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bulkheads and smaller retaining walls.This article gives an overview of steelpiling and its uses; reasons for coating it;shop coating of new steel piling; andways to access, inspect, and performmaintenance coating of installed steelpiling.

Steel Piling and Its UsesSteel piling is available in a variety ofshapes, lengths, thicknesses, and alloys.Several ASTM standards describe someof the salient characteristics of steel pil-ings: ASTM A857/A857M-07,Standard Specification for Steel SheetPiling, Cold Formed, Light Gage; ASTMA328/A328M-07, StandardSpecification for Steel Sheet Piling; and

heet piling is commonlyused in construction. Pilesare commercially availablein a variety of shapes, sizes,and materials. Common pil-ing materials include steel,aluminum, concrete, FRP-composite, and vinyl. Steel is

by far the dominant material, althoughthe use of corrosion-resistant compositeand vinyl piling is increasing. Because oftheir inherent corrosion resistance, com-posite and vinyl piles are not painted. Intheory, these materials can be advanta-geous in a corrosive marine environ-ment. In practice, however, their use islimited to light and medium duty appli-cations, such as marine and freshwater

Coating SheetPile Structures:An Overview

SBy Timothy Race, Kaked LLC

Uncoated sheet pileCourtesy of the U.S. ArmyCorps of Engineers

ASTM A6/A6M-08a, StandardSpecification for General Requirementsfor Rolled Structural Steel Bars, Plates,Shapes, and Sheet Piling.1

Steel piling comes in many shapes,including H, U, Z, and flat sections.Combinations of shapes can be used tofulfill specific engineering and aestheticrequirements. Piles typically have inte-gral interlocks that allow the piles to beconnected as they are installed in thefield. Optional interlock bars and cor-ners facilitate the installation of virtual-ly any configuration, but interlockshave a small degree of play and are notwatertight. Sealants and seal weldingare used for applications that requirethe structure to be water-impermeable.Performed after field installation, sealwelding creates a simple continuousweld that provides a watertight seal.Alternatively, flexible organic sealantsare applied to piling structures prior tofield installation, which also facilitatesfuture maintenance painting.Piling is used for many structures,

both temporary and permanent.Examples include retaining walls, quaywalls, bridge abutments, seawalls, bulk-heads, cofferdams, basements, under-ground parking garages, in-ground haz-

37

mat containment barriers, load bearingfoundations (e.g., water tanks), groinwalls for beach erosion, and wing wallsfor bridges and culverts. Sheet piling haseven been installed as a barrier alongsections of the shared border betweenthe U.S. and Mexico.

To Coat or Not to CoatPilings used for temporary structuresare not typically coated. In fact, the vastmajority of piling for both temporaryand permanent structures is installedwithout a coating system or any othermeans of corrosion protection.Paints are sometimes used for visibili-

ty and aesthetics, such as on the pilewalls of basements and undergroundparking garages, land-sited retainingwalls, and water storage tank founda-tions. In general, atmospheric exposedsheet piling is coated to improve appear-ance.For pilings installed in corrosive envi-

ronments, piling manufacturers suggestthat protective coatings, thicker steel, orhigher yield strength steel be used toensure that the design life of the struc-ture is met. Higher yield strength steelcompensates for loss of section causedby corrosion but does not prevent cor-

rosion itself. For piling installed in cor-rosive environments, often only a rela-tively small area is exposed to highlycorrosive elements. For example, con-sider a marine bulkhead constructedof 50-foot-long piles. If the combineddepth of the low water, tidal, andsplash zones (the most corrosive areas)is a modest 5 feet, then only 5% of thetotal area of the piles will be subject tohigh rates of corrosion. Coating, some-times supplemented with cathodic pro-tection, can be a more cost-effectiveapproach than over-engineering thestructure in part or as a whole.Alternatively, thicker piles overall

or piles reinforced with additional sec-tional thickness in the zone of greatestcorrosion can also be used. (A pile canbe reinforced by welding plates oranother section of piling onto the mainpiling to add thickness just to the areawhere the corrosion rate is highest.Reinforcement eliminates the need touse a thicker pile over the entirelength [height] of the piles.)Selecting a higher yield strength

steel can effectively increase sectionthickness. For example, a higher yieldstrength steel that increases sectionthickness by 30% may only modestlyincrease the cost by approximately2%. In some cases, the zones of great-est corrosion may not match the areasthat are most highly stressed. Pileshave bending forces from side loads,but the loads are not equal. So thebending forces in piles are not likethose caused by grabbing a stick atboth ends and bending it. In the lattercase, the maximum load is at the cen-ter, right where you expect the stick tobreak. The static and dynamic loads ona pile will vary with height based onhow deep the pile is driven, whether ithas tiebacks and where they are, therelative depth of the water, tidal heightchanges, and wave action. So the maxi-mum bending force that will collapse

Driving piles coated with CTECourtesy of the U.S. ArmyCorps of Engineers

Jotun Paints, Inc.P. O. Box 159 • Belle Chasse, LA 70037 • USAToll Free: 800.229.3538 • Fax: 504.394.3726

www.jotun.com/us

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> soil > atmospheric. This rank order isa broad generalization, and, within thesecategories, the severity can be furthersubdivided, yielding overlaps and disor-der within the generalized ranking.Sheet pile installed in undisturbed

natural soils does not need to be coated.In practice, pilings used to constructseawalls, bulkheads, and retaining wallswill be backfilled on the soil side, whichmay increase the corrosion rate andrequire protective coatings or designcompensation. (Corrosion rates are

the wall is not necessarily at the centerof the pile. The area with the highestcorrosion rates may or may not coin-cide with the location of highest loading.Designers are encouraged to use cost

engineering to aid in the decisionprocess. Major suppliers of sheet pilinghave compiled general information andtools to assist the designer in selectingthe most cost-effective approach toachieve the desired durability.The general order of environmental

corrosiveness is: saltwater > freshwater

higher for backfilled areas due to soilaeration, affecting about the first 10 feetbelow soil grade.) Some soils, such asaggressive natural soils and fills, may beas corrosive as or more corrosive thanseawater and will also warrant the useof protective coatings or corrosion com-pensation through design. In its guidespecification for engineering in tropicalregions, the U.S. Navy has specific guide-lines for protecting sheet pile in tropicalmarine environments, with special con-sideration given to pile driven incoralline soils with low resistivity.2 Inthis case, coatings are used to protectthe soil side of pile structures.Sheet pile continuously immersed in

seawater has a low enough corrosionrate that painting is not required.However, mill scale on sheet piling mayfacilitate pitting of bare steel in seawaterimmersion. Therefore, piling to beimmersed in seawater is usually paintedfor corrosion protection and sometimessupplemented by application of eitherimpressed current or sacrificial cathodicprotection. If the piling is to be coatedfor immersion service, the mill scale isfirst removed as part of surface prepara-tion.The marine tidal zone and, especially,

the low water level, are quite aggressive,so piling in these areas is usually coatedfor protection and may again be supple-mented by cathodic protection. Themarine splash zone is also very aggres-sive,, and piling in the splash zone is usu-ally painted; however, cathodic protec-tion is not applicable. Exposed pileabove the splash zone is typically treat-ed the same as the splash zone.

Coating of New Sheet PilingIf a new sheet pile structure is to becoated, application almost always occurswithin a shop facility. Surface prepara-tion and shop coating offer tremendouscost savings over field coating. Piles aretypically cleaned using centrifugal blastmachines to achieve either an SSPC-SP6, Commercial Blast Cleaning, or SSPC-

38 www.paintsquare.comJ P C L A p r i l 2 0 0 9

Coating Sheet Pile Structures

The American Reinvestment and Recovery Act (ARRA) of 2009, which includes

approximately $130 billion in stimulus funding for construction, allots $4.6 billion

for U.S. Army Corps of Engineers (USACE) construction, maintenance, opera-

tions, and related activities, some of which may involve work on steel pilings on

Corps projects. Here’s the general breakdown of the money for the USACE.

• Construction: $2 billion

• Operation and Maintenance: $2.075 billion

• Mississippi River and its Tributaries: $375 million

• Formerly Utilized Sites Remedial Action Program:

$100 million

• Investigations: $25 million

• Regulatory Program: $25 million

For details about ARRA funding, visit www.recovery.gov.

Stimulus Funds for Corps of Engineers Projects

Corroded pile revealed during levee inspection. Courtesy of the U.S. Army Corps of Engineers

SP 10, Near-White Blast Cleaning. Shop-applied coating systems are usu-

ally two- or three-coat systems. Thetypes of products used are variable, butgenerally they are the same types usedfor any similar industrial application.Epoxy primers and intermediate coatsare typical, with polyurethane topcoatsused for preservation of appearance.Coating suppliers and end users havenot conferred royal status to any singlecoating material or system. Most sys-tems offered and specified for immer-sion and soil applications have filmbuilds of 12 mils and up. The only U.S.-based standard for coat-

ing sheet pile is ASTM A950/A950M-99 (2007), Standard Specification forFusion-Bonded Epoxy-CoatedStructural Steel H-Piles and SheetPiling.1 The powdered coating is electro-statically applied and heat cured.Fusion-bonded epoxy (FBE) coatingshave good edge retention and few pin-holes in the finished product. Like otherepoxy coatings, FBE is tough and well-suited to the rigors of shipping and fieldinstallation. FBE has only fair resistanceto cathodic disbondment and is not thebest choice for use with cathodic protec-tion. The traditional workhorse coating for

protecting sheet piling is coal tar epoxy(CTE), covered under the standardSSPC-Paint 16. CTE is well-suited toburied soil, freshwater and marineimmersion, and tidal and splash zoneexposures. CTE does not perform wellin direct sunlight and is available only inblack and dark reds; it is not used for itsaesthetic properties. CTE is more flexi-ble and impact-resistant than manyepoxy coatings, and it retains theseproperties even at low temperatures.Coating flexibility and impact resistancehelp reduce coating damage before andduring piling installation. The U.S. ArmyCorps of Engineers (USACE) and otherowners specify CTE for use on perma-nent sheet pile structures. USACE alsospecifies an epoxy zinc-rich primer for

marine applications. The nominal two-coat thickness of CTE is 18 mils.USACE also allows the use of two- andthree-coat epoxy polyamide systems onsheet pile. Polyamide systems may alsobe enhanced by application over anepoxy zinc-rich primer.3

Other coating materials have beenshown to be well-suited to protect sheetpiling. One study showed that the long-term performance of flame-sprayed alu-minum with a topcoat sealer gave thebest protection in a cold water marineenvironment, and a polyester glass flakecoating gave the best protection in awarm water marine exposure. CTE witha zinc-rich primer performed well atboth of the locations.4

A research program sponsored by theAmerican Association of State Highwayand Transportation Officials in coopera-tion with the Federal HighwayAdministration produced a report thatprovides recommendations for metalliz-ing systems to use on sheet piling andprovides a standard practice.5 USACErecommends aluminum thermal spraycoatings for piling exposed to seawater.6

In addition to metallized coatings, hot-dip metal coated pilings, including zinc,zinc/aluminum alloy, and aluminum arecommercially available. Hot-dip metalcoatings on sheet piling offer the sameeconomies as for other applications.Interested specifiers should refer to lit-erature available from the AmericanGalvanizers Association.7 The designershould consider the size of piling thatwill be used on a project because thereare practical limits on the overall lengthof a sheet that can be dipped into thegalvanizing bath. The designer shouldalso consider whether the added cost ofproviding corrosion protection to bothsoil and water sides is warranted.The world’s largest steel producer rec-

ommends CTE at a nominal 18-milthickness or glass-filled epoxy for sea-water immersion.8 For freshwaterimmersion, the company recommends a12-mil-thick system of epoxy polyamine

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primer and epoxy polyamide topcoat.For aesthetic purposes, the system canbe supplemented with an aliphaticpolyurethane topcoat. The companyalso recommends epoxy/polyurethanesystems for atmospherically exposedpiling.

Inspection and Maintenanceof Coated Sheet Piling

All coatings eventually reach the end oftheir service life when they no longerprotect the underlying surface.Maintenance schedules and repairoptions are evaluated by means ofinspection.

Access and Inspection of Sheet PileInspection of coated sheet pile is chal-lenging because direct access to the coat-ed surface is generally limited. In prac-tice, inspection is often performed by

trained divers, but devices have beendeveloped for remote inspection, includ-ing robotic crawlers and manually posi-tioned instruments. Divers and remoteinstruments can conduct visual observa-tions as well as perform physical mea-surements, including pit depth, ultrason-ic steel thickness, film thickness, andelectrochemical processes. Soil side inspection is generally not

possible; however, the soil side is usual-ly the area of least concern because ofthe generally low rate of steel corrosionin most soils (except as noted earlier). Insome cases, soil resistivity is measuredas a means of assessing the relativeseverity of the soil side exposure. Direct inspection may be conducted if

the structure can be dewatered. Directaccess allows evaluation by qualifiednon-diving inspectors in a dry environ-ment. With few exceptions, dewatering

of a structure is seldom a practical alter-native. Portable limpet dams (essentiallyminiature portable cofferdams) havebeen developed to facilitate inspectionas well as maintenance of sheet piling inthe dry. The width and depth of accessare limited by practical considerations.Installation and movement of the deviceis straightforward and fairly rapid. Thelimpet dam must be customized tomatch the specific shape and profile ofthe piling. When the limpet dam is con-figured with straight sidewalls and abottom with a toothed design matchingthe piling profile, the dam can be secure-ly attached to the pile wall, and the con-tained area is dewatered by pumping itdry.The results of the inspection can be

used to determine the necessary courseof action. Sometimes the pile structuremay warrant structural repair, rather

Coating Sheet Pile Structures

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divers to perform surface preparationand coating application underwater. While many types of coatings are

suitable for use on new sheet piling, thesame is not true for the maintenance ofsheet pile structures. If dewatering is apractical alternative, and if dry condi-tions can remain long enough, then mostof the coatings mentioned for shopapplication on new piles may be used. Coating selection is limited however,

when productivity is paramount andcoated surfaces must be returned rapid-ly to wet service. Suitable systems arethose that either cure very rapidly orcure underwater. Such products mayinclude 100% solids epoxy, polysulfide-modified epoxy, and polyurea applied

by plural-component spray. If it is notsealed, metallizing may be used toreturn piling to service immediately. Ifsealed with a fast-cure product, metal-lized piling may be returned to servicerapidly.

than just maintenance painting. In sucha case, structural repair may be accom-plished by welding additional steel plateto the affected piles to increase sectionalthickness and strength. Sometimes, anew sheet pile wall must be installed,typically by driving new piles in front ofthe existing piles. The new and old wallscan be connected with tie rods to takeadvantage of the existing anchorage ofthe old piling structure.

Access and Maintenance PaintingAccess for maintenance painting has thesame limitations as for inspection.Dewatering may be accomplished with alimpet dam or other damming devicesthat allow the water elevation to be low-ered to the extent necessaryto perform maintenanceoperations in the dry.Earthen, rock, pile, andinflatable dams may be suit-able for blocking inlets orisolating sections of canals.Dewatering is accomplishedby pumping out water.From a practical standpoint,the water does not need tobe removed all of the wayto the mud line. In fact, com-plete dewatering may com-promise the integrity of thepiling walls and may harmthe local animal and plantlife. Most repairs will beperformed in the zones ofhighest corrosion, which isnear the waterline in fresh-water and from the lowwaterline through thesplash zone in seawater. The dewatering of open

water structures such asseawalls and other water-front structures may require the con-struction of a cofferdam. This practicecan be quite expensive and may nega-tively impact commerce or security.Where dewatering cannot be accom-plished, it may be necessary to utilize

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Caribbean resort bulkhead repainted in the dry to just below lowwaterline. Dewatering was accomplished by damming canal inletand lowering water level using pumps. Courtesy of the author

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Products specifically formulated forunderwater application are not widelyavailable. There are perhaps six to eightmanufacturers of such products.Applying coatings underwater is bothdifficult and slow because of the surfacepreparation quality required; poor initialadhesion; and potential applicationdefects, including floating, lifting, andsagging.Underwater surface preparation may

include hand cleaning, grinding, andwater and abrasive blasting with zero-thrust equipment. Removal of all loosecoating and loose rust as well as allmarine organisms is generally specified. Underwater coatings are applied by

roller, brush, or trowel. Older products,referred to as splash zone putties, weremixed and applied with a gloved hand.The putty-like coatings worked but werevery slow to apply. Newer products areapplied using pressure-fed rollers andbrushes. Products available for under-water application are 100% solids,including epoxy polyamine and polysul-fide-modified epoxy coatings. The addi-tion of fiber reinforcement to these prod-ucts reportedly improves applicationproperties by reducing floating.9

Summary Permanent sheet pile structures areeither designed with a corrosionallowance or coated to achieve therequired design life. Surface preparationand coating are best accomplished in the

fabrication shop. Techniques are availableto inspect sheet pile structures installedin seawater and freshwater. If mainte-nance coating is necessary, operationsshould be performed in the dry, but ifdewatering is impractical, underwater-applied coatings may be used.

References1. ASTM International, West Conshohocken, PA.

2. U.S. Navy, UFC 3-440-05N Tropical Engineering.

3. U.S. Army Corps of Engineers, UFGS 09965 Painting: Hydraulic Structures.

4. A. Kumar, V. L. Van Blaricum, and A. Beitelman, “Twenty Year Field Study of The Performance of Coatings in Seawater,” U.S. Army Construction Engineering Research Laboratories, IL, and Boy, J.H., Oak Ridge Institute for Science and Education and U.S. Army Construction Engineering Research Laboratories, IL.

5. James A. Ellor, Walter T. Young, and John Repp, “Thermally Sprayed Metal Coatings to Protect Steel Pilings: Final Report and Guide.”

6. U.S. Army Corps of Engineers, UFGS-09971 Metallizing: Hydraulic Structures.

7. www.galvanizeit.org.8. ArcelorMittal, Piling Handbook, 8th Edition, www.arcelormittal.com.

9. Jeff Longmore, “The Development and Evolution of Underwater Coatings,” CoatingsPro November 2006.

Coating Sheet Pile Structures

Tim Race is the founder and owner of Kaked, a new coatingsconsulting firm in Elmhurst, IL. Previously, he worked for theArmy Corps of Engineers and CCC&L. Mr. Race has been anactive member of SSPC since 1986. He serves on theStandards Review Committee as well as several others. Raceis also a member of the Federation of Societies for CoatingsTechnology, NACE International, and the American ChemicalSociety. He has written for JPCL and other journals.