Corrosion protection of steel piles

How bridges get built · Driven piles · Corrosion protection of steel piles

Also called: sacrificial thickness, cathodic protection, pile coatings, concrete jackets

How it is done

Define the exposure zones along each pile (atmospheric, splash, tidal, low-water, immersed, buried) and the design life; take corrosion rates from EN 1993-5 or the local port standard, with site data where available.
Allow a sacrificial thickness: in temperate seawater about 3.5 mm per 100 years where permanently immersed or intertidal and about 7.5 mm in the splash and low-water zone; warm, polluted or Gulf waters need more, or coatings plus cathodic protection instead.
Shop-apply coatings (glass-flake epoxy, polyurethane or polyethylene) to the splash and tidal zones and well below the scour line after blast cleaning; test thickness and holidays.
Protect the coating in handling and driving (padded slings, guides that do not scrape), and repair damage above water after driving.
Install cathodic protection for the immersed and buried zones: aluminium-alloy sacrificial anodes welded or clamped to the piles, or an impressed-current system for large structures, with electrical continuity between piles.
In the splash zone add concrete jackets or petrolatum-tape and HDPE wraps, or fill the upper pile with reinforced concrete so the steel shell is not relied on there.
Survey after installation and at intervals: CP potentials, anode condition and coating state.

Key numbers

Corrosion allowance in temperate seawater (EN 1993-5, per exposed face): about 3.5 mm per 100 years immersed or intertidal; about 7.5 mm per 100 years in the splash and low-water zone.
Unprotected steel in the splash zoneabout 0.1-0.3 mm per year, more in warm seas or with accelerated low-water corrosion.
CP protection criterion in seawater-800 mV versus Ag/AgCl or more negative.
Initial design current density for bare steel in seawater: about 0.15-0.25 A/m2 (DNV-RP-B401).
Splash-zone coatingstypically 400-1,000 micrometres dry film.
Costabout 5-15 % of the pile cost.

Where it fits

All steel piles in seawater, brackish estuaries and contaminated ground.

Where it does not

Trusting a coating damaged in driving; the splash zone is where piles fail first.

Choosing it

Choose sacrificial thickness alone for buried and permanently immersed zones of short-life or easily inspected structures; it cannot protect a splash zone for 100 years on its own.
Choose coatings plus cathodic protection for 100-year marine bridges: CP protects the immersed part, coatings and jackets the splash zone.
Prefer concrete piles or concrete-filled heads where splash-zone maintenance cannot be guaranteed.
Prefer impressed current over sacrificial anodes for very large structures or high current demand, if the owner can maintain the power supply and monitoring.

Plant, pace and money

PlantCoating facility, anode installation by divers, CP monitoring.

ProductivityAdds days per pier.

Cost5-15 % of the pile cost; the game's marine-grade durability option covers this.

Risks and controls

What goes wrong

Coating damage during driving, anode depletion, stray currents.

Quality assurance

Coating thickness and holiday tests, CP potential surveys after installation.

Origins

Humphry Davy demonstrated cathodic protection in 1824 with zinc and iron fixed to the copper sheathing of Royal Navy ships; sacrificial-anode protection of steel marine piling became routine after the Second World War, and accelerated low-water corrosion of steel piling was recognised in UK ports in the 1980s and 1990s.

Examples

Gulf sea bridges specify cathodic protection on all piles; Japanese ports wrap the tidal zone.

Case studies

Duluth-Superior Harbor, Lake SuperiorUSA · 1998 onwardDivers found steel sheet piling in this freshwater harbor corroding far faster than expected, with localised holes near the waterline; it became the reference case of accelerated freshwater corrosion, linked to microbial activity.

Haneda Airport D-Runway, TokyoJapan · 2010The pile-supported jacket section was designed for a 100-year life with titanium-clad steel protecting the splash zone and cathodic protection below.