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Copyright ©1996, Technology Publishing Company

protective lining forms abarrier between the sub-strate and the cargo of

the tank, with the aim of preventing sub-strate corrosion, maintaining product puri-ty, and decreasing erosion. It can also im-prove the ease of decontaminating andcleaning the tank. In mild steel tanks, a lin-ing allows a reactive or corrosive cargo tobe stored in a vessel that, if unprotected,would be attacked by the cargo.

For a lining to be successful, it mustdo the following:• insulate the cargo from the reactive sub-strate, • prevent or minimize the permeation ofany element of the cargo or another elec-trolyte through the coating film to the sub-strate/lining interface,• resist corrosion products that may devel-op from or on the substrate,• form a full and continuous film with ahigh level of integrity and low levels ofmoisture vapor transmission, and• display excellent adhesion and cohesion.

Although the time to failure varieswidely, most tank linings fail. While failurecannot be avoided completely, prematurefailure can be minimized. This article willoutline crucial steps for maximizing the lifeof a protective lining in carbon steel tanks

and vessels that hold aggressive chemicals.These steps address important factors oftenoverlooked when specifying, applying, andinspecting new or replacement linings. Thechoice of lining type is obviously crucialbut is beyond the scope of this article.

Service Environment

The specifier must accurately and compre-hensively define the environment in whichthe lining is expected to serve.

Tank Content First, the tank content must be describedfully, including the following aspects:• liquid or solid nature, including what itmight be diluted with;• the concentration;• the temperature;• the fill level; and• the cyclic process that might be involved(which may include changes in fill level,concentration, and cycle time, as well astemperature).

Understanding the cyclic process towhich a tank is subject involves evaluatingexactly what sequence of activity will occurin the tank. (The plant operations staff canprovide this information for a relining job,

Maximizing the Life of

Tank Linings

Aby Mark B. DromgoolKTA-Tator Australia

62 / Journal of Protective Coatings & Linings


while the design engineer should be con-sulted for lining of new process vessels.)

For instance, in a condensate/boilerfeed tank, the vessel could be filled withcold water and have boiler treatment chem-icals added; it may then have elevated tem-perature condensate added into (or worse,onto) the tank surface as the boiler waterrecycles. The tank may then reach an oper-ating level of 115-125 F (46-52 C) with theboiler’s normal draw-off and condensatereturn. When the night or weekend boilerload changes, tanks of this type have beenknown to rise to 195-205 F (90-96 C). Thefrequency and mode of adding boiler treat-

ment chemical must also be considered. Isit, for instance, continuously added in ametering system, or is it shock-dosed everyweek (given a high dosage in a short time),which will indicate an elevated peak inchemical concentration?

When determining the contents of thetank, one must often consider the pH and

the type of acid or alkali. Differing types ofacid or alkali can have a vastly different ef-fect on the durability of the lining. If thetank is to contain an aggressive chemical,then its solvency, its effect on the film dueto its hydroscopic nature, or other film ef-fects should be determined. If there aremixes of chemicals, their effects can be dif-ficult to determine. The cumulative effectsof combinations can be unpredictable with-out accurate analysis of these conditions.

Outage DemandsAnother aspect of service environment isthe plant shutdown or outage demands on

the coating. Is it necessary, for example, toallow for a clean-out process that could in-volve steam cleaning, high pressure water-jetting, or alkaline or acidic rinsing? It iscommon practice in the petrochemical in-dustry to steam out tanks by filling thempartially with water and then running livesteam or condensate into the vessel until it

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MARCH 1996 / 63

When a tank is to berelined, its history andthe performance of linings in similarenvironments can beinvaluable.Photos courtesy of the author.


propriate use of dissimilar metals. In oneexample with which the author was in-volved, a mild steel tank with an epoxycoating system was fitted with a large stain-less steel impeller. In less than 6 months,the tank was perforated with corrosion.Small areas that were poorly coated or in-accessible in the mild steel tank shell wereforced to be very active anode sites be-cause of the large surface area of stainlesssteel acting as a cathode. A similar failureoccurred on an elevated temperature, boil-er feed water tank that had a large coppercoil as the inlet pipe and stainless steelitems fitted to the tank along with galva-nized components. If possible, it is worthchanging the construction materials inthese conditions or insulating the electricalconnection between the dissimilar metals.

Tank HistoryMost of the considerations above are rele-vant if the tank is new or going into a newprocess where there is no history. If thetank is being relined or if a new tank wasconstructed to replace an existing tank,then a thorough investigation of the previ-ous service environment of the tank or theexperience of other users of tanks in thesame environment is very useful.

Assuming the present lining is to beremoved and replaced and the process is toremain substantially unchanged, the exist-ing lining and its manufacturer must befully and accurately identified. Additionaldetails such as its age, composition, andhistory, including whether the lining wasrecoated or repaired through its life, willgive a good indication of its effectiveness.Obviously, its original and subsequent suit-ability should be addressed. If, however,the lining has performed well for at least 10years, or failed because of mechanical dam-age or a change in process, then the liningand its application procedure may be con-sidered satisfactory. Full analysis of a failedor deteriorated lining can be made by a

overflows. This type of service could de-stroy a lining that was designed to with-stand many harsh chemicals but was notdesigned for or capable of withstandingthis combination of cleaning processes.

In another instance, the concentrationof a tank cargo may rise significantly duringthe process sequence because of evapora-tion of some of the water, which could in-crease the aggressiveness of the cargo.

Temperature and Temperature GradientThe temperature and temperature gradientacross the tank structure, including the lin-ing, must also be evaluated. Organic coat-ings have a coefficient of thermal expan-sion significantly greater than most steelsubstrates. The extent of this thermal ex-pansion changes whether the tank is ther-mally insulated or not. In certain instances,the stress from the differing thermal expan-sion rates is enough to exceed the bondstrength between the lining and the sub-strate or between individual layers in thelining. Thick films are particularly suscepti-ble to cracking from thermal expansion.Failures often occur at a localized over-building of the lining.

Effects of Dissimilar MaterialsAnother often overlooked effect is causedby dissimilar metals in the tank. It may beeasy to assume that the tank is all carbonsteel. Further investigation, however, oftenreveals that flange bolts, float sensingequipment, or other mechanical or electro-mechanical devices are made of a dissimilarmetal, such as copper or stainless steel, thatcould markedly affect the ability of the lin-ing to survive. In some cases, the design orspecification for these items may need tobe amended. Examples are stainless steelbolts, stainless steel agitators, and copper-or zinc-coated components for temperaturesensing or fill height determination.

Gross failures of tank linings and en-tire tanks have been caused by the inap-

Making Linings Last



reputable coating consultant, a knowledge-able coating manufacturer, or a coatingtesting laboratory.

It is a good idea to learn if there hasbeen other satisfactory use in similar expo-sures by other users. Plants with similarprocesses, similar chemistry, and similartank lining services can be canvassed aboutthe success of the lining types they haveused. If the process has been undertaken inanother environment, useful history canoften be extrapolated for the planned pro-ject. If the planned service has not beenundertaken before, it is valuable to selectcandidate lining materials and prepare anumber of test panels. Panels can be im-mersed, or partly immersed in the chemicaland, given sufficient time for the evaluationand confirmation, important comparativedata about the various candidate optionscan be gleaned.

If a coating has failed in a particularservice, it is a mistake to automatically re-place it with the same material unless otherfactors have caused the early breakdown. Ifthe only data available are from acceleratedimmersion exposures, treat these test re-sults cautiously. Such testing may givesome indication of performance and ex-pected coating life, but there can be short-comings in the extrapolation of short accel-erated exposure times.

Service Environment and Lining RecommendationsWhen seeking a confirmed recommenda-tion from a coating manufacturer or coatingconsultant, always ensure that they have allthe exposure data such as chemicals, pHand concentration, temperature, pressure,and any cyclic nature of the operation.Even at the expense of some proprietaryinformation being forwarded to these peo-ple, it is very important that they are fullyaware of every factor that could have animplication for the lining’s service life.When seeking recommendations from

these sources, insist on a written specifica-tion with a summary of the environmentthat the lining is to withstand. This canhave significant benefits if there is a failure.

Once the service environment andcandidate linings are determined, compara-tive exposure testing is worthwhile if timeallows. Relining plans should always bedone enough in advance so that compati-bility testing or side-by-side comparabilitytesting can be undertaken before the workis scheduled. Assuming that the system op-tions can be narrowed down to a few can-didate materials, it is important not to eval-uate their merits on price alone. Other

important selection factors are the reputa-tion of the manufacturer, the performancehistory of each lining, and the ability of thechosen system to be repaired and main-tained. If one of the candidate materials,once it has been in service, is extremelyhard to repair or needs subsequent coats,another lining may be a better investment.

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Linings must be able to withstand conditions during service outages as well as during immersion service.


The ease and versatility of applicationshould also be considered. Linings that canbe applied with conventional or airlessspray equipment may have advantagescompared to linings requiring specialist orplural component application equipment.Such equipment may be difficult to maneu-ver or operate and, in unskilled hands, maynot yield the desired film properties.

Surface Preparation

The highest level of surface preparationpossible is strongly recommended in alltank lining work. The mechanical condition

of the tank must be addressed as part ofthe evaluation of the tank for surfacepreparation.

Mechanical Condition of the TankThe condition of the welds and the plateedges, the presence of weld spatter and thegeneral continuity of the surface, and the

radius of guillotined or gas-cut (flame-cut)edges must be satisfactory to ensure the ad-hesion and integrity of the lining system tobe applied. The condition of the surface it-self, whether new or being relined, must beassessed, particularly for the presence ofoil, grease, or soluble salts. All of theseitems quickly attack tank linings.

Condition of Existing LiningFor relining projects where the existing lin-ing has not completely deteriorated, it isworthwhile to evaluate the life expectancyof the existing lining system until full re-moval is required. If there is only localizeddamage (blistering and minor pitting), the

lining does not necessarily need to be fullyremoved. It may be better to evaluate thethreat to the substrate’s integrity and, if thesubstrate is not at risk, leave the existinglining in service for as long as possible.When the substrate’s integrity is at risk,however, a full coating removal and re-placement should be planned.

Making Linings Last


A lining failure inside a cement sludge tank

caused by poor site preparation and poor

coating of thefield welds.


In the author’s experience, spot repairwith localized blast on the deterioratedareas has sometimes caused massive failureby blistering in areas adjacent to the repairareas, due to overblast damage. Previouslysound coating has suffered pinprick dam-age from the abrasive stream impinging onnon-target surfaces. Even if microscopic atfirst, this damage has opened a paththrough the old coating that allows thetransmission of water vapor or electrolyteto the substrate, causing blisters. In someinstances, where 50 percent to 80 percentof a tank surface has been spot blasted orspot and sweep blasted, the anniversary in-spection showed massive damage on allsurfaces adjacent to the spot blast zones.

Spot blasting should be consideredonly if less than 10 percent of the tank sur-face requires repair. For damage above 10percent, it is preferable to delay recoatinguntil more of the residual value of the lin-ing has been consumed, when a full blastcan then be planned. The incremental costof extending to a full blast is generally notexcessive and can certainly be more attrac-tive when weighed against durability andcost per year of service.

If spot blasting and repair are consid-ered essential, then workers must fully andadequately mask the areas adjacent to thezone of repair so that there is no threat ofdamage to sound areas. This can be doneby taping insertion rubber, rubber sheeting,tarpaulins, or heavy cardboard sheetaround the repair zone to confine or re-strict any threat of overblast damage.

Sequence for Surface PreparationPre-job planning should include developinga sequence for surface preparation. Relin-ing projects may call for a blast/wash/blastsequence to remove or lower the solublesalt levels that may be underneath the filmor to allow the mechanical condition of thetank to be checked thoroughly, especiallyat welds, plate edges, and other areas diffi-

cult to protect. A double blast sequence ishighly recommended for tank lining or re-lining projects. It allows the old lining to befully removed for tank inspection, but italso allows greater productivity per dayonce the second or final whip blast (Brush-Off Blast, SSPC-SP 7) is under way.

Typical production blasting rates forremoving an old lining inside a tank can bebetween a quarter and a third of the rate atwhich a whip blast of a previously cleanedsurface can be completed. Therefore, largerareas can be lined after a single day’s re-blast production. This means fewer joints inthe lining, less contamination from dena-tured coating or abrasive, and less chanceof overblast damage while maintaining pro-duction rates than if the first coat is appliedimmediately after the first blast.

A blast holding primer that is compat-ible with the lining system should also beconsidered. This primer generally allowsfaster lining of blasted surfaces with quick-er drying. Holding the blast with a primeralso minimizes the chance of damaging aslower drying, full thickness lining that hasbeen applied to an adjacent surface duringthe previous shift or day. The use of a blastholding primer also saves the multiple mix-ing and wasting of high build material thatwould be needed to coat the limited day’sproduction from a single blast process,thereby reducing the potential for errors inmix ratio. It can also allow for the use of amore economical abrasive for the initialblast, one that might not generate the re-quired surface profile but could bechanged for the final blast when significant-ly less abrasive is needed to achieve theprofile specified. Before the second blast,the surface should be fully checked for sol-uble salts and oil or grease. Detection kitsfor each are commercially available.

Climate ControlThe specifier should consider humidity andclimate control, ventilation, and air circula-

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MARCH 1996 / 67


tion inside the tank during surface prepara-tion and coating application. Dehumidifica-tion equipment will help to hold the blast.Ventilation removes dust to give the blastand spray operator good visibility and toavoid the possibility of contaminating thenewly applied wet lining. Both dehumidifi-cation and ventilation equipment must bedesigned for the tank size, volume, andconfiguration, or they will be ineffective.

Heating the tank in cooler weatherwill also help in most cases with the qualityof the tank lining. Care must be exercised,however, to ensure that the well estab-lished cold wall effect of high internal tem-peratures and a low substrate temperaturedoes not lead to blistering and damage.

Abrasive SelectionThe type and size of abrasive are importantto the work. The abrasive should producethe profile shape and height required toensure acceptable lining adhesion to thesubstrate. Abrasives should be chosen withcharacteristics that minimize shattering and,more important, minimize embedment intothe substrate. Many of the heavy angulargrits, particularly chilled iron or steel grit,can damage a lining if they are used as thefinal abrasive. Minute pieces of these metal-lic abrasives can fracture and become em-bedded in the substrate. The abrasives andthe tank substrate are often dissimilar met-als. Embedded abrasives can therefore setup a corrosion cell. They can also remainas protrusions as well as embedments thatthe lining cannot encapsulate and fullycover. A non-metallic abrasive that is lowdusting and low fragmenting is preferredfor tank lining. It should be graded to pro-vide even cleaning and to produce an evenprofile shape and height.

There is much debate about profilerequirements. The most crucial element isthe profile shape rather than the height.Because the profile height is a measurableitem, too many specifiers and inspectors

concentrate on the specified height. Be-yond a certain point, the profile height hasless of an effect on adhesion than does theshape of the surface roughness generated.The most effective abrasive is one that pro-duces a uniform, jagged tooth with thegreatest increase in effective surface areabut with a height that is approximately 25to 30 percent of the final dry film thickness(dft). The maximum profile height is 2.3 to3 mils (58 to 76 micrometers) for most coat-ings. Very few organic or inorganic coatingsrequire a profile height above 4 mils (102micrometers). The most common excep-tions are ultra high build materials andthermal spray metallic coatings.

Substrates to be lined should never beblasted with spherical abrasives such assteel or chilled iron shot, or any other abra-sive that produces a similar peened shape.Disbonding will result. Zinc silicate coat-ings, which have a metallurgical as well asa chemical bond to the steel surface, canreadily detach from a shotblasted substrate.

HousekeepingAnother part of evaluating surface prepara-tion is determining the method of removalof the spent abrasive and paint waste fromthe tank interior. Is it to be swept out or re-moved by vacuuming? Before a lining isapplied, the blast cleaned surface shouldbe vacuumed as the final step. Sweeping or air blowing will not fully remove thefinely shattered abrasive from within theprofile shape. If not removed, the shatteredabrasive interferes with the lining’s adhe-sion to the substrate and provides a site forosmotic blistering.

Coating Materials

Getting the MaterialBefore the project begins, the amount ofcoating required must be calculated and or-dered. The amount can be determined only

Making Linings Last



by accurately measuring or calculating thesurface areas involved and allowing for allcontingencies. Having the lining on site be-fore surface preparation is complete willalso allow the contractor to check batchnumbers. Ideally, the lining materials need-ed for a project or a definable part of aproject will come from the same batch.

When lining materials arrive on site,the contractor or inspector should verifythat the product specified matches theproduct received. For multi-pack products,the sizes of all components should match.That is, the part B component should bethe correct size ratio for the part A. A num-ber of tank lining failures have been causedby mixing the part A component for a one-gallon (four-liter) kit with the part B for afive-gallon (20-liter) kit or vice versa. Forlinings that require solvent to be added, thesolvent should be the one recommendedby the manufacturer, not a local substitu-tion. A more economical solvent may beused to clean out application equipment aslong as it is flushed out and there is nochance of it being mixed with the productduring application.

StorageThe lining material should be stored on sitein a secure and weatherproof location. Ifthe coating work is to be performed out-side the normal conditions of temperature,60 to 75 F (16 to 24 C), then the coatingshould be stored in a controlled tempera-ture environment. The ideal storage tem-perature for most protective coatings is be-tween 68 and 75 F (20 and 24 C). In manyinstances, a heated or cooled storage roomwith temperature controls will be neededto maintain this range. The consistency ofmixing, thinning, application effectiveness,flow, cross-linking, and final cure dependon the lining temperature at the time ofmixing. Lining containers should also bestored in a place that will keep them freefrom contact with water. Because of their

chemical resistance, many tank linings aremulti-component materials. Often, at leastone of the components is sensitive to mois-ture. If coating containers are left in theopen and are allowed to heat and coolthrough weather cycles, water can be intro-duced into the coating even through thesealed lids as the unfilled space in the con-tainer expands and contracts with tempera-ture. Solvents, too, are very sensitive tocontamination with water, particularly be-cause the dished lids of the larger contain-ers or drums can allow water to pond if ex-posed. Storage under a tarpaulin can benearly as bad as storing the materials in theopen because lining materials can sweatunder the tarp.

Mixing the LiningsOnce the lining is ready to be mixed, thematerial should be withdrawn from storage.If temperatures are outside the ideal rangenoted above, withdrawal should be timedso there will be no delay before mixing.Once the blasted surface is nearly ready tobe lined, the selected spray equipmentshould be assembled and tested. Testingshould be carried out using the solventcompatible with the lining. With airlessspray, filling and pressurizing the unit willassist in flushing the fluid lines and check-ing for system leaks.

The order of mixing components isoften overlooked. Once both componentshave been selected, the lower viscosity(less thick) component should be stirredfirst. This will often be the curing agent orcatalyst for the lining. Even though it mayappear homogeneous, it should always bestirred or fully dispersed. The lower viscosi-ty component should be stirred first be-cause it will be easier to clean the mixingequipment before use on the more viscouscomponent. The second or heavier bodiedmaterial is then stirred without any curingagent. Stirring the second component aloneensures that all elements from within the

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MARCH 1996 / 69

Metallic

abrasives

embedded

in a metal

substrate

can set

up a

corrosion

cell if the

metals

are

dissimilar.


drum are fully blended and that it is at aconsistency adequate for spray application.Breaking any lumps from the sides and set-tlement off the bottom of the container,preferably with a stick before completepower stirring, is the first step.

Once the heavier component is fullydispersed and while it is under agitation,the part B component is added. (Often,more than 1 person is needed to mix thelining.) During the addition of the secondcomponent, the product should be underagitation to prevent the chance of solventshock (shocking the pigment out of the so-lution by adding too much solvent), whichcan happen if stirring is not performed uni-formly while the components are blended.Some linings require an induction timeafter all components are fully dispersed.The requirements for an induction time arenormally given on the manufacturer’s prod-uct data sheet.

It is always sound practice to mix the full kit of the multi-component packrather than try to proportion it by eye. Evenwith considerable experience, it is very dif-ficult to get an accurate ratio of a multi-pack coating without some method ofweighing or volumetrically measuring theconstituent components.

If the lining must be thinned for therecommended application method, itshould be performed after the inductiontime. Otherwise, the lining could be over-thinned because it heats up during induc-tion and becomes less viscous.

Lining Application

Proper Application ConditionsIf the lining is not applied under controlledclimatic conditions, then application andsubsequent drying and curing should betimed to occur when the conditions will bemost suitable. Early morning or late after-noon are often not ideal for application

and cure because temperatures and humid-ity levels change most then. Success de-pends upon satisfactory air temperatures,substrate temperatures, and conditions ofrelative humidity and dew point. Theseconditions need to be maintained through-out the application and initial curing. Con-densing moisture or dropping substratetemperature during cure is extremely detri-mental to the lining’s performance.

Condition of the EquipmentSuccessful lining application also dependssignificantly on cleanliness of the equip-ment, in particular, freedom from oil andwater in the compressed air supply and inthe paint mixing and fluid lines. Generallyspeaking, the manufacturer’s recommenda-tion for application equipment is a goodplace to start even though other equipmentsetups can be successful.

Selecting the Application SequenceAs with surface preparation, the sequenceof coating application can have a signifi-cant impact on lining performance.

The blast and prime process, as op-posed to the blast and full coat or doubleblast sequence, has advantages for liningapplication as well as for surface prepara-tion. The need for extreme cleanliness be-tween coats and freedom from contamina-tion during the intercoat interval can alsodictate this coating sequence. Because of itsfast dry characteristics, a blast holdingprimer or a low viscosity first coat can pre-vent dust contamination. Its tolerance forearly recoating with a high build lining canimprove the overall integrity of the lining.The holding primer also allows welds andcorners to be stripe coated before the firsthigh build coat. If the blast holding primeris not used, then when the stripe coating isperformed, the areas not coated might nothold the blast long enough for the full coatto be applied. If the holding primer is notused, then it is better to apply the stripe

Making Linings Last



coat after the first full build coat is appliedand can be recoated.

Stripe coating is critical. During theconversion of a wet coating into a dry film,the normal internal curing stresses inside alining have a tendency to pull the dryingcoating away from edges and sharp cor-ners. Even with the careful rounding ofthese edges in the mechanical preparationof the tank, some thinning of the dry coat-ing will result. Stripe coating is designed toalleviate this low dft to help provide a uni-form minimum dft on all areas of the tank.Areas for stripe coating are edges, corners,and welds, as well as the localized zoneswhere access with the spray equipment isdifficult, such as on the backs of angles oron the reverse of stiffeners.

A quick-drying primer is preferred fortank lining application. Once the primer iscured enough to be relined without dam-age, a stripe coat of the high build shouldbe applied, followed by a full spray appli-cation of the same lining. Once the stripeand full coats have dried, with the correctrecoat interval, the dft should be checked.This approach allows a high probability ofachieving the required dft. If dfts on edges,welds, and corners are still low, then theintermediate film thickness readings will in-dicate where attention is still required.

Quality Assurance during Lining OperationsThe applicators should be advised of thetarget dfts per coat and the wet film thick-nesses required to achieve the dfts. Over-building can be as detrimental as under-building in tank lining applications,especially because of solvent entrapmentand insufficient cure. Both can lead to blis-tering and coating detachment. An applica-tion sequence and the necessary equipmenthelp ensure that the largest possible area ofthe tank’s internal surface can be coatedwith good access and with an even spraypattern that will give reliable film thickness-

es. Attention to welds, edges, and cornersdictates that not only should they receive astripe coat, but they should also receivecareful spray attention. They should besprayed on both sides or on all exposedsurfaces. It is not uncommon, when in-specting tank linings, to find uniform filmthicknesses on plate surfaces while only 1side of the welds is lined adequately.

A color contrast should exist betweeneach lining in a system, including the stripe coating, to help measure dfts. Unfortunately, many tank lining materialsare manufactured in only 2 colors, for in-stance, white and buff. However, for the

sake of the color contrast, it is often satis-factory to make a partial blend of the twocolors and convert it with the correct ratioto give an intermediate shade that will bedifferent enough where the color contrastis required.

Lighting and ventilation are againmajor issues for coating application. It is

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A fish holding tank inside a tuna fishing vessel before relining. The difficulty of access caused by the ammoniarefrigerant piping should be consideredwhen preparing a specification for relining.


very difficult to apply a uniform coatingthickness if the applicator has minimal visi-bility or if there are excessive spray mistand solvent fumes inside the tank.

Flameproof or explosion-proof light-ing is extremely important in any situationwhere solvent vapor is present. For ade-quate ventilation, the air movement shouldbe sufficient to assure that the maximumconcentration of vapor does not exceed 10 percent of the lower explosive limit forthat vapor.

Cleanliness at all stages of the finalsurface preparation and coating applicationis very important. Cleanliness extends topreventing perspiration drips in the tankand preventing dirt or other foreign matter,including abrasive debris, from becomingembedded in the tank lining. Developing a system for access and housekeepingensures maximum cleanliness at all stagesof work.

At all stages of the surface prepara-tion and lining application, the applicator,the supervisor, and the full crew must assume responsibility for ensuring quality.Quality is not as simple as achieving a dft within the specified narrow range.Often, factors such as intercoat cleanliness,observation of the climatic and substrateconditions, and time for curing are not asobvious as dft when the coating system is complete, but can be significantly moreimportant in ensuring the integrity of the lining.

Testing and Inspection

Even though these items are last in the dis-cussion, they should be included in everystage of the process, from determining theneed to line or reline to returning the ves-sel to service. Whether the inspection iscarried out by an independent third partyinspector or by the client’s own representa-tive, key points include the following.

Pre-Job MeetingA pre-job meeting that includes the client,the contractor, the inspector, and, possibly,the specifier is vital. All elements of thework should be discussed, particularly thecriteria for acceptance and the proposalsfor the sequence of activities. Correctlyconducted, this meeting should clarify thedemands of the project for all parties.

One procedure that the author hasadopted at the pre-job meeting for tank lin-ing work is preparing a written summary of key specification details for the supervi-sor. Often this document can be as simpleas a one- or two-page summary of the climatic condition limits, the restrictions,the lining system, the interval betweencoatings, the wet and dry film thicknesses,the solvent type, and any other relevant in-formation such as the inspection accep-tance criteria and referenced standards.While the summary does not replace theneed for the supervisor to understand thecomplete project specification, it is valuablefor quick reference.

On-Site InspectionInspection has many stages. The first in-spection of the original condition shouldinclude a thorough visual check and rectifi-cation, if needed, of all welds and steel-work conditions. Verifying the detectionand removal of visible oil, grease, and dirt should receive priority at this sametime, too.

Once the first blast is performed, aninspection can provide information aboutthe condition of steelwork and the heightand shape of the blast profile. Even thoughthe surface will be reblasted, checking theprofile at this time can help to determine ifthe final surface will meet the specified cri-teria once the final blast is performed. Ad-ditionally, it can provide early indicationsof possible problems with achieving thespecified profile on zones affected by heat,such as welds. On such zones, where met-

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allurgical differences create a harder sur-face, it is often difficult to achieve the pro-file specified. In this author’s view, manyfailures around tank welds may be causedby this phenomenon.

After the first blast, the inspectorshould also look for evidence of oil, grease,dirt, or soluble salt on the steel. These con-taminants may have been introduced byblasting or by the workers themselves.Many tank lining failures show evidence ofa perfect hand print that was made on theblasted surface before application. Removalof these contaminants may require wash-ing, rinsing, steam cleaning, or solvent wip-ing. If oil or grease is persistent, then swab-bing with a 1:1 mix of methanol and waterhas proved to be very effective. Steamcleaning between a double blast sequenceis recommended for removing soluble saltsfrom steel surfaces.

Inspection after the final blast shouldinclude a visual confirmation that the blast,vacuum or final clean, and profile meet thespecification. The blast cleanlinessachieved, it should be remembered, is thecondition evident at the time the lining isapplied, not the level when blasting wascompleted.

Inspection should also include an ob-servation of the lining mixing, visual confir-mation of the components, and recordingof the batch numbers and quantities thatare prepared. At all stages, the climatic andsubstrate conditions need to be measuredand recorded.

Once lining application has begun,the inspection should include checking wetfilm thicknesses; confirming that flow, lev-eling, and atomization are appropriate; andassuring that the first coat is free of pin-holes. If deficiencies in lining handling orapplication cannot be corrected with spraytechnique, timely adjustments can be madeto the application equipment; mixing, thin-ning, or the temperature of the lining; orother variables.

After the first coat, a full inspectioncan give valuable guidance to the applica-tor and the supervisor so that the balanceof the application can rectify any non-con-formance in the system so far. It is particu-larly useful to detect and highlight areasthat are missed, or those that are high orlow in dft. Finding such areas at this pointcan often save the application of an addi-tional coat if the indications are that thepresent technique will not achieve the de-sired final film.

Methods of highlighting non-confor-mance should be considered. It is not asound idea to use wax crayons or felt tip

pens. Chalk is generally superior, providingthe color does not interfere with the subse-quent lining. Bright colors have beenknown to show through the next wet coat.

The inspector should look for sweat-ing on the first coat, particularly with epoxies, which will always be detrimentalto adhesion of subsequent coats. The

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Chalk marks highlight non-conformance found during inspection.


1:1 mixture of methylated spirits in water isan effective remedy, and because of themiscibility and easy evaporation of the mix-ture, residual water is not a problem.

The inspector should also note theneed for recoating or repair. If deficienciesare found in any coat, they should be recti-fied before application continues, particu-larly if there is a sequence of differing coat-ings in the lining system. (The argumentthat applicators will fix up the shortfall withadditional finish coat should not be accept-ed.) Similarly, the inspector should observethe stripe coat methods, discuss the op-tions, and ensure full compliance.

Checking the cure of each coat is im-portant. If accelerated or retarded curing isevident during the inspection of the firstcoat, the problem is worth investigating. Inone instance where a slowly curing firstcoat was ignored and a finish coat was ap-plied, the lining failed. Investigation re-vealed that the mix ratio for the first coatwas incorrect. Even though the primer wascoated with a finish having a correct mixratio, the tank lining failed because of thepoor integrity and inadequate chemicalstructure of the primer. This failure resultedin a rather expensive removal and replace-ment procedure that could have beenavoided if the warning signs of slow curehad been heeded. If there is doubt aboutthe integrity of any part of the system, it isbetter not to continue rather than risk theconsequences of a non-conforming lining.

Once the system is applied, finalchecks will include a full dft check, a thor-ough visual continuity check for missed orthin areas, and verification of a touch-upprocedure for any non-conforming zones.Once a satisfactory visual continuity checkis completed, the lining must have enoughtime to cure before the tank is put into ser-vice. Unfortunately, the outage time for thetank relining often includes only the mini-mum time calculated without any al-lowance for lost time. When only the mini-

mum cure time is allowed, the cure is oftencompromised because of inspection, re-work, or climatic changes that slow cure. Ifthe tank is filled before cure is complete,disastrous failure may result.

Continuity testing with high or lowvoltage equipment as appropriate for the lining type and thickness should be carried out if specified. Continuity testing,however, can be performed only when the coating is cured and dft has beenchecked completely. Continuity testingmust be performed in accordance with thestandard specified. If touch-up is needed,the procedure must be authorized by thelining manufacturer.

RecordkeepingOne of the last stages of inspection is tocomplete a full and final report, includingall achievements, non-conformances andtheir rectification, full details of the liningused, batch numbers, and climatic andother relevant data. This report will oftenbe the only permanent record of all aspectsof the lining project. The report can be ex-tremely useful, whether the coating servesfor many years or fails prematurely.

Anniversary InspectionFrequently, the last duty of the inspector isto perform the anniversary inspection ap-proximately 12 months after the tank is putinto service and just before the contractor’smaintenance period expires.

Conclusion

To maximize the life of a tank lining sys-tem, take the time, plan the work, and stickto the plan. Compared to a poorly plannedproject with a resulting lining life of only afew years, a properly planned, well execut-ed lining project can add as much as 12 or15 years to the achievable operating life ofthe system. JPCL

Making Linings Last

Mark B. Dromgool,general manager and principal of KTA-Tator

Australia, has been in theprotective coatings

industry for over 19 years. Ten years of his experience has included

the management of several large grit blasting

and application shops, a galvanizing operation,

and large field and site coating teams.

During this time period, Dromgool gained

extensive experience inworking on a variety of

structures, includingbridges, tanks, structural steel, wastewater plants, pulp and paper plants,

as well as chemical, mining, and

petrochemical facilties.In 1993, Dromgool

formed Akarana Coating Services,

a protective coatings engineering and

consulting firm. Twoyears later he joined n

KTA-Tator.Dromgool is a member

of SSPC and an Executive of the Blast

Cleaning & Coating Association of Australia.

He can be contacted at KTA-Tator Australia,

136 Lord Street, Richmond,Victoria 3121,

Australia; 61/3/9428-9339;

fax: 61/3/9428/9131


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