Invert Abrasion Testing of CSP Coatings · PDF filesimulated abrasion test and the NCSPA ... 4...

I n v e r t A b r a s i o n Te s t i n g o f C S P C o a t i n g s

Prepared for:

NATIONALCORRUGATED STEELPIPE ASSOCIATIONMarch 2002

The present study contained three primaryobjectives:

■ Establish a relationship between thesimulated abrasion test and the NCSPADurability Guide (Appendix 1). Modifythe test rig to establish abrasion condi-tions that correspond to a Level 3,Moderate Abrasion.

■ Establish the performance of galva-nized and coated CSP under test

parameters that represent this condi-tion, enhancing our understanding ofthe abrasion mechanisms (i.e., theinfluence of abrasive, slope, and flowon the resultant abrasion).

■ Qualify innovative coating materials toimprove the durability of culvertinverts in the severe and moderateabrasive environments.

R e p o r t a n d R e s u l t s 1

O b j e c t i v e s

1. The previously developed test methodcan simulate Abrasion Levels 1–4 as listedin the NCSPA Durability Guide.

2. The test method has been modified toevaluate Level 3 abrasion resistance.

3. A variety of invert coatings havedemonstrated good performance underLevel 3, Moderate Abrasion. Thisincludes:

– Polymer Precoat– Polymer Modified Asphalt– Polymer Modified Asphalt over

Polymer Precoat

4. Two coating systems have been quali-fied for Level 4, Severe Abrasion. PolymerCoated CSP with Polymer ModifiedAsphalt invert treatment and AsphaltPaved performed well in the Level 4,Severe Abrasion simulation.

5. Changes in either bedload, pipe slope,or both may impact the severity of theabrasive environment.

C o n c l u s i o n s

As a result of continued interest inimproving the durability of corrugated

steel pipe products, the industry has spon-sored extensive research on improvedcoating materials. The bulk of thisresearch concerns field investigations ofCSP. While many of these studies indi-cated a long life for CSP, the industrycontinually is searching for improvedmaterials to extend life in general and toprovide a suitable service life in the mostdemanding exposures. In support of thisobjective, fundamental laboratory studiesunder controlled circumstances are neces-sary to understand the underlying mecha-nism of failure, thus allowing enhanceddurability designs.

The track record of CSP is well estab-lished, yet the industry would like toexcel with new technologies available.The use of tough, abrasion-resistantorganic barrier coatings will enhance theprotection afforded by the metallic coat-ing by extending its life. Even in “non-abrasive” service environments, abrasionresistant coatings contribute to a robustcoating system by providing a barrier thatprotects the metallic coating from thesoil, atmosphere, and water. This willextend service life in any environment.

The primary area of concern in mostcases is the CSP invert. NCSPA has devel-oped a test protocol for new CSPcoatings1 to extend invert life. These testsevaluate coating performance underdefined conditions. The standardized testscan be used to qualify new and existingmaterials based on performance compar-isons to control materials.

Exposure of candidate coatings to acontrolled laboratory representation ofservice conditions helps yield comparable,repeatable results. The results of suchtests, however, can suffer limitations sincethere is no way to accelerate time. Thus

mechanical abrasion can be acceleratedyet time-dependent phenomena like cor-rosion can not usually be accelerated.Such tests can be enhanced by the deter-mination of a time-degradation relation-ship over the testing period. Using thistime-degradation relationship, one may beable to make predictions over service peri-ods significantly longer than laboratorytest duration.

A testing protocol provides the abilityto single out a characteristic of a particu-lar material for evaluation (e.g., abrasionresistance). This protocol is limited tosearching for improved corrugated steelpipe invert protective materials or coat-ings to obtain superior performance ofCSP. It is not the intent to compare typesof pipe materials such as reinforced con-crete pipe (RCP) or plastic pipe. Therehas been no attempt to broaden the scopeof the test protocol to incorporate appli-cable test that would be considered pru-dent if working with RCP (e.g., chlorideor sulfate concentrations) or HDPE (e.g.,environmental stress cracking).

The original Tier 31 simulated abrasiontest contained a very severe level of abra-sion that would be outside of the recom-mended service environment fortraditional CSP materials. The Tier 3 testwas originally designed to be a short-termdestructive test that would quickly pro-vide relative performance results. Toextend the usefulness of the full-scaleabrasion testing developed by theNCSPA, it was desirable to expand thescope of the abrasion test to include alter-native, lower levels of abrasion. This willallow the industry to position coatingproducts in the marketplace based ondurability and resistance to various levelsof abrasion. This report presents theresults of testing conducted to character-ize various abrasion test parameters.

I N V E R T A B R A S I O N T E S T I N G O F C S P C O AT I N G S2

B a c k g r o u n d

1 Evaluation Methodology for Corrugated Steel Pipe Coating/Invert Treatments, National Corrugated Steel Pipe Association, March,1996.

The NCSPA Test Protocol includes threetiers of test procedures for the evalua-

tion of a new coating. Tiers 1 and 2 areintended to confirm the basic suitabilityof the coating for use on CPS. Coatingsproperties such as freeze-thaw resistance,water absorption, and abrasion resistanceare measured on laboratory test panels.The coatings materials discussed hereinhave already passed these tiers of testing.This report concentrates on the third tierof testing—the accelerated abrasion test.

Accelerated Abrasion Tests Apparatus

Figures 1A and 1B show a photographand a design drawing of the acceleratedabrasion test apparatus. The apparatusdesign considers the simulation of watervelocities and bedloads establishedthrough the experience of others as dele-terious to the performance of asphaltcoated CSP. In the test rig, seawater isdrawn through the pumping manifolds to4-inch PVC pipe, expanding to 12 inchPVC through a 90° elbow to a 5-footlength of horizontal PVC pipe. The waterthen flows into a 5-foot length of 12- to18-inch transition section of galvanizedCSP that connects to a second 5-footlength of CSP. This second pipe has anopening in its crown for the entrance ofbedload material. In the standard test pro-

tocol, the next section is the 10-foot testsection of CSP (with the test coatingapplied). The test section then connectsto a 5-foot length of galvanized CSP thatempties into a large plastic sump. For thepurposes of the present testing, three five-foot “test sections” were used to maximizethe amount of data that could be gener-ated with each test run.

A hopper in the sump retains the dis-charged bedload material, preventing itsentrance into the pumps. This hopper isconnected to a hoist that then connects torail assembly with rollers. The hoist androller combination allows for the abrasivematerial to be dropped back through therig. The pump manifolds are connected tothe sump by 4-inch PVC pipe. Plasticlined pumps with plastic impellers and theuse of PVC pipe leave the CSP as theonly metallic components of the systemwith which the circulating water contacts.Provision is made, but not shown on thedrawing, for continuous refreshment ofthe circulating water with fresh water,preventing unwanted increases in the cir-culating water temperature or changes inseawater chemistry. Three pumps circulatethe seawater medium.

Calculations, based upon the Manningequation indicate that this rate, flowingthrough 18-inch CSP will attain a velocityof about 11 feet per second with the pipebeing half full, if the pipe slope is about


P r o c e d u r e s

TABLE 1 Summary of Test Conditions

Test Run Dates Stone Type Hours Flow Rate Hours Flow Rate Angle of FlowHigh (550 gpm) Low (50 gpm) (from horizontal)

1 Dec 23 – Jan. 7 Stone 28 254 12°

2 Jan 12 – Jan 25 None 30 229 12°

3 Feb 10 – Feb 19 Rock 20 190 12°

4 Mar 8 – Mar 13 Stone 28 254 12°

5 Jun 24 – Jul 15 Stone 30.5 375.5 2°

6 Sep 13 – Sep 24 Stone 27.5 236.25 2°

7 Jun 12 – Jun 22 Stone 30 233 2°

8 Jun 26 – Jul 7 Stone 34 214.5 12°

12°. This rig has been designed to allowfor adjustments to be made in the slope ifdesired. Preliminary testing was per-formed with the rig aligned with a 12°slope in order to evaluate the acceptabil-ity of this slope. These tests determined ifthe design parameters caused detectabledamage to asphalt coating within a rea-sonable period.

The total test duration is approximatelytwo weeks (10 working days) with a totalof about 25 tons of rock being passedthrough the test and control piping.During the period in which the abrasive isintroduced, seawater flow rate throughthe piping is approximately 550 gpm. Anorifice controls the rate of bedload flowinto the test stream. Dispatching the bed-


FIGURE 1A. Accelerated Abrasion Test Apparatus.

FIGURE 1B. Accelerated Abrasion Test Apparatus Schematic.

Hoist Rail

Overflow

Makeup Water

Pump Manifold

12 Degrees

Hopper

Test Section

10'0"

Control

5'0"


load in 25 ton batches allowsfor cyclic bedload and immer-sion exposure which may bevaried to simulate actual fieldconditions. Furthermore, assess-ment of the coating after each“bedload event” allows for accu-rate measurement of the incre-mental impact of each event.

Alternate Abrasion Conditions

The objective of this effortwas to use the NationalCorrugated Steel PipeAssociation (NCSPA) full-scale(Tier 3) test rig to qualify coatings for usein various levels of abrasion and tie thoseabrasion levels to the NCSPA DurabilityGuide.

To accomplish these goals, various pipeslopes and abrasive materials were used inan attempt to simulate varying exposureenvironments. The Tier 3 test protocol isdesigned to test the abrasion resistance ofa corrugated steel pipe coating by passingaggregate, accelerated by flowing seawa-ter, through test sections of pipe. Theaccepted test method is to position thetest section at an 11 degree angle fromhorizontal and pass 3⁄4" trap rock throughthe pipe using 550 gpm flowing seawater.As part of an effort to develop a morecomprehensive test procedure, a differentaggregate and different flow geometrywere tested. The aggregate examined wasa 3⁄8" local stone, propelled by 550 gpm,and the new flow angle used was a 2-degree angle from horizontal. TABLE 1

shows the test conditions during test runswith different aggregate or flow geometry.

As can be seen in Table 1, there weretwo materials used for the bedload—3⁄4"trap rock and a 3⁄8" local stone. FIGURE 2shows both materials. The 3⁄4" trap rockwas the more severe of the two bedloadmaterials because of size, angularity, andhardness of the material. It is commonlyused as bed materials for railroads in theEastern US. The 3⁄8" local stone is consid-ered to be less severe because it is smaller,rounded, and softer stone. It has a varietyof common uses including landscaping.

Coating thickness measurements werethe primary method of tracking coatingdeterioration. A series of measurementswere made on the upstream edge of thecorrugation. The measurements weremade on 1-inch spacing starting at thebottom of the pipe. Exact locations weremarked so that the coating loss could beaccurately tracked.

FIGURE 2. Bedload Materials (3⁄4" trap rock on left, 3⁄8" local stoneon right)

The following discussion presents theresults of the testing performed during

this project. The test results are groupedby coating type.

Galvanized Pipe

Four test were run with standard G210galvanized CSP meeting ASTM A929 forZinc Coated Steel Sheet. TABLE 2 presentsa summary of the test conditions and theresults.

FIGURE 3 shows the thickness of galva-nizing before and after testing under thevarious abrasion conditions. This figureshows that the wear patterns of the galva-nizing are similar for all stone sizes andangles of flow—that is, the wear is con-centrated in the invert of the pipe.However, there is decreased wear at asmaller angle of flow than at the standard12-degree angle. Furthermore, there is adecreased wear using the less severe bed-load material even at the higher angle. Itis difficult to differentiate between therelative effect of the bedload material andthe pipe angle. Each of the changesappears to have a similar magnitude ofreduction in the coating wear.

Polymer Precoat

Five test were run with pipe fabri-cated from ASTM A742 PolymerPrecoated Sheet for Sewers and Drains.TABLE 3 presents a summary of the test

conditions and the results. In previoustesting under the most severe abrasionconditions, there was exposed galvaniz-ing at the crests of the corrugation.None of the less-abrasive test scenariosevaluated showed any consistentexposed galvanizing. Coating loss waslimited to less that half of the film thick-ness in these tests.

There was no exposed galvanizingafter testing at either slope using thesmaller bedload. FIGURE 4 shows the thick-ness loss around the invert of the pipefor each of the tests. Notice that there isno data for the original test conditions(3⁄4" Rock and 12 degree slope). We candeduce that the maximum coating lossfor this condition was greater than 10mils since exposed galvanizing wasobserved. The data suggest that at alower flow angle the coating loss wasmore uniform across the bottom quad-rant of the pipe section. However, at ahigher flow angle the coating loss wasmuch greater at the very bottom of thepipe than the loss at a 2-degree flowangle, even with the same bedload mate-rial. The data for the polymer precoatsuggests that the impact of bedloadmaterial and pipe slope is similar in rela-tive magnitude.

Asphalt Paved

One test was run with asphalt pavedgalvanized CSP. TABLE 4 summarizes the


R e s u l t s &D i s c u s s i o n

TABLE 2 Summary of Test Results for Galvanized Pipe

Test Bedload Slope max Thk Max Exposed NotesRun Loss (mils) Galv (sq cm)

Rock 12° 2.4 N/A Data from control sections in previous work

1 3⁄8 Stone 12° 1.6 N/A Similar to 3⁄4 Rock wear at same slope

5 3⁄8 Stone 2° 1.2 N/AStone collect in the corrugations during the test

6 3⁄8 Stone 2° 0.7 N/A

2 None 12° 0.1 N/A No visible wear

test conditions and results. FIGURE 5 showsa photograph of the asphalt pipe after thetesting. There was no exposed galvanizingafter testing. Signs of wear were observedon the bottom (paved) section of theinvert, characterized by a rough textureand extending 2-inches on either side of

the paved section. Remainder of asphaltcoating is duller than original possiblyindicating some wear of the coating. Nodetectable loss was observed after testing.It is important to note that the test doesnot consider the effect of aging on asphaltperformance.


TABLE 3 Summary of Test Results for Polymer Precoat Pipe

Test Bedload Slope Max Thk Max Exposed NotesRun Loss (mils) Galv (sq cm)

Rock 12° 10 9.5 Data from original study

1 3⁄8 Stone 12° 4.7 0 One lockseam beginning to show coating disbondment

4 3⁄8 Stone 12° 4.2 0 No exposed Galvanized,max loss at invert

5 3⁄8 Stone 2° 1.6 0

6 3⁄8 Stone 2° 1.2 0

2 None 12° 0.5 0 No visible wear

FIGURE 3. Galvanized Thickness Loss Under Different Test Conditions

130-2.5

-2

-1.5

-1

-0.5

0

140 150 160 170 180 190 200 210 220 230

Location in Culvert

Thic

knes

s Lo

ss (m

ils)

3/8 Stone, 11 degrees




No Bedload, 12 degrees

FIGURE 4. Polymer Precoat Thickness Loss Under Different Test Conditions

130-5

-4

-3

-2

-1

0

140 150 160 170 180 190 200 210 220 230

Location in Culvert

Thic

knes

s Lo

ss (m

ils)





No Bedload, 12 degrees

Galvanized with “Truflo” PolymerModified Asphalt

Two tests were run on G210 galvanizedCSP with “Truflo” polymer modifiedasphalt. TABLE 5 presents a summary of thetest conditions and the results. FIGURE 6shows one of the areas where galvanizedhas been exposed on a corrugation afterTest Run 3. FIGURE 7 presents the measuredthickness losses as a function of locationin the invert. The data demonstrated theeffect of different abrasive on the abrasionresistance of the material. Clearly the lesssevere abrasive resulted in less wear asmeasured both by thickness loss and byexposed galvanizing.

“Truflo” over Polymer Precoated Galvanized

Three test were run on polymer pre-coat CSP with “Truflo” polymer modifiedasphalt invert treatment. The first samplethat was tested (Test Run 3) was dippedinto the modified asphalt such that thebottom 90-degrees of the pipe had anasphalt coating over the polymer.


TABLE 4 Summary of Test Results for Asphalt Paved Pipe


3 3⁄4 " Rock 12° N/D 0 Too thick and inconsistent to measure loss with any degree of accuracy

FIGURE 6. Polymerized asphalt over galvanizingafter test run 3.

TABLE 5 Summary of Test Results for Galvanized with Truflo Polymer Modified Asphalt


3 3⁄4 Rock 12° >50 1.47 Exposed galvanizing at 5 locations

4 3⁄8 Stone 12° 3 0.2 Exposed galvanizingat one location

TABLE 6 Summary of Test Results for Truflo Polymer Modified Asphalt Invert Treatment over Polymer Precoat Pipe


3 3⁄4 Rock 12° 38 0 Dipped invert coating

FIGURE 5. Asphalt paved pipe after test.

TABLE 6 presents a summary of the testconditions and the results. This dippedmaterial did quite well in the most severeabrasion test. There was no exposed gal-vanized material after the test. This andasphalt coated and paved are the onlyCSP coating systems that have per-formed this well at the highest abrasionlevel. There was substantial thicknessloss that exposed some of the polymerprecoat in some areas. In those areasthere did not appear to be any abrasivedamage of the polymer precoat as aresult of the test.

FIGURE 8 shows the thickness loss ofeach of these coatings after the test.

The paved inverts showed the samecold flow phenomenon as was observedon the galvanized pipes. FIGURE 9 shows anexample of the cold flow on the polymercoated pipe from Test Run 8. Note thatno galvanizing was exposed during eitherof these tests


FIGURE 9. Polymer modified asphalt paved invert over Polymer Precoat afterTest run 8.

FIGURE 7. Polymer Modified Asphalt Thickness Loss Measured After Testing

130

0

-5

-10

-15

-20

-25

-30

-35

-40

-45

-50

140 150 160 170 180 190 200 210 220 230

Location in Culvert

Thic

knes

s Lo

ss (m

ils)


3/4 Rock, 12 degrees

FIGURE 8. Polymer Modified Asphalt Over Polymer Precoat

130

0

-5

-10

-15

-20

-25

-30

-35

-40

-45

-50

140 150 160 170 180 190 200 210 220 230

Location in Culvert

Thic

knes

s Lo

ss (m

ils)




I N V E R T A B R A S I O N T E S T I N G O F C S P C O AT I N G S1 0

Product Usage Guidelines for Corrugated Steel Pipe

ENVIRONMENTAL RANGES:• Normal Conditions: pH = 5.8 – 8.0 (for R > 2000 ohm-cm)

• Mildly Corrosive: pH = 5.0 – 5.8 and/or for R = 1500 to 2000 ohm-cm

• Corrosive: pH < 5.0 (for R < 1500 ohm-cm)

ABRASIONInvert Protection/Protective Coatings can be applied in accordance with thefollowing abrasion criteria. Abrasion velocities should be evaluated on thebasis of frequency and duration. Consideration should be given to a fre-quent storm such as a two year event (Q2) or mean annual discharge(Q2.33) or less when velocity determination is necessary.

ABRASION LEVELSThe following qualitative definitions are provided as guidance to evaluateabrasion conditions when necessary.

Non-Abrasive (Level 1): No bedload regardless of velocity; or storm sewerapplications.

Low Abrasion (Level 2): Minor bedloads of sand and gravel and velocitiesof 5 ft./sec. or less.

Moderate Abrasion (Level 3): Bedloads of sand and small stone or gravelwith velocities between 5 and 15 ft./sec.

Severe Abrasion (Level 4): Heavy bedloads of gravel and rock with veloci-ties exceeding approximately 15 ft./sec.

■ This Guide provides environmental ranges for CSP products. Service Life of CSP will vary within these ranges. For estimating average invert service life, refer to the Service Life Predictionsection in this Guide or the Durability chapters of the AISI publication Handbook of Steel Drainage & Highway Construction Products or the Modern Sewer Design. ■ This Guide is not a sub-stitute for professional engineering advice and is made without guarantee or representation as to results. Although every reasonable effort has been made to assure its accuracy, neither the National Corrugated Steel Pipe Association nor any of its members or representatives warrants or assumes liability or responsibility for its use or suitability for any given application.

Zinc Coated (Galvanized)

Aluminum Coated Type 2

Asphalt Coated

Asphalt Coated and Paved

PolymerIzed Asphalt Invert Coated*

Polymer Precoated

Polymer Precoated and Paved

Polymer Precoated w/ PolymerIzed Asphalt

Aramid Fiber Bonded Asphalt Coated

Aramid Fiber Bonded and Asphalt Paved

High Strength Concrete Lined

Concrete Paved Invert (75mm (3”) Cover)

Shaded Circles IndicateApplicable Coatings

See AISI Chart

COATING Normal

Condit

ions

Mildly

Corros

ive

Corros

ive

Provide

s Add

itiona

l

Soil

Side Prot

ectio

n

Non-Abra

sive/L

ow

Abra

sion (

Lvl. 1

& 2)

Modera

te Abra

sion

(Le

vel 3

)

High Abra

sion

(Le

vel 4

)

Use Asphalt Coated Environmental Ranges for Fully Coated Product

WAT E R S I D E

Note: Coatings listed under additional soil side protection are generally considered to provide 100 years service life from a soil side perspective within appro-priate environmental conditions.1

†

†

Appendix A:CSP Durability Guide

M A Y 2 0 0 0

CSP Durability GuideCSP Durability Guide 1255 Twenty-Third St., NWWashington, DC 20037Phone: (202) 452-1700

Fax: (202) 833-3636E-mail: [email protected]: www.ncspa.org

A p p e n d i x A 1 1

National Corrugated Steel Pipe Association C S P D U R A B I L I T Y G U I D E 2

Environmental Guidelines for Corrugated Steel Pipe

Protective Coatings and PavingsAll corrugated steel pipes have a metallic coatingfor corrosion protection. When the coating select-ed does not provide the required service life or isoutside the appropriate environmental conditions,an alternate coatings system can be selected. Oftenthe required service life can also be achieved byincreasing the sheet thickness; this alternativeshould be weighed against the cost of supplementalcoatings. Galvanizing is the most widely usedmetallic coating and is the basis for the Service LifeChart shown on page 4.

A. METALLIC COATINGSZinc-coated (Galvanized) Steel (AASHTO M36,ASTM A929) is produced with a coating weight of610 g/m2 (2 oz/ft2) of surface (total both sides) toprovide zinc coating thickness of 86 µm (0.0017in.) on each surface.4 Ounce Zinc-coated (Galvanized) Steel (ASTMA929) is a new coating produced with a coatingweight of 1220 g/m2 (4 oz/ft2) of surface (totalboth sides) to provide zinc coating thickness of 86µm (0.0034 in.) on each surface. This coating hasbeen evaluated in the lab and is currently beingevaluated in field installations. Initial lab tests haveindicated increased corrosion and abrasion protec-tion. Specific performance recommendations willbe provided when further data is available.Aluminum Coated Type 1 (AASHTO M36, ASTMA929) is an aluminum coating with 5 to 11% sili-con. It is produced with a coating weight of 305

g/m2 (1 oz/ft2) of surface (total both sides) to pro-vide a coating thickness of 48 µm (0.0019 in.) oneach surface. Service life will be addressed whensufficient data becomes available.Aluminum Coated Type 2 (AASHTO M274, ASTMA929) is a pure aluminum coating (no more than0.35% silicon). It is produced with a coating weightof 305 g/m2 (1 oz/ft2) of surface (total both sides)to provide a coating thickness of 48 µm (0.0019in.) on each surface.

B. NON-METALLIC COATING & PAVINGSAsphalt Coated (AASHTO M190, ASTM A849). Anasphalt coating is applied to the interior and exteri-or surface of the pipe with a minimum thickness of1.3 mm (0.05 in.) in both fully coated and halfcoated.Invert Paved with Asphalt Material (AASHTOM190, ASTM A849). An asphalt material is used tofill the corrugations and provide a minimum thick-ness of 3.2 mm (1/8 in.) above the crest of the cor-rugations for at least 25% of the circumference ofround pipe and 40% of the circumference for pipearch.Invert Paved with Concrete Material (ASTM A849,ASTM A979). A 75 mm (3 in.) thick concrete layeris placed in the installed pipe for at least 25% of thecircumference of round pipe and 40% of the cir-cumference for pipe arch.Fully Lined with Asphalt Material (ASTM A849).An asphalt material is used to fill the corrugations

and provide a minimum thickness of 3.2 mm (1/8in.) above the crest of the corrugations providing asmooth surface over the entire pipe interior.Fully Lined with Concrete Material (ASTM A849,ASTM A979). A high strength concrete material isused to fill the corrugations and provide a mini-mum thickness of 3.2 mm (1/8 in.) above the crestof the corrugations providing a smooth surfaceover the entire pipe interior.Invert Coated with Polymerized Asphalt Material(ASTM A849). A polymer modified asphalt materi-al is used to provide a minimum thickness of 1.3mm (0.05 in.) for at least 25% of the circumferenceof round pipe and 40% of the circumference forpipe arch. Generally used for invert treatmentsonly.Invert Paved with Polymerized Asphalt Material(ASTM A849). An asphalt material is used to fill thecorrugations and provide a minimum thickness of1.3 mm (0.05 in.) above the crest of the corruga-tions for at least 25% of the circumference ofround pipe and 40% of the circumference for pipearch.Polymer Precoated (AASHTO M245, ASTM A742).A laminate film is applied over protective metalliccoatings. The 10/10 grade (10 mils thickness, eachside) is the primary product used. Aramid Fiber Bonded Asphalt Coated (ASTMA885). An aramid fiberfabric is embedded in thezinc coating while it is still molten, which improvesbonding to the asphalt coating.

2 3 4 5 6 7 8 9 10 11 12

Water & Soil Resistivity

2,000 to 10,000ohm–cm

Water & Soil Resistivity> 10,000ohm–cm

Water & Soil Resistivity

> 2,000ohm–cm

*Use Asphalt Coated Ranges

for FullyCoated Product

MaximumAbrasion Level

Zinc Coated (Galvanized)(see AISI chart)

Aluminum Coated Type 2 (Min. Resistivity 1500)

Zinc Coated (Galvanized) (see AISI chart)

Asphalt Coated

Asphalt Coated and Paved

Aramid Fiber Bonded Asphalt Coated

Aramid Fiber Bonded and Asphalt Paved

(see AISI chart) Polymerized Asphalt Invert Coated*

Polymer Precoated (Min. Resistivity 100 ohm-cm)

Polymer Precoated and Paved (Min. Resistivity 100 ohm-cm)

2

2

Aluminum Coated Type 2 (Min. Resistivity 1500)2

2

2

3

3

3

4

2

3

pH pH



A. METALLIC COATINGS

As discussed above, CSP coatings can be classifiedinto two broad categories, metallic and non-metal-lic coatings and pavings. Metallic coatings com-mercially available include zinc (galvanized) andaluminum coated (Type 2). Several non-metalliccoatings are available as shown in this document.The following discussion explains the differencesand similarities of the two metallic coatings.

All metals form some type of corrosion productwhen they corrode, regardless of whether they areprotective metallic coatings such as aluminum orzinc, or the base steel. Typically the corrosionproduct, such as an oxide, is more stable and itsbuildup will result in a decreasing corrosion rate. Inpractice, corrosion products formed through thegalvanic cell (pit) may be deposited in small dis-continuities in the coating and serve to stifle furthercorrosion just as films of corrosion products pro-tect solid surfaces. Thus, the development ofscales on metal surfaces is an important consider-ation when using metals in waters.1

Zinc-Coated (Galvanized)2

Zinc corrodes much more slowly then steel in nat-ural environments and it galvanically protects steelat small discontinuities in the coating. Its excellentresistance to corrosion is due to the formation ofprotective films on zinc during exposure. On theaverage, the rate of attack of zinc is approximately1/25 that of steel in most atmospheres and variouswaters.

High corrosion rates in strongly acidic and strong-ly alkaline solutions can be attributed to theabsence of film on the metal surface (stable filmsare present on the surface when the corrosion ratesare low). Lab test indicated stable films in the pHrange from about 6 to 12.5.

Aluminum Coated Type 2"Aluminum is a reactive metal, but it develops apassive aluminum oxide coating or film that pro-tects it from corrosion in many environments."3

This film is quite stable in neutral and many acidsolutions but is attacked by alkalies greater than apH of 9. From a corrosion standpoint, aluminumhas an advantage over galvanized in lower pH andin soft water due to the formation of the oxide film.(Soft waters are generally classified as waters witha hardness of 50 parts per million CaCo3 or less.)The coatings are essentially equal under abrasion8

and in waters where the zinc oxide film forms rap-idly.

Service LifeThe service life of zinc coated galvanized is deter-mined using the AISI Chart on page 4. This chartpredicts a variable service life based on pH andresistivity of water and soil and has been an indus-try standard for many years. Many specifyingagencies view service life of aluminum coated type2 as having additional service life over galva-nized.4,5,6,7This advantage varies throughout thecountry from minimal to significant depending onthe environment and the geographic location.Users are encouraged to review the practices intheir area.

For the purposes of this Guide, aluminum coatedtype 2 can provide a service life range of a mini-mum 1.3 times the AISI chart for galvanized(roughly 1 gage) and up to to 75 years (possiblymore) in the appropriate environmental conditions.This is consistent with the range of practice bystate and federal specifying agencies. The specificmultiplier used for design purposes should bebased on comparable experience under similarenvironmental conditions. There may be condi-tions where the actual performance is more than orless than this range. The significant advantageappears to be either for more corrosive effluent orsoft waters where the protective scale forms rapid-ly for aluminum. In benign environments or whereprotective scales form rapidly on zinc, there may belittle advantage.

AISI Method for Service Life PredictionThe service life of CSP can be reasonably predictedbased on the environmental conditions, the thick-ness of the steel, and life of the coating. The mostpractical method of predicting the service life of theinvert is with the AISI (American Iron and SteelInstitute) chart shown on page 4.9 This chart isbased on 16 gage galvanized CSP with a 610 g/m2

(2 oz/ft2) coating and can be applied to other thick-nesses with the appropriate factor. See discussionabove for estimating the service life of aluminumcoated type 2.

The AISI chart, which gives service life in termsof resistivity and pH, was developed from a chartoriginally prepared by the California Department ofTransportation(Caltrans).10 The Caltrans study ofdurability was based on life to first perforation inculverts that had not received any special mainte-nance treatment. The results included the com-bined effects of soil-side and interior corrosion, aswell as the average effects of abrasion. For pipeswhere the pH was greater than 7.3, soil-side corro-sion controlled and life could be predicted by resis-tivity. For pipes where the pH was less than 7.3, theinterior invert corrosion generally controlled andboth resistivity and pH were important. In the fieldinspection of 7000 culverts in California forCaltrans, Richard Stratfull, Lead Project

Investigator, states he “has no memory of a corro-sion perforation being initially found other than inthe invert.” At least 70 percent of the pipes wereexpected to last longer than the chart prediction.

The consequences of small perforations areminimal in a gravity flow pipe such as most stormsewers and culverts and do not accurately reflectthe actual service life. Because of this fact, theoriginal curves were converted by Stratfull to aver-age service life curves using data on weight lossand pitting in bare steel developed by the NationalInstitute of Standards and Technology. Sincestorm sewers and culverts are usually designedwith a structural safety factor of at least 2.0, a sig-nificant safety factor of 1.5 remains at the end ofthe service life predicted by the chart. Thus, use ofthe chart is considered reasonably conservative.The Caltrans Method may be appropriate for useunder pressure applications. Where service life iscontrolled by invert performance, rehabilitation ofthe invert at the end of the predicted life can extendservice life significantly

Soil-Side DurabilityA study performed by Corrpro Companies in 1986found that soil-side durability is generally not thelimiting factor in designing CSP systems. “Surveyresults indicate that 93.2 percent of the plain galva-nized installations have a soil-side service life inexcess of 75 years, while 81.5 percent have a soil-side service life in excess of 100 years.”11

The study also found that soil moisture contentsbelow 17.5 percent did not exhibit any acceleratedcorrosion. “Under most circumstances, corrosionrates are directly related to soil moisture content.However, for galvanized steel storm sewer and cul-vert pipe, the soil moisture content primarily affectsthe activity of any chloride ions present and thechloride’s acceleration of the corrosion. Where thesoil moisture content was below 17.5 percent, thechloride ion concentration did not have a significantaffect on the corrosion rate of the zinc coating.”

A computer program to estimate soil-side serv-ice life is included in “Final Report, Condition andCorrosion Survey of Corrugated Steel StormSewers and Culvert Pipe,” and is available fromNCSPA.

Service Life for Corrugated Steel Pipe

A p p e n d i x A 1 3


Steps in Using the AISI ChartThe durability design chart can be used to predictthe service life of galvanized CSP and to select theminimum thickness for any desired service life.Add-on service life values are provided in the tableon page 5 for additional coatings.1) Locate on the horizontal axis the soil resistivity

(R) representative of the site.2) Move vertically to the intersection of the sloping

line for the soil pH. If pH exceeds 7.3 use thedashed line instead.

3) Move horizontally to the vertical axis and readthe service life years for a pipe with 1.6 mm(0.064 in.) wall thickness.

4) Repeat the procedure using the resistivity andpH of the water; then use whichever service lifeis lower.

5) To determine the service life for a greater wallthickness, multiply the service life by the factorgiven in the inset on the chart.

Additional Service LifeAdditional service life can be provided by increas-ing the thickness of the base steel in accordancewith the factors shown in the Chart for EstimatingAverage Invert Service Life or with the use of addi-tional coating systems. Add-on service life valuesare provided in the Tables on page 5.

B. NON-METALLIC COATING & PAVINGS

Non-metallic coatings offer advantages over metal-lic coatings in the form of increased abrasionresistance, wider environmental ranges and longerservice life. Inherent in these coatings is less vari-ability in performance which is why specific add-onservice life values are recommended under variousabrasion levels.

Asphalt Coated – Asphalt coatings are generallyused for soil-side protection but also provide addi-tional waterside protection. Numerous studies haveconcluded that asphalt coating typically provides10 years additional service life to the inside of thepipe.12,13,14,15,16 Asphalt coatings provide muchhigher service life on the soil-side and inherentlyextend the environmental ranges for soil condi-tions. According to Corrpro11, “study results indi-cate that the addition of an asphalt coating mayhave provided a soil side service life in excess of100 years.”

Asphalt Coated and Paved – Asphalt coated andpaved provide both additional service life andadded abrasion protection on the water side of thepipe. Based on several studies, coated and paved isconsidered to provide an additional 30 years serv-ice life under most abrasion levels.12,13,15,16,17,18

This is considered a very conservative estimate fornon abrasive and low abrasion (level 1 and 2).

Polymerized Asphalt Invert Coated – Polymerizedasphalt provides improved adhesion and abrasionresistance over standard asphalt products.8 Fullscale abrasion tests conducted by Ocean CityResearch indicate no deterioration of the coatingunder moderate abrasion (level 3)19.

Based on independent test lab results using testmethod ASTM A926, results indicate that the com-mercially available polymerized asphalt coatinglasts at least 10 times longer than standard asphaltcoating and at least three times longer than stan-dard culvert coated and paved. 5

Polymer Precoat – Polymer precoat providesexcellent adhesion to the base steel and extendedcorrosion and abrasion resistance. The service liferecommendation are based on extensive lab andfield tests.8,19,20,21,22 According to PSG22, "No cor-rosion was observed on any of the coated (polymercoated) pipes. We can not find any data to suggestthe pipe coating would not provide at least onehundred years service." Sites contained environ-mental conditions with Resistivity as low as 100ohm-cm and pH as low as 2.1. In addition, PSGconducted current requirement testing that isdesigned to determine corrosion activity of a given

AISI Chart for Estimating Average Invert Life for Galvanized CSP

Thickness (mm) 1.3 1.6 2.0 2.8 3.5 4.3(in) .052 .064 .079 .109 .138 .168

Gage 18 16 14 12 10 8Factor 0.7 1.0 1.3 1.8 2.3 2.8

Aluminum Coated Type 2 : See Discussion

Years = 3.82R0.41

10020

40

60

80

100

100,00010,0001,000

pH = 7.3pH > 7.3 pH = 7.0 6.5

6.0

5.0

4.0

3.0

Resistivity (R), ohm-cmYears = 35.85 (Log10 R-Log10 (2160-2490 Log10 pH))

Aver

age

Inve

rt Li

fe, Y

ears



REFERENCES

1. “Corrosion Basics: An Introduction,”National Association of CorrosionEngineers, 1984.2. “Zinc: Its Corrosion Resistance,”C.J. Slunder and W.K. Boyd, 1971.3. “Corrosion Engineering,”Mars G.Fontana, 1986.4. “Federal Lands Highways DesignGuide”, FHWA.5. “California Highway Design Manual,Fifth Edition.”6. Orgeon Department ofTransportation.7. Hydraulics Manual, WashingtonState Department of Transportation,1997.8. Ocean City Research, “Evaluation

Methodology for CSP Coating/InvertTreatments,” 1996.9. Modern Sewer Design, AISI, 1990.10. “Durability of CSP,” RichardStratful, Corrosion Engineering, Inc.(DU-250)11. “Condition and Corrosion Survey:Soil Side Durability of CSP,” CorrproCompanies, March, 1991.12. “Performance Evaluation ofCorrugated Metal Culverts in Florida,”R.P. Brown, R. J. Kessler, Florida DOT,1975. (DU-173)13. “Durability of Corrugated MetalCulverts,” John E. Haviland, Peter J.Bellair, Vincent D. Morrell, New YorkDOT, Bureau of Physical Research,1967. (DU-163)14. “Life Cycle Cost for Drainage

Structures,” Technical Report GL-88-2,Department of the Army, February,1988.15. “Louisiana Highway ResearchDrainage Pipe Study,” David G. Azar,1972. (DU-147)16. “Performance Evaluation ofCorrugated Metal Culverts in Georgia,”Southeast Corrugated Steel PipeAssociation, 1987. (DU-174)17. “Culvert Performance Evaluation,”Materials Division, Washington StateHighway Commission, 1965.18. “Durability of Asphalt Coating andPaving on Corrugated Steel Culverts inNew York,” W.W. Renfrew, TRB, 1984(DU-155.19. Ocean City Research, 1999.20. “Evaluation of Drainage Pipe by

Field Experimentation andSupplemental Laboratory 10.Experimentation, Final Report,”Louisiana Transportation Research,1985.21. “Experimental Culvert Pipe, STH80,” Wisconsin DOT, 1996.22. “Field inspection of PolymerCoated CSP,” PSG CorrosionEngineering & Ocean City Research,1998.23. “Pipe Coating Study: Final Report,”Indiana Department of Highways,September, 1982.24. “Durability of Culverts and SpecialCoatings for CSP,” FHWA, 1991

WATER SIDE

COATING Level 1 & 2 Level 3 Level 4 References

Asphalt Coated 10 N/R N/R 12, 13, 14, 15, 16

Asphalt Coated and Paved 30 30 30 12, 13, 15, 16, 17, 18, 19

Polymerized Asphalt Invert Coated* 45 35 N/R 5, 8, 19

Polymer Precoat 80+ 70 N/R 8, 19, 20, 21, 22

Polymer Precoat and Paved 80+ 80+ 30 22, 23

Polymer Precoat with Polymerized Asphalt Invert Coated 80+ 80+ 30 19, 22

Aramid Fiber Asphalt Coated 40 N/R N/R 20

Aramid Fiber Asphalt Paved 50 40 N/R 20

High Strength Concrete Lined 75 50 N/R 10,24

Concrete Invert Paved (75mm (3 in.) cover) 80+ 80+ 50 10, 24

Add-On Service Life for Non-Metallic Coatings (in years)

Estimated Service Life

structure. The current requirement data showspolymer coated structures have up to 10,000 timesless corrosion versus bare G210 galvanized.Recent tests conducted by Ocean City Researchindicate polymer coated withstanding abrasionlevel three conditions.19(Note: Corrosion condi-tions at the extreme limits of the environmentalranges may require adjusting add-on service lifevalues).

Polymer Precoat and Asphalt Paved – Polymerprecoat and asphalt paved benefits from the excel-lent adhesion of the polymer precoat to the basesteel and the subsequent adhesion of the paving tothe precoat. According to laboratory and fieldtests, 22,23 the combination of the three coatingsresults in a pipe which is highly resistant to acidic

effluent. The bituminous material has much betteradhesion to the polymeric coating than it does tothe galvanizing.

Polymer Precoat with Polymerized Asphalt InvertCoated – Full scale abrasion tests conducted byOCR show equal performance of the polymerizedasphalt over polymer precoat as standard asphaltpaved.19 This system has the same bonding char-acteristics as the polymer precoat and paved. Fieldsites also indicate improved adhesion.22

Aramid Fiber Asphalt Coated/ Aramid FiberAsphalt Paved – The fibers embedded in zinc pro-vide an anchor for the asphalt coating or paving toimprove adhesion.

High Strength Concrete Lined – Concrete liningsare typically used for improved hydraulic perform-ance but also provide additional abrasion protec-tion and extended service life. The use of highstrength concrete and metallic coated steel providethe high service life values.

Concrete Invert Paved – Concrete inverts provideextreme abrasion protection and extended servicelife. According to Stratfull10, “metal pipe with aninvert paved with concrete should provide an indef-inite service life if it is of sufficient width, thicknessand quality. By calculation, a 4-inch thick coatingover the invert steel could be expected to postponeits initial time to corrosion by approximately 7.7times greater than a 3/4 inch coating.”

N/R Not recommended

The National Corrugated Steel PipeAssociation (NCSPA) encourages the

development of coating and invert treat-ments to improve the service life of theirproducts in certain aggressive environ-ments. These are primarily abrasive envi-ronments but can also include highlyacidic, alkaline, and low resistivity envi-ronments. To help guide the developmentof candidate materials that would protectand extend the life of the invert of corru-gated steel pipe (CSP), the NCSPA, alongwith AISI, has funded a program todevelop and qualify a comprehensive test-ing protocol. This Protocol is not a stan-dard or specification. The existence of theProtocol does not preclude anyone frommanufacturing, marketing or purchasingproducts, nor from using products,processes or procedures whether or nottested in accordance with the Protocoland, if tested, regardless of test results.

In addition to evaluating the candidatematerials improved properties, there are anumber of qualities exhibited by existingCSP coatings that must be retained by thenew materials. Most prominent amongthese qualities is the ability to be cost-effectively applied to CSP. Other qualitiesinclude impact resistance, freeze-thawresistance, resistance to microbial attack,and resistance to ultraviolet deterioration.Finally, the candidate material is notexpected to be an environmental orworker health risk. In today’s regulatoryclimate it is difficult to predict the typesof materials which will pose problems inthe future. However, the new candidatematerials will be screened for compliancewith existing regulations (e.g. heavy metalcontent, VOC content) and potentialfuture risks identified.

Screening Evaluation

The purpose of this initial screening isto provide a mechanism by which unsuit-able materials can be screened out prior totesting. Because of the wide variety ofpossible coating material technologies

that may be tested in accordance with thisprotocol, it is difficult to set specific crite-ria for initial screening. The screeningprocess is intended as an initial step toeliminate unreasonable candidates. Theflowchart at the end of this appendixaddresses three key issues; performance,environmental/ worker health, and feasi-bility of application. There is a finalcheckpoint for “other concerns.”

Evidence of Possible Performance (Block 1).Before evaluating any candidate material,there must be some evidence that it maybe appropriate for the CSP service envi-ronment. This could be limited laboratorytesting or documented service in a similarenvironment (e.g. pipelines). The purposeof this block is merely to ensure that test-ing is not blindly conducted on materialsthat are not applicable to CSP serviceenvironments. If no information on thematerial performance is available it shouldnot be evaluated.

Environmental/Worker Health Compliance(Block 2). Compliance issues include EPA,OSHA and other state and/or federalcompliance regulations. This evaluationprotocol can not purport to address allissues of regulatory compliance, if onlybecause of the changing regulations.Environmental and worker health issuesmust be the responsibility of the manufac-turer and end user. However, it is impor-tant to identify possible problems prior toembarking on an extensive series of tests.

Application/Manufacturing Concerns(Block 3). Prior to evaluating a candidatematerial, consideration must be given tohow it will be applied to CSP. There aretwo options for CSP coating application:application to coil steel prior to corrugat-ing or application to the CSP after fabri-cation. There are special issues associatedwith either application method whichshould be considered prior to testing.

For materials applied after the manufac-ture of the CSP, the effects of surface con-

A p p e n d i x B 1 5

Appendix B:Coating Test Protocol

tamination on coating adhesion must beconsidered. During corrugation and cut-ting, machining oils are left on the pipethat will affect adhesion. Cleaning stepsrequired for their removal must be identi-fied. The dry time of the coating materialis also important as it may affect industrialengineering concerns such as productionschedules and work flow. Tendency of thecoating to sag must be considered todetermine if spinning is required to coataround the pipe circumference. Any con-cerns with the material’s adaptability tospraying, brushing, and pour/dip applica-tion should also be addressed at this stage.

For coatings applied to coil steel, man-ufacturing concerns center around theeffects of production operations on thecoating quality. Specifically, the ability ofthe coating to adhere to the lock seamand to rerolled ends should be considered.Shipping, handling, and installation willcause some damage to any coating; how-ever more susceptible coatings should beidentified.

Other Concerns (Block 4). This step allows forthe consideration of unforeseen issues thatmay be encountered with new technologycoating materials. It is important that allpotential issues be addressed prior toembarking on the three tier test program.

Tier 1 – Qualification Tests

Qualification testing consists of anarray of physical tests conducted to evalu-ate the relative performance betweencoating materials. These tests are con-ducted as a preliminary evaluation of coat-ing performance. These test results willallow poor performers to be eliminatedwithout further, more elaborate testing.All issues involved in coating deteriora-tion are not considered in these tests.Passing these tests qualifies the coatingfor the more realistic abrasion, simulation,and field tests in Tier 2 and 3. Six stan-dard tests are described, others may beadded depending on the intended applica-tion of the coating. Manufacturers datamay be considered acceptable for certainof these tests at this stage.

Freeze/Thaw Resistance (Column 5).Freeze/Thaw testing shall be conducted inaccordance with ASTM A742/A742M,“Specification for Steel Sheet, Metallic-

Coated, and Polymer Precoated forCorrugated Steel Pipe.” If any coatingdamage occurs due to this cycling, thecoating is unacceptable for applicationwhere freeze/thaw is a major concern.

UV/Weathering (Column 6). UV acceleratedweathering tests will be conducted in gen-eral accordance with ASTM 4587,“Practice for Conducting Tests on Paintand Related Coatings and Materials Usinga Fluorescent UV-Condensation Light-and Water-Exposure Apparatus.” Types ofdamage recorded are observations of colorchange, cracking, blistering, chalking andany other damage the UV exposure mayhave caused.

Chemical Resistance (Column 7). It is notwithin the scope of this protocol to testfor all combinations of chemical resist-ance. However, it is expected that all can-didate materials will pass the chemicalresistance (imperviousness) testing con-ducted in accordance with paragraph 9.6of ASTM A742/A742M, “Specification forSteel Sheet, Metallic-Coated, andPolymer Precoated for Corrugated SteelPipe” or ASTM G20, “Test Method forChemical Resistance of PipelineCoatings.” Additionally, if the coating isbeing designed for improved resistance tospecific, harsh conditions (e.g., high acid-ity or alkalinity), similar testing shall beconducted in an appropriate environment.If the coating shows any softening, thin-ning, disbondment, etc. it will not be con-sidered for further testing.

For characterizing metallic coatingresistance without an organic topcoat indifferent electrolyte chemistries, it may bedesirable to run additional screening tests.Two suggestions include a corrosion ratetest (e.g., polarization resistance) and aporosity test.

Coating Adhesion (Column 8). Coating adhe-sion tests are conducted to quantify theresistance of a coating to disbond fromthe substrate it is protecting. There are avariety of adhesion tests provided byASTM.

Some tests for metallic coatings involvebending the coated material around smalldiameter rods and evaluating adhesion. Allmetallic and organic coatings applied tocoil will be tested in accordance withASTM D 4145 “Standard Test Method for


Coating Flexibility of Prepainted Sheet.”The coating should show negligible fail-ure at the 1-T bend which is representa-tive of a lockseam bend radius.

Organic coating adhesion is oftenmeasured by applying tensile forces withcalibrated apparatus or adhesive tape.Organic coating adhesion will be evalu-ated before and after a 30-day exposure tocathodic disbondment current in accor-dance with ASTM G8 “Test Method forthe Cathodic Disbondment of PipelineCoatings.” The coating is expected toshow less than 4 in2 disbondment afterthis test.

Impact Resistance (Column 9). Impact resist-ance will be tested on organic coatings.Mechanical damage to the coating systemfrom impact can occur on CSP duringshipping, handling, and installation.Impact resistance is evaluated using thefalling weight method in general accor-dance with ASTM A742/A742M“Specification for Steel Sheet, Metallic-Coated, and Polymer Precoated forCorrugated Steel Pipe.” This method usesan apparatus with a vertical appendageand fixed weight. The weight is droppedfrom varying heights. The height atwhich the dropped weight causes coatingdamage that exposes the substrate is usedto calculate the impact energy. Thereshall be no observed damage when sub-ject to 35 in. lb. force from a 0.625-inchdiameter punch.

Microbial Activity (Column 10). If it is deter-mined that microorganisms may have aneffect on the coating in its applicationenvironment, tests will be conducted inaccordance with ASTM G22, “Practice forDetermining Resistance of Plastics toBacteria.” Biodegradation effects will beevaluated in a laboratory environment.This involves subjecting test coating spec-imens to prepared cultures of variousorganisms that affect the adhesive quali-ties of a coating. These effects are moni-tored and documented over the length ofthe exposure period. There shall be noeffect of microbial attack on the coating.

Other Concerns (Block 11). Tests will also beconducted for any other qualitiesexpected to be of concern. If the candi-date material is acceptable to the levelrequired for the particular application,

then the material may proceed to Tier 2 -Abrasion Testing.

Tier 2 - Abrasion Testing

Blocks 12 and 13. If the candidate material isnot intended for use in an abrasive envi-ronment then this portion of the testing isnot performed. If the candidate material isintended for an abrasive environment thenthe level of its abrasion resistance neces-sary for the application must be deter-mined. The abrasion resistance will becharacterized relative to a control materialsuch as galvanized or asphalt coated CSP.

Block 14. The bedload abrasion test con-sists of a rotating drum apparatus. Thetest simulates an abrasive bedload by pass-ing water and abrasive material over thetest pipe specimen at tangents to the cir-cumference of the pipe. In this test whilethe drum is rotating the test specimenspass through a slurry of water and abra-sive material. The test apparatus is a 2-foot in diameter and 8 inch thick drumrotated by an electric motor. A 10-inch x5-inch size curved piece of coated coilsteel is bolted to the inside circumferenceof the drum. Water and abrasive materialare also placed in the drum. At variousintervals the specimens are removed andweighed. Coating damage is quantified byweight loss of the coating per cycle.

Block 15. The rotary disk test is conductedby rotating a flat coated disk in a roundtest chamber that holds the specimen,water, and abrasive material. Flat pieces ofcoated coil steel are cut and backed on aflat steel plate which is rotated within thechamber. As the disk with the test coatingrotates it passes through the slurry ofwater and abrasive material which wear atthe coating material. Coating damage isquantified by intermediate thicknessmeasurements along the radius of the disk.The diameter (and thus relative velocity)of observed coating damage is recorded.

Block 16. When the necessary number ofcycles of the above tests have been com-pleted, the samples are removed and ana-lyzed. An evaluation process now takesplace to verify if the coating meets theestablished criteria for performance in theapplication environment. Acceptable coat-ings proceed to Tier 3 – Simulation

R e p o r t a n d R e s u l t s 1 7

Testing. Unacceptable coatings shouldnot be considered for the particular appli-cation.

Tier 3 – Accelerated AbrasionSimulation Testing

The purpose of this test is to subject afull size pipe coated with the test materialto a variable abrasive bedload under con-trolled conditions. The abrasion resistancenecessary can be quantified by character-izing the abrasive nature of the intendedrange of applications. Factors that shouldbe considered in the application environ-ment are flow velocity, size and amount ofabrasive, and the slope of installation.Once these characteristics are determined,standards of performance for the simula-tion testing may be defined.

It is expected that some candidatematerials will be designed to have anabrasion threshold lower than that usedfor preliminary testing. The test apparatusis designed to accommodate various flowand abrasion levels. Currently there arethree potential levels for the testing:

■ Level “L” (Low) – non-abrasive condi-tions of no bedload and very lowvelocities (< 5 fps).

■ Level “I” (Intermediate) – abrasiveconditions with bedloads and velocities

representing the predominate expectedfield conditions. (TBD per test objec-tives)

■ Level “H” (High) – highly abrasivebedload designed to accelerate fieldabrasion conditions. The test condi-tions shall mimic those used in thedevelopment of the protocol: >10fpsvelocity of a seawater medium and 3/4-inch trap rock bedload, 25 tons in tendays.

The physical properties of the candi-date material will be closely monitoredthrough the test. For organic, barrier-typecoatings damage is quantified by measur-ing the electrical resistance between thecorrugated pipe and an internal electrode.In addition the % coating loss is deter-mined. For metallic coatings, the electro-chemical potential and the coatingthickness are measured to indicate coatingloss.

Field Testing

Field performance data is an excellentmeans of giving confirmation to results oflaboratory testing and at the same timepresenting an opportunity for improve-ment of the candidate material.


National Corrugated Steel Pipe Association1255 Twenty-Third Street, NWWashington, DC 20037-1174Phone: 202.452.1700 ■ Fax: 202.833.3636Email: [email protected] ■ www.ncspa.org

American Iron and Steel Institute1101 17th Street, NW, Suite 1300Washington, DC 20036-4700www.steel.org/infrastructure

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