Wind Turbines: Challenges Associated with Corrosion Protection

Learning Outcomes• At the conclusion of this webinar you will be

able to:– Define the coating-specific sections– Define challenges associated with corrosion

protection of wind turbines– Define wind turbine performance standards– Define corrosion protection methods for

wind turbines– Define industry standards for corrosion

protection of wind turbines– Define coating systems used to protect wind

turbines

Two Wind Markets – Onshore and Offshore

Three Coatings Sections - Onshore

Rotor Blades

Nacelle

Tower

Five Coatings Sections – Offshore

Rotor Blades

Nacelle

Tower

Substructure

Mooring

Challenges in Corrosion Protection of a Wind Turbine• Most wind farm owners/operators

are looking for a 20-25 year service life on all coatings.

• In general, coating manufacturers and tower fabricators may be asked to provide a joint warranty for a specific time frame

Challenges in Corrosion Protection of a Wind Turbine – Onshore • Wind turbines are

usually placed in rural, often remote areas, making future maintenance challenging and expensive

• Wind turbines can stretch hundreds of feet in the air, making accessibility difficult

Challenges in Corrosion Protection of a Wind Turbine – Onshore • On-Shore Wind Turbines

face the following challenges:– Dew/condensation with

or without salinity– Exposure to UV light– Wind blown debris– Extreme temperature

ranges• 130 F (54 C) to -80F

(-62 C)

Challenges in Corrosion Protection of a Wind Turbine – Offshore • In addition to the

previous challenges, off-shore wind turbines face:– Mechanical loads

• Floating Ice• Biofouling in

Submerged Zones– Variation in Weather

Conditions• Wind and Waves

Rotor Blades Performance Standards• Coated rotor

blades must be free of imperfections. Each surface imperfection on a wind turbine blade results in additional drag, and thus, decreases efficiency

Rotor Blades Performance Standards• Rotor blades flex when in use,

therefore so must there protective coatings– Coatings must flex without fracturing– Coating must be able to retain

adhesion to the base coat and substrate when rotor blades flex

Rotor Blades Performance Standards• Coatings applied

to Rotor Blades must be abrasion resistant. With Rotor Blades up to 5 MW (mega watts) being installed, they are susceptible to wind blown debris

Nacelle Performance Standards

• The nacelle must be protected from corrosion using a protective coating system

• The inside must be kept clean and dry. Climate is controlled using dehumidifiers

Tower Section Standards• The tower consist of three sections:

– Steel Tower which is protected with a coating

– Sub-Structure of the tower if sub-merged in water is protected by cathodic protection in conjunction with a coating system. If on-shore just a coating system is necessary

– Mooring is protected with a coating

Tower System Requirements

• ISO 12944 deals with performance requirements for protective paint systems– Defines test methods used to

determine the composition of the separate components of the paint systems

– Defines laboratory performance test methods for assessing the paint systems

– Defines criteria for evaluating results

Tower System Requirements

• Typical evaluation criteria is:– Degree of blistering and cracking

(ASTM D 714 or ISO 4628)– Degree of rusting (SSPC VIS 2, ASTM D

610 or ISO 4628)– Degree of chalking (ISO 4628)– Degree of flaking (ISO 4628)– Adhesion (ASTM D 4541 or ISO 4624)

Tower System Requirements

• Creep from scribe after 4200 hours of exposure to stresses of:– UV Light– Condensation– Salt Spray– Freezing– Immersion in Sea Water (ISO 2812)

• Cathodic disbonding after 4200 hours per ISO 15711

Tower System Requirements• ISO 12944 defines five corrosion

categories:– C1 (not corrosive interior atmosphere)

up to C5-I and C5M (Industrial and Marine)

– Most wind farms are rural areas, C3 (Moderate Load)

– According to Part 5, C3 categories should be coated with a multi-coat system with a DFT of 6-10 mils

Tower System Requirements

• ISO12944 Part 5 defines expected time of protection for various coating systems

• Low Durability– (2 to 5 years)

• Medium Durability – (5 to 15 years)

• High Durability – (greater than 15 years)

On-Shore Typical Coating Systems• Three Coating System

– Epoxy Zinc-Rich Primer (2 to 4 mils)– Epoxy Intermediate Coat (4 to 6 mils)– Polyurethane Topcoat (2 to 4 mils)

• High Performance Two Coat Systems– Epoxy Zinc-Rich Primer (3 to 4 mils)– Polyurethane Topcoat (4 to 5 mils)

Off-Shore Corrosion Protection

• Standards for off-shore wind turbine protection are:– ISO 12944– NORSOK M 501

Off-Shore Corrosion Protection

• ISO 12944 characterizes the conditions to which offshore wind turbines are exposed to as C5 M or IM 2 (immersion)

• C5 M categories are non-immersed and should be coated with a multi-coat system with DFTs in the range of 12 to 20 mils

• IM 2 indicates structure is immersed and should be coated with a multi-coat system with DFTs in the range of 20 to 40 mils in conjunction with cathodic protection

Off-Shore Corrosion Protection

• NORSOK M-501 specifies similar systems

• Atmospheric exposure should have a minimum DFT of 13 mils

• Immersed exposure should have a minimum DFT of 18 mils

Typical Off-Shore Above Splashzone Coating Systems• Three Coating System

– Epoxy Zinc-Rich Primer (2 to 4 mils)– Epoxy Intermediate Coating (2 Coats at

4-6 mils)– Polyurethane Topcoat (2-4 mils)

Typical Off-Shore Under Splashzone Coating Systems• Two Coat System

– Epoxy Coating (2 coats at 8-10 mils)

• NOTE- For areas under water (immersion service) NORSOK requires cathodic protection to be used in conjunction with coating system– Install impressed cathodic corrosion protection– Weld sacrificial anodes

Looking Ahead• Self repairing coatings

– Healing agents/inhibitors release from microcapsules when coating gets damaged

Summary• Coating wind turbines can be

challenging due to the complicated design of the structure and environmental location. To assure corrosion protection, industry standards must be followed and qualified coatings applied.