Industrial Insulation Materials: Selection, Thickness and Cladding

Quick Answer

Industrial insulation is selected first by temperature and second by water behaviour, because water is what destroys insulation systems and the pipe underneath them. Mineral wool (rock and glass) covers roughly -200°C to 650°C, is inexpensive and the general industrial default, but it absorbs and holds water. Calcium silicate serves 650-1,000°C with high compressive strength, making it the choice at supports and under traffic, though it also holds water and is alkaline. Cellular glass is closed-cell, completely impermeable to water and vapour, and spans -265°C to 430°C — the premium answer for cryogenic duty and for corrosion-under-insulation-prone hot service. Aerogel blankets have the lowest thermal conductivity of any practical material (roughly 0.015-0.020 W/m·K), are hydrophobic yet vapour-permeable, and deliver equal performance in about a third to a half the thickness, at several times the price. PIR and polyurethane foam cover -180°C to 120°C in cold and chilled service. The critical band for corrosion under insulation on carbon steel is approximately 50°C to 175°C, with the worst damage where the system cycles through the dew point; for austenitic stainless steel, external chloride stress corrosion cracking is a risk from about 50°C to 175°C and insulation must be certified low in leachable chloride.

A gas processing plant in the Gulf replaced 1,400 metres of 8-inch carbon steel piping after nine years of service. The pipe was insulated. It was also almost entirely gone in places — wall loss above 60% at a dozen locations, through-wall at three.

The insulation was mineral wool with aluminium cladding, installed to specification. The problem was that the line ran at 95°C intermittently, sat at ambient when the unit was down, and had cladding joints facing upward on the horizontal runs with no sealant. Rainwater and washdown water entered at every joint, soaked into the mineral wool, and sat against 95°C carbon steel.

Hot, wet carbon steel with dissolved oxygen is the ideal corrosion cell. The insulation did not cause the corrosion; it created a permanently damp, oxygenated, warm annulus and then hid it from view for nine years.

The replacement cost just over 900,000 USD including scaffolding, shutdown and reinstatement. A cellular glass system with properly lapped and sealed cladding at the original installation would have added roughly 70,000 USD.

Insulation is not just a thermal component. It is a water management system, and when it fails at that job it destroys the asset it was installed to protect.

What Insulation Is Being Asked to Do

Insulation gets specified for one reason and then has to deliver several:

Heat conservation. Reducing heat loss from hot surfaces, directly saving fuel. The commercial driver on steam, hot oil and process heating lines.

Process temperature control. Keeping product within a temperature band — preventing wax deposition in crude lines, preventing freezing in water lines, maintaining viscosity in heavy fuel oil, keeping sulphur above its freezing point.

Cold conservation. Reducing heat gain into refrigerated, chilled and cryogenic systems, where energy cost per unit of heat gain is far higher than on the hot side because refrigeration has a coefficient of performance well below one at low temperature.

Condensation control. Keeping the outer surface above the ambient dew point so moisture does not form. On cold systems this is often the governing design criterion rather than energy — insulation thickness is set by dew point, not by heat gain.

Personnel protection. Limiting touchable surface temperature, typically to 60°C or below for sustained contact. A hot surface can be insulated for personnel protection with much less thickness than for energy conservation, which is why "personnel protection only" is a distinct specification class.

Fire protection. Fireproofing on structural steel, vessel supports and critical valves, to delay temperature rise during a pool or jet fire. A different standard and different materials from thermal insulation.

Acoustic attenuation. Reducing noise break-out from high-velocity gas lines, control valves and let-down stations. Requires mass as well as absorption, so acoustic systems typically combine mineral wool with a heavy limp mass layer.

Often one system must do several. A steam line needs heat conservation and personnel protection. A cryogenic line needs cold conservation, condensation control and absolute vapour sealing. The specification must state all the requirements, or the installed system will meet only the one that was written down.

The Materials

Mineral wool (rock wool and glass wool)

Spun fibres of melted rock, slag or glass, bound with a resin, supplied as pipe sections, slabs, blankets and wired mats.

• Temperature: roughly -200°C to 650°C for rock wool; glass wool typically to 450°C. Binder burns out above about 230-250°C, giving an initial smell and smoke on commissioning and leaving the fibre structure intact but more friable.
• Thermal conductivity: about 0.035-0.045 W/m·K at 50°C, rising with temperature
• Density: 40-160 kg/m³ depending on form and application
• Water: absorbs and retains water. Hydrophobic treatments help initially but do not survive long-term wetting. Wet mineral wool loses most of its insulating value and holds water against the pipe.
• Cost: lowest of the common industrial materials
• Uses: steam and hot process piping, vessels, ducts, boilers, acoustic insulation, fire protection grades

The general industrial default. Appropriate wherever water ingress can genuinely be prevented and where the temperature is outside the critical CUI band — or where it is inside the band and the owner has made a conscious decision to inspect.

Calcium silicate

A rigid moulded material of hydrated calcium silicate with reinforcing fibres.

• Temperature: up to 650°C standard, to 1,000°C in high-temperature grades
• Thermal conductivity: about 0.055-0.075 W/m·K — poorer than mineral wool
• Compressive strength: high, typically above 0.5 MPa. This is its defining advantage.
• Water: absorbs water readily and is alkaline. It also holds water for a very long time because of its closed structure and mass.
• Uses: high-temperature piping and vessels, pipe support inserts where insulation must carry load, areas with foot traffic or mechanical abuse, fire protection

Calcium silicate at a pipe support is often the correct answer even on a line insulated with something else, because mineral wool crushes under load and creates a thermal bridge plus a water trap. Load-bearing inserts matter.

Its alkalinity is an advantage against chloride SCC on stainless steel — alkaline conditions inhibit it — but the water retention is a serious disadvantage for carbon steel CUI.

Cellular glass

Crushed glass foamed with a blowing agent into a rigid, closed-cell block of glass bubbles.

• Temperature: -265°C to 430°C
• Thermal conductivity: about 0.040-0.055 W/m·K
• Water: completely impermeable. Closed glass cells absorb no water and transmit no vapour. Water vapour permeability is effectively zero.
• Compressive strength: high, typically 0.5-1.6 MPa depending on grade
• Non-combustible, no smoke, no binder
• Chemically inert, no leachable chlorides
• Rigid and brittle — needs careful handling and correctly fitted joints, usually bedded in a compatible mastic
• Cost: 3-6× mineral wool
• Uses: cryogenic and LNG service, chilled water, hot service where CUI is a serious threat, buried piping, below-grade applications, tank bases and vessel supports

Cellular glass is the material that solves the CUI problem by construction rather than by maintenance. Because it cannot absorb water, even a failed vapour barrier does not create a wet annulus — water runs out rather than soaking in. On a plant where access for insulation inspection is difficult or where the consequence of a leak is severe, the premium repays itself.

Aerogel blanket

Silica aerogel reinforced in a fibre batting, supplied as flexible blanket.

• Temperature: -200°C to 650°C depending on grade
• Thermal conductivity: approximately 0.015-0.020 W/m·K at ambient — the lowest of any practical industrial insulation
• Thickness: delivers equivalent performance in roughly one-third to one-half the thickness of mineral wool
• Water: hydrophobic (repels liquid water) but vapour-permeable, so moisture that enters as vapour can leave rather than condensing and being trapped
• Flexible and conformable — wraps complex geometry, valves, flanges and small-bore lines easily
• Cost: 5-10× mineral wool by volume, less by installed thermal performance in space-limited work
• Uses: space-constrained retrofits, subsea and offshore where weight and diameter matter, tracing and jacketing of complex fittings, CUI-mitigation retrofit over existing lines, personnel protection on congested piping

Aerogel changes the economics wherever space, weight or installation access is the constraint rather than material cost. Re-insulating a congested module where mineral wool would not physically fit, or where increased diameter would clash, is a typical case.

Polyisocyanurate (PIR) and polyurethane (PUR) foam

Rigid closed-cell plastic foam.

• Temperature: -180°C to about 120°C (PIR slightly higher than PUR)
• Thermal conductivity: about 0.022-0.028 W/m·K — excellent
• Water: closed cell, low absorption, but vapour-permeable over time, so a separate vapour barrier is mandatory on cold service
• Combustible — must be assessed for fire performance; often unacceptable in hydrocarbon process areas without protection
• Uses: chilled water, refrigeration, LPG, cold storage, district cooling, pre-insulated pipe systems

Expanded perlite

Expanded volcanic glass, bonded into rigid blocks or supplied loose-fill.

• Temperature: to 650°C in block form; loose fill used in cryogenic tank annular spaces
• Thermal conductivity: about 0.050-0.070 W/m·K
• Water: absorbs water, though silicone-treated grades resist it initially
• Uses: high-temperature piping and vessels, loose-fill in double-wall cryogenic tanks, boiler and furnace casings

Loose perlite in the annulus of a double-wall LNG or liquid oxygen tank, often under vacuum, is a mature technology and remains standard for large flat-bottom cryogenic tanks.

Ceramic fibre

Alumino-silicate fibre blanket, board, paper and module.

• Temperature: 1,100°C to 1,600°C depending on grade
• Low heat storage, excellent thermal shock resistance
• Uses: furnace and kiln linings, back-up insulation behind refractory, high-temperature ducting, expansion joint fill

Properly a refractory material rather than a thermal insulation, and it belongs with refractory selection. Note that respirable crystalline silica forms after prolonged high-temperature exposure, so removal of used ceramic fibre has specific handling requirements.

Comparison

Thickness

Insulation thickness is calculated, not chosen from a habit.

Heat conservation thickness is an economic optimisation: the cost of heat lost against the installed cost of insulation, over the asset life, at the actual fuel price and operating hours. The economic thickness rises with fuel price, with operating hours, and with surface temperature. Standards such as ASTM C680 provide the heat transfer calculation method, and tools such as the NAIMA 3E Plus methodology implement the economic optimisation.

A useful check: on steam systems above about 200°C running continuously, economic thickness is usually greater than what plants install. Underinsulation is far more common than overinsulation.

Personnel protection thickness is set by the maximum allowable touch temperature, usually 60°C for sustained contact or 70°C for incidental contact, with ambient and wind speed assumptions stated. Much thinner than economic thickness on hot lines. Specify it explicitly where that is the only requirement.

Condensation control thickness on cold systems is set by keeping the outer surface above the design ambient dew point. This governs in humid climates: in Gulf coastal conditions at 40°C and 85% relative humidity, the dew point is around 37°C, which leaves very little margin and drives thickness up substantially. Getting this wrong produces a chilled water line that drips continuously, soaks its own insulation, and corrodes.

Freeze protection thickness is calculated from the required cooling time to reach 0°C under design minimum ambient, usually in combination with heat tracing rather than instead of it.

Multi-layer construction is standard above about 350°C and above roughly 75-100 mm total thickness:

• Staggered joints between layers prevent straight-through thermal paths
• Each layer accommodates its own thermal movement
• Allows different materials in each layer — for example calcium silicate as the hot layer with mineral wool outside, or cellular glass against the pipe with mineral wool outside for high temperature with CUI protection

Corrosion Under Insulation

CUI is the single largest cause of insulation-related asset loss, and it is invisible until the pipe fails.

The critical temperature band for carbon steel is approximately 50°C to 175°C. Below 50°C corrosion rates are slow; above about 175°C the surface stays dry because water boils off. In between, the steel is warm, wet and oxygenated, which maximises corrosion rate.

Cyclic service is worse than constant service. A line that runs hot and then cools to ambient draws in moist air as it cools, condenses water inside the insulation, and repeats the cycle. Intermittent and standby lines suffer disproportionately. Lines below the CUI band in normal operation but passing through it on startup and shutdown are frequently the worst affected.

For austenitic stainless steel, the threat is external chloride stress corrosion cracking (ESCC), roughly 50°C to 175°C as well. Chlorides concentrate as water evaporates at the hot surface, and 304 and 316 crack transgranularly at chloride concentrations far below what the bulk water contains. Insulation for stainless steel must be certified to low leachable chloride limits — ASTM C795 and C692 set the requirements, and specifying "insulation suitable for stainless steel to ASTM C795" is the practical instruction.

Design measures that actually work:

1. Choose a non-absorbent material in the CUI band and for cyclic service. Cellular glass is the strongest option; aerogel's vapour permeability also helps because trapped moisture can escape.
2. Coat the steel. The insulation is not the corrosion barrier; the coating is. Modern practice is a high-temperature coating system applied to the pipe before insulating — thin-film inorganic copolymer or epoxy phenolic systems rated for the service temperature. A coated pipe under wet insulation survives; a bare one does not. This is the highest-value single measure.
3. Seal the cladding properly. Lap joints oriented to shed water, laps of 50-75 mm, circumferential joints at the bottom on vertical runs and facing down on horizontals, sealant at every joint, and bands at adequate spacing.
4. Eliminate water entry points. Penetrations, supports, nozzles, instrument connections, valves and flanges are where water gets in. Removable boxes with proper weatherproofing at valves and flanges, sealed terminations at penetrations, and drains at low points of the cladding.
5. Vapour barrier on cold service, continuous and sealed, on the warm side — which for cold service is the outside. A vapour barrier with a single unsealed penetration admits moisture continuously, and ice forms inside the insulation.
6. Inspection ports and planned removal. On lines where CUI is credible and the material is absorbent, plan periodic insulation removal at known high-risk locations rather than waiting for a leak.
7. Avoid absorbent insulation in known wet locations — under drip points, near cooling tower drift, in washdown areas, at deluge-protected equipment.

Cladding and Weatherproofing

The cladding is the water management layer, and it fails more often through workmanship than material choice.

Aluminium — 0.6-1.0 mm, usually with an integral moisture barrier film on the inside face. Light, inexpensive, easy to form, good appearance. Corrodes in marine and acidic atmospheres and galvanically against stainless steel.

Stainless steel — 0.4-0.6 mm, typically 304 or 316. Durable, fire-resistant, suitable for offshore and marine. More expensive and harder to form. Required in many fire-exposure cases because aluminium melts at around 660°C.

Galvanised steel — lower cost, used indoors and in non-aggressive environments.

Glass-reinforced plastic (GRP) and PVC jacketing — chemical resistance, used in corrosive and washdown areas, and over cold systems. Fire performance must be checked.

Mastic and membrane systems — applied over insulation on irregular shapes, vessel heads and complex geometry where sheet metal cannot be fitted economically.

Workmanship points that determine whether the system survives:

• Laps oriented to shed water downward, never upward
• 50-75 mm minimum lap
• Sealant at all longitudinal and circumferential joints on horizontal runs
• Banding at 300-450 mm centres, stainless steel bands on stainless cladding
• Expansion provision — hot lines move, and cladding that cannot move tears open at the joints
• Terminations at flanges, supports and penetrations sealed and weathered, with removable covers at items needing access
• Drain holes at genuine low points, and nowhere else
• No self-tapping screws through cladding on hot service where they create a leak path and a thermal bridge

Common Specification Mistakes

1. Absorbent insulation in the CUI band with no coating on the steel. The Gulf gas plant example: nine years to 60% wall loss and 900,000 USD.

   Prevention: Coat the pipe with a high-temperature CUI coating before insulating, and prefer non-absorbent insulation in the 50-175°C band and in cyclic service.

2. Insulation not certified for stainless steel chloride limits. Leachable chloride from the insulation cracks 304 and 316 piping.

   Prevention: Specify insulation qualified to ASTM C795 with C692 testing for all austenitic stainless steel in the 50-175°C range.

3. No vapour barrier, or a vapour barrier with unsealed penetrations, on cold service. Moisture migrates in continuously, condenses, freezes, and destroys both the insulation and the pipe.

   Prevention: Specify a continuous sealed vapour barrier on the outside of cold insulation, with all penetrations, supports and terminations sealed, and inspect the seal before cladding.

4. Condensation thickness calculated against average conditions, not design dew point. In humid coastal climates the line sweats, soaks its insulation and corrodes.

   Prevention: Calculate against the design maximum ambient and relative humidity for the site, and state the assumed surface emittance and wind speed.

5. Mineral wool at pipe supports. It crushes, creating a thermal bridge, a cold spot and a water trap exactly where water collects.

   Prevention: Specify load-bearing inserts — calcium silicate or cellular glass — at all supports, sized for the actual support load.

6. Cladding laps facing upward on horizontal runs. Every joint becomes a funnel.

   Prevention: Specify lap orientation and sealing explicitly on the insulation specification, and inspect installed work against it.

7. No removable covers at valves and flanges. Either they are left uninsulated, wasting heat and creating a burn hazard, or they are insulated solid and the next maintenance job rips the system open and reinstates it badly.

   Prevention: Specify removable, reusable insulation boxes or blankets at all valves, flanges and instruments requiring access.

8. Single-layer construction at high temperature and high thickness. Joints provide straight-through heat paths and the system cannot accommodate thermal movement.

   Prevention: Specify multi-layer construction with staggered joints above about 350°C or 75-100 mm thickness.

9. PIR or PUR foam specified in a hydrocarbon process area without fire assessment. Combustible insulation in a fire-exposed location.

   Prevention: Check fire performance requirements against the area classification and fire scenario, and use non-combustible materials where required.

10. Aluminium cladding specified in a marine or coastal atmosphere, or against stainless steel. Pitting and galvanic corrosion.

    Prevention: Use stainless steel or GRP cladding in marine, coastal and chemically aggressive environments, and avoid aluminium in direct contact with stainless equipment.

11. Thickness copied from an old specification instead of calculated at current fuel prices. Energy costs have changed; economic thickness moved with them.

    Prevention: Recalculate economic thickness at the current fuel price and operating hours for any significant new insulation scope.

Supply from Kasko Makine

Kasko Demir Çelik Makine supplies insulation materials and accessories for process plant, pipelines and buildings:

Insulation materials

• Rock wool and glass wool: pipe sections, slabs, blankets, wired mats, loose fill
• Calcium silicate: pipe sections, blocks, boards, load-bearing support inserts
• Cellular glass: pipe sections, blocks, fabricated shapes, tank base board
• Expanded perlite: blocks, pipe sections, loose fill for cryogenic annular space
• Aerogel blanket in standard and high-temperature grades
• PIR and PUR rigid foam pipe sections and boards for cold service
• Ceramic fibre blanket, board, paper and modules for high-temperature duty
• Insulation certified to ASTM C795 for austenitic stainless steel service

Cladding and finishing

• Aluminium sheet and coil, plain and stucco-embossed, with and without moisture barrier
• Stainless steel 304 and 316 cladding sheet
• Galvanised steel cladding
• GRP and PVC jacketing
• Bands, clips, screws, rivets and wire in galvanised and stainless
• Mastics, sealants, vapour barrier mastics and membrane systems
• Pre-formed fitting covers, elbow and tee covers, end caps
• Removable and reusable insulation jackets for valves, flanges and instruments

Associated supply

• High-temperature CUI coating systems for pre-insulation application
• Pipe supports, shoes and insulated support assemblies
• Electrical and steam heat tracing
• Steam traps and condensate equipment
• Carbon steel and stainless piping, flanges and fittings

Engineering support

Send a line list with operating and design temperatures, service, pipe size and material, site ambient and humidity, and the governing requirement for each line — heat conservation, personnel protection, condensation control, freeze protection, acoustic or fire — and we will return an insulation specification with material, calculated thickness, layer configuration and cladding for each line, with the calculation basis stated. For CUI-prone scopes we will flag the lines in the critical band and recommend coating and material measures.

Certification

Material data sheets and test certificates, thermal conductivity data to ASTM C177 or C335, ASTM C795 and C692 chloride certification for stainless-steel-compatible materials, reaction-to-fire classification, asbestos-free declarations, and dimensional and density test reports.

Logistics

Standard mineral wool, calcium silicate and cladding sheet generally ship in 2-4 weeks. Cellular glass and aerogel typically 4-8 weeks depending on quantity. Fabricated and pre-formed shapes 4-6 weeks. Shipping from Istanbul by road to Europe, the Caucasus and Iraq, and by sea to Gulf, African and Asian destinations.

Send your line list with temperatures and service and we will return an insulation specification with calculated thicknesses within four working days. Reach us at info@kaskomakine.com or WhatsApp +90 (537) 521 1399.

Continue Reading: Piping and Process Series

• Corrosion Under Insulation: Causes and Prevention
• Refractory Linings: Selection and Installation
• Steam Traps: Types, Selection and Failure
• Carbon Steel Pipe: Grades and Standards

Frequently Asked Questions

Q: Which insulation material should I use for high-temperature piping?
A: Rock wool covers up to about 650°C and is the economical default where water ingress can be prevented. Calcium silicate serves to 650°C standard and 1,000°C in high-temperature grades, and its high compressive strength makes it essential at pipe supports. Above 1,000°C the material becomes ceramic fibre. Multi-layer construction with staggered joints is standard above about 350°C.

Q: What is the temperature range for corrosion under insulation?
A: For carbon steel the critical band is approximately 50°C to 175°C. Below 50°C corrosion is slow, and above about 175°C the surface stays dry because water boils off. Cyclic and intermittent service is worse than constant service because each cooling cycle draws in moist air and condenses water. For austenitic stainless steel, external chloride stress corrosion cracking occurs over roughly the same range.

Q: Why use cellular glass instead of mineral wool?
A: Cellular glass is closed-cell and completely impermeable to liquid water and water vapour, so it cannot create a wet annulus against the pipe even if the cladding leaks. Mineral wool absorbs and holds water, which both destroys its insulating value and drives corrosion under insulation. Cellular glass costs roughly four times as much but removes the CUI mechanism by construction rather than relying on maintenance.

Q: How thick should pipe insulation be?
A: Thickness depends on the governing requirement. Heat conservation thickness is an economic optimisation of fuel cost against installed insulation cost, calculated per ASTM C680 methods. Personnel protection thickness is set by limiting touch temperature to around 60°C and is much thinner. Condensation control on cold lines is set by keeping the surface above design ambient dew point, which in humid coastal climates drives thickness up substantially.

Q: What insulation is safe for stainless steel pipework?
A: Insulation in contact with austenitic stainless steel between about 50°C and 175°C must be certified low in leachable chloride, because chlorides concentrate as water evaporates at the hot surface and cause external chloride stress corrosion cracking. Specify insulation qualified to ASTM C795 with ASTM C692 testing. Calcium silicate's alkalinity is helpful, and cellular glass contains no leachable chlorides at all.

Q: Does aerogel insulation justify its cost?
A: Aerogel blanket has a thermal conductivity of roughly 0.015 to 0.020 W/m·K, so it delivers equivalent performance in about one-third to one-half the thickness of mineral wool. It costs several times more per volume, so it is justified where space, weight or installation access is the constraint — congested retrofits, offshore modules, complex fittings and small-bore lines — rather than in open-route piping where thickness is free.

Q: What causes insulation cladding to leak?
A: Almost always workmanship rather than material. The common faults are lap joints oriented upward so they funnel water in, laps shorter than 50 mm, missing sealant at circumferential joints, no expansion provision so hot lines tear the joints open, unsealed terminations at supports and penetrations, and self-tapping screws driven through the cladding. Valves and flanges without properly weathered removable covers are the single biggest entry point.