hen conducting a coating failure investigation, theinvestigator’s first inquiries should be “What was sup-posed to be done,” and “Does it make sense?” The

answers to these questions are typically revealed in the specification forthe project. However, in this “Case from the F-Files,” there was very lit-tle information in the specification to guide the investigation; and therewas little information available from the application, because in-processinspection was not performed. These circumstances made the failuremuch more challenging to resolve, and the resolution was based solely onthe results of the field and laboratory investigations, along with the expe-rience of the investigator.

The StructureThe structure, a drawbridge, carries vehicular traffic over an inter-coastal waterway (Fig.1). The bridge consisted of a 24-foot closed verticalclearance with 91 feet of horizontal clearance in the center span. Thestructure raises and lowers on demand, 24 hours a day with no restric-tions. The bridge deck and walkways on both sides consisted of opengrating. Railings, guardrail, and curbing on the lift span sections wereconstructed of steel. In addition, there was a pedestrian walkway under-neath and parallel to the bridge on the mainland side of the structure.The appearance of the bridge indicated that it had been painted after theoriginal coating application. The new coatings were, as reported by per-sons on the job site, applied to reduce the onset of corrosion and toimprove aesthetics.The coating history of the structure was essentially unknown.

Widespread corrosion was evident, despite the fact that the structurewas repainted approximately three years earlier. There were norecords identifying the degree of surface preparation or the type ofcoating system most recently applied or identifying the original coat-ing system.

The Field InvestigationThe field investigation includedvisual examination of failing andnon-failing areas, nondestructiveand destructive coating thicknessmeasurements, adhesion assess-ments, and sample collection for lab-oratory analysis.

J P C L J a n u a r y 2 0 1 0 13www.paintsquare.com

Continued

C a s e s f r o m t h e F - F i l e s

The Case of...Improper Selection of a Maintenance StrategyTakes Corrosion Protection from Bad to Worse

By Valerie Sherbondy, Senior Chemist, KTA-Tator, Inc.Richard Burgess, KTA-Tator, Inc., Series Editor

W

Fig 1: Bridge overview

Fig 2: Corrosion at stringer of floor beam connection

Fig 4: East flanking span looking toward the east lift spanFig 3: Corrosion of a flanking span girder

and bearing

J P C L J a n u a r y 2 0 1 014 www.paintsquare.com

Physical Assessment of CoatingCondition and Sample AcquisitionThe physical condition of the existingcoating system was evaluated by mea-surement of coating thickness (total andindividual layers) and adhesion. The con-dition of the substratewas also examined.A representative test area is shown inFig. 6. Destructive coating thickness mea-surements were obtained in accordancewith ASTM D 4138, “Test Method for

Measurement of Dry FilmThickness of Protective CoatingSystems by Destructive Means(Tooke Gage).” Testing was per-formed to identify the number oflayers present and the thicknessesof the individual layers. Table 1shows the results. Measurementswere also obtained by non-destructive means in accordancewith ASTM D 7091,“Nondestructive Measurement ofDry Film Thickness ofNonmagnetic Coatings Applied toFerrous Metals and Nonmagnetic,Nonconductive Coatings Applied

to Non-Ferrous Metals.” Table 2 showsthe data.Coating adhesion was measured

according to method A (X-cut) and B(cross-cut) of ASTM D 3359, “StandardTest Methods for Measuring Adhesionby Tape Test,” and according to ASTMD6677, “Standard Test Method forEvaluating Adhesion by Knife.” Thescale for rating the tape adhesion rangesfrom 5 (excellent) to 0 (poor); the scale

evidence of previous pitting corrosionon the girder. The flanking span gird-ers also exhibited corrosion on flangeedges and spot corrosion on the webs.The exposed bolted connections forthe concrete diaphragms also exhibit-ed corrosion. Figure 4 illustrates thecondition of the east flanking spangirders and the lift span section coun-terweight. Edge corrosion was presenton the counterweight and girders, and

the color of the finish coat (light blue)indicated color fading due to weather-ing.Although the amount of rusting

depicted in Figs. 2–4 appeared relative-ly minor, the distribution was wide-spread and affected all of the steel mem-bers to some degree. Sites exhibiting themost advanced corrosion (Fig. 5) weredifficult access areas that were evident-ly not fully cleaned during the mostrecent maintenance painting.

Visual ExaminationThe coating system contained a blue fin-ish coat, much of which was faded andchalked in areas exposed to sunlight,either directly or reflected off of thewater. Approximately 3% of the steelsurfaces contained corrosion, predomi-nantly on edges, connections, and cor-ners. Although the coating history wasnot revealed by records, maintenancepainting had been performed in thepast, as evidenced by surfaceswhere the older coating layerswere missing beneath the mostrecent applications. Some sec-tions of the structure containedpitting corrosion beneath intactcoatings.Although the corrosion was

localized, it was consistentlypresent on nearly all similarconnections. A prime exampleof this was where lift sectionfloor stringers were attachedto floor beams (Fig. 2). All suchconnections had some corro-sion evident. Careful examina-tion of the area (as seen in Fig. 2) alsoshowed the presence of rust on thesides of rivet heads and bolted connec-tions (nuts) near the corners of theconnection plate. The corrosionbrought into question the thorough-ness of surface cleaning and coatingoperations during the most recentmaintenance painting activities.Figure 3 depicts the presence of cor-

rosion at bearings supporting flankingspan girders. These areas also show Continued

C a s e s f r o m t h e F - F i l e s

Fig 6: A test area on an interior web girder showing good adhesion atthe X-cut and poor adhesion at the cross-cut.

Fig 5A: Corrosion above lift span girderFig 5B: Grating strips and angle iron benath sidewalk

grating and curb Fig 5C: Grating slots that are covered from above

In this game, you can’t win with poor substitutions.

Trust Only Genuine Graco® PartsGenuine Graco parts will keep you up and running longer. That’s because

they’re engineered and rated specifi cally for your Graco high-pressure

protective coatings equipment.

Why compromise?Download your free High-Pressure Airless Accessories parts catalog at www.graco.com/JPCL or call 877-844-7226

© 2010 Graco Inc. 340512 Rev. B© 2010 Graco Inc. 340512 Rev. B

M ADE I N THE U SAM ADE I N THE U SA

Click our Reader e-Card at paintsquare.com/ric

G

Click our Reader e-Card at paintsquare.com/ric

H

for rating the knife adhesion rangesfrom 10 (excellent) to 0 (poor). The spac-ing between the incisions was 5 mm formethod B. Table 3 shows the results ofthe adhesion testing.The gray primer remained on the sub-

strate at the adhesion test sites. The weakplanewas the interface of the gray primerand blue intermediate coat. In some cases,the gray primer split cohesively. Cross-cut adhesion was performed to furthercharacterize the adhesion/cohesionproperties of the coating system.Typically, this method is limited to use oncoating films less than 5mils’ thick.The steel substrate was

examined where destruc-tive testing and samplecollection were per-formed. The substratebeneath intact coating wasfree of corrosion and millscale. The substrate wastoo dark to determine thedegree of abrasive blastcleaning that may havebeen performed.Seven sampleswere col-

lected from the bridge for subsequent lab-oratory analysis. The samples includedboth coating chips and corrosion product.

Laboratory InvestigationThe laboratory investigation includedmicroscopic examination of coatingsamples to determine the number oflayers and confirm the field coatingthickness data, infrared spectroscopyfor coating resin identification, andquantitative chloride analysis of thecorrosion products collected.

Microscopic ExaminationMicroscopic examination was con-ducted using a digital microscope.Individual coating layers wereobserved in cross-section. The exami-nation confirmed that four coating lay-ers were present on each of the sam-ples examined. The thickness of theoriginal coating was relatively low,with the original primer ranging from1 to 2 mils and the original topcoatranging from 1 to 6 mils. The mostrecent coating system was compara-tively thicker, with the new primer

ranging from 10 to 15 mils and thenew topcoat ranging from 2 to 6 mils.The heavy thickness of the primermay have been specified to provideincreased barrier protection.Increased thickness, however, can leadto cracking of the coating system if itis not formulated for thick-film appli-cation. At this point in the failureinvestigation, it was unknown if theheavy thickness contributed to thefailure. The thickness results are pro-vided in Table 4.

Infrared Spectroscopic AnalysisInfrared spectroscopic analysis wasperformed to identify the generic coat-ing type of the four coating layers. Thefrequency and intensity of bands on theinfrared spectra produced by the coat-ings were interpreted by the spectro-scopist and the resin types were identi-fied. The blue topcoat removed from theeast counterweight panel and the liftspan floor beam was consistent with apolyurethane resin. The thick metallic(the appearance was consistent with analuminum pigment) intermediate coat

was consistent with anepoxy. The light blue coatremoved from the westend of the railing wasalso consistent with apolyurethane. The grayprimer on the bottomsurface of the lift spanfloor beam was consis-tent with inorganic zinc.

Quantitative ChlorideAnalysisCorrosion productsremoved from span 11,

stringer #1, interior flange, were ana-lyzed for soluble chloride content. Aportion of the sample was weighed andthen boiled in distilled water for 45 min-utes, filtered, diluted to volume, andtested using an ion specific (chloride)electrode. The sample contained 18ppm chloride. Although this concentra-tion may not appear to have much sig-nificance, it is equivalent to 18 micro-grams (µg) of chloride per gram of cor-rosion product.

17

C a s e s f r o m t h e F - F i l e s

Continued

Area Description

Flanking Span Girders

Lift Span Girders

Lift Span Floor Beams

Lift Span Stringers

Lift Span Outriggers

Counterweight Panels

Miscellaneous Items

Sidewalk Railing

Deck Curb

Average Thickness (mils)

21.0

20.5

23.7

24.2

22.4

23.6

21.3

20.0

22.3

Thickness Range (mils)

13.0–34.0

15.7–27.3

17.3–35.3

16.2–36.0

17.4–29.8

17.0–31.9

10.7–44.4

10.9–32.2

16.5–27.0

Table 2: Total Coating Thickness on Steel Spans (ASTM D 7091)

Layer

Topcoat

Intermediate

Intermediate

Primer

Color

Blue

Dark Gray

Blue

Light Gray

Flanking Span Girder

2–3 mils

7–10 mils

1–2 mils

2–3 mils

Lift Span Floor Beam

2.5–4 mils

11–13 mils

1.5–2.5 mils

2–2.5 mils

Lift Span Stringer

1.5–3 mils

10–12.5 mils

2–3 mils

1–2.5 mils

Counterweight Panel

2–3 mils

7–11 mils

4–6 mils

1–2.5 mils

Table 1: Individual Layer Thickness Values (ASTM D 4138)

J P C L J a n u a r y 2 0 1 0www.paintsquare.com

J P C L J a n u a r y 2 0 1 018 www.paintsquare.com

Clic

kou

rRea

dere

-Car

dat

pain

tsqu

are.

com

/ric

Clic

kou

rRea

dere

-Car

dat

pain

tsqu

are.

com

/ric

The Failure Mechanism: Putting theField and Laboratory Investigations

TogetherThe existing coatings on the structureappeared to represent two differentapplications, each consisting of twocoats, a gray first coat and a blue finishcoat. The original system appeared toinclude an inorganic zinc primer and ablue polyurethane finish. The grayintermediate coat appears to be alu-minum epoxy mastic with a bluepolyurethane finish coat. The latter twocoats appeared to be an overcoat sys-tem. There were locations where over-coating repairs were performed andwhere pitting corrosion was evidentunder the more recently applied, intactcoatings.The finish coat was clearly chalked

but returned to a bright blue color whenwiped with a rag and solvent.The degree of rusting was estimated

at 3% of the overall surface and wassimilar in distribution on the flankingspans and liftspans. However,the rust was notevenly distributedacross all surfaces.Corrosion was orig-inating at seams,connection plates,and steel edges aswell as difficult-to-access areas. Theareas of difficultaccess showed thegreatest degree ofsection loss anddeterioration andrequired attention

to prevent further metal loss.Where the coating was intact, the

thickness ranged from 20.0 mils to24.2 mils for different bridge compo-nents, which was remarkably uniform.The overall range of coating thicknessover the entire structure ranged from10.7 to 44.4 mils. Adhesion was rela-tively poor at the primer-intermediatelayer interface, but only when subject-ed to cross-cut adhesion using 5 mmspacing, which is more rigorous onthicker films. X-cut adhesion wassomewhat better, which was attrib-uted to the cohesive strength of thethick gray intermediate coat. Despitethe relatively poor adhesion of thecoating system as revealed by theadhesion testing, there were no areasof spontaneous delamination, peeling,or blistering. However, the distribu-tion of corrosion suggested that theareas were not cleaned well during therepainting.

J P C L J a n u a r y 2 0 1 0 19www.paintsquare.com

C a s e s f r o m t h e F - F i l e s

ClickourReadere-Card

atpaintsquare.com/ric

Continued

Sample Identification

North Girder, West Lift

(inside web near 3rd

Beam)

Span 11, Stringer #1

Outside Web

East Life Span Floor

Beam End

Coating Layer Color

Blue Topcoat

Black/Silver

Light Blue

Bottom Gray

Blue Topcoat

Black/Silver

Light Blue

Bottom Gray

Blue Topcoat

Black/Silver

Light Blue

Bottom Gray

Thickness (mils)

2.1–4.2

13.5–14.7

2.5–3.6

1.0–1.3

2.5–2.8

14.0–14.7

1.1–1.7

1.0–1.8

4.1–6.0

10.2–12.8

6.0–6.4

1.8–1.9

Table 4: Cross-sectional Coating Thickness Data

Test Procedure

ASTM D 3359 (X-Cut)

ASTM D 3359 (Cross-Cut)

ASTM D 6677 (Knife)

Flanking

Span Girder

1A

0B

6

Lift Span

Girder

4A

0B

6

Lift Span

Floor Beam

2A

0B

6

Counterweight

Panel

4A

0B

8

Table 3: Results of Adhesion Tests on Visually Intact Coating

J P C L J a n u a r y 2 0 1 020 www.paintsquare.com

Conclusions and RecommendationsThe original coating system appeared toconsist of an inorganic zinc primer anda polyurethane topcoat. This thin-filmcoating system was not robust enoughto provide long-term barrier protectionof the steel surfaces in the intercoastalwaterway environment. The applica-tion of an overcoat system was proba-bly not the best recommendation for therehabilitation of this structure. Theadvanced degree of corrosion indicatedthat moisture was penetrating the coat-ing system in areas where it was appliedat thicknesses lower than were recom-mended and in difficult-to-access areas.Analysis of the corrosion products

removed from the structure indicatedthat chloride ions were present. Therewas no evidence that chloride remedia-tion had been performed when thestructure was overcoated. The presenceof chloride ions accelerated the corro-sion process even beneath the coatingsystem, until rust and rust staining

Clic

kou

rRea

dere

-Car

dat

pain

tsqu

are.

com

/ric

F - F i l e s

Valerie Sherbondy is

a senior chemist for

KTA-Tator, Inc., a

consulting and engi-

neering firm special-

izing in industrial

protective coatings.

Ms. Sherbondy has been employed by

KTA since 1990 and has provided labo-

ratory support for the investigation of

hundreds of coating failures and coating

testing programs. In addition, Ms.

Sherbondy serves as the Laboratory

Quality Assurance Officer, overseeing

the A2LA and NELEC accreditations of

the laboratory. She holds a BS in chem-

istry and a BS in business from the

University of Pittsburgh and is an SSPC

Certified Protective Coating Specialist

(no. 467-921-0326), a member of the

American Chemical Society (ACS), and a

committee chair for NACE International.

J P C L J a n u a r y 2 0 1 0 21www.paintsquare.com

1-800-835-5858 www.sprayclaims.com

Overspray Problems? We Have the Solution!DAMAGE CONTROL: Control overspray costs through our fast, professional overspray removalservice, guaranteed to minimize claims.

COMPETITIVE PRICING: Realistic pricing without additional charges for travel or accommodations.

EXPERIENCE: Forty-two years of experience removing paint, epoxies, urethanes, asphalt, tar,concrete, and other contaminants from all types of vehicles.

STATE-OF-THE ART TECHNOLOGY: Overspray is removed with a gentle, advanced cleaning systemwhich limits the use of razor blades, buffers, sandpaper, rubbing compounds, or clay products.

IMMEDIATE ACTION: Trained and uniformed technicians are mobilized quickly to handle your problems.

COMPLETE CLAIMS MANAGEMENT: Signed preinspection forms and release statements fromsatisfied claimants help to limit the liability of contractors and insurance companies.

ClickourReadere-Card

atpaintsquare.com/ric

ClickourReadere-Card

atpaintsquare.com/ric

C a s e s f r o m t h e F - F i l e s

eventually became visible.Cleaning and recoating of the struc-

ture was not a simple task. There weremany surface configurations, laminarcorrosion, and open grating to consider.Additionally, the advanced deteriora-tion of some of the metal led the owner’sengineer to dictate steel replacement aspart of the current coating and mainte-nance plan.Pressure washing to reduce surface

chloride concentrations and solventcleaning to remove grease and oil conta-

mination were required. The bridge isbuilt over saltwater and is subject tocontamination from atmospheric depo-sition of chloride, so surface chlorideassessment after surface preparationand between applications was required.The cleaning specification for the deckgrating and tops of stringers, beams, andgirders included high-pressure waterjet-ting with abrasive injection to minimizewear on grating surfaces. Additionally,the use of water would remediate chlo-ride contamination.

A Near-White blast (SSPC-SP 10)was specified for all remaining surfaces.A three-coat system consisting of anorganic (epoxy) zinc-rich primer, epoxyintermediate, and polyurethane topcoatwas specified. In addition to this con-ventional system, an epoxy penetratingsealer was recommended for surfacesthat could not be fully abrasive blastcleaned to a near-white condition. Thiswas to be applied following the zinc-richprimer and before an intermediatestripe coat.

THE MBX®

BRISTLE BLASTERInnovative Power Tool Surface Preparation

Clean and Profile in a Single Step

Near White/White Metal Clean

2.7 – 3.3 mil Profile

Pneumatic & Electric Tools

877 629-8777 info@mbxit.comwww.mbxit.com

J P C L J a n u a r y 2 0 1 022 www.paintsquare.com

Clic

kou

rRea

dere

-Car

dat

pain

tsqu

are.

com

/ric

Clic

kou

rRea

dere

-Car

dat

pain

tsqu

are.

com

/ric