelines
9.6.2.2 Submarine pipelines
9.6.3 Cathodic disbondment testing
9.7 Coating breakdown predictions
9.7.1 Coatings for fixed structures
9.7.2 Ships’ coatings
9.7.3 Pipeline coatings
References
10 Sacrificial anodes
10.1 What properties do we need?
10.1.1 Potential
10.1.2 Current
10.1.2.1 Instantaneous output
10.1.2.2 Capacity, consumption rate and efficiency
10.2 Zinc alloys
10.2.1 Background
10.2.2 Present day alloys
10.2.3 Limitations
10.2.3.1 Elevated temperature
10.3 Magnesium alloys
10.4 Aluminium alloys
10.4.1 The benefits
10.4.2 Alloy research
10.4.3 Alloy development
10.4.4 Al-Zn-Sn and Al-Zn-Hg alloys
10.4.5 Indium-containing anodes
10.4.5.1 Al-Zn-In
10.4.5.2 Al-Zn-Mg-In
10.4.6 Al-Zn-Ga and Al-Ga
10.4.7 The future
10.4.7.1 The toxicity of indium?
10.4.7.2 Al-Zn and Al-Zn-Mg
10.5 Non-standard anodes
10.5.1 Limiting the polarisation of the cathode
10.5.1.1 The need
10.5.1.2 Alloy composition
10.5.1.3 Passive electronic components: resistors
10.5.1.4 Passive electronic components: diodes
10.5.2 Anodes for rapid polarisation
10.5.2.1 Motivation
10.5.2.2 Hybrid systems
10.5.2.3 Dual anodes
10.5.2.4 Shaped anodes
10.6 Future developments
10.7 Electrochemical testing
10.7.1 Parameters measured
10.7.1.1 Potential
10.7.1.2 Capacity
10.7.2 Testing modes and objectives
10.7.2.1 Screening tests
10.7.2.2 Performance tests
10.7.2.3 Deep water
10.7.2.4 Elevated temperature
10.7.2.5 Biofouling
10.7.2.6 Polluted environments
10.7.2.7 Seabed sediments
10.7.2.8 Estuarine waters
10.7.2.9 Pre-qualification and production testing
10.7.3 Testing configurations
10.7.3.1 Constant current tests
10.7.3.2 Constant potential tests
10.7.3.3 Free-running tests
10.8 Anode resistance
10.8.1 Relevance to design
10.8.2 How is R[sub(a)] calculated?
10.8.3 What the codes advise
10.8.3.1 Slender stand-off anodes
10.8.3.2 Shorter stand-off anodes
10.8.3.3 Long flush-mounted anodes
10.8.3.4 Short flush-mounted anodes and bracelets
10.8.4 Validation of resistance formulae
10.8.4.1 In-service testing
10.8.5 Anode clustering
10.8.5.1 The problem
10.8.5.2 The consequences
10.8.5.3 The solution
10.9 Anode design and manufacture
10.9.1 Who does the design?
10.9.2 The anode specification
10.9.3 Anode inserts
10.9.3.1 Insert configuration
10.9.3.2 Insert surface preparation
10.9.4 The casting process
10.10 Quality control
10.10.1 Sampling
10.10.2 Dimensional and weight tolerance
10.10.3 Casting quality
10.10.3.1 Non-destructive examination
10.10.3.2 Destructive examination
10.11 Anode installation
References
11 Impressed current systems
11.1 The electrode reactions
11.1.1 Cathodic reactions
11.1.2 Anodic reactions
11.1.2.1 Consumable anodes
11.1.2.2 “Non-consumable” anodes
11.2 ICCP anodes
11.2.1 Requirements
11.2.2 Onshore origins
11.2.3 Anode development
11.2.3.1 Early ICCP anode alloys
11.2.3.2 Mixed metal oxide (“MMO”) anodes
11.2.4 Anode configuration and resistance
11.2.5 Anode shields
11.2.5.1 Why do we need anode shields?
11.2.5.2 Anode shield size
11.3 Basic design
11.3.1 Cathodic current demand
11.3.2 System output calculations
11.3.2.1 Current
11.3.2.2 Voltage
11.3.3 Design calculation process
11.3.4 Anode locations
11.4 Power supplies
11.4.1 What we need to know
11.4.2 The basics
11.4.3 Manual control
11.4.4 Automatic control
11.5 Control inputs
11.5.1 Ag|AgCl|seawater
11.5.2 Zinc reference electrodes
11.5.3 Dual references
11.6 Cables
11.6.1 Conductors
11.6.2 Insulation
11.6.2.1 What is required?
11.6.2.2 What do the codes say?
11.6.2.3 Candidate materials
11.6.2.4 Current practice
11.6.2.5 Mechanical protection of cables
11.6.2.6 Cables connections
11.7 Stray current interference
11.8 ICCP system safety
11.8.1 Transformer-rectifiers
11.8.2 Diver safety
References
12 The effect of CP on mechanical properties
12.1 Introduction
12.1.1 Outline
12.1.2 Some basics
12.2 Materials of interest
12.2.1 Structures
12.2.1.1 Medium-strength steels (SMSY < 550 MPa)
12.2.1.2 Higher strength steels (>550 MPa)
12.2.2 Pipelines
12.2.3 Equipment
12.3 Fatigue
12.3.1 What is it?
12.3.2 S-N testing
12.3.2.1 Plain specimens
12.3.2.2 Notched specimens
12.3.3 Fracture mechanics
12.3.3.1 Basics
12.3.3.2 The Paris law
12.3.4 Reliability of testing
12.4 Corrosion fatigue
12.4.1 Discovery
12.4.2 Characterisation
12.4.3 Theories
12.4.4 Stress ratio (R-value)
12.5 The effect of CP
12.5.1 Information from S-N testing
12.5.2 The interaction with CP
12.5.3 The fracture mechanics perspective
12.5.4 S-N testing versus crack growth rate data
12.6 The codes
12.6.1 Code development
12.6.1.1 Laboratory testing
12.6.1.2 The Cognac fatigue “experiment”
12.6.1.3 Further testing
12.6.2 Using the codes
12.6.2.1 Overview
12.6.2.2 Elements and fatigue loadings
12.6.2.3 Select the S-N curve
12.6.2.4 Assessment
12.6.3 The role of the CP engineer
12.7 Hydrogen embrittlement
12.7.1 The problem
12.7.2 What is the source of atomic hydrogen?
12.7.3 What does the atomic hydrogen do?
12.7.3.1 A simplistic view
12.7.3.2 A less simplistic view
12.8 Low- and medium-strength carbon steels
12.9 High-strength low-alloy steels
12.9.1 General
12.9.2 Fasteners
12.10 Corrosion-resistant alloys
12.10.1 Stainless steels
12.10.1.1 Classes
12.10.1.2 Austenitic stainless steels
12.10.1.3 Ferritic stainless steels
12.10.1.4 Duplex stainless steels
12.10.1.5 Martensitic stainless steels
12.10.2 Nickel alloys
12.10.2.1 Solid solution alloys
12.10.2.2 Precipitation-hardened alloys
12.10.3 Copper alloys
12.10.4 Titanium
References
13 Fixed steel structures
13.1 Structures for hydrocarbon production
13.1.1 Early sacrificial anode systems
13.1.2 Early ICCP systems
13.1.3 Deeper waters
13.1.4 To coat or not?
13.1.5 Weight saving
13.1.5.1 Same problem – different solutions
13.1.6 Into the sunset?
13.2 Offshore wind farms
13.2.1 Development
13.2.2 Foundation options
13.2.3 Monopiles
13.2.3.1 Is external CP needed?
13.2.3.2 CP design – codes
13.2.3.3 CP design – challenges
13.3 Harbour structures
13.3.1 Historical background
13.3.2 Current densities
13.3.3 Sacrificial anodes
13.3.4 ICCP systems
13.3.4.1 Seabed anodes
13.3.4.2 Pile-mounted anodes
13.3.4.3 Conventional “onshore” anodes
13.3.4.4 Harbour structures versus platforms
13.3.4.5 How not to do it
13.4 Allowances for current drainage
13.4.1 Simple rules
13.4.2 Well casings
13.4.3 Other buried steelwork
13.4.4 Concrete reinforcement
13.5 CP retrofits
13.5.1 What is a “retrofit”?
13.5.2 Information on retrofits
13.5.3 Do we need to retrofit?
13.5.3.1 Design mishaps
13.5.3.2 Life extension
13.5.3.3 Unnecessary retrofits
13.5.4 Retrofit requirements
13.5.5 Current demand
13.5.6 Retrofit strategies
13.5.6.1 ICCP vs sacrificial anodes
13.5.7 Retrofit implementation
13.5.7.1 Sacrificial anodes
13.5.7.2 Impressed current
13.5.7.3 Connections
13.6 The future
References
14 Submarine pipelines
14.1 Early submarine pipelines
14.2 Pipeline types
14.2.1 Flowlines
14.2.1.1 General
14.2.1.2 Production flowlines
14.2.1.3 Injection and gas lift flowlines
14.2.2 Trunk and service lines
14.2.2.1 Export lines
14.2.2.2 Sea lines
14.2.2.3 Service pipelines
14.2.3 Risers
14.3 Code-based CP design
14.3.1 Methodology
14.3.2 Example calculation
14.3.2.1 Pipeline condition
14.3.2.2 Design factor
14.3.2.3 Current demand
14.3.2.4 Anode design – mean current
14.3.2.5 Anode design – final current
14.4 Anode spacing
14.4.1 Early practice
14.4.2 Extending the spacing
14.4.2.1 The crucial resistance
14.4.2.2 A worst-case approach
14.4.2.3 Norsok method
14.4.2.4 Potential attenuation
14.4.2.5 Recommendation
14.5 Electrical isolation: offshore
14.5.1 Early offshore practice
14.5.2 Recent codes
14.5.3 Current drain
14.5.4 Stray current interference
14.6 Pipeline landfalls
14.6.1 Some problems
14.6.2 Isolation
14.7 Hot pipelines and risers
14.7.1 Ekofisk alpha
14.7.2 CP criteria
14.7.2.1 Protection potential
14.7.2.2 Protection current density
14.7.2.3 Coating breakdown
14.7.2.4 Bracelet anode performance
14.7.3 Flow assurance
14.7.3.1 Keeping the product flowing
14.7.3.2 Insulation
14.7.3.3 Direct electrical heating
14.7.4 Seawater cooling
14.7.4.1 Pipelines
14.7.4.2 Subsea coolers
14.8 Pipeline retrofits
14.8.1 Why retrofit?
14.8.1.1 Something went wrong
14.8.1.2 Life extension
14.8.2 When to retrofit?
14.8.2.1 What you cannot see…
14.8.2.2 Lost in the Iron Mountain®
14.8.3 Retrofit strategies
14.8.3.1 Basic cases
14.8.3.2 Connecting anode sleds to pipelines
14.9 CRA and flexible pipelines
References
15 Ships and floating structures
15.1 Ships’ hulls
15.1.1 Early days
15.1.2 CP design
15.1.2.1 Differences between fixed structures and ships
15.1.2.2 Current demand
15.1.3 Propellers and shafts
15.1.3.1 Materials
15.1.3.2 Bonding
15.1.3.3 Current demand
15.1.4 Rudders
15.1.4.1 Bonding
15.1.4.2 A cautionary tale
15.1.5 Sacrificial anode systems
15.1.5.1 Development
15.1.5.2 Design
15.1.6 Impressed current
15.1.6.1 Early days
15.1.6.2 Present day systems
15.1.6.3 Fitting-out
15.1.6.4 Laying-up
15.1.6.5 Alongside berths
15.1.7 Non-ferrous hulls
15.1.7.1 Aluminium
15.1.7.2 Copper and Cu-Ni hulls
15.1.7.3 Pleasure craft
15.2 Floating installations
15.2.1 Drill ships and semi-submersibles
15.2.1.1 Some history
15.2.1.2 A recent example
15.2.2 FPSOs
15.2.2.1 Hulls
15.2.3 Tension leg platforms
15.2.4 Moorings
15.2.4.1 Tethers and tendons
15.2.4.2 Chains
15.3 Jack-up rigs
References
16 Internal CP
16.1 “Fully sealed” systems
16.1.1 Corrosion threats
16.1.1.1 Corrosion by dissolved oxygen
16.1.1.2 What really happens to the oxygen?
16.1.1.3 What happens then?
16.1.1.4 What about MIC?
16.1.2 Is CP needed?
16.2 Leaking systems
16.2.1 Monopile foundations
16.2.2 Corrosion implications
16.2.3 Internal CP of wind turbine foundations
16.2.3.1 A touch of schadenfreude?
16.2.3.2 Code guidance
16.2.3.3 Lessons learned
16.2.3.4 But is CP needed?
16.2.4 Water ballast tanks
16.2.4.1 Ballast water and its management
16.2.4.2 Corrosion management
16.3 Steel structures containing aerated seawater
16.3.1 Sea chests
16.3.2 Seawater intakes
16.3.2.1 Multi-metal systems
16.3.2.2 Shore-side seawater intakes
16.3.2.3 Seawater lift caissons
16.4 Seawater piping systems
16.4.1 Unlined carbon steel
16.4.2 Lined carbon steel
16.4.3 Corrosion resistant alloys
16.4.3.1 Materials for handling seawater
16.4.3.2 CRAs: selection and vulnerabilities
16.4.3.3 Internal CP of stainless steel pipework
16.4.3.4 Resistor-controlled cathodic protection
16.5 Heat exchangers
16.5.1 A corrosion machine
16.5.2 Early CP systems
16.5.3 Seawater exchangers
References
17 Modelling
17.1 What is a model?
17.2 Physical modelling
17.2.1 Full scale
17.2.2 Reduced scale – reduced conductivity
17.2.3 Reduced scale – full conductivity
17.3 Early computer applications
17.4 Computer modelling – the basics
17.4.1 The convenience of the computer
17.4.2 Potential and current distribution
17.4.3 The Laplace equation
17.4.4 Solving Laplace
17.4.4.1 The need for a number-cruncher
17.4.4.2 Defining the space
17.4.4.3 Defining the boundaries
17.4.4.4 The finite element method (FEM)
17.4.4.5 The boundary element method (BEM)
17.4.4.6 FEM versus BEM
17.4.4.7 Other software approaches
17.5 Computer modelling – applications
17.5.1 Early days
17.5.2 Moore’s law
17.5.3 When modelling gets it wrong
17.5.4 The boundary conditions
17.5.4.1 The anodes
17.5.4.2 The cathode
17.5.5 What can computer modelling tell us?
17.5.5.1 Reasons to be careful
17.5.5.2 Uncoated steel structures
17.5.5.3 Coated structures
17.5.5.4 Sacrificial anodes
17.5.5.5 Internal spaces and complex geometries
17.6 Going forward
References
18 CP system management
18.1 Surveying, inspection and monitoring
18.1.1 The need for measurement
18.2 Measuring the potential
18.2.1 The story so far
18.2.2 Alternative references
18.2.2.1 Standard hydrogen electrode
18.2.2.2 Saturated calomel half-cell
18.2.2.3 Silver chloride electrode
18.2.2.4 Silver chloride (0.5 M KCl) electrode
18.2.2.5 Copper sulfate electrode (CSE)
18.2.2.6 Zinc
18.2.3 Errors in potential measurement
18.2.3.1 Operatives
18.2.3.2 Equipment and operatives
18.2.3.3 Temperature
18.2.3.4 Liquid-junction or diffusion potential
18.2.3.5 The IR problem
18.2.3.6 IR-error mitigation
18.2.3.7 The effect of seawater flow
18.2.4 Potential surveys – structures
18.2.4.1 Dip-cell surveys
18.2.4.2 Diver and ROV surveys
18.2.4.3 Survey frequency – sacrificial systems
18.2.5 Potential surveys - pipelines
18.2.5.1 Background
18.2.5.2 Trailing wire surveys
18.2.5.3 ROV surveys
18.2.5.4 Beach crossings and shore approaches
18.2.5.5 Telluric currents
18.2.5.6 Survey frequency
18.2.6 Fixed potential monitoring
18.2.6.1 Structures
18.2.6.2 Pipelines
18.3 Current measurement
18.3.1 ICCP systems
18.3.2 Sacrificial systems
18.3.2.1 Current clamp meters
18.3.2.2 Monitored anodes
18.4 Current density measurement
18.4.1 Fixed monitoring
18.4.1.1 Current density plates and probes
18.4.1.2 Field gradients
18.4.2 Surveys
18.4.2.1 Pipelines
18.4.2.2 Structures
18.5 Interaction
18.5.1 Sacrificial systems
18.5.2 ICCP systems
18.5.2.1 General
18.5.2.2 Harbours
18.5.2.3 Ships and boats
References
Index