jacketing over insulation

Proper selection of jacketing over insu-lation in most industrial settings is justas important as the selection of the

insulation. An insulation jacket thatfails may cause the entire insulationsystem to fail. Many jacketing materials

are selected on the basis of the initialcost, when in fact, this is perhaps thelast item to consider during the selec-

tion process. This article discusses thematerials, environmental conditions,surface size and design considerations

essential to proper jacketing for hot andcold operating systems.

Examples from industrialinsulation systems highlightthe proper selection of jacketing.

Examples from industrialinsulation systems highlightthe proper selection of jacketing.

jacketing overinsulationBY JOHN W. KALIS

Corrugated panels and tank head. Photo courtesy of Proto Corp.

List of Conditionsto Consider whenSelecting Jacketing

Indoor or Outdoor ExposureMany engineers and specificationwriters believe that since theequipment and pipe are indoors,the jacket or finish is simply thereto hold the insulation in place.The operations that take place in a

building may require wash downareas or periodic checking ofsprinkler systems. The responsibleperson should visit the site andpersonally inspect the conditions.If it’s a new facility, he or she

should question the project engi-neer or manager in order to learnabout all of the conditions.

Chemical ExposureAny process that produces a chemical that can shorten the

life of the jacket and insulation system must be a concern.Most manufacturers will provide information on the chemi-cal resistance of their jacketing.

Temperature and/or Fire ExposureTemperature exposure may be a consideration where the

insulated pipe of equipment may be within inches of a non-insulated hot pipe or equipment. Even when two insulatedpipes are side by side and the jacketing is touching the inner-face, temperature can exceed the allowable temperature ofthe jacket. This is especially true where non-metal jacketingis a consideration.

Equipment and pipe systems containing combustibleproducts may require protection with an insulationjacket that will resist chemical fires of 1700°F. for twohours. The jacketing material is usually stainless steel.Galvanized aluminum is an option, however, it is notrecommended on stainless steel pipe and equipment

since the zinc may leach from the galvanized aluminumand contribute to stress corrosion cracking.

Mechanical Abuse ExposureThis condition is the most difficult to evaluate. Again,the engineer must review the physical location of thepipe and equipment. The jacketing may be located adja-cent to a vehicle traffic area or below a work area. Foottraffic on horizontal pipe and tank roofs is common.“Keep Off” signs do not work.

The resilience of the insulation may determine the jacket-ing. For example, a rigid insulation such as calcium silicatemay require a lighter metal jacket than mineral wool or fiber-glass insulation. This could be true where there is a pipe rack,and valves or flanges require maintenance from a ladder.

Personnel SafetyThis is a concern on hot operating systems. The emissivityof the jacket surface can make a considerable difference inthe surface temperature of the jacket. Run some insulatedpipe systems using the North American InsulationManufacturers Association’s 3E Plus® program using various

jacketing materials and their respective emissivities. Thehigher the jacket emissivity, the lower the surface tempera-

ture. The surface temperature can vary byas much as 40°F. The surface temperatureshould not exceed 140°F. The data input,

such as the average high ambient air tem-perature and the wind speed, is critical. Itis best to be conservative with a highambient temperature and low wind speedwhen in doubt.

Jacketing PipeJacketing insulated pipe should be a sim-ple task–the main goal being prevention ofmoisture migration. This may be true on arefinery site, where the piping is done inlong runs without interruption, but for

chemical facilities the average straight runmay be five feet to a valve, flange or ell. Aslong as the pipe jacketing that overlaps theseams is installed in a watershed fashionand properly secured, the insulationshould remain dry.

The greatest problem occurs with jack-et interruptions such as valves, flanges andfittings. The joint between the pipe jacketand the valve and flange cover jacket canfail. Many times it is caused by an insuffi-cient overlap on the pipe insulation sys-

tem. It is important to extend the flange orvalve insulation cover over the pipe insu-lation at least two inches or the thicknessof the pipe insulation, whichever is great-est. This will provide a surface area largeenough to compensate for any movement

between the pipe jacketing and the flangeand valve covers.

ExampleSeveral years ago an insulation contractorcompleted work on piping for a sulfuric acid

plant. At startup, the pipe insulation jacket-ing pulled away from the flange and valvecovers leaving open gaps. The contractorhad the valve and flange covers pre-fabricat-ed in the shop. The pipe insulator terminat-ed the insulation at the flanges and valves

where he thought was appropriate. Uponcompletion of the pipe insulation, the flangeand valve covers were installed. The coversdid not overlap the pipe insulation and jack-et properly. The expansion of the hot pipecaused the joint to separate and open,

exposing the pipe insulation.

EllsJacketed pipe ells are another source ofmoisture migration into the insulation. It

begins with the typical two-piece metal ellinstalled with one of the tangent endsoverlapping the metal pipe jacketing in anon-watershed fashion. At a typical plantsite, it is not uncommon to find 10 percent

of the metal ell covers installed incorrectly.

In addition the overlapping seams at thethroat and heel seldom fit tight with a ¾”minimum overlap. Where an ell is turnedhorizontally, the seams must also be inwatershed configuration. A bead of caulk-ing sealant on these seams would also

help. Until recently, two-piece metal ell cov-

ers were limited to smaller size piping sys-tems. With a pipe ell larger than 12 inches,a metal gore system was an alternative.Metal gores are labor intensive and subject

to failure with the radial seams that haveto be secured and sealed. Metal ell coversare now available for pipe up to 24 inchesby 6 inches with 1 ½ diameter bends. Thiswill help eliminate wet insulation and becost effective on large piping insulation

systems. (See photo above.)april2001

insulation outlook

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First, it is important to consider thefollowing environmental conditionswhen selecting jacketing:

Photo courtesy of Associated Insulation. A pressed elbow is now available up to 24”x6”.Photo courtesy of Sproule Manufacturing Co.

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OptionsIn the United States, the jacketing standardon pipe and small equipment for industri-al and other applications is 16-mil thickrolled aluminum. This jacketing over pipeinsulation will resist most weather andabuse exposure. It is available in a variety

of thicknesses, from 6-mil to 50-mil. Thisroll jacketing can be ordered with anacrylic coating of severalcolors or Tedlar® (polyvinylfluoride) coated for severechemical exposure. The

rolled aluminum can beordered with a smooth,stucco embossed and cor-rugated finish. The corru-gations are circumferential,which provides additional

strength and rigidity.Another feature the corru-gations have is theimproved sealing of the cir-cumferential overlappingseams. It is surprising that

this material is not ingreater use. Some jacketingmanufacturers offer 3’-and4’-wide aluminum rolls.There are some industrialsites that use the 4’-wide

rolls. The advantagesinclude fewer circumferen-

tial seams and greater coverage produc-tion. However, the insulators would haveto become familiar with the 4’ rolls for it to

be cost effective. Polyvinyl Chloride (PVC) jacketing is

being used more extensively in industrialapplications. At one time, it was the choiceonly for the food industry. Now, with theultra-violet (UV) resistance, higher temper-

ature resistance and low flame/smoke rat-ings, PVC is being applied in areas whereonly metal jacketing was used. Although20-mil thick PVC jacketing is commonlyused on many applications it should belimited to indoor applications in areas

where there is no exposure to any abuse.The minimum thickness for industrialapplications, indoors and outdoors, shouldbe 30-mil thick PVC roll jacketing. The useof PVC the past several years has provedthat solvent welding of the joints can effec-

tively seal the seam permanently whenapplied correctly. A note of caution: PVCless than 30-mil thick may not solvent-bond correctly at the seam. It is recom-mended that the insulator experiment withthe PVC cement on sample pieces to

become familiar with the application. Besure to order the PVC roll jacketing pre-

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Aluminum jacketing over 2” FSK fiberglass board. Photo courtesy of Polyguard Products.

30-mil thick PVC jacketing on pipe next to PVC jacketed tank. Photo courtesy of Proto Corp.

curled for piping applications, otherwise,the longitudinal seam may be difficult toseal.

Composite JacketingWhere pipe insulation requires total pro-tection from the weather, impact and

harsh chemicals, composite flexible jack-et in rolls may be the solution. This jack-et is a composite of Tedlar® (polyvinylfluoride), two layers of Hypalon®, fiber-glass reinforcing and Mylar® (polyesterfilm). Where insulation jacketing is to

serve as a vapor retarder, the material isavailable with a corrosion resistant alu-minized Mylar. This material is easy toinstall by overlapping the seams andsealing it with a matching pressure-sen-sitive tape.

A 60-mil thick rubberized bitumencompound finished with a thick aluminumfoil facing is available. It is resistant to theweather and is an excellent vapor retarder.This rolled material has a contact adhesiveon one side for ease of application and is

ideal or HVAC and process rectangularducts located outdoors on building roofs. Itcan be applied over the duct insulation ordirectly to the surface. The Sheet Metaland Air Conditioning Contractors' NationalAssociation (SMACNA) recommends a

minimum 50-mil elastomeric membranefor protection on exterior ducts. (See photoon p. 14.)

Factory AppliedJacketing on InsulationThere is factory applied jacketing that affordsexcellent insulation protection. It is a 30-milthick PVC polyester coated fabric jacket thatis resistant to weather, most chemicals,

mechanical abuse and serves as a vaporretarder for cold systems. The jacket has aself-sealing longitudinal flap. The flexiblemelamine insulation with a wide service tem-perature range comes with this jacket in allpipe sizes. Installing the insulation and jacket

in a single application can be cost effective formany piping projects. The factory-applied

jacket comes in a variety of colors for pipeidentification. (See photo below.)

Many types of insulation materials are

available with ASJ (All Surface Jacket),vapor retarder. The ASJ product is a variantof the FSK (Foil-Scrim-Kraft), also know asFoil-Reinforced-Kraft. Many insulation man-ufacturers and fabricators provide this jack-eting on their insulation. It is generally a

one-piece section of pipe insulation thatsnaps on the pipe and is secured with a self-sealing longitudinal seam. The butt jointsare sealed with matching tape.

The aluminum foil component on thisjacketing uses a foil ranging from 0.000285”

to 0.00033” thick. Mechanical abuse, severehandling or wrinkling of this thin foil maycompromise the performance as a vaporretarder on cold operating systems. Wherethis abuse is apparent, there is currently anASJ/FSK jacket available using nominal

0.001” (1-mil) foil. (See photo on p. 18.)

In areas where this jacketing can get wet,additional jacketing over the factory-appliedjacket must be installed.A word of caution: If the operation of the

process is dual-temperature, cycle or shut

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Melamine foam insulation pre-jacketed witha polyester fabric reinforced PVC covering.

Photo courtesy of Accesible Products(Techlite Insulation).

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Mon-ecoSupplied Digital

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down periodically, the dew point of thejacketing inner-face can be reached. Whenthis happens, the vapor-moisture can col-

lect between the jackets causing deteriora-tion of the ASJ/FSK jacket or corrosion tothe outside metal jacket. If this condition isa possibility, then install a single jacket. Ifthat is not possible, and the outside jacket

is metal, specify the

2.5-mil Poly/Surlyn®vapor retarder back-ing. The standard 1-mil poly/kraft back-ing will not protectthe metal jacket from

corroding inside out.

JacketingSmall Tanksand Vessels

(By definition, for thisarticle, small tanksand vessels shall beless than 40 feet in

diameter.) Verticaltanks and vessels,less than 40 feet indiameter account forapproximately 95 per-cent of all equipment.

Industrial chemicaland petrochemicalplants are the great-est users of equip-ment in this sizerange. These sites

can have more than athousand small ves-

sels and tanks. More than 80 percentrequire some type of insulation system.This accounts for an impressive amount ofinsulation and jacketing.

The following parameters serve as aguide for minimum jacketing on the sidewallof vertical tanks and vessels for outdoorapplications. Indoor applications may beless restrictive.● Up to 5 feet in diameter: 16-mil thick

smooth rolled aluminum jacketing or30-mil thick, smooth roll PVC jacket-

ing; secured with minimum ½”- wideby .015 stainless-steel banding.

● Up to 10 feet in diameter: 16-mil thick

smooth rolled aluminum jacketing or16-mil thick 1¼”-deep corrugated pan-eling or 50-mil thick corrugated PVCpaneling; secured with minimum ¾”-wide by .020 stainless-steel banding.

● Up to 20 feet in diameter: 24-mil thick

1¼”-deep corrugated aluminum pan-els or 50-mil thick corrugated PVC pan-eling. Secured with minimum ¾”-wideby .020 stainless-steel banding.

● Up to 40 feet in diameter: 24-mil thick1¼”-deep corrugated aluminum pan-

els or 24-mil thick galvanized alu-minum; secured with minimum 1¼”-wide by .020 stainless-steel banding.

The following parameters serve as a guidefor minimum jacketing on the heads of

vertical tanks and vessels for outdoorapplications: The metal and PVC shall becut in gore segments.● Up to 10 feet in diameter: 24-mil thick

smooth rolled aluminum, 16-mil thicksmooth galvanized aluminum, 10-mil

smooth stainless steel or 40-mil thick,smooth PVC.

● Up to 30 feet in diameter: 24-mil thicksmooth rolled aluminum, 16-mil thicksmooth galvanized aluminum, 16-milthick smooth stainless steel or 50-mil

smooth PVC.● Up to 40 feet in diameter: 32-mil thick

smooth rolled aluminum, 24-mil thicksmooth galvanized aluminum or 16-mil thick smooth stainless steel.

The metal jacketing is normallysecured with sheet-metal stainless-steelscrews on 4” centers at the seams.Secure the PVC by solvent welding theseams and screws where necessary.

It should be noted that recently a

tank, 23 ft. 6 in. in diameter with adome roof was successfully jacketedwith PVC. This is the largest knowntank roof to be jacketed with a pre-engineered PVC gore segment system.The sidewalls were jacketed with new

designed 0.060-mil thick PVC corrugat-ed panels and the head was jacketed

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ASF/ FSK jacket available in 1-mil foil. Photo courtesy of Compac Corp.

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with a pre-engineered 0.060-mil thickPVC segments in gore form. (See photoabove.)

Jacketing Large Tanksand EquipmentEquipment such as storage tanks is a

major investment to every company. Notonly in terms of the initial investment, butalso in the event the tank fails from exter-nal corrosion. A leakage of contents couldcause an environmental disaster.

Wind conditions are one of the most

critical items to consider when evaluatinga jacketing system for large tanks. Thetank size usually dictates the type of jack-eting to be used over the insulation. Largertanks require heavier jacketing. This isnecessary to overcome high winds on large

tank areas.For example, several storage tanks,

approximately 50 feet in diameter, locatedon a bay were subjected to a gale forcewind. The tanks were insulated and jack-eted with 16-mil thick rolled smooth alu-

minum jacketing. Upon evaluating thedamage, apparently the wind was able to

lift the overlapping circumferential seam ofthe jacket. The banding was ½”-wide steelwith light duty expansion springs and was

not secured to the jacket. The uplift of thejacket caused the banding to fail. In addi-tion, the expansion springs were practical-ly straight pieces of metal. Once the firstcourse of jacketing failed, the succeedingcourses also failed.

It was evident from the damage thatthe greatest force of wind was across thebody of water. This was purely an under-designed jacketing system. The tank walljacketing should have been at least 24-milthick, deep-corrugated aluminum panels,

secured with ¾”-wide by 0.020 thick stain-less steel bands and heavy-duty stainless-steel expansion springs. To prevent thebands from sliding up or down, J-hooks orbelt loops could be used. Finally, securethe vertical panel seams with screws on 4”

centers.Another area of concern is that usually,

roofs receive the greatest damage fromwind. A case in point: A new 60’ diametertank, located in the Midwest where thewind blows continually, was completely

insulated to maintain temperature controlof the contents. The sidewall was jacketedwith corrugated aluminum paneling andthe conical roof insulation was jacketedwith a metal standing seam system. Theowner indicated that the completed insula-

tion work was only several weeks old,when he noticed that the metal roof jacketwas vibrating violently. Upon inspection,the jacket was vibrating and there weresigns of the metal jacket tearing at thestanding seams in several locations. Two

weeks after the inspection, I was informedthat the entire roof jacketing ripped awayfrom the tank and was scattered about thecounty. The loss of this roof jacketing wasnot the result of hurricane or gale forcesbut 20-mph winds, normal to this part of

the country. Fortunately, no one wasinjured. The cause appeared to be thatjacket tie-downs were not sufficient orproperly distributed and that there was noattempt to flash around the roof where itoverlaps the sidewall. This 2” opening at

the roof overhang allowed the wind to fun-nel under the roof jacket which increased

23.6 diameter x 16’ high with dome roof. PVC corrugated panels and PVC tank heads.Photo courtesy of Proto Corp.

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1900 West 47th Place, Suite 115 • Westwood, KS 66205Phone 913-722-1066 • Fax 913-722-6899 • Toll Free Number 866-722-1066

Al BradleyWeb site: www.humpedelbow.com Email: [email protected]

the normal wind forces, causing it to uplift,like wind would do to an umbrella. Theinsulation became exposed to the weather,

requiring total replacement by the contrac-tor. This failure could have been avoidedby following proper design.

Study EngineeringCriteriaA national document from the AmericanNational Standards Institute (ANSI) A58.1“Minimum Design Loads for Buildings andOther Structures” addresses wind loads on

roofs and walls of buildings and structures.This wealth of design information is alsoapplicable to vertical tank wall and roofjacketing.

The document gives the expectedextreme wind velocity in various areas of

the country. Consider the following exam-ple: Around the gulf coast, 100 mph is typ-ically used in the calculations, while inCleveland, Ohio 75 mph is used. There arefactors for the height of the tank roof aswell as the roof pitch. There is even a wind

gust factor that varies by location.Using ANSI A58.1 as a guide, the fol-

lowing tank roof insulation jacket windforce is calculated. The tank is within 100miles of the gulf coast, with a basic wind

velocity of 95 mph. The tank height is 30feet to the center of the pitched roof andthe roof pitch is 20 degrees. Since tanks arecircular, the windward side of the roof isthe same in any direction with the greatestwind force. By calculating per ANSI A58.1,

the design wind pressure on the roof is–21.3 lb./sq. ft. The minus sign indicatesthat the force is an uplift pressure. Thedesign engineer must now determine thatthe tie-down straps, bolts, cables and anyother means, to safely secure the roof jack-

et with an upward wind-load pressure of–21.3 lb./sq. ft.

Similarly, the tank wall jacketing canalso be evaluated for wind resistance.Several companies offer a pre-engineeredwall paneling and roof systems designed

for tanks of all sizes. They have alreadyengineered the systems to comply with theextreme wind and weather conditions.

The pre-engineered insulation systemsfor the tank sidewalls are usually compos-ites of insulation adhered to the jacketing.

The insulation for these systems is poly-isocyanurate, glass fiber or mineral wool.For tanks operating up to 250°F the PIRinsulation is commonly used. Above250°F, glass fiber or mineral wool boardand blanket insulation is installed.

There are two methods of insulatingthe vertical tank sidewalls. ● One method is with 4’ x 8’ panels,

installed horizontally around the tank.These panels are usually 32-mil thickaluminum with an acrylic enamel fin-

ish on the outside and insulationadhered to the inside. The panels arepre-curved to the radius of the tank.They come with an elastomeric seal onthe vertical locking seam and securedwith 3”-wide metal banding. The com-

pression spring assemblies on thebands are designed for severe loading.

● The second method involves 2’-wide,continuous vertical panels, manufac-tured to the height of the tank. Theinsulation is pre-adhered to jacket. The

vertical seam is double rolled to makeit weather proof. The panels are

april2001

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60’ diameter x 40’ high storage tank insulated with 1 1/2” thick PIR on the walls and 3” thickmineral wool on the roof. Photo courtesy of Associated Insulation.

secured to the tank with metal ties heldin place with metal cables wrappedaround the tank.

The roof system is usually determinedby the configuration and size of the roof.Cables or rods are secured to the roof, withbolting or welding. Usually the insulationis installed on the roof separately and thenthe jacketing is installed over the insula-

tion. The common metal used for thisapplication is 24-mil thick galvanizedaluminum with a vapor retarder backing.

Where the tank roof is flat or conical,the jacketing may by 2’-wide metal sheet-ing with a doubled rolled standing seam.

The seams will run parallel over the entireroof and the metal ties secure the jacket-ing to the cables or rods.

Where the tank roof is elliptical or hasa high pitch the panel system becomesmore complex. If the curvature is too great

then double rolled standing seams may notbe an option. In this case a series or pan-els must be pre-cut like gore segments and


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HowredP/U March 2001 p.53Do not output page!



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circle # 13 on reader service cardcircle # 12 on reader service card

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installed with screws at the seams.Large tanks, and especially tanks that are heated, require expansion joints

on the roof systems.

The companies that offer these pre-engineered paneled systems can becontracted to complete the entire project. However, the materials and know-how is available for installation by individual insulation contractors. Manyinsulation contractors have successfully installed these panel systems. Thesesystems may be adaptable to smaller tanks. (See photo on p. 22.)

Final NotesAs you can see, many considerations go into selecting and installing jacket-ing. The proper selection of jacketing is as essential as the insulation. Knowyour environment, your surface and design parameters, and installationoptions before beginning work.

Poly/Surlyn® is a registered trademark of DuPont.Tedlar® is a registered trademark of DuPont.

Hypalon® is a registered trademark of DuPont.Mylar® is a registered trademark of DuPont.

John W. Kalis, Jr., P.E. is a consultant engineer retired from E.I. Dupont Co.He currently provides service to clients through his own firm, J.W. KalisEngineering Company, Inc., Medford, N.J. He is a member of ASTM C-16Thermal Insulation Committee and the National Association of CorrosionEngineers. To contact John, call (609) 654-0927.

jacketing over insulation

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