Corrosion Prevention Strategies for Steel Structures

Understanding Corrosion in Steel Structures

Corrosion represents one of the most significant challenges facing steel infrastructure across Canada, with annual costs estimated at over $46 billion nationwide according to the National Research Council. For structures in Atlantic Canada, the combination of maritime climate conditions, salt-laden air, and freeze-thaw cycles creates an particularly aggressive environment that can accelerate corrosion rates by 200-400% compared to inland locations.

At its core, corrosion is an electrochemical process where steel returns to its natural oxide state through reactions with oxygen and moisture. This seemingly simple process involves complex interactions between the metal substrate, environmental factors, and protective systems. Understanding these mechanisms is essential for engineers and facility managers responsible for maintaining structural integrity and extending service life.

In Nova Scotia and throughout the Maritime provinces, steel structures face unique challenges that demand specialized prevention strategies. From coastal processing facilities in Lunenburg County to industrial infrastructure along the Halifax Harbour, the corrosive potential of our environment requires proactive engineering approaches rather than reactive maintenance.

Environmental Factors Affecting Corrosion in Atlantic Canada

Maritime Climate Considerations

The Atlantic Canadian climate presents a perfect storm of corrosion-accelerating factors. With annual precipitation averaging 1,400-1,500 mm in most of Nova Scotia and relative humidity frequently exceeding 80%, steel surfaces remain wet for extended periods. This time-of-wetness is a critical factor in corrosion kinetics, as electrochemical reactions require an electrolyte to proceed.

Chloride contamination from sea spray can travel up to 50 kilometres inland under certain wind conditions, though concentrations are highest within 5 kilometres of the coastline. In communities like Amherst, situated near the Bay of Fundy with its dramatic tidal variations, airborne salt deposition can reach 300-500 mg/m²/day during storm events—levels that classify the environment as C4 (High) to C5 (Very High) on the ISO 9223 corrosivity scale.

Temperature and Freeze-Thaw Effects

Nova Scotia experiences approximately 100-150 freeze-thaw cycles annually, with temperatures fluctuating above and below 0°C frequently between November and April. These cycles cause several problems for steel structures:

• Coating stress: Differential thermal expansion between steel substrates (coefficient of approximately 12 × 10⁻⁶/°C) and protective coatings can cause cracking and disbondment

• Moisture infiltration: Ice formation in existing coating defects wedges openings wider, allowing accelerated under-film corrosion

• De-icing salt exposure: Road structures and equipment near transportation corridors face additional chloride loading from winter maintenance operations

• Condensation cycling: Daily temperature swings create repeated wetting and drying cycles that concentrate corrosive species on steel surfaces

Industrial and Agricultural Influences

Beyond natural environmental factors, industrial emissions and agricultural operations contribute additional corrosive agents. The Cumberland County region, for example, hosts various agricultural operations where ammonia and organic acids can accelerate corrosion of nearby steel structures. Understanding the complete environmental profile of a site is essential for selecting appropriate protection strategies.

Protective Coating Systems

Multi-Coat Systems for Severe Environments

For steel structures in Maritime environments, a properly designed multi-coat system remains the most cost-effective corrosion prevention strategy for most applications. A typical high-performance system for C4/C5 environments includes:

• Surface preparation to SSPC-SP 10 or Sa 2½: Near-white metal blast cleaning achieving a surface profile of 50-75 micrometres

• Zinc-rich primer: 75-100 micrometres dry film thickness (DFT), providing cathodic protection at coating breaks

• Epoxy intermediate coat: 125-200 micrometres DFT, offering barrier protection and chemical resistance

• Polyurethane topcoat: 50-75 micrometres DFT, providing UV resistance and colour/gloss retention

This system, totalling 250-375 micrometres total DFT, typically provides 15-25 years of protection in severe maritime environments when properly applied. The Canadian General Standards Board (CGSB) and provincial transportation authorities specify similar systems for critical infrastructure.

Hot-Dip Galvanizing

Hot-dip galvanizing provides excellent protection for structural steel components, offering both barrier and sacrificial protection. The zinc coating, typically 85-125 micrometres thick on structural sections, corrodes preferentially to protect the underlying steel. In Atlantic Canadian conditions, galvanizing provides approximately 20-40 years of service life depending on specific exposure conditions.

Key advantages of galvanizing include:

• Complete coverage including edges, corners, and interior surfaces of hollow sections

• Metallurgical bond between zinc and steel prevents undercutting

• Self-healing capability where minor damage is protected by surrounding zinc

• Lower lifecycle cost compared to paint systems for many applications

For maximum protection in severe environments, duplex systems combining galvanizing with high-performance topcoats can extend service life to 50+ years. This approach is increasingly specified for critical infrastructure projects across Nova Scotia.

Thermal Spray Coatings

Thermal spray metallic coatings (zinc, aluminium, or zinc-aluminium alloys) offer an alternative to hot-dip galvanizing for large structures or field applications. Applied using arc-spray or flame-spray processes, these coatings can achieve thicknesses of 150-300 micrometres and are sealed with appropriate topcoats.

Thermal spray zinc-aluminium (85/15) coatings have demonstrated exceptional performance in marine environments, with properly applied systems providing 40+ years of protection on offshore structures. For industrial facilities and marine infrastructure throughout Atlantic Canada, thermal spray coatings represent a viable option where hot-dip galvanizing is impractical.

Cathodic Protection Systems

Sacrificial Anode Systems

Cathodic protection (CP) provides electrochemical protection by making the steel structure the cathode in a controlled corrosion cell. Sacrificial anode systems use metals more active than steel—typically zinc, magnesium, or aluminium alloys—to provide protection without external power.

For marine and buried structures in Nova Scotia, sacrificial anode systems offer several advantages:

• No external power required, reducing operational complexity

• Self-regulating current output based on coating condition

• Lower installation costs for smaller structures

• Minimal maintenance requirements

Design parameters for sacrificial systems must account for soil or water resistivity, which varies considerably across Atlantic Canada. Marine environments typically exhibit resistivities of 20-30 ohm-cm, while soil resistivities in Nova Scotia range from 1,000 to 50,000 ohm-cm depending on composition and moisture content.

Impressed Current Systems

For larger structures or higher-resistivity environments, impressed current cathodic protection (ICCP) systems use external power to drive protective current from relatively inert anodes to the structure. These systems offer greater flexibility and current output but require ongoing monitoring and maintenance.

ICCP systems are commonly employed for:

• Large marine structures and wharves

• Buried pipelines and storage tanks

• Reinforced concrete structures in chloride-contaminated environments

• Complex structures where sacrificial systems cannot provide adequate current distribution

Modern ICCP systems incorporate remote monitoring capabilities, allowing engineers to track protection levels and system performance in real-time—a valuable feature for facilities management across distributed sites.

Design Strategies for Corrosion Prevention

Geometry and Drainage Considerations

Effective corrosion prevention begins at the design stage, where thoughtful detailing can dramatically reduce maintenance requirements and extend service life. Key design principles include:

• Eliminate water traps: All horizontal surfaces should incorporate minimum 3% slopes to promote drainage

• Avoid crevices: Seal or eliminate gaps between mating surfaces where moisture can accumulate and oxygen depletion creates differential aeration cells

• Provide access: Design structures with adequate clearance for inspection and maintenance coating operations

• Consider splash zones: Provide enhanced protection for areas subject to intermittent wetting, which experience the highest corrosion rates

Material Selection and Compatibility

Selecting appropriate materials and ensuring galvanic compatibility between connected components prevents accelerated corrosion at joints and connections. When dissimilar metals must be joined, appropriate isolation measures—insulating washers, coatings, or gaskets—should be specified to prevent galvanic coupling.

Weathering steels (ASTM A588/A709 Grade 50W) offer an alternative approach for certain applications, developing a protective oxide layer that limits further corrosion. However, weathering steel performance in Atlantic Canada requires careful evaluation, as high chloride exposure can prevent proper patina formation and accelerate corrosion rather than limiting it. These steels are generally not recommended within 2 kilometres of salt water or in areas with heavy de-icing salt use.

Connection and Fastener Protection

Connections represent critical areas requiring enhanced protection, as crevices, stress concentrations, and geometric complexity create challenging conditions. Best practices include:

• Specifying hot-dip galvanized or stainless steel fasteners for exposed connections

• Sealing bolt heads and nuts with appropriate coating systems

• Using corrosion-inhibiting compounds in threaded connections

• Designing bolted connections to minimize crevice areas and facilitate drainage

Inspection and Maintenance Programmes

Inspection Protocols

Regular inspection forms the foundation of effective corrosion management, allowing early detection of coating degradation and corrosion initiation before significant damage occurs. For steel structures in Atlantic Canadian environments, recommended inspection frequencies include:

• Annual visual inspections: General assessment of coating condition, drainage, and obvious corrosion

• Detailed inspections every 3-5 years: Systematic evaluation including coating thickness measurements and adhesion testing

• Structural assessments every 10 years: Comprehensive evaluation including thickness measurements at critical sections

Documentation of inspection findings using standardised protocols such as ASTM D610 (rust grade) and ASTM D714 (blistering) enables trending of condition data over time and supports maintenance planning decisions.

Maintenance Coating Strategies

Timely maintenance coating prevents minor coating failures from developing into major corrosion problems. The optimal maintenance strategy depends on current condition, remaining service life requirements, and economic factors:

• Spot repairs: Appropriate when coating breakdown affects less than 5-10% of surface area

• Overcoating: Application of compatible maintenance coatings over properly prepared existing systems

• Full recoating: Complete removal and replacement when widespread coating failure or substrate corrosion is present

Surface-tolerant coating technologies have advanced significantly, allowing maintenance coating over firmly adherent existing coatings with minimal surface preparation in many situations. These products can reduce maintenance costs by 30-50% compared to full blast and recoat approaches when properly specified.

Economic Considerations and Lifecycle Analysis

Corrosion prevention investments must be evaluated on a lifecycle cost basis, considering initial costs, maintenance requirements, service life, and potential failure consequences. For typical industrial structures in Maritime environments, protective coating systems represent 5-10% of initial construction cost but can account for 40-60% of total lifecycle maintenance expenditure.

Key factors in economic analysis include:

• Design service life: Matching protection system capability to structural service life requirements

• Maintenance access costs: For elevated or complex structures, access costs may exceed coating material and labour costs

• Operational disruption: Production losses during maintenance shutdowns often dwarf direct maintenance costs

• Failure consequences: Safety-critical structures warrant higher initial investment in protection systems

Studies indicate that every dollar invested in appropriate corrosion prevention saves $10-25 in future maintenance and replacement costs. For critical infrastructure and industrial facilities, the business case for robust corrosion protection is compelling.

Partner with Experienced Engineering Professionals

Effective corrosion prevention requires integrated consideration of environmental conditions, material selection, protective systems, and maintenance programmes throughout the structure's lifecycle. From initial design through ongoing asset management, engineering expertise ensures optimal protection strategies that balance performance requirements with economic constraints.

Sangster Engineering Ltd. brings extensive experience in corrosion assessment and prevention strategies for steel structures throughout Nova Scotia and Atlantic Canada. Our team understands the unique challenges presented by our Maritime environment and provides practical, cost-effective solutions tailored to each client's specific requirements.

Whether you are planning new construction, evaluating existing asset condition, or developing maintenance programmes for industrial facilities, our professional engineers can help you implement corrosion prevention strategies that protect your investment and ensure structural integrity for decades to come. Contact Sangster Engineering Ltd. in Amherst, Nova Scotia to discuss your corrosion prevention challenges and discover how our engineering expertise can support your infrastructure needs.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.