Corrosion Prevention

Understanding how corrosion occurs:

Corrosion Defined:
- Electrochemical degradation of metals
- Requires: anode, cathode, electrolyte, connection
- Energy release (reverse of metal extraction)
- Can be prevented by breaking the circuit

Corrosion Types:

Uniform Corrosion:
- Even material loss
- Predictable
- Easiest to design for
- Most common type

Galvanic Corrosion:
- Dissimilar metals in contact
- More active metal corrodes
- Galvanic series determines behavior
- Avoid or electrically isolate

Pitting:
- Localized, severe attack
- Stainless steels susceptible
- Chloride environments
- Difficult to detect

Crevice Corrosion:
- In tight gaps
- Oxygen differential
- Gaskets, fasteners, joints
- Design to eliminate crevices

Intergranular:
- Along grain boundaries
- Sensitized stainless steels
- Improper heat treatment
- Welding can cause

Stress Corrosion Cracking:
- Stress + corrosive environment
- Cracking without warning
- Material-environment specific
- Very dangerous

Erosion-Corrosion:
- Flow accelerated corrosion
- Protective films removed
- Piping, pumps, valves
- Flow control helps

Environmental Factors:

Moisture:
- Essential for most corrosion
- Humidity effects
- Immersion vs. atmospheric

Temperature:
- Generally accelerates corrosion
- Dew point condensation
- Extreme cold also problematic

Chemicals:
- Chlorides (pitting)
- Acids
- Alkaline conditions
- Specific to material

Oxygen:
- Often cathodic reaction
- Differential aeration cells
- Not always bad (passivation)

Techniques to prevent corrosion:

Material Selection:

Corrosion-Resistant Alloys:
- Stainless steels (passive film)
- Nickel alloys (aggressive environments)
- Titanium (seawater, chemicals)
- Selection based on environment

Considerations:
- Cost vs. life
- Maintenance requirements
- Replacement cost
- Safety criticality

Protective Coatings:

Organic Coatings (Paints):
- Barrier protection
- Multiple coat systems
- Surface preparation critical
- Maintenance required

Paint System Components:
- Primer: adhesion, inhibition
- Intermediate: thickness, barrier
- Topcoat: appearance, UV protection

Metallic Coatings:

Galvanizing:
- Zinc coating on steel
- Hot-dip or electroplated
- Sacrificial protection
- Very effective for atmospheric

Plating:
- Chrome, nickel, zinc
- Decorative or protective
- Various processes
- Application specific

Thermal Spray:
- Zinc, aluminum
- Thick coatings possible
- Field application
- Infrastructure common

Conversion Coatings:
- Phosphate (paint prep)
- Chromate (being replaced)
- Passivation (stainless)
- Anodizing (aluminum)

Cathodic Protection:

Galvanic/Sacrificial:
- More active metal protects structure
- Zinc or magnesium anodes
- Simple, limited current
- Marine and buried structures

Impressed Current:
- External power supply
- Greater current capacity
- Adjustable
- Pipelines, tanks, marine

Design Considerations:

Avoid:
- Dissimilar metal contact
- Crevices and traps
- Sharp edges
- Weld undercuts

Include:
- Drainage provisions
- Access for inspection
- Coating-friendly design
- Replaceable components

Managing corrosion through inspection:

Inspection Methods:

Visual Inspection:
- First line detection
- Training required
- Systematic approach
- Documentation

Thickness Measurement:
- Ultrasonic testing
- Monitor material loss
- Trending critical
- Remaining life assessment

NDT Methods:
- Radiography (internal)
- Magnetic particle (surface)
- Dye penetrant (surface)
- ACFM (alternating current field)

Monitoring:

Corrosion Coupons:
- Weighed samples
- Exposed to environment
- Removed and measured
- Actual corrosion rate

Corrosion Probes:
- Real-time monitoring
- Various technologies
- Automated data collection
- Process control input

Electrochemical:
- Linear polarization resistance
- Electrochemical noise
- Advanced monitoring
- Process industries

Maintenance Strategies:

Preventive:
- Scheduled coating maintenance
- Anode replacement
- Inhibitor treatment
- Based on time/condition

Predictive:
- Condition-based maintenance
- Trending inspection data
- Remaining life calculation
- Optimize intervention timing

Coating Maintenance:

Inspection:
- Visual condition
- Adhesion testing
- Thickness measurement
- Holiday (pinhole) detection

Maintenance Painting:
- Spot repair
- Overcoating
- Full removal and recoat
- Preparation critical

Life Extension:

Assessment:
- Current condition
- Remaining life estimate
- Criticality evaluation
- Economics

Options:
- Enhanced inspection
- Repairs and remediation
- Upgraded protection
- Replacement planning

Corrosion expertise in careers:

Career Roles:

Corrosion Engineer:
Prevention and control:
- Material selection
- Coating specification
- Cathodic protection design
- $75,000-$115,000

Coating Inspector:
Quality verification:
- Surface preparation
- Application inspection
- Testing and documentation
- $50,000-$80,000

Integrity Engineer:
Asset management:
- Inspection programs
- Remaining life assessment
- Risk-based maintenance
- $80,000-$120,000

Materials Engineer:
Broader material focus:
- Material selection
- Failure analysis
- Research and development
- $75,000-$110,000

Certifications:

NACE/AMPP:
- Cathodic Protection Technician
- Cathodic Protection Specialist
- Corrosion Technician
- Coating Inspector (CIP Levels)

SSPC:
- Protective Coatings Inspector
- Various specialty certifications

Value:
- Industry recognized
- Career advancement
- Salary premium
- Global recognition

Industries:

Oil and Gas:
- Pipelines
- Offshore platforms
- Refineries
- Storage tanks

Marine:
- Ship hulls
- Port structures
- Offshore
- Coastal infrastructure

Infrastructure:
- Bridges
- Buildings
- Water/wastewater
- Power generation

Manufacturing:
- Product corrosion protection
- Plant equipment
- Process equipment
- Finished goods

Skills Development:

Technical:
- Corrosion mechanisms
- Prevention methods
- Inspection techniques
- Material compatibility

Practical:
- Coating application
- Inspection procedures
- Cathodic protection testing
- Failure analysis

Corrosion expertise supports long-term asset management across industries.