Correctly specify insulation for process equipment and piping

Covered are the most suitable insulation materials for certain applications, the most economic material and thickness to use, and how the total insulation system should be designed.

Insulation serves as thermal barrier to resist the flow of heat. When insulation is installed over the piping or equipment to minimize heat losses, the insulation is categorized as heat conservation. Software programs for determining heat losses are based on ASTM C 680 (I). If heat conservation insulation is calculated to determine the most cost – effective thickness for piping or equipment, then the insulation is categorized as economic insulation. Methods for manually deterning economic thicknesses using various graphs and precalculated charts are given in Turner and Malloy (2). However, modern software programs available from industrial associations calculate economic thickness based on after-tax annual cost basis. The thickness with the lowest annual cost is reported as the economic thickness. Some of the economic data needed to calculate economic thicknesses are fuel cost, depreciation period, annual fuel inflation rate, annual hours od operation, return on investment, effective income tax rate, annual insulation maintenance costs, and installed costs. To obtain accurate economical thicknesses, it is best to solicit installed costs from a local contractor likely to bid on the work.

Personnel or operator protection insulation is used to protect employees from burn injuries. There is no federal regulation requiring the use or the personnel protection to limit the maximum surface temperature accessible to employees. The U.S. Ocupational Safety and Health Administration (OSHA) 1910.261 (k) (11) does require insulation on all exposed steam and hot water pipes at paper mills within 7 vertical feet of grade or 15 inches horizontal in access to employees. ASTM C 1055 (3) can serve as a guide for time versus temperature on surfaces that can produce burn injuries. But, the use of the personnel protection insulation is simply an owner`s requirement to protect employees. The most common requirement for personnel protection insulation for general service by owners is to limit the maximum surface temperature to 140 ºF at a design ambient temperature of 70 ºF and 0 mph wind velocity. An average ambient temperature is used instead od a maximum one, because it is more practical. However, in specific work areas the design ambients should reflect more actual conditions. Since piping insulations is usually manufactured in 3 ft horizontally from the point of access to hot piping.

Condensation control

Insulation for condensation control is installed to prevent heat gain, to prevent corrosion, and to keep surfaces dry so standing water as a slip hazard to personnel is avoided. To be effective, condensation control insulation must have a continuous vapor barrier and offer an adequate thickness. A continuous vapor barrier is necesary to maintain the insulation is a dry state. Without it, ambient water vapor would be absorbed through the insulation and condence on the cold metal surface, regardless of the benefit of the insulation. Water absorbent insulacion materials are 16 to 20 times more conductive in the wet state than when dry, and therefore they are ineffective. For materials that are nonabsorbent such as cellular glass, a vapor barrier is required only at joints to maintain a continuous vapor barrier. Thickness for condensation control must be calculated according to carefully selected ambient conditions that are practical, since humidity levels grater than 90% will require excessive thicknesses. For example, cold piping in an outdoor application at 85% relative humidity and 90 ºF ambient temperature would require a couple of inches of glass fiber. However, using the same design, except at 95% relative humidity, the required thickness for condensation control would be more than double. Since humidity levels higher than 90% occur for relatively short periods of time, and realizing that no amount of insulation will keep surfaces dry when at 100% humidity, then practical designs conditions should be used for sizing thicknesses.

Freeze protection

Insulation finds occasional use for freeze protection. This insulation is installed along with heat tracing, steam coils, and heat panels to prevent process media from solidifying. Thicknesses for freeze protection are sized according to the power requirements of the heating source for the equipment. Otherwise, 1-2 inches is generaly used. Freeze protection insulation is also installed on outdoor concree structures in extreme northern climates. For example, Figure 1 shows an outdoor tile block stock-chest at a Minnesota paper mill that should have had freeze protection insulation installed. The concrete block suffered extensive freeze/thaw damage from absorbed water through cracks in the internal tile lining. The seeping water froze, expanded as ice, and caused spalling destruction to the block. Another type of freeze protection is frost line insulation, which is used to protect buried structures from destruction by rapid freezing and thawing inf frost susceptible soils.

Corrosion control

Insulation is sometimes employed for the single purpose of corrosion control. Dew point corrosion on interior stack liners and flue gas ductwork is prevented by insulation to maintain metals surface temperatures above dew point for corrosive gases. Figure 2 shows the bottom of carbon steel ductwork damaged by dew point corrosion from condensing acids, because the ductwork was not insulated.

Thermal insulation can serve as fire protectionv to equipment supports, high temperature insulation materials with stainless steel jackets can be extended over saddles. Lugs, and legs as fireproofing. Extending the equipment insulation over supports is more economical than applying reinforced, dense concrete or lightweight cementitious fireproofing products.

Insulation materials

To provide effective thermal insulation, a material must resist the flow of heat by the use of small, enclosed pockets or bubbles containing air or a gas. Each of these pockets or bubbles has to be small enough so that there is resistance to gas flow such that little heat is transferred by convection from one side of the gas pocket to the other. The insulation material must consist of a tortuous path of these bubbles or pockets to reduce heat travel through solid matter by conduction. The measure of a material to resist heat flow, its thermal conductivity, is the amount of heat transferred through a unit area of a material in a unit time, through a unit thickness. Thermal conductivity is usually expressed in Btu-in/ft^2*h*ºF and shown graphically by curves according to a mean temperature. Manufacturers test thermal conductivities of materials to ASTM C 335, C 177m abd C 518. Figure 3 shows the thermal conductivities of several insulation materials.

Maximum and minimum service temperature capabilities are also primary properties to examine in the selection for a suitable insulation material (Table 1). For example, organic polymeric insulation materials, such as polyolefins and polyisocyanurates, are limited to no greater than 300ºF. Fibrous organic polymeric insulation materias at higher temperatures.

Physical and mechanical properties

After thermal properties, the next most important group or properties of insulation to evaluated relate to physical and mechanical performance and how they relate to the durability of the insulation system. For example, compressive strength is important in locations where mechanical abuse is ecpected. The resistance of an insulation to crush means it will support a weather barrier jacket. This underlying support by a strong insulation material means that the weather barrier will remain tight at seams and flashing, thus, preventing water instrusion. Insulation material with high compressive strenght are calcium silicate, cellular glass, and perlite silicate. Block insulation made of these materials should be used in the roofs of tanks and vessels where maintanance personnel may walk. Compared to dense block insulation at 13 lb/ft^3, low-density fibrous insulation at 3 lb/ft^3 istalled on shell walls may result in loose metal jackets, because of the compression by strapping.

Another important property is resistance to water absorption. If an insulation material absorbs water, then the thermal conductivity increases. Water-saturated insulation can serve as an inmersion enviroment to the equipment surface, causing corrosion if not provided with a protective coating or constructed of a passive alloy. Cellular glass is a nonabsorbent insulation with a closed-cell construction. It is often used where leaking process media can result as a combustion source for ignition if the insulation becomes saturated. For example, cellular glass is used on piping and equipment with cooling systems employing heat transfer fluids. Piping carrying hazardous wastes should also use nonabsorbent insulation, because saturated insulation must be disposed of as hazardous waste. As a alternative, hazardous liquids can be kept out of absorbent insulation by solvent welded polyvinyl chloride (PVC) jackets or coated fabric coverts. In some applications, the ability of an insulation to wick water away from the equipment syrfacem rather than trapping the water behind the insulation, is helpful in preventing corrosion. Perlite silicate has slight wicking properties and is a possible substitute for cellular glass, when water incursion is a consideration.

Not only does thermal resistance decrease as the temperature rises as shown in figure 3, but also mechanical and physical properties break down. Manufacturers publish physical and mechanical properties that are determined at room temperature, and not at elevated temperatures. Actual in-use properties may be only a graction of those in published data. For example, organic insulation materials or inorganic fibrous materials with inorganic resinous binders will lose compressive strenght at elevated temperatures as the organics degrade.

Building codes dictate the fire performance characteristics of insulation materials. Code defined Classed I areas usually restrict materials to an ASTM E 84 flame spread index of 25 or less. Most insulation materials fall into the Clas I category with a maximum flame spread index of 25, and a smoke developed rating of 50 or less. Materials wich may not qualify for Class I areas include polyirethane foams, flexible elastomeric foams, and asphalt based mastic coatings. If a manufacturer does not advertise the fire index ratings, then the material should not be assumed to meed code requirements.

Besides the properties of the insulation, practical aspects of installing the insulation should also be considered. Insulation materials are selected for their economic efficiency and suitability for fitting over the configuration of a particular piece of equipment. For example, because calcium silicate is difficult to install over a fiber-reinforced plastic (FRP) tank, a fibrous insulation material would be a better choice. Economic effiency not only relates to the material cost if the insulation, but also to the degree og defficulty in installing iy by the contractor.

Insulation Costs

A constractor`s cost of installing insulation is based on material costs, the degree of difficulty of installing the specified system, productivity rates, overhead, profit, and other factors. Table 2 shows typical installed costs for different insulation systems for an industrial facility using open shop labor. A wide range of costs exists. For instance, a simple one piece hinged section of glass fiber an ASJ jacket is ledd than half the cost of the more difficult applied cellular glass block sections strapped to the pipe, and then wrapped with glass fiber plastic sheet. ASJ is a factory installed glass-fiber-reinforced kaft paper/aluminum foil laminate.

Of course, these systems are not interchangeable, in that they are used for very different applications. This table also illustrates the importance of selecting a suitable weather barrier for the insulation since installing a PVC. FRP, or stainless steel jacket can increase the cost of the insulation system by 50%. Since costs can easily fluctuate depending on the system design and the local labor enviroment, budgetary prices should always be solicited from a local contractor for estimating purposes.

Design tips

Here are some general tips about insulation costs to know when designing insulation systems:

• Stainless steel, FRP, and PVC jackets are more expensive than aluminum or galvanized jackets
• Molded insulation is more expensive than preformed
• Strapping is more expensive than screws
• A double layer is more expensive than a single layer of the same total thickness
• Thicker insulation does not necessarily mean it is more economical
• Tie wire is more expensive than glass fiber reinforced strapping tape
• Conventional insulation over flanges and valves is more expensive than removable covers
• Preformed fitting covers are more expensive than conventional insulation
• A more dense insulation is more expensive than a less dense type
• A more corrosion resistant metal jacket is more expensive than a less resistant one

Contractors usually offer cost reductions in bid proposals as alternatives to project specifications. Good judgement should be used in deciding if less expensive alternative methods as short cuts offer a real benefit. For example, using single layer insulation instead of double layer insulation requires good workmanship to minimize heat loss and hot spots at insulation joints. Or, reducing insulation costs by using a less dense insulation material can result in more damage to weather barriers over equipment in high traffic areas.

Weather barriers protect insulation

Insulated piping and equipment usually receive some type of installed weather barrier to protect the insulation in an industrial enviroment. Metal jackets are the most common barrier. Material selection for metal jackets should be based on corrosion resistance to the inmediate process enviroment. Aluminum is the industry standard material; however, it is not suitable in caustic or chlorineladen enviroments. Stainless steel is useally substituted for aluminum in these corrosive envoroments. Metal jackets should have sufficient thickness and be provided with a profile for strength. The most common thickness for aluminum jacket over piping insulation is 0.016 inches, and 0.0010 inches for stainless steel. Jackets are manufactured with corrugated or stucco embossed profiles. Such a profile is simply sheet metal with an embossed profile that appears similar to the rough finish of stucco coatings. These profiles provide strength for the jacket to resist denting. Piping is provided with 3/16 inches corrugation, and ¼ inches for equipment.

For large structures, such as badhouses, scrubbers, and ductwork, the lagging is usually 0.032 inches – thick aluminum, 24 gage galvalume ( a steel sheet having a coating of aluminum-zing alloy applied by a continuous hot-dipping process), or 24 gage galvanized steel. Profile is 2 ½ in.- deep corrugated or 4-in. box rib. The metal lagging for these structures is typically provided in a colored finish to match siding on adjacent buildings. Polyvinylidene fluoride (PVDF) is the coating with the best long term performance.

Nonmetallic materias are uses in corrosive enviroments, where a metal jacket is not suitable. PVC plastic jackets , glass fiber jackets, and fluoropolymer-coated fabrics are common weather barriers used in these applications. PVC jackets are the standard where there are frequent washdowns and cleaning, suck as sanitizing in food and beverage plants. By solvent welding at all lap seams, these jackets can also serve as vapor barriers for cold service to prevent condensation. Where metal or plastic jackets are not practical or cannot fit around the configuration of the equipment, mastic coatings are applied over the equipment. Mastic coatings are available as weather barriers or vapor barriers and are sprayed or brushed directly over the insulation. Water-based vinyl acrylic mastics are used as weather barriers with water vapor permeance greater than 1 perm (g/Pa*s*m^2). Chlorosulfonated polyethylene and asphaltic cut backs are used for vapor barrier mastics with water vapor permeance at about 0.02 perms. Glass fiber fabric is used to bridge moving joints during thermal expansion by impregnating the fabric between two coats of mastic.

Nonmetallic weather barriers have highemittance values, and therefore, contribute to lowering insulation thickness requirements. When using such weather barriers, the surface temperatre will be closer to the ambient air temperature than if a metal jacket were used. This is an important consideration for personnel protection and condensation control insulation. The reason is thar a lower insulation thickness is sufficient for nonmetallic jacket than for a metal one. For example, a 6-in. dia. chilled-water pipe insulated for condensation control with cellular glass at 90ºF ambient and 80% relative humidity will require 3 inches less insulation using a mastic coating than if a metal jacket were wrapped around the insulation.

Other materials in the insulation system

The use of prefabricated removable insulated covers is an excellent method of insulationg equipment that requires frequent access. Manways, access doors, flanged heads, valves, flanges, pumps, and other maintained items should receive prefabricated covers.

Removable covers can be simply taken off and reinstalled without damage to the insulation or weather barrier. They are field sized and then shop fabricated using blanket insulation, such as glass fiber, mineral fiber, or ceramic fiber, and encased in a sewn coated fabric as the weather barrier. Usually, a silicone coated glass fiber fabric is used as the weather barrier cover, although other materials, are available such as chlorosufonated polyethylene, polytetrafluoroethylene, polyvinyl fluoride, and polyethylene terephthalate. When removable cover is used in a completely dry enviroment, the insulation can be enclosed in stainless steel netting held together by hog rings (rounded staples). A standard guide for removable insulation covers is ASTM C 1094 (4).

Conventional insulation is secured to piping by tie wire and strapping. For fibrous insulation that is telatively light, glass fiber reinforced tape may be used. Pipe insulation with an integral all service jacket is secured with a self-sealing lap system. Equipment insulation is secured with strapping or weld pins. Pin tasteners when used on tanks constructed of stainless steel should be og the same grade of stainless steel. If pin fasteners are used on tanks constructed of titanium, FRP or if the vessel is ASME code stamped, then the fasteners should be attached using epoxy cement. Metal jackets installed over piping insulation are secured with either self-tapping screws or metal strapping. Screws provides more securement for piping lagging, although screws are ledd expensive to install. Metal lagging over equipment uses a combination of screws and strapping.

Flashing of insulation is a necessary component of any weather barrier system, because it directs water away from cutouts in the insulation jacket. When water gets through the weather barrier, it can increase the thermal conductivity of the insulation and corrode the equipment. Flashing uses a combination of metal sheet and sealant. Metal sheet is cut to the required shape, formed. And secured with screws over the cutout. Sealant is caqulked between the flashing sheet and the existing equipment lagging. Figure 4 illustrate proper flashing of tank protrusions with a flashing drip ledge over a valve, flashing over an anchor bolt chair, and flashing at the cutout for an agitator.

Leak indicators in insulation systems are installed at flanges for detection of leaks and to channel vapor or liquid away from the insulation. Leak indicators are particularly important where leakage could cause autoignition of saturated insulation (5). These devices are comprised of a sealed surface clamped around a flanged connection and a small drain tube projecting downward out of the insulation system.

Nondestructive testing (NDT) inspection plugs are becoming more commonly incorporated into insulation systems for equipment. These plugs allow for immediate access to the equipment shell for ultrasonic testing of shell thickness, without the need to tear off the insulation system. Inspection plugs usually consist of a 2 ½ inch dia. Elastometric-like gasket inserted into a drilled hole through the insulation, and a metal cap to cover the rubber plug. Fibrous blanket insulation is used to fill the hole behind the gasket. Plugs are typically installed at the planned locations for future ultrasonic testing. For example, plugs are installes at 0.9, 180, and 270 deg. Azimuths on 3-6ft vertical centers.

Design documents

An insulation specification is usually generated in parallel to the piping and instrumentation diagrams (P&IDs) and piping specifications, because insulation codes and thicknesses must be established early in design. Design data sheets should state the thickness of insulation required for the equipment and and detail the type of insulation supports required. Insulation thickness must be known during the design of the vessel so that the insulation support widths can be sized. Insulation supports perform various functions for the insulation system. They physically hold up the insulation on vertical sidewalls, serve as an anchor for metal jackets, cap insulation from water egress, and provide tie-off points for strapping. Insulation supports should be designed to allow migrant water to drain past and down the equipment surface (6). Rod ring supports at 3/8 inch. dia. welded on bar stubs spaced every 12 inch. are preferred. In this setup, a rod encircles the circumference of the vessel. The rod is held off by bar stubs at 12-in. centers.

Angles or bars which can collect water and cause corrosion should not be welded directly to vertical surfaces as insulation supports. The exception is the weather leg, which is an inverted angle seal welded at the roof or shell junction of a tank or vessel. It serves as flashing to prevent water on the roof from flowing down into the insulation. Insulation and metal jackets should be fitted under the weather leg.

Based on the equipment list and P&IDs, a list of equipment to be insulated should always be generated for the insulation contractor. This list should describe specific insulation requirements for each particular piece of equipment. For example, it should define thickness, type of insulation, weather barrier protection, and the equipment vendor`s drawing number. Also, any other special notes should be included such as removable covers on manways, and specific areas where insulation may not be required such as on skirted bottom heads or heat exchanger heads.

Inspection of contractor`s installation

Inspection of installed insulation is performed visually and by heat detection. The correct use of specified materials can be verified by invoices and boxes the materials came in. Materials should be inspected for damage. For instance, metal lagging should not be dented or corroded, insulation should not be crushed, cracked, deformed, or wet from exposure to weather. The position of fasteners shouls be measured to ensure that they they are located with the correct spacing and are tightly securing. Weather barriers should always be positioned for water shed. Flashing should be correctly fitted with proper overlap and adequately caulked with sealant. Removable insulation covers should be examined to ensure correct sewing, that seams are watertight, and the cover fits completely over the surface without exposed equipment surfaces.

Surface thermometers and infrared radiation heat guns can be used to perform thermal analysis of insulated surfaces. Thermal inspection is especially important for fabricated insulation panels that are installed o equipment with corner joints such as precipitators, baghouses, conveyors, and hoppers. If corner joints are not tight, or convection flue stops are not correctly installed, the thermal inspection will detect the heat leak.

Maintenance of insulation

Insulation systems should be regularly inspected to see that they are undamaged and relatively effective. The primary cause of ineffectiveness is penetration of the weather barrier, allowing water to saturate the insulation and increase thermal conductivity. Problems here are : penetrations of weather barriers such as holes in jackets, or loose fasteners in jackets require repair; and missing screws or loose strapping, which should be replaced or repaired.

A less obvious and more common problem is the flashing. Polymeric sealants degrade with age, and eventually lose their elastomeric properties and crack. Sealants should be inspected at least once a year and replaced as needed to ensure that water is being directed away from the insulation.

When thermal analysis indicates excessive surface temperature or that condensation collects on surfaces, maintenance may not necessarily be required. A knowledgeable examination of the insulation design conditions should be performed first before assuming that the insulation is defective. The insulation may be performinf as originally designed, although ambient conditions are outside design parameters. For example, insulated chilled water piping may sweat when humidity exceeds the design 85%.