TR-113584-V3

Steel Penstock Coating and Lining RehabilitationA Hydropower Technology Roundup Report,Volume 3

Technical Report

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WARNING:Please read the License Agreementon the back cover before removingthe Wrapping Material.

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EPRI Project ManagerM. A. Blanco, P. E.

EPRI 3412 Hillview Avenue, Palo Alto, California 94304 PO Box 10412, Palo Alto, California 94303 USA800.313.3774 650.855.2121 [email protected] www.epri.com

Steel Penstock-Coating andLining RehabilitationA Hydropower Technology Roundup Report, Volume 3TR-113584-V3

Final Report, August 2000

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CITATIONS

This report was prepared by

HCI Publications 410 Archibald Street Kansas City, MO 64111

Principal Investigator M. A. Hosko C. Vansant

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Steel Penstock-Coating and Lining Rehabilitation: A Hydropower Technology Roundup Report, Volume 3, EPRI, Palo Alto, CA: 2000. TR-113584-V3.

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REPORT SUMMARY

Steel penstocks and the coating and lining systems that enhance their structural integrity and serviceability are part of the infrastructure for a majority of the worlds hydroelectric projects. This Hydropower Technology Roundup report aims to provide managers and technical staff responsible for hydropower plants with up-to-date information to enable them to assess the need for and implement the cost-effective rehabilitation of steel penstock coatings and linings.

Background One million meters of penstock are in-service in North America, and at least 2.5 million meters are in service through out the world. Coatings and linings are key to managing the structural integrity and serviceability of penstocks, providing corrosion protection, water tightness, and aesthetics. Yet, because of the latent nature of coating or lining problems, the continual advancements in coating/lining technologies, and evolving OSHA and environmental protection regulations, expertise in coating and lining management among hydropower project staff is limited. While much information about coating and lining technologies exists, it is not organized to provide guidance to help hydropower staff cost-effectively manage steel penstock coating and lining rehabilitation. This report aims to fill this information gap.

Objective To clarify the penstock coating and lining information needed by EPRI Hydro Target

members and other hydropower producers

To describe the state-of-the-art materials and best practices for the refurbishment of steel penstock coatings and linings

To present recent case studies of penstock coating and lining applications

To develop and provide a generic specification that individual companies can adapt for their own use when requesting bids for and managing coating and lining rehabilitation work.

Approach The investigators assembled and reviewed pertinent and recent conference reports, publications, and other literature on the maintenance, repair, and replacement of steel penstock coatings and linings. They surveyed EPRI member organizations to help determine what information was relevant and surface current issues and perspectives on coating and lining challenges. They consulted individual industry experts to provide state-of-the-art information on penstock coating and lining rehabilitation practices and collected product-specific information from product manufacturers. This information, including a standardized specification template for use during coating and lining rehabilitation, was peer reviewed at an EPRI Forum on Steel Penstock

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Coating and Lining Rehabilitation held during the fourth quarter of 1999. Finally, the investigators contacted selected hydropower companies to provide case study material.

Results This Hydro Tech Roundup report provides an understanding of the elements necessary for undertaking rehabilitation work whether maintenance, repair, or replacement of coatings and linings of in-service steel penstocks. It includes a standardized specification on diskette, describes several case studies, and provides listings of useful information sources, contacts, and websites. It also provides insights into ongoing research regarding steel penstock coating and lining and future trends.

EPRI Perspective Faced with competition, increasingly rigorous environmental standards, and on-going licensing requirements, hydropower project owners need to know about the technology options available and under development to make their facilities more compliant, protective of the environment, and competitive. They need information about the benefits and costs of alternative technologies and the successful practices and strategies used for their implementation. EPRIs Hydropower Technology Roundup report series will provide a clearinghouse for worldwide information on key topics and new and emerging technologies, including case studies and resources. This volume presents an overview of the state-of-the-art of steel penstock coating and lining rehabilitation, including inspection, condition assessment, and execution, and provides a specification template on diskette to facilitate rehabilitation work. Technology Roundup reports are published several times a year.

Keywords Coatings Linings Rehabilitation Steel Penstocks Hydro Hydropower

EPRI Licensed Material

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ACKNOWLEDGMENTS

Special thanks and acknowledgment are made to those individuals and organizations whoseassistance and contributions have been helpful during the development of this report.

As consultants and contributors:Thomas L. Kahl, Kleinschmidt Associates, Pittsfield, MERichard D. Stutsman, Jeffco Painting and Coating, Vallejo, CA

For hosting the Steel Penstock Forum:Matthew Gass, Hetch Hetchy Water & Power, Moccasin, CA

The following contributors provided information and perspectives via personal communications:Tom Bortak, Bureau of Reclamation, Denver, CONiels Nielsen, BC Hydro/Powertech Labs, Burnaby, British ColumbiaDavid L. Parry, BC Hydro, Vancouver, British ColumbiaYoga Yogendran, BC Hydro/Powertech Labs, Burnaby, British Columbia


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CONTENTS

1 UNDERSTANDING THE SITUATION....................................................................................1-1A Brief History of Steel Penstocks and Coatings/Linings......................................................1-1Defining the Scope of the Coating and Lining Rehabilitation ................................................1-3

Objectives.........................................................................................................................1-3Exterior Coating Alternatives............................................................................................1-3Interior Lining Alternatives................................................................................................1-3

Report Organization ..............................................................................................................1-4

2 INSPECTION AND CONDITION ASSESSMENT OF STEEL PENSTOCKS ........................2-1Steel Penstock Inspection.....................................................................................................2-1Coating and Lining Condition Assessment ...........................................................................2-5

Common Defects and Failure Modes...............................................................................2-5Coating and Lining Inspection Instruments ......................................................................2-6Coating and Lining Condition Description ........................................................................2-7Overall Condition Assessment .........................................................................................2-9Development of Alternatives ............................................................................................2-9

3 STATE-OF-THE-ARTSTEEL PENSTOCK COATING AND LININGREHABILITATION.....................................................................................................................3-1

Coating and Lining System Materials....................................................................................3-1Exterior Coating Systems.................................................................................................3-4

Zinc primer/acrylic topcoat...........................................................................................3-5Zinc primer/epoxy/urethane topcoat ............................................................................3-5Moisture-cured zinc/urethane ......................................................................................3-5Bitumastic coal tar .......................................................................................................3-5

Interior Lining Systems.....................................................................................................3-6Epoxy primer and topcoat............................................................................................3-6Primer and 100% solids epoxy topcoat .......................................................................3-6


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Single component elastomeric polyurethane...............................................................3-7Plural component100% solids polyurethane ............................................................3-7Plural component100% solids polyurea ...................................................................3-7

Water-tight Liner Considerations......................................................................................3-8Water-tight liner strength .............................................................................................3-8Single versus plural component materials for water-tight liners ..................................3-8

Surface Preparation ..............................................................................................................3-9Application Techniques .......................................................................................................3-12Quality Assurance ...............................................................................................................3-14

4 GETTING THE JOB DONEGENERIC SPECIFICATIONS AND OTHERCONSIDERATIONS ..................................................................................................................4-1

Development of a Generic Specification ...............................................................................4-1Manufacturers and Material Selection...................................................................................4-4

Job Structure and Manufacturers Representatives .........................................................4-4Other Commercial Considerations ........................................................................................4-8

Contractor Qualifications ..................................................................................................4-8Inspection Options............................................................................................................4-8Value of Lost Project Benefits During Rehabilitation........................................................4-9Additional Warranties .......................................................................................................4-9Added Generation Benefits ..............................................................................................4-9Cost and Schedule Estimates ..........................................................................................4-9

Ongoing Laboratory and Field Test Programs ....................................................................4-11Current Test Programs...................................................................................................4-12

Coating rust ...............................................................................................................4-12Multiple overcoating assessment...............................................................................4-13

Future Trends and Potential Areas for Coatings and Lining Improvement .........................4-13Materials.........................................................................................................................4-13Surface Preparation .......................................................................................................4-14Application......................................................................................................................4-14

5 CASE STUDIESSTEEL PENSTOCK COATING AND LINING REHABILITATION ..........5-11 Inspection, Condition Assessment, and Alternative Action PlansMoccasin,California ..........................................................................................................................5-1

Project Background .....................................................................................................5-1Holm Project Penstock............................................................................................5-2


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Kirkwood Project Penstock .....................................................................................5-2Moccasin Project Penstocks ...................................................................................5-2

Inspection and Condition Assessment.........................................................................5-3Site Conditions.............................................................................................................5-3Recommendations and Action Plan for Hetch Hetchy Moccasin Penstocks ...............5-3Materials and Engineers Opinion of Budgetary Costs and Schedules .......................5-3

2 Penstock Coating MaintenanceBC Hydro, British Columbia .....................................5-4Project Background .....................................................................................................5-4BC Hydros Approach to Condition Assessment .........................................................5-5Project Background .....................................................................................................5-6Inspection and Condition Assessment.........................................................................5-6Scope of Work .............................................................................................................5-6Site Conditions.............................................................................................................5-6Surface Preparation.....................................................................................................5-6Application ...................................................................................................................5-7Quality Assurance and Inspection ...............................................................................5-7Cost and Schedule ......................................................................................................5-7

3 Exterior CoatingMoisture Cured UrethaneBureau of Reclamation, Idaho..............5-7Project Background .....................................................................................................5-7Inspection and Condition Assessment.........................................................................5-7Scope of Work .............................................................................................................5-8Site Conditions.............................................................................................................5-8Materials ......................................................................................................................5-8Surface Preparation.....................................................................................................5-8Application ...................................................................................................................5-9Quality Assurance and Inspection ...............................................................................5-9

4 Interior LiningKingston Mills, Ontario, Canada...........................................................5-9Project Background .....................................................................................................5-9Inspection and Condition Assessment.........................................................................5-9Scope of Work .............................................................................................................5-9Materials ......................................................................................................................5-9Surface Preparation.....................................................................................................5-9Application .................................................................................................................5-10Cost and schedule .....................................................................................................5-10


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Added Benefits ..........................................................................................................5-105 Interior Lining100% Solids PolyurethaneEl Dorado, California ............................5-10

Project Background ...................................................................................................5-10Inspection and Condition Assessment.......................................................................5-10Scope of Work ...........................................................................................................5-11Site ConditionsAccess and Weather......................................................................5-11Materials ....................................................................................................................5-11Surface Preparation...................................................................................................5-12Application .................................................................................................................5-12Quality Assurance and Inspection .............................................................................5-12Cost and schedule .....................................................................................................5-13Added Benefits ..........................................................................................................5-13

6 Interior Lining100% Solids PolyurethaneClarks Falls, Vermont ..........................5-13Project Background ...................................................................................................5-13Inspection and Condition Assessment.......................................................................5-13Scope of Work ...........................................................................................................5-14Site Conditions...........................................................................................................5-14Materials ....................................................................................................................5-14Surface Preparation...................................................................................................5-14Application .................................................................................................................5-14Quality Assurance and Inspection .............................................................................5-15Cost and Schedule ....................................................................................................5-15

7 Interior LiningHigh Solids Elastomeric PolyurethaneSalisbury, Vermont .............5-15Project Background ...................................................................................................5-15Inspection and Condition Assessment.......................................................................5-16Scope of Work ...........................................................................................................5-16Materials ....................................................................................................................5-16Surface Preparation...................................................................................................5-17Application .................................................................................................................5-17Quality Assurance and Inspection .............................................................................5-17Cost and Schedule ....................................................................................................5-17

6 REFERENCES AND RESOURCES.......................................................................................6-1References............................................................................................................................6-1Resources .............................................................................................................................6-2


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Manufacturers/Instrument Suppliers .....................................................................................6-3

A GENERIC STEEL PENSTOCK COATING AND LINING REHABILITATIONSPECIFICATION ...................................................................................................................... A-1

Generic Steel Penstock Coating and Lining Rehabilitation Specification .............................A-1Part 1GENERAL................................................................................................................A-1

Description of Work ..........................................................................................................A-1Site Conditions .................................................................................................................A-2Reference Standards and Codes .....................................................................................A-3Other Requirements: Safety and Environmental ..............................................................A-4Quality Assurance and Quality Control (QA/QC)..............................................................A-4Submittals.........................................................................................................................A-5

Part 2PRODUCTS.............................................................................................................A-5Delivery, Handling and Storage........................................................................................A-5Surface Preparation Products ..........................................................................................A-6Exterior Coatings..............................................................................................................A-6Interior Linings..................................................................................................................A-7Touch-Up Materials ..........................................................................................................A-7

Part 3EXECUTION ............................................................................................................A-7Work Sequence................................................................................................................A-7Penstock Access ..............................................................................................................A-8Surface Preparation .........................................................................................................A-8Repair of Steel Defects ....................................................................................................A-9Application......................................................................................................................A-10Inspection and Tests ......................................................................................................A-11Repairs and Remedial Coating Work .............................................................................A-13Final Acceptance............................................................................................................A-13


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LIST OF FIGURES

Figure 4-1 Relative Cost Exterior and Interior Coating and Lining Rehabilitation....................4-11


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LIST OF TABLES

Table 1-1 Principal Methods of Joining Steel Plates and Penstock Seams...............................1-2Table 2-1 Steel Penstock Inspection Information ......................................................................2-2Table 2-2 Steel Penstock Physical Condition Inspection...........................................................2-4Table 2-3 Coating and Lining Inspection Techniques, Instruments, and Uses..........................2-6Table 2-4 Adhesion Test, ASTM Test Method 3359 Cross Hatch Rating Scale........................2-7Table 2-5 Description of Coating/Lining Condition.....................................................................2-8Table 2-6 Sample Coating and Lining Inspection Form...........................................................2-10Table 3-1 Selection of Coating/Lining Systems .........................................................................3-2Table 3-2 Generic Steel Penstock Exterior Coating and Interior Lining Specification

Options...............................................................................................................................3-4Table 3-3 Comparison of Performance and Service Life Properties for Internal Water-

tight Penstock Liners..........................................................................................................3-9Table 3-4 Surface Preparation Techniques .............................................................................3-10Table 3-5 Application Techniques............................................................................................3-13Table 3-6 Quality Assurance Techniques................................................................................3-15Table 3-7 Sample QA/QC Inspection Report...........................................................................3-16Table 4-1 General Specification Contents .................................................................................4-2Table 4-2 Generic Steel Penstock Coating and Lining Specification Contents .........................4-3Table 4-3 Available Materials for Exterior Coating Systems......................................................4-5Table 4-4 Available Materials for Interior Lining Systems..........................................................4-7Table 4-5 Penstock ParametersImpacts on Rehabilitation ..................................................4-10


1-1

1 UNDERSTANDING THE SITUATION

It is estimated that there are nearly 3 million feet of in-service penstock in North America,perhaps at least 8 million feet worldwide. Many hydroelectric projects have steel penstocks thathave not been relined or re-coated for many years and which, at the very least, deservecompetent evaluation as to the condition of existing linings and coatings. Determinations need tobe made as to when relining/re-coating is required.

Where relining/re-coating is indicated, selecting appropriate materials and methods ofapplication deserves special attention. The state-of-the-art for relining/re-coating systems (bothmaterials and application methods) has evolved rapidly in recent years and, typically, simplyrestoring existing systems is neither feasible nor desirable.

Failure to perform timely relining/re-coating can, however, be costly in terms of requirements toperform excessive maintenance, or replacement on deteriorating systems. Also, energyproduction losses can mount due to interior surface roughness. And the prospect, howeverremote, of penstock failure due to wall thinning and corrosion is almost always worth avoiding.

Evaluation of an in-service penstock for structural strength and serviceability should be includedin any penstock rehabilitation project, and there are many sources for information. However,while much literature and specification exists for coatings and linings in general, very littleguidance exists for the specific area of coating and lining rehabilitation. Assuming that thepenstock structural strength meets design criteria, or current operating conditions, how does oneaddress serviceability concernscorrosion protection, appearance, and water-tightness? Theobjective of this Tech Roundup report is to answer this question and provide information onrehabilitation.

A Brief History of Steel Penstocks and Coatings/Linings

The original design of in-service penstocks and the coating and lining systems used have directbearing on the type of rehabilitation to be performed. The following discussion should beconsidered general background information on the history of in-service steel penstocks.[21]

While there has been considerable variation in the methods used for fabricating variouspenstocks over the years, Table 1-1 is a general guide to fabrication technologies used forconstructing penstocks from steel plates.


Understanding the Situation

1-2

Table 1-1Principal Methods of Joining Steel Plates and Penstock Seams

Longitudinal Seams(Shop Construction)

Circumferential Seams(Field Construction)

Steel PenstockVintage Riveted Forge-welded Welded1 Riveted Welded1

MechanicallyCoupled

Late 1800s1920 X X

19201925 X X

19251960 X X

1960present X X X1Gas or metal arc.

In general, exterior coatings systems were applied to steel penstocks as follows:

Coal tar based exterior coating materials were specified for penstocks up until the mid -1970s, primarily because of their excellent corrosion protection on steel, good penetrationand adhesion to marginally cleaned surfaces, and ease of application.

Some of the common exterior coating systems found in steel penstock rehabilitation workinclude:- Lead-based (>600 PPM) coatings, such as 1925 red-lead primer- Graphite paint (1925)- Cement mortar coatingscombinations of sprayed cement, sand, and water, with

excellent corrosion protection characteristics

Since the mid-1970s, exterior systems have been confined to two and three part organicprimer and topcoat(s).

Similarly, interior linings systems have changed over the years:

Linings used from the late 1800s to 1940 included molten coal tar with a 15- to 20-year life.The use of these systems was discontinued due to embrittlement over time, which resulted incracks. Many of these penstocks are candidates for relining for life extensions.

From 1940 to 1960, coal tar enamels were used with a 20- to 30-year life. Because of theidentification of the presence of carcinogens in products with high volatile organiccompounds (VOCs), use of coal tar enamel products with a high VOC content was largelydiscontinued. The emergence of environmental regulations controlling the use of materialswith VOCs also required additional compliance for application and removal.

1960 to 1980 saw the use of coal tar epoxies with a 15-year life. These products were only tobe applied in thin films (1216 mils) and were still a derivative of coal tar withenvironmental restrictions.



1-3

1980 to present has seen the increased use of high performance 100% epoxies with anexpected 25- to 30-year life.

Defining the Scope of the Coating and Lining Rehabilitation

Given the wide range of installed steel penstocks that one encounters in practice, therehabilitation of a particular project can involve a broad scope of design, operational, andmaintenance/life extension considerations. The distinction between strength and serviceability ofan in-service steel penstock must be made. This document specifically expands techniquesassociated with extending the serviceability of the structures with coatings and linings, assumingthat structural strength is not an issue. The reader is directed to other sources of information oninspection, evaluation, and rehabilitation of steel penstocks for strength and integrity.[2,3,4]

ObjectivesIt is important to define the objective of the coating/lining rehabilitation project, that is, whatpurpose the exterior coating or interior lining should achieve. The options are shown below.

Exterior Coatings: Corrosion Protection, and/or Appearance Interior Linings: Corrosion Protection, and/or Water-tightness

Based on the inspection and condition assessment, the coating/lining system alternatives can thenbe defined.

Exterior Coating Alternatives

The primary criteria for determining which exterior coating system to use are the standardconsiderations of cost, service life, site conditions, and condition of the existing steel. Thebiggest tradeoffs (cost and service life differences) for an existing penstock are in the surfacepreparation. If a coating system has failed and the steel substrate is rusting, full or partialremoval will be warranted. If the primer is still good, or only touch-up is required, overcoatingcan be done with minimal service preparation, to achieve increased service life at a lower costthan complete removal and re-coating.

The best alternative for certain existing penstocks may be no coating. If the penstock is in arelatively dry environment where rusting does not occur or occurs slowly, the rate of materialloss may be so slow that it may not be cost-effective to apply any protective coating.

Interior Lining Alternatives

An important step in choosing among interior lining options, is to determine whether the lining isonly for corrosion protection, or for both corrosion protection and water-tightness. Two commonexamples where water-tightness can be a desired characteristic are:



1-4

A riveted penstock where the rivets are still structurally sound but there is seepage throughthe seams. Continued seepage can induce rivet corrosion and loss of strength.

A shell that has too many pinholes to weld repair, and yet has enough strength to resist all theloads. In this case, an internal lining can be particularly useful where the pipes exterior isinaccessible, such as, where the pipe passes through a concrete thrust block or bridgeabutment.

As with the exterior coatings, benign neglect is also an alternative. Numerous penstocks, usuallyburied, exist where the shells interior surface after the internal biological growth and tuberclesare removed is not rusted or cratered, and there has not been appreciable loss of material to thecritical penstock members (e.g., shell). An internal liner would probably not be necessary forthese penstocks.

Report Organization

Based on the clear need and interest in the topic of steel penstock coating and liningrehabilitation, this document was designed around the following elements:

AudienceThe hydro project owner faced with an aging steel penstock, experiencingserviceability concernsappearance, deterioration, pitting and/or corrosion, leaking, metalloss, and perhaps hydraulic head loss.

ScopeThis document focuses on in-service steel penstocks, both exposed and buried orencased penstocks.

TerminologyThroughout the document, coating refers to materials applied to exteriorsurfaces, and lining refers to materials applied to interior surfaces.

Codes, Standards, and ReferencesThe industry has excellent resources related to steelpenstock rehabilitation. The application of these resources is referenced extensively withinthe document.

PurposeAssuming structural strength is not an issue, when does a penstock need to be re-coated or relined? The document discusses inspection and rating systems for exterior orinterior coating/linings that aid in making this decision.

FocusTo provide information on the state-of-the-art in products and techniques, as well asa useful toola generic specification for application to rehabilitation projects.

This report is organized into five subsequent sections that describe how to successfully develop aplan and execute a coating and lining rehabilitation project scope:

Section 2Inspection and Condition Assessment discusses:

- How to inspect the condition of the aging penstock- How to analyze the condition and what is needed to rehabilitate the coating/lining system

for the operating conditions



1-5

Section 3State-of-the-art contains:

- Information on materials to help select the right coating/lining system

- How to prep the surface to match the system and condition- How to apply materials, and what equipment and techniques are and should be used- How to monitor, and assure a quality job- both during and after performance of the work

Section 4Getting the Job DoneDevelops a Generic Coating/Lining Specification, and otherconsiderations. It also discusses Ongoing Research and Future Trends.

Section 5Case Studies of Steel Penstock Coating and Linings presents several case studies andlessons learned.

Section 6References and Resources provides information sources, contacts, and websiteinformation.

Appendix A contains the Generic Specification developed specifically for this report.


2-1

2 INSPECTION AND CONDITION ASSESSMENT OFSTEEL PENSTOCKS

Several key guidelines have been recently prepared by the hydroelectric industry to assess theconditionstrength and structural integrityof in-service penstocks.[2,3,4] While the scope ofthis document is steel penstock coating and lining rehabilitation, it is essential to understandwhat affects the overall condition of the penstock, and the reader is directed to these documentsto gain a thorough background.

Steel Penstock Inspection

Coating and lining inspection is part of a comprehensive inspection program for steel penstocks.The coating and lining inspection and evaluation is conducted to analyze the condition of thepenstock and determine what is needed to update the coating/lining system as appropriate for theoperating conditions.

The first step in a comprehensive inspection program is to gather information about the designand operating history of the penstock as well as the physical environment, as outlined inGuidelines for Evaluating Aging Penstocks.[2]

Necessary information includes:

Design and construction history History during operation Physical condition assessment

Table 2-1 expands on the informational needs in these areas.

The next step is a physical condition inspection, which is a key part of developing plans andrecommendations for rehabilitation. The referenced document, Guidelines for Inspection andMonitoring of In-Service Penstocks is a useful guide for a comprehensive inspection program.[3]This inspection program could include:

Exterior inspection

Interior inspection

Geotechnical inspection

Control structures and electrical/mechanical equipment inspection


Inspection and Condition Assessment of Steel Penstocks

2-2

Table 2-1Steel Penstock Inspection Information

Topic Information Detailed InformationDesign and

constructionhistory Design drawings Current as-builts

Design criteria Internal and external loadsConstruction materialsType of flowOther design allowances

Foundation information (geologyand soils)

Drill logsHistory of seismic activity

Design calculations Hydraulic, structural, geotechnical, andoperational

Supplier or fabricator information Specifications, drawings, testingConstruction information Field records and changes, as-built

drawings, photographsHistory duringoperation

Records and observations SafetyLeakageSettlementHorizontal and vertical movementSlope stability observationsGeometric changesDrainage and groundwater levelsEquipment changesThermal/weather conditionsRemedial actions taken

Operating characteristics Existing conduit and equipment valve andgate closure timesFlow restrictions and operations

Steady state conditions Operating recordsReservoir rule curvesHeadwater and tailwater rating curvesGenerating (or pumping) utilization

Unsteady state or transient flowconditions

Load acceptance and rejectionValve openings and closingsWater column separation

Proposed changes to existingoperations

Any future expected modifications



2-3

Table 2-1(Continued)

Physical conditionassessment

Dimensions and shape

Inside surfacesOutside surfacesPenstock supportVibrationGeotechnical Ground movements

Water related effectsSurrounding slopesRock and soil tensionTunnel portalsFoundation testingAnchor/thrust blocksAlignmentDewatering/ liner drainsTunnel liner grout portsStandpipes/surge tanksOperating equipmentSpecial appurtenances

Cold weatherassessment

Freeze-thaw effects

Seismicassessment

Ground movementSlope movementEmergency ActionPlan/instrumentation

Corrosion conditionassessment

Exterior/interior ConditionWall thicknessCathodic protection

Thermalassessment

Temperature differentials

Acousticalassessment

Sound transmissionSound reflectionSafety regulations

Water-tightness Freeze thaw damage, vegetationgrowth, invertebrate development

Exterior loadings Buried penstocks-soil/groundwaterPenstocks on supports

Water quality Sediment load, pH, chemistryReference: Guidelines for Evaluating Aging Penstocks, ASCE 1995.[2]



2-4

Table 2-2 summarizes the information gathered during a physical condition inspection.

Table 2-2Steel Penstock Physical Condition Inspection

Inspection Components Inspection TechniquesExterior inspection Configuration: distortion, settlement Visual observations, survey methods

Joints: welds and rivets Visual observationOther features: anchor blocks, thrustrings, rocker and slide supports,saddles, and ring girders

Visual observation

Leakage Visual observationVibration Visual observationCoatings Visual observationWall loss: corrosion Visual observation

Non-destructive testing (NDE)Destructive testing (DT)

Interior inspection Configuration: distortion, settlement Visual observation, survey methodsJoints: welds and rivets Visual observationOther features: drains, grout holes Visual observationLeakage Visual observationLinings Visual observation and testingWall loss: corrosion Visual observation

Non-destructive testing (NDE)Destructive testing (DT)

Geotechnicalinspection

Geologic setting History and hazard review

Alignment Field reconnaissanceFoundation Field reconnaissanceInstrumentation Review records

Control structuresand electrical/mechanicalequipmentinspection

Shut-off systems:Intake gatePenstock valveTurbine shut-off valve/wicket gatesAutomatic shut-off systems

Visual observationOperational testingEmergency operation testing

Hydraulic systems:TurbinesPumps

Visual observationOperational testingEmergency operation testing

Other: valves, breakers, governors Visual observationOperational testingEmergency operation testing

Reference: Guidelines for Inspection and Monitoring of In-Service Penstocks, ASCE 1998.[3]



2-5

Coating and Lining Condition Assessment

A comprehensive inspection program will undoubtedly turn up the need for coating and liningrehabilitation and other essential rehab work. Once it has been determined that coating/liningrehab work is necessary, the owner should more thoroughly assess the condition of the existingcoating and lining systems. A coating and lining survey can generally take the form of aninspection, ideally by station or by selected periodical locations along the alignment. A samplesurvey form has been included as a useful tool to document the condition of existing coatingsand lining, and to assess the scope of the rehab project. The following terminology could be usedwhen conducting a survey for purposes of consistency and comparisons over time.

Common Defects and Failure Modes

These terms, which are consistent with the definitions provided in recent publications, may beused when conducting a coating/lining survey.[3] BlisteringTrapped water or solvents reacting with the metal or contaminants in or under

the coating create pressure that is evidenced by blistering. Low profile blisters or open,ruptured blisters are indicators of the state of the coating adhesion. Abrasion will openblisters, exposing steel to more active corrosion.

AdhesionFlaking and lifting as well as blistering are indications of poor coating bonding,usually as a result of insufficient or improper surface preparation. Adhesion testingbymaking a series of parallel cuts to the substrate, applying and removing tapemay revealdirt, scale, or other foreign matter under the coating, which can cause breakdown.

DelaminationThis condition is the same as adhesion except that separation is between thecoating layers.

Voids, bubbles, pinholes, holidays, and cratersCaused when air is entrapped in the coating,usually occurring during spraying. The bubble that develops may break later and create apinhole, which can cause corrosion. The coating system applied over a deep anchor profilemay not be thick enough to cover the profile and could result in pinhole corrosion, referred toas holidays.

FadingUltraviolet light exposure may cause the top layer to fade. CheckingSlight breaks in the film that do not penetrate to the substrate, but show the

undercoat. CrackingDeep cracks extending to the substrate caused by coating shrinkage or excessive

thickness.

UndercuttingBlistering or peeling of the coating where exposed corroded steel is causingadjacent coating to lift.

Abrasion damageDamage caused by mechanical motion of particles on mating parts. Mud-cracking or alligatoringExtensive, wide cracks or breaks in the coating film that do

not penetrate the substrate.



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Mildew growthOccurs in damp shaded areas of an exposed penstock; caused by fungalgrowth.

Chalking erosionGradual thinning of the finish coat, exposing the undercoats. BleedingSurface flotation of the undercoats to the topcoat.

Coating and Lining Inspection Instruments

Table 2-3 summarizes various inspection instruments and tests and their purposes. Non-destructive examination (NDE) and destructive techniques (DT) are included.

Table 2-3Coating and Lining Inspection Techniques, Instruments, and Uses

Technique NDE/DT1 Description UsesVisual (VT) NDE Visual observation Cracks, pinholes, defectsKnife/pick DT Hand held tool Check for defect depthRule NDE Hand held tool Check for defect depthPit Gage NDE Hand held tool Measures depthTape Adhesion TestASTM D-3359

DT Method A: X-cuts to substrate,apply and pull-off tapeMethod B: Parallel cuts tosubstrate, apply and pull-off tape

Checks for coatingadhesion to substrate

Tensile Adhesion TestASTM D-4551

DT A test dolly is adhered to thesurface and force is applied untileither the test poundage isreached or the dolly is detached

Checks tensile adhesionstrength

Dry Film ThicknessSSPC-PA-2Measurement of DryPaint Thickness withMagnetic Gages

NDE Magnetic pull-off (Type I)Magnetic probe (Type II)For instrument description seeSection 3

Measures the coatingdry-film thickness (DFT)

Dry Film ThicknessASTM D-4138-94

DT Paint inspection gages (PIG)Scratch or Tooke gages cut across-section through the coatingfor examination with a microscope

Determines dry filmthickness (DFT)

Advanced Techniques:Liquid Penetrant (LT)Magnetic Particle (MT)Ultrasonic (UT)Radiography (RT)

NDE Instruments and procedures usedfor specific purposes

Cracks, steel thickness,coating or liningthickness, defect depths

1NDENon-destructive evaluation; DTdestructive test.Reference: Guidelines for Inspection and Monitoring of In-Service Penstocks, ASCE 1998.[3]



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Adhesion tests, conducted by the destructive pull method, result in a determination that thecoating/lining has either an adhesion failure defined as a failure between two distinct paintlayers or between the substrate and the first layer of paint, or a cohesion failure defined as afailure or break within one coat of paint (the coating/lining breaks within itself). This isparticularly useful when determining whether overcoating is warranted or a total removal and re-coating is required.

Coating and Lining Condition Description

The general objective of a coating/lining inspection is to rate the condition of the coating andlining.

Several rating schemes for evaluation of the coating/lining condition are used. One scheme is theASTM D-3359 Standard Test Method for Measuring Adhesion by Tape Test, which includes twomethods. The adhesion test is a qualitative test, which can be used to rate the adhesion of acoating/lining system.[14] The test consists of either Method A, an X-cut on the coating/liningfilm or Method B, a series of parallel cuts both horizontal and vertical made in the coating all theway down to the substrate. Tape is then applied and pulled off. The remaining coating in the areaaround the cuts is evaluated as shown on Table 2-4.

Table 2-4Adhesion Test, ASTM Test Method 3359 Cross Hatch Rating Scale

ClassificationMethod A ASTM Descriptions

ClassificationMethod B

ASTM Cross Hatch Rating Scalebasedon 6 parallel cuts

Class 5A No peeling or removal. Class 5B The edges of the cuts are completelysmooth; none of the squares of the lattice isdetached.

Class 4A Trace peeling or removalalong incisions or at theirintersections.

Class 4B Small flakes of the coating are detached atintersections; less than 5% of the area isaffected.

Class 3A Jagged removal alongincisions up to 1/16 in.(1.6mm) on either side.

Class 3B Small flakes of the coating are detachedalong the edges and at intersections of thecuts; The area affected is 5% to 15% of thelattice.

Class 2A Jagged removal alongincisions up to 1/8 in. (3.2mm) on either side.

Class 2B The coating has flaked along the edges andon parts of the squares. The area affected is15% to 35% of the lattice.

Class 1A Removal from most of thearea of the X under thetape.

Class 1B The coating has flaked along the edges ofthe cuts in large ribbons, and whole squareshave detached. The area affected is 35% to65% of the lattice.

Class 0A Removal beyond the area ofthe X.

Class 0B Flaking and detachment worse than Class 1.



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Other coating/lining rating schemes include the one contained in the SSPC-VIS 2/ASTMStandard D 610 and the 1998 ASCE guidelines.[17,3] A comparison of these is shown in Table2-5. The SSPC-VIS 2, Standard Method for Evaluating Degree of Rusting on Painted SteelSurfaces provides a pictorial standard to be used for comparative purposes representing variousamounts of visible rust on painted steel surfaces. The pictorial standard provides photographsthat compare the as-found condition (mill scale, mill scale and rust, 100% rust, and rust withpits) to the degree of cleaning executed (Brush-off Blast SSPC-SP 7, Commercial Blast SSPC-SP 6, Near-White Blast SSPC-SP 10, or White Metal Blast SSPC-SP 5). These verbal descriptorscan be widely interpreted by the inspector; however, the point is to apply a consistent measure ofthe degree of corrosion found during the inspection.

Table 2-5Description of Coating/Lining Condition

SSPC-VIS 2/ASTM D 610 StandardDescription of Rust Grades

ASCE GuidelineCoating/Lining Surface Rating Scheme

RustGrades Description

Grade/Level Description

10 No rusting, or < 0.01% ofsurface rusted.

9 Minute rusting, < 0.03% ofsurface rusted.

G1/Excellent Non-deteriorated coating/liningsurface, 0 to 0.1% surface corrosion.

8 Few isolated rust spots,



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Overall Condition Assessment

A suggested penstock inspection checklist was developed in the ASCE Guidelines. Itemsincluded in the checklist for a complete penstock inspection are:[3] Penstock shell

Couplings/expansion joints Joint conditions Penetrations

Anchor blocks Exposed support systems Coatings/linings

Buried/partially buried systems

Table 2-6 contains a sample coating and lining inspection form for use in completing a conditionassessment for each location along a penstock.

Development of Alternatives

Following an inspection of the condition of in-service penstocks, alternative actions forrehabilitation can be developed, including options for ongoing inspection, evaluation,monitoring, maintenance, and full rehabilitation.

Alternative action plan recommendations can be proposed based on some time schedule,depending on the size and scope of the rehabilitation. For example, these may includerecommendations for:

Immediate action (within the next year), Short-term action, such as a 1- to 3-year time frame, and Long-term action, such as a 3- to 8-year period.



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Table 2-6Sample Coating and Lining Inspection Form

SAMPLE COATING AND LINING INSPECTION FORM Page ___ of ___Station: Project: Date:Client Representative Inspector(s)

Penstock DescriptionDiameter Material Coating

Area/Access/Slope

Weather

Defects in Coating/Lining Location A B C D E

Tests Performed:

Overall Condition Assessment:

Blistering Delamination/Fading Voids/Craters/Pinhls

Checking/Cracking Mildew/Aq Gwth

Lining Adhesion

Test GradeDFT Test INTERIOREXTERIOR Steel Thickness

Coating Adhesion

Test GradeDFT Test Comments/Methods

NOTES

Station ( Orientation Looking Downstream)Lining

For purposes of this report, we define the following alternative actions:

Spot InspectionPerform a cursory spot inspection of coating and lining at several locationson the penstock during a one- or two-day period.

Coating/Lining InspectionPerform a detailed penstock coating and lining inspection,documenting the full length of the penstock, to include observations of leakage at rivets,seams, and welds.

Structural EvaluationPerform an engineering assessment of structural strength of theexisting penstock based on its actual documented condition.

Maintenance PatchingRequires wire brush or power tool removal of loose coating/liningmaterials, collection of debris, application of primer and topcoat with either the same or acompatible material.



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Over-coatMay require high pressure water washing to remove loose coating materials,collection of wash water, application of primer and topcoat of a material that will adhere toexisting coating material.

Re-coatMay require high pressure water washing to remove loose coating materials,collection of wash water, performance of the appropriate level of SSPC standard abrasivesurface preparation for the selected material, prime and topcoat with the coating material.

RelineMay require high pressure water washing to remove loose lining materials,collection of wash water, performance of the appropriate level of SSPC standard abrasivesurface preparation for the selected material, and application of the lining material.

Deciding on a plan of action includes considerations of schedule, budgetary costs, and materials.Determination as to whether to over-coat or remove and re-coat is often a difficult decision. Forexternal coatings, the over-coat alternatives include both maintenance spot patching and a totalover-coat . When rusting and corrosion first appear, it is generally acceptable and cost effectiveto extend the service life of the penstock by spot repair. This is essentially localized overcoatingas the loose material is removed by hand- or power-tools and a repair is made, usually of thesame material.

The decision to discontinue maintenance spot repair and install a totally new overcoat or removeand re-coat is typically based on economics comparisons between the value of periodicmaintenance expenses and the cost of a new system. Almost always, the cost of overcoating isless than the cost for total removal of the existing system and re-coating, and if correctly applied,can provide service lives in excess of 20 years. However, it is important to ensure that anexisting system can be effectively over-coated by evaluating the extent of the corrosion on theexisting surface, the total thickness of the existing coating, and the adhesion of the existingcoating layers.

Generally, penstocks with 3% to 10% of the total exterior surface area rusted may be candidatesfor overcoating. As discussed above, non-destructive testing can be performed to determine thedry film thickness of the existing coating and the number of layers or coats. Generally, existingcoating systems less than 20 mils can be successfully over-coated. Finally, the critical parametersfor determining whether an existing system will support an additional layer of coating are theadhesion criteria. As discussed, adhesion test can be conducted by either the pull-off tape method(ASTM D-3359) or the adhesion dolly method (ASTM D-4551). Intra-coat, inter-coat, andsubstrate adhesion results should show a 5 (A or B) for the tape test, and preferably pull offstresses exceeding 300500 psi from the Elcometer test for the overcoat to be successful.

When evaluating over-coat materials, it is prudent to first apply some material test patches inrepresentative locations and monitor performance for a few seasons. Frequently, this can be doneas part of an interim spot maintenance repair program. It is important that the test patches havethe same level of surface preparation that would be used in a large scale overcoating program.Discussions with the material manufacturers to determine the applicability of the materials to theexisting system also proves invaluable in selecting the appropriate course of action.



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Where relining/re-coating is indicated, selecting appropriate materials and methods ofapplication deserves special attention. The following sections discuss these elements as well asspecification elements for various conditions.


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3 STATE-OF-THE-ARTSTEEL PENSTOCK COATINGAND LINING REHABILITATION

Coating and Lining System Materials

This section outlines what coating/lining system to recommend and specify for the conditionsencountered, taking into consideration surface preparation, application techniques,environmental and physical constraints, and ways to ensure a quality job.

The Society for Protective Coatings (formerly the Steel Structures Painting Council, SSPC) hasformulated descriptions of various industrial environmental exposures or zones. For purposes ofsteel penstock applications, both exterior and interior, the coating/lining system is defined asfresh water immersion. Additional factors involved in selecting an appropriate coating /liningsystem include:

The existing condition of the surfacecorrosion (pitting), water-tightness (leaking), etc. Type of surface to be coatedriveted joint construction or welded Life or serviceability needs Surface preparationcost associated with condition and accessibility Service and application temperatures and conditions, both weather and steel temperature Final appearance (gloss or color) for applications Value of a quick cure time to reduce loss of generation during the job (for interior lining

projects)These items are discussed below and are summarized on Table 3-1.

The overall purpose of the system servicecorrosion/appearance or water-tightnesshas beendiscussed previously, and is the key to the family of coating/lining products to be considered.


State-of-the-ArtSteel Penstock Coating and Lining Rehabilitation

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Table 3-1Selection of Coating/Lining Systems

Basis Inspection System Purpose Considerations ConditionsSystem

Selection

Structuralconditionokay?

Performexteriorinspection

Exterior corrosionprotection/appearance

Operatingenvironment

Temperate

High light

Humid

Standard epoxy

UV protection

Moisture-cured

Service life Short

Longer

Bitumastic

Other systems

Structuralconditionokay?

Performinteriorinspection

Interior corrosionprotection or water-tightness or both?

Corrosion protection-

(Thin mil lining)Lost generation

Service life

Longer cure time

Shorter curetime/longer life

Epoxy

100% epoxy

Water-tightness andcorrosion protection

(Thick mil lining)

Lost generation

Service life

Applicationtemperature

Longer cure time

Long life

Applicationtemperaturerestrictions

Singlecomponentmaterials

Lost generation

Service life

Applicationtemperature

Shorter cure time

Long life

More flexibletemperatureconditions

Pluralcomponentmaterials

The construction joints and discontinuities on the exterior of penstocks pose special problemsthat must be assessed on a case-by-case basis. As an example, penstocks that are supported onsteel or concrete saddles will experience corrosion between the shell and their contact to thesaddle. These areas need to be cleaned and painted as well as possible, which is difficult toaccomplish. The areas of contact should be caulked to prevent water from entering and causingfurther corrosion. A pathway for drainage should be incorporated at a low point.

Welded or riveted connections should receive a strip coat to ensure adequate film build-up forcorrosion protection. Appurtenances, such as manholes or other extensions, should not bepainted closed.



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The decision to proceed with a rehabilitation coating or lining project can also includeconsideration of the service life of the new material. Generally, these may fall into the followingexpectations are reasonable:

Exterior Coatings: 1015 years Interior Linings: 2025 years

Generally, the range of service life is related to the surface preparation achieved, with shorterlives being related to poorer quality adhesion. The ability to achieve good surface preparation isinfluenced by access and site conditions, and surface preparation remains the single most costlyprocess for both interior and exterior applications.

The operating environment is also key to the selection of an appropriate coating/lining system.There are a number of manufacturers of coatings and linings that can respond to varyingenvironmental and atmospheric conditions. Matching the system to the need involvesconsideration of all these factors. In addition, the manufacturers recommended surfacepreparation, temperature parameters, and final dry film thickness (DFT) are essential to asuccessful application.

Interestingly enough, selection of color does come into play. For interior applications, lightcolors tend to allow for easier illumination during subsequent inspections. Exterior colorselection can be influenced by ambient temperatures. For example, in northern regions, lightcolors can promote ice formation. Extremes of hot ambient temperature on dark coloredpenstocks may induce large thermal movements.

Finally, for interior applications, the value of lost generation during an outage could be anelement in the selection of a coating that allows for quick cure for immediate immersion service.

Table 3-2 outlines general recommendations for exterior coating and interior lining systems. Forcompleteness, the surface preparation requirements and final thickness ranges are included.These parameters are discussed in subsequent sections. Specific manufacturer products arediscussed in Section 4 and further discussions with manufacturers representatives on the specificapplication is always recommended.



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Table 3-2Generic Steel Penstock Exterior Coating and Interior Lining Specification Options

Service/Purposeof Coating Coating Material Options Surface Preparation1

Final CoatingThickness

Corrosion protectionand /or appearance

Zinc primer/acrylic topcoat, orZinc primer/epoxy intermediatecoat/ urethane topcoat

Remove original coating2 bySSPC-SP 6 or 10

Thin mil coating(49 mils)

Corrosion protectionand /or appearance

Moisture-cured urethane Over-coat marginally cleanedsteel or top-coat over tightlyadhered old coatingSSPC-SP 2, 3, or 6


Corrosion protection Bitumastic coal tar Over-coat marginally cleanedsteel or top-coat over tightlyadhered old coatingSSPC-SP 2, 3, or 6Remove loose rust and oilgrease etc.(SSPC-SP 2, 3, or 10)


Service/Purposeof Lining Lining Material Options Surface Preparation1

Final LiningThickness

Corrosion protection Primer and epoxy topcoatPrimer and 100% solids epoxy

Remove original lining2 byeither SSPC-SP 5 and/or 10

Thin mil lining(



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Zinc primer/acrylic topcoat

The zinc base coat provides corrosion protection and is applied after surface preparation asrecommended by the manufacturer.

The acrylic topcoat adds color but is short-lived and requires re-coating at 5- to 10- yearintervals. However, provided no breakdown of the coating system is noted, maintenance staff canusually re-coat to restore appearance directly over the existing system.

Zinc primer/epoxy/urethane topcoat

This option provides significantly more corrosion protection than the primer/topcoat system. Theepoxy color may chalk over time and become dull; therefore, a topcoat of urethane is added toprevent UV light deterioration. This three-part application process does require more material,skill, and application time, but provides a slightly longer (>10 years) system life.

Two component epoxies are coatings activated by adding a curing agent (sometimes calledconverter, activator, hardener or catalyst) to the resin base. There are several kinds of curingagents, including polyamine, polyamide, and isocyanate.

Polyamine produces a film with excellent chemical and immersion resistance. Polyamine-cured coatings tend to have short pot lives and care must be taken to apply the coating soonafter mixing. In addition, polyamine systems are sensitive to moisture and in combinationswith cool temperatures will blush and generate amine bloom which degrades adhesion ofsuccessive coats of materials.

Polyamide produces a film with less tendency to blush than the polyamine and generallyhas better wetting characteristics to the substrate. It also has better chemical resistance, but ismore toxic.

Isocyanate produces a film that cures at lower temperatures (below 50 degrees F).

Moisture-cured zinc/urethane

Moisture-cured systems systems that rely on moisture for curing have a great advantageover other systems in cases where moist or humid environmental conditions cannot be avoidedduring application. The material is a little more expensive, but this can be balanced out withsavings in application cost and long-term durability.

Bitumastic coal tar

This coating has traditionally been the common material for exterior application. It has theadvantage of increasing corrosion protection with marginal surface preparation. It is now seeingless application than in the past because of its relatively high VOC content and exposure ofworkers to carcinogenic compounds. However, it still could be applied in spot repair over anexisting system. Several different formulations have been used over the years, including:



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Coal tarwith a high VOC content

Coal tar epoxieswhich may contain a high VOC

Coal tar enamelswhich are formulated with low or no VOC content

Interior Lining Systems

As outlined in Table 3-1, five principal system options are suggested for use in interior liningapplications for either corrosion protection and/or water-tightness:

Epoxy primer and topcoat Primer and 100% solids epoxy topcoat Single component elastomeric polyurethane

Plural component100% solids polyurethane Plural component100% solids polyurea

All of the interior lining options provide corrosion protection. The 100% solids polyurethane andpolyurea options also provide water-tightness.

Epoxy primer and topcoat

This is the lining system most commonly used for standard applications. Because these materialsare typically 50% to 70% solids materials (the remainder is solvent), they generally take 34coats in order to achieve the required film thickness (primer and 23 coats of the topcoatmaterial). Because these are solvent-based materials, cure times are slow, particularly whentemperatures are low. If the solvent is not allowed to fully evaporate between coats, inner coatadhesion problems can occur. They can be applied with standard conventional and airless sprayequipment.

Primer and 100% solids epoxy topcoat

Usually the primer is the same material as the topcoat. Because these materials are composed of100% solids, they can be applied in two coats to achieve the required film thickness. Since thesematerials do not have solvents in them, they cure more quickly than other materials, but maycure slowly at lower temperatures. These materials usually require special spray equipment(plural component), and can be installed faster and at a broader range of temperatures than othersystems.

The 100% solids epoxy provides significantly more corrosion protection than standard epoxy,but requires a bit more skill to apply. A 100% solids epoxy eliminates the potential for solvententrapment associated with high build-up and multiple coats.



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Single component elastomeric polyurethane

This is a high solids single component modified polyurethane that when applied in 50 to 100 milDFT thickness provides an elastic waterproof membrane. Its advantages are that it only requiresconventional single component spray equipment, the material cost is less than plural componentmaterials, and it has good properties such as low permeability, high adhesion, and flexibility.

The material disadvantages include a minimum material temperature of 60 degrees F, and a shortpot life, varying from 45 minutes at 60 degrees F to 10 minutes at 90 degrees F. These materialsalso have a tendency to run and sag on vertical surfacesonly approximately 40 mils DFT canbe applied in a single coat, thus requiring two coats to achieve water-tightness. The singlecomponent polyurethanes have longer curing times (48 hours at 70 degrees F) prior toimmersion.

Plural component100% solids polyurethane

These materials are usually primerless and can be applied in 1 or 2 coats. They require specialplural-component spray equipment (discussed in subsequent sections) for application, and eachcomponent must be heated to decrease viscosity. They cure very quickly (to touch in about 5minutes), and are temperature insensitive for curing. This advantage allows the system to bereturned to service in about 24 hours.

Plural component100% solids polyurea

A 100% solids plural component polyurea applied in 50 to 100 mil DFT provides an elasticwaterproof membrane. Its advantages are that it can be applied in temperatures ranging from 20degrees F to 400 degrees F. Thickness up to 250 mil DFT can be applied in a single coat, and ithas fast cure time, no volatile organic compounds (VOC), and has excellent materialcharacteristics such as low permeability, chemical resistance, elongation, corrosion protectionand high adhesion. Material disadvantages are that it requires specialty plural component sprayequipment, and should be applied only by a manufacturers certified contractor, and relativelyhigh material cost.



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Water-tight Liner Considerations

Water-tight liner strength

The most important thing when looking at an aging penstock and considering the lining is todetermine if the existing shell is strong enough for the loads. None of the water-tight liners(including fiberglass) add structural strength to the penstock because the materials have such alow modulus of elasticity and tensile strength. Thus the steel still must carry the internalpressures of the system. An analogy would be a balloon inside a pipe, where the balloons verylow stiffness and tensile strength causes it to just be a force against the pipes interior diameter.

But an internal water-tight liner can provide enough local strength to bridge small pinhole leaks.This can be improved by embedding fiberglass or plastic mesh in the coating.

Single versus plural component materials for water-tight liners

The differences between plural and single component materials is significant. Plural componentshave the advantage of no odor, no limiting pot life, no solvent, and instantaneous set up withessentially no cure time. The polyurea plural components also can be applied in conditions of 0degrees F, thereby eliminating the need for costly penstock heating. The disadvantage of pluralcomponent materials is that they require special equipment and personnel, meaning there are lessapproved contractors available, and therefore are more costly. The single componentdisadvantages/advantages are; fumes as the material cures, requires multiple (at least two) coatsto reach 80 mils, and less chemical resistance than plural components. The comparativeadvantages are lower cost and easier installation.

Table 3-3 shows a comparison of liner strength and service life for these materials. This tablewas developed from manufacturers product data sheets and contains material technicalperformance information that is the quantitative results of specific material testing. The relativeimportance of various technical properties will vary with the site conditions and the purpose ofthe coating system. Some examples are:

Abrasion resistance would be more important for a penstock on a water system with a highersediment load and suspended solids

A higher material tensile strength would improve the ability of a water-tight lining materialto bridge pinholes and minimize leakage

A higher adhesion strength would help prevent lining delamination from a penstock exposedto large thermal growth and contraction cycling



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Table 3-3Comparison of Performance and Service Life Properties for Internal Water-tight PenstockLiners

Property

ElastomericPolyurethane

Note 1

100% SolidsPolyurethane

Note 2

100% SolidsPolyurea

Note 3

Tensile Strength (psi) 565 TO 650 Note 4 3,000 Note 10 2,125 Note 10

Elongation 345425% Note 4 65% Note 10 250% Note 10

Adhesion to Steel (psi) 1,000 Note 5 >1,500 Note 15 1,2502,000 Note 13

Abrasion (mg) 3 Note 6 56 Note 6 250 Note 12

Hardness >60 Note 7 6570 Note 11 50 Note 11

Moisture Vapor Trans.Rate (Perms) Note 8

0.05 Note 16 0.1 (at 10 mils) 0.025 Note 9

Salt Spray Corrosion(Hours)

2,000 Note 14 NA NA 1,000 Note 14

Notes:1 TNEMEC 262 Elasto-shield (single component product)2 POLYBRID 705 (plural component product)3 VERSAFLEX FSS/50DM (plural component product)4 ASTM D-4125 ASTM 4541, Cured 14 days at 75 degrees F and 50% relative humidity6 ASTM D-4060 (CS-17 wheel, 1,000 grams load), 1,000 cycles7 ASTM D-2240 (Shore A)8 A perm equals 1 grain of H2O/hour/ft

2 per 1-inch difference in Hg pressure across the membrane

9 ASTM E-9610 ASTM D-63811 ASTM D-2240 (Shore D)12 ASTM D4060 (1,000 grams, 1,000 rev., H-18)13 Epoxy Primer = 1,250 psi, bare steel > 2,000 psi14 ASTM B-117 Salt Fog Corrosion Resistance15 Elcometer pull16 ASTM D-1653

Surface Preparation

It is generally believed that fully 60 to 80% of all premature coating failures are attributable toinadequate or improper surface preparation.[14] Therefore, this step in the overall coating/liningprocess is vital.

The basic procedure could include:

Pre-inspectionTo inspect and mark any particular areas for different or special cleaning ormethods

Pre-cleaningTo remove any contaminants such as oil or grease, which could involvesolvent cleaning



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Cleaning operationsTo the appropriate standard as required by the coating/lining systemmaterial

The primary specifications for surface preparation are contained in the SSPC/NACE standards asoutlined in Table 3-4. These methods are universally recognized and match the coating/liningsystem with the surface preparation.

Table 3-4Surface Preparation Techniques

Specification Title DescriptionApplication/Commentary

SSPC-SP 1 Solvent Cleaning Removal of oil, grease, dirt, soil, salts,and contaminants by cleaning withsolvent, vapor, alkali, emulsion ofsteam.

Used to pre-clean any areasof grease or oil

SSPC-SP 2 Hand Tool Cleaning Removal of loose rust, mill scale, andpaint to degree specified, by handchipping, scraping, sanding, and wirebrushing.

SSPC-SP 3 Power Tool Cleaning Removal of loose rust, mill scale, andpaint to degree specified, by power toolchipping, scraping, sanding, andgrinding.

SSPC-SP 5 / NACE 1 White Metal BlastCleaning

Removal of all (100%) visible rust, millscale, paint, and foreign matter by blastcleaning by wheel or nozzle (dry or wet)using sand, grit, or shot.

Highest cost

SSPC-SP 6 / NACE 3 Commercial BlastCleaning

Blast cleaning until two-thirds (66%) ofthe surface area is free of all visibleresidues.

SSPC-SP 7 / NACE 4 Brush-Off BlastCleaning

Blast cleaning of all except tightlyadhering residues of mill scale, rust,and coatings, exposing numerousevenly distributed flecks of underlyingmetal.

SSPC-SP 10/ NACE 2 Near-White BlastCleaning

Blast cleaning nearly to White Metalcleanliness, until at least 95% of thesurface area is free of all visibleresidues.

SSPC-SP 11 Power Tool Cleaning toBare Metal

Abrasives not used.

SSPC-SP 12 / NACE 5 Surface Prep andCleaning of Steel byHigh and Ultra-HighPressure Water Jetting

Water only

Reference: [17]



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For penstock coating and lining rehabilitation, surface preparation is usually performed utilizinga combination of techniques. Generally, preparation begins with removing oil, grease, and dirtfrom the substrate, using a solvent (SSPC-SP 1). Hand and Power Tool Cleaning (SSPC-SP 3and SP 4) can be performed in limited areas; however, most surface preparation is either done bywater jetting (SSPC-SP 12) or by one of the abrasive blasting techniques.

The key to successful surface preparation is generating a surface or anchor profile. Anchorpattern profile is generally defined as the peak to valley depth (or height) caused by the impact ofan abrasive onto the substrate. The surface profile increases the surface area, providing amechanical anchor to which coatings and linings can adhere.

While water jetting does not create a surface profile, as does abrasive blasting, it can be very costeffective for removing old material and corrosion byproducts. Water jetting may be moreeffective than abrasive blasting at removing coal tar enamels and materials in deep pits. This isparticularly true if the existing coal tar is very thick. Abrasive blasting alone often generates somuch heat that the thick coal tar softens and becomes very sticky and difficult to remove. Waterjetting followed by abrasive blasting mitigates this problem.

Water jetting equipment includes a power source (generator), water jetting unit, high-pressurehoses, water, and personal protective equipment. The equipment is simpler than that required forabrasive blasting. Water jetting cleans but does not impart a profile into the steel. The SSPCstandard for water jetting is contained in SSPC-SP 12. Included in that standard are varioussurface preparation and cleanliness conditions.

Water jetting is the only process that will remove salts or chlorides. Many project owners useabrasive cleaning only to find out later that the coating/lining fails because chlorides were left onthe surface. If salts or chloride contamination from ambient air is a consideration, water jetsurface preparation may be indicated, as a secondary step prior to application.

Abrasive blasting techniques are contained in the standards SPPC-SP 5, 6, and 10. Abrasiveblasting requires a generator, compressor, blast pot, abrasive (expendable or recyclable), hoses,recycling equipment (if required), and personal protective equipment. Abrasive blasting impartsa profile or surface roughness into the steel as it cleans. There are different blast cleaningstandards by SSPC/NACE for the specified steel cleanliness as shown on Table 3-4. The aircompressor air should be checked for oil contamination at least every 4 hours.

Both water jetting and abrasive blasting can be performed by hand methods and automated spinblasting. Abrasive blasting is a much more costly and labor intensive process.

Removal of existing coatings and linings, particularly those with lead or hazardous materials,may require containment and disposal procedures. These are comprehensively discussed in theSSPC guides on environmental protection. Guide 6 describes procedures for containing debrisgenerated during paint removal operations, Guide 7 contains guidelines for disposing of lead-contaminated surface preparation debris, and Guide 10 outlines specifications and testing ofcoatings for VOC compliance.[18]



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Once the surface preparation has been completed, several standards are used to evaluate thereadiness. These include:

NACE RP0 287-95 Field Measurement of Surface Profile of Abrasive Steel Using a ReplicaTape, which is a test method that measures the anchor pattern profile depth. Testex Press-O-FilmReplica Tape, is used, which is a fast, simple pull-off tape that can measure surface profile andprovide a record of the test.

Several alternate comparative tests can be used, such as:

The Keane-Tator Surface Profile Comparator, which are durable reference discs designed tovisually determine the surface profile of various sand, shot, or grit/slag abrasive cleanedsurfaces.

Clemtex anchor profile chips, a comparative method that uses samples of patterns.

Other photographic standards can also be used to compare readiness:

SSPC-VIS 1-89Visual Standard for Abrasive Blast Cleaned Steel (Standard ReferencePhotographs). This is a photographic standard depicting the appearance of previously unpaintedsteel prior to and after abrasive blast cleaning. The photographs supplement the written SSPCSurface Preparation Standards.

SSPC-VIS 3Visual Standard for Power- and Hand-Tool Cleaned Steel (Standard ReferencePhotographs). This is a photographic standard depicting the appearance of unpainted, painted,and welded steel prior to and after power and hand tool cleaning. The photographs supplementthe written SSPC Surface Preparation Standards.

SSPC-VIS 4(I)/NACE No.7Interim Guide and Visual Reference Photographs for SteelCleaned by Water. This new publication features reference photographs that illustrate theappearance of unpainted rusted steel surfaces before and after water jetting, with additionalphotographs that depict the occurrence of light, moderate, and heavy flash rusting after waterjetting. It is intended for use as a supplement to SSPC-SP 12/NACE No. 5 standard.

An international standard, ISO 8501-1 (also referred to as the Swedish Standards) is alsoavailable to compare hand, power tool, and blast cleanliness.

Application Techniques

There are several diff

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