orrosion under insulation is a major problem. when

3 2 A S H R A E J o u r n a l a s h r a e . o r g M a r c h 2 0 0 3

orrosion under insulation is a major problem. When insulationbecomes wet (because of poor installation practices, subsequent

abuse or failure to specify good vapor barrier and waterproofing ma-terials), it “creates the potential for corrosive failure of the piping.”1

Whether pipes are above ground or buried, proper design and installa-tion techniques can control corrosion.

or anodes with a power source to provideprotective current to the cathode.

The oil and gas industry has used pipecoatings and tapes successfully for manyyears. These vary in type, from the firstcoal tar brush on coatings covered with aspiral wrapped bitumen tape, to today’sepoxy, urethane, urea, and FBE (fusionbonded epoxy) coatings.

The pipeline industry (loosely definedas the oil and gas industry and theuninsulated piping used as transmissionlines) and the insulation industry (deal-ing with insulated piping systems) dif-fer in their practices in some respects, butthe success and growth in the pipelinecoating industry raises the question ofwhy other industries are not using thisknowledge to protect pipes and processsystems.

Pipeline coating obviates the need toreplace piping systems every few years,

avoiding the cost of such expensiveprojects. It also prevents conflict withenvironmental groups, the U.S. Environ-mental Protection Agency and local gov-ernment.

Coating Selection ConsiderationsThe proper selection of coating materi-

als is important. When selecting coatingsfor metals under insulation, consider:

• System operating temperatures,• Application and site requirements,• Surface preparation requirements,• Environmental requirements during

surface preparation and application, and• Compatibility with insulating

materials.

System Operating TemperaturesA coating has to be flexible enough to

withstand the expansion and contractionof the piping system when temperaturescycle. Temperature fluctuations cancause a loss of adhesion between thecoating and the metal, which allows wa-ter to reach the pipe. High temperaturescan cause certain coating types to flow,

By Patrick J. Dunn, Associate Member ASHRAE, and Richard Norsworthy

Basic Corrosion ControlThe sidebar discusses the four neces-

sary elements for the corrosion processto occur. However, certain external fac-tors will cause variance in the corrosionrate after the corrosion process begins.Examples of factors affecting corrosionrate would be hot/cold cycling expan-sion and contraction (stress cracking) andwet/dry cycles.

One of the most effective ways to con-trol corrosion is to use a properly selectedand applied corrosion coating. Since1971, U.S. government regulations re-quire oil and gas companies to coat (witha corosion control coating) all pipelinesbefore they are buried or submersed. Ca-thodic protection (CP) also is requiredon all buried and submersed transmis-sion and gathering pipelines to protectmost areas of coating defects. CP is theinstallation of external galvanic anodes

About the AuthorsPatrick J. Dunn is vice president for PolyguardProducts, Mechanical Division, in Ennis, Texas.Richard Norsworthy is NACE InternationalCorrosion Specialist for Lone Star Corrosion Ser-vices in Lancaster, Texas.

CCCCC

The following article was published in ASHRAE Journal, March 2003. © Copyright 2003 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. It is presented for educational purposes only. This article may not be copied and/or distributed electronically or inpaper form without permission of ASHRAE.

M a r c h 2 0 0 3 A S H R A E J o u r n a l 3 3

The Corrosion ProcessMetal corrosion requires four elements: an anode, a

cathode, an electrolyte (e.g., moisture), and an electricalpath (e.g., metal) joining the anode and cathode.

The anode is the part of the metal where corrosionoccurs. It actually sacrifices itself as it releases positivelycharged metal ions into the electrolyte and electrons areleft behind in the metal. These electrons flow through themetal to protect the cathode. The cathode is protectedbecause various ions or compounds in the electrolyteconsume electrons.

An electrolyte is a solution capable of conducting elec-trical current in the form of ionic flow. An electrical path isa connection between the anode and cathode wherecurrent in the form of electrons can flow. Free electronsdo not flow in the electrolyte, only in a metal path.

Corrosion occurs because anodes and cathodes areinherent in all metals, and all metals are electron con-ductors. Anodic and cathodic components can be mi-croscopic in size or rather large in some cases.Therefore, three of the four requirements for the corro-sion process are inherently present in every metal. Theonly remaining element required for the corrosion pro-cess to begin is an electrolyte.

Anodic and cathodic areas develop where chemicalshave deposited, where there are temperature differences,and where there are damp areas. Chlorides and otherindustrial contaminants in the electrolyte can cause anarea to become anodic. The contamination may bepresent on the metal surface before it is coated or insu-lated. Once these areas become wet, corrosion begins.

The corrosion of metals requires the following conditions:• An anode, a cathode, an electrical path, and an elec-

trolyte must all be present;• The anode and cathode must be in contact with the

same electrolyte;• The metal must electrically connect the anode and

cathode for electrons to flow; and• The anodic (oxidation) and cathodic (reduction) re-

actions must be equivalent and simultaneous.

crack, or sag. Low temperatures can cause some coatings tobecome less flexible or brittle.

Some coatings work well at cold temperatures, while otherswork well at high temperatures. New entries into the metalprotection industry have achieved temperature ranges between–320°F and 350°F (–196°C and 177°C), with prospects of coat-ings up to 900°F (149°C) for specialized applications on equip-ment that cycles from cold or ambient up to highertemperatures. This cycle accelerates the corrosion process.

Application RequirementsSome types of coatings require extensive surface prepara-

tion, even heating the pipe before applying the coating. Othercoatings can be applied with minimal surface preparation andapplication equipment. Field application becomes more diffi-cult because of confined space, safety, and environmental con-cerns. Inspection to ensure proper coating coverage andthickness is cumbersome.

Liquid coatings can be applied by brush, glove, or spraymethod (e.g., air, airless, or plural component). Tape coatingscan be applied in a “cigarette wrap” or by spiral wrapping byhand or machine. On insulated systems, tapes will affect theinner diameter (ID) and the fit of the insulation. Some types oftapes are applied using heat, usually a propane torch. Powdercoatings, such as fusion-bonded epoxies (FBE) are applied toa hot (normally 450°F to 488°F [232°C to 253°C]) pipe sur-face and are applied in a specialized pipe coating plant withtemperature and humidity control.

Surface PreparationSurface preparation is the most critical part of any coating

process. Care must be taken to perform the best possible sur-face preparation for the application. Experts in the coatingindustry advise that two-thirds of the cost of any good coatingjob should go into surface preparation.

Blasting with an abrasive helps to clean the surface andprovides the proper anchor pattern to which the coating willadhere. Before blasting, any oil, grease, or other debris must beproperly removed. Blasting only spreads oil and grease con-tamination—it does not remove it. Contaminants on the metalsurface, such as chlorides and other salts, must be removed byproper washing and rinsing techniques. Mill scale, rust, andother such surface contaminants can usually be removed byproper blasting. Wire brushing by hand or machine is accept-able for some types of coating. Water blasting, with and with-out abrasives, may be used in other situations. This must beperformed with the proper methods and equipment.

The introduction of mineralization surface conversion tech-nology (see sidebar) in the insulation industry reduces theamount of surface preparation required before installing thecompound. Sand blasting is not necessary, even on rustedpipes. The main requirements are to remove oil or salt filmsthat may be on the pipe surface and the removal of scale rust

This article is based on a presentation at the 23rd Annual Meeting ofthe International Institute of Ammonia Refrigeration.

with a wire brush, or water blasting.The type of surface to be coated dictates the type of surface

preparation and coating to be used. New carbon steel can becleaned and blasted easily, compared with corroded or pittedsteel in used systems. Corroded or used metal systems mayhave surface contaminants such as chlorides or salts that mustbe properly removed before blasting. Stainless steel surfacesare very hard, making it difficult to create an anchor pattern.Certain types of stainless steel should not be blasted with steelgrit or shot because the carbon in the blast material itself cancause corrosion problems. Non-carbon blast materials, brushes,

Corrosion


or grinding disks should be used instead.Unique circumstances will dictate exceptions to any of these

recommendations. Nevertheless, preparing the substrate in someway is always important. Other types of metal not mentionedhere should be studied and tested to determine the most effec-tive method of surface preparation.

Compatibility With Insulating MaterialSome types of insulating materials may be abrasive (e.g.,

cellular glass), and as the pipe moves, the coating material willbe damaged. Other insulating materials may cause the coatingto deteriorate, become soft or brittle, or lose other properties(especially if the insulation becomes wet). The thickness ofmost coatings is within the ID tolerance of insulation prod-ucts. However, insulation fabricators may have to alter sometolerances of the ID of their insulation to provide products thatfit over certain coatings. Coating selection and insulation char-acteristics should be considered jointly when specifying a sys-tem. In their wet state, some corrosion coatings react withfabricated foam insulations; therefore, coatings must be al-lowed to cure completely before installing insulation.

TestingThe pipeline industry has developed an effective way to

provide good unbiased information about products to its con-stituents through an industry-sponsored testing program, most“off the shelf ” products available have these test results avail-able. The industrial refrigeration industry, the commercial in-sulation industry, and industrial insulation industry shouldconsider the same.

Product SelectionCurrently, the market offers a variety of coating products

and materials. All of the considerations that must be taken intoaccount make product specification confusing. Vendors canbe helpful in providing information, and technical supportfrom the coating manufacturer and is recommended for newsystems. Again, the NACE Web site and corrosion articles pro-vide a wealth of knowledge concerning corrosion testing andproduct comparisons after testing.

Surface ConversionTechnology (Minetics)

Surface conversion technology, or minetics, is the abil-ity to grow very thin minerals on metal surfaces for usefulpurposes. Engineered surfaces form when mineral-form-ing reactants are delivered to the surface of a metal ormetal containing article via novel modifications of knownbase formulations (e.g., paint, gel, grease, aqueous sus-pension).

Substrates contribute donor ions to react and/or inter-act with delivered reactants, forming a very thin layer ofmineral that chemically bonds to the surface of the sub-strate that has been measured to be a few monolayersthick. In many applications, lattice-forming oxides anchorto this surface-adhesion layer and polymerize into a three-dimensional inorganic framework structure until the finalcoating thickness is 50–200 angstroms.

Engineered mineralization products have been devel-oped to deliver the mineral-forming reactants in a varietyof formulations including paints, coatings, synthetic gels,greases, thread dressing, sealants, adhesives, and wa-ter gels.

Typical MetalSurfacesMetal OxidesMetal CarbonatesMetal Hydroxides

Delivery Coating

Result: PolymerizedMetal Silicate Lattice

Protected Surface

Extended Surface

Mineral Formation

SpecificationsA well-written specification that details the coating process

is crucial in any corrosion coating project. Specifications shouldinclude surface preparation requirements and application pa-rameters. Each coating system must have its own specifica-tion, and each project must be carefully specif ied. Thespecification is not “one size fits all.”

InspectionTo ensure that the coating and surface preparation processes

are properly performed, in progress inspection is a must. In-spection ensures that the surface preparation and coating pro-cess is properly performed in the right conditions at the correct

Brush application of coal tar coating.

Corrosion


thickness and that it has been allowed to properly cure. Voidsor thin spots in coatings are potential corrosion sites, special“holiday” detection devices are available to detect these voids,and these areas should be identified and repaired before insu-lating. Mineralization conversion technology is quite forgiv-ing and voids can exist without detrimental affect.

Many people associate corrosion coatings on pipes or ves-sels with house painting and assume that the process is thatsimple, it is not.

In the insulation industry, coatings are rarely specified onthe pipe and protection of the system is provided by the vaporretarder jacket and/or mechanical jacketing. Mineralizationtechnology gels are superior under insulation as they will buffermoisture that may enter the system, making it harmless to thepipe itself. This process of buffering raises the pH of water tocreate a passivating environment. Certain metals (amphoteric)such as zinc and aluminum will corrode at high pHs, so onemust study the pH levels to determine if these metals can beprotected with this material.

Types of CoatingsTypes of coating choices on the market include:• Liquid coatings: epoxies, urethanes and polyureas,• Tapes and shrink sleeves,• Brushable coal tar or asphalt-based corrosion coatings,• Mineralization coatings, and• Fusion-bonded epoxies and multilayer coating.Liquid epoxies are excellent choices for coating pipes. Ba-

sic epoxies are two-component materials that are mixed andnormally applied by spray or brush. Some epoxies are appliedwith multicomponent equipment that mixes the componentsat the applicator gun. Epoxies must be mixed in the properratio. If the mixture is not correct, the epoxy does not cureproperly or perform well. Specific environmental concerns needto be addressed since fumes and cleanup are important criteria.

“Phenolic epoxies are excellent coatings for higher-tem-perature applications up to 300°F (149°C). Modified epoxyphenolic coatings offer good abrasion resistance and are moreflexible than most epoxy phenolics.”2 Phenolic epoxies areapplied by experienced applicators using heated multicom-ponent equipment.

Urethanes and polyureas are also excellent coatings for cold

(Right) Rubberized bitumen tape applied to steel pipe.

Advertisement in the print edition formerly in this space.


process piping and vessels. Most urethanes have limited use forhigher temperature operations at greater than 150°F (66°C). Ure-thanes are flexible and can be applied in one thick coat with aheated spray system. Moisture can be detrimental to some ure-thane applications, but moisture-cure urethanes perform well forapplications where moisture is a problem during application.

Certain types of corrosion-control tapes provide excellentcorrosion protection for pipes on systems that operate at tem-peratures of 150°F (66°C) or less. Tapes are relatively easy toapply. Most require a primer in or-der to adhere properly to the pipe,and the primer must cure properlybefore the tape is applied. Tapes varyfrom 25 to 100 mils in thickness,thus, the insulation material musthave the proper ID to enable the in-sulation to fit over the tape.

Asphalt or coal tar-based materi-als do not require mixing, thinning,or other special treatment. They areeasily applied by brush or paintglove in one or two coats. Surfacepreparation requirements are not asstringent for these materials as theyare for many other coatings. Thesecoatings are good for irregularshapes, are flexible, adhere well tothe steel, are resistant to most chemicals, and can be repairedeasily. They have fair abrasion and impact resistance. They dorequire a certain amount of time to cure properly. At tempera-tures below 0°F (–18°C), this type of coating may become lessflexible; at temperatures above 120°F (49°C), some of thesecoatings may become too soft or tend to run to the bottom ofthe pipe.

Mineralization Conversion CompoundsMineralization conversion compounds are new to the insu-

lation industry. As the name implies, these coatings create a

mineralization bond with a pipe, a “new” surface. They can beeffective on systems at temperature ranges from –50°F to 250°F(–46°C to 121°C). Excess coating from the application acts asa reservoir in the event of mechanical damage to the minerallayer, or the intrusion of an electrolyte. Corrosion cannot takeplace in this mineralized layer on the pipe.

The greatest benefit of this type of technology is if the vaporbarrier is compromised and moisture enters the system, it cantravel directly to the pipe’s surface and remain there without

corrosion taking place. The excesscoating from the installation processchemically binds the water (buffer-ing it) so that it cannot corrode thepipe. Only removal of the excess coat-ing with cleaner can alter the protec-tion provided to the piping system.

Mineralization surface conversioncompounds can be applied to alltypes of pipes. They not only pre-vent corrosion but also prevent stresscracking when applied to copper orstainless steel systems.

Mineralization surface conversioncompounds are effective on new pip-ing, valves, tanks, vessels, and ap-purtenances. This type of compoundis equally effective in the retrofit

market where reinsulation of compromised systems normallyrequires replacing corroded pipes, fittings, valves, or other com-ponents. Conversion compounds can obviate the need to re-place piping that is somewhat corroded but will remain intact ifno further corrosion occurs. In the past, this was not an option. Ifthe metal retains sufficient physical integrity for the pressures itcontains, it can be wire brushed or water blasted to remove anyloose rust scale or corrosion scale before the pipe is treated withthe conversion compound and reinsulated. This type of applica-tion will create the same mineral bond in old piping as new.

The use of surface conversion compounds will revolution-

(Left) Insulated pipes in a 5% aerated salt bath. (Center) Same pipes 365 days into test. (Right) Pipe inspection after 365 daysin salt solution. No corrosion in surface conversion treated areas.

Application of rubberized bitumen vapor re-tarder/weather barrier membrane on ammoniarefrigeration piping system.

Corrosion


ize corrosion control on below-ambient systems under insula-tion. The life expectancies of these systems will be increased,and with proper insulation, vapor barrier, and mechanical pro-tection. Corrosion is not a problem only on below ambientpiping systems, however the 250° F (121°C) temperature lim-its of conversion compounds limits them primarily to belowambient systems where moisture drive to the pipe can occur.

Rehabilitation of Existing SystemsRehabilitation of insulated piping systems can be performed

with many of these coatings. For systems where surface prepa-ration is difficult and minimal surface preparation is performed,mineralization conversion compounds are the best option.Tapes are an option if the fabricator can supply insulation withthe proper ID. Brushable coal tar and asphalt-based coatingscan be considered. Retrofit conditions usually do not permitspray application, limiting your options.

The most cost-effective method for rehabilitation withoutreplacement is the minimal cleaning required by mineraliza-tion surface conversion technology. Removal of loose scalewith a brush or water jet is sufficient preparation prior to in-stallation of mineralization coatings. Though this technologymay appear new to many, it has been used in military andautomotive applications for more than 15 years with provenhistories for mechanical uses such as anti-seize on flange bolts,anti-corrosion on moving parts such as bridge rockers, andanti-corrosion of protected, yet concealed steel cable.

InsulationThe insulations used for above freezing yet below ambient

piping are quite broad including fiberglass, elastomeric plas-tics, elastomeric rubber, mineral wool. It also can include sub-zero insulations such as polyisosyanurates, polystyrenes,cellular glass and phenolics. Surface conversion compoundsare less attractive for chilled water systems as failure of thesesystems due to corrosion is not an environmental issue as muchas a possible property damage issue. Failures of chilled watersystems can occur within five years due to advanced corrosionactivity. The use of surface conversion compounds would elimi-nate such early demise of the piping system, however, conver-sion gel manufacturers will not put a figure on it as the choiceand installation of ALL components in the system contributeto the life of the system.

Insulation types are fairly limited for below-freezing pipingsystems; cellular glass, polyisosyanurates, polystyrenes, andphenolics are normally the insulations of choice. The manu-facturers of these products publish technical literature thatdescribes their uses, temperature limitations, and design crite-ria. The job criteria (atmospheric conditions, process system,and plant environment) should determine the insulation bestsuited to a specific job. The fact that an “ammonia system” isbeing designed is not enough information on which to base aninsulation specification. Although the basic design criteria of



the system may be known, the environment into which thesystem is being installed must be considered before specify-ing types of insulation and insulation thicknesses.

Insulation thickness is critical to the success of the system.Worst-case atmospheric job conditions should be used whencalculating insulation thickness. This condition may only ex-ist one week per year, but that single worst-case could create acorrosive environment that eventually could cause the prema-ture demise of a system.

Installation of the insulation is as critical as the choice ofinsulation itself. Improperly sealed insulation can allow mois-ture to migrate to the pipe, providing the electrolyte necessaryto begin the corrosion process.

Insulation manufacturers literature normally suggests perm-rated joint sealants for their insulations. It is important to usejoint sealants to slow the migration of water vapor to the pipeif a breach in the vapor barrier occurs. Since there are atmo-spheric conditions present during all installations, water va-por will be trapped in the system when the vapor barrier issealed. Consulting with an insulation fabricator is helpful givenhow closely fabricators work with the insulation manufactur-ers and how frequently they deal with insulation specifica-tions on cold piping systems.

Surface Conversion ApplicationMineralization surface conversion compounds are designed

to be bead applied to the bore of the inside layer of insulationby the insulation fabricator to minimize installation cost. Thenumber of beads in the ID of the insulation depends on thepipe size being insulated. A bead is also applied at one end ofthe insulation piece to act as “insurance” at every joint. Due tothe physical properties of the compound, it can be applied andshipped to the job site without sagging or skinning over.

The installation process is simple. The insulator installs thepipe cover and rotates the insulation around the pipe and lon-gitudinally to distribute the compound onto the pipe. Thebeauty of the buffering system is that 100% coverage is notcritical. Using this installation method, testing shows that cov-erage of better than 98% is achieved with this rotation andsliding of the insulation.

Vapor Retarders and Protective JacketsOne of the most critical components on cold systems is the

vapor barrier, or vapor retarder as commonly stated. Vapor bar-riers, or retarders, come in various forms. They include prod-ucts such as ASJ paper, FSK paper, vapor barrier mastic, Mylar’s,proprietary polymers, and laminated self-adhesive membranes.The recent introduction of low-perm, peel-and stick, self-heal-ing vapor barrier membranes are just what the doctor ordered!Although the cost is approximately three times that of ASJpaper (a retarder), cost should not deter the specification ofthese membranes! These new membranes are UV stable in-

doors and can eliminate the need for an additional mechanicaljacket, (making them comparatively less expensive) where me-chanical protection isn’t required.

For exterior applications, laminated rubberized bitumen self-sealing membranes have been produced with various “skins”to make them impervious to the elements.3 These membraneseliminate the need for expansion slip joints by providing 400%elongation before rupture; they expand and contract with thesystem. Insulation can be applied, and then one peel-and-stickjacket provides an excellent perm rating (0.00046 US perms),ultraviolet stability, excellent emissivity, and sealed weatherprotection.

Currently, the standard specification is for a vapor retarderjacket to be installed under a protective mechanical jacket,such as PVC or Aluminum. The vapor retarder of choice is mostcommonly ASJ paper, which, if “crinkled” has lost its vaporretarder properties. Furthermore, the seal on a metal or PVCjacket is only as good as the installer is with the glue gun orcaulking gun. Engineers also are finding that expansion andcontraction of piping systems with PVC or metal jacketingcan generate friction between the vapor retarder and jacket,eventually wearing through the vapor retarder.

For a below-ambient insulation system to be successful andnot contribute to the corrosion process, it must be specified inthe following manner:

• Using a corrosion control coating or treatment,• Tailoring the insulation to the application and environment,• Calculating adequate insulation thickness,• Properly sealing the joints,• Applying a superior vapor barrier, and• If necessary, install a mechanical jacket to protect vapor

barrier from physical abuse.To be specific, the ultimate system available today would

be a joint-sealed, closed cell foam insulation, bore coated witha mineralization conversion compound, sealed with a self-heal-ing low-perm vapor barrier and mechanically protected withan aluminum or PVC jacket where necessary for mechanicalabuse protection. Exterior systems would be jacketed with self-healing, vapor barrier membrane without a mechanical jacket.The cost of such a system would be approximately 30% higherthan typical systems being installed today.

Comments have been made about the insulation industryand how difficult it is to change the status quo, if the industrywants to solve this serious corrosion under insulation prob-lem, it has to change the specification and installation pro-cesses. Engineers must work closely with fabricators to findsolutions to this aspect of the problem; it is not beyond afabricator’s capability. Communication levels among engineer-ing entities and insulation fabricators, installers, and manu-facturers must increase. Alternate innovative products are notalways submitted under the guise of increasing a contractorsprofit margin. Better, alternative methods in the industry must

Corrosion


For More InformationCorrosion Testing• www.nace.org

• www.insulation.orgCoatings

Insulation Thickness• The National Insulation Association (NIA) provides freesoftware for insulation thickness calculations atwww.pipeinsulation.org.

• The Midwest Insulation Contractors Association publishesan excellent installation reference tool, National Commer-cial & Industrial Insulation Standards, available in book andCD form, (www.micainsulation.org/standards/index.html),which contains detailed drawing plates and informationaltables for the insulation industry.

• www.micainsulation.org/standards/index.html• www.nace.org• www.smacna.org

be considered on their merit rather than on the perceived in-tent of the presenter.

ConclusionsCoating the pipe before insulation is applied will not solve

all of the corrosion problems that exist in this industry, but itwill result in definite improvements. Through testing, properselection of materials and methods, and well-written and de-tailed specifications, tremendous improvements can be madein controlling corrosion problems. The following suggestionsare recommended for industry:

• The industry must be committed to preventing corrosion(primers or no coating are unacceptable);

• Testing and insulation specifications must be developedand must outline specific coating systems for each application;

• Inspection and testing must be performed; and• Only the best vapor barriers, waterproofing materials, and

insulations should be used.On most projects, the initial cost to properly prepare, coat,

and install insulation and vapor barriers is minimal comparedwith the overall project cost and invaluable when consideringthe cost of repair or replacement and re-insulation of corrodedsystems (not even considering the losses in production due tosystem downtime). Systems installed today that are “valueengineered” make obsolescence an integral part of a system.Reducing corrosion failures results in significant long-termfinancial benefits. The safety and environmental issues relatedto these failures must also be factored into the cost savings.

References1. Jackson, C.W. 1997. “Insulation: an investment worth protecting.”

Insulation Outlook.2. Norsworthy, R. 1998. “Coating proves effective on hot oil pipe-

lines.” Pipeline and Gas Journal March.3. 2002. Insulation Outlook April.


orrosion under insulation is a major problem. when

Documents