Thermal Insulation: Types, System and Standards

1. Thermal Insulation Types:

Based on the functional requirements, the Insulation Material is classified into 2 types as below

Hot Insulation:

Insulation used on hot surfaces for the purposes of Heat Conservation or for the purpose of Personal Protection.

Following material are typically used as Hot Insulating Material

Material Temperature Thermal Conductivity
(mW/ Cm O C)
Range (O C)
Mineral Wool (unbonded)

0.48 (Note 1)


Mineral Wool (bonded)

0.43 (Note 1)


Glass Wool

0.43 (Note 1)


Calcium Silicate



Notes: 1) Thermal Conductivity at 50 OC

Cold Insulation:

Insulation Used on cold surface for the purpose of Cold Conservation or for the purpose of avoiding Condensation.

Following Materials are typically used as Cold Insulating Materials

Material Temperature Thermal Conductivity
(mW/ Cm O C)
Range (O C)
Polyurethane Foam 0.29 (Note-1) -150 to 110
Expanded Polystyrene Foam
Expanded Perlite Foam
0.32 (Note-1) -150 to 80

Notes: 1) Thermal conductivity at 0 OC.

2. Thermal Insulation System

Insulating Material:

Normally the Insulating Materials are available in unbonded mats and bonded or foamed preformed Pipe Sections/ Slabs to suit various applications. Polyurethane Foam and Expanded Perlite Foam can also used by in-situ foaming.

Protective Coating:

Normally thermal Insulation is provided with an external covering for protection against entry of water or process fluid, mechanical damage, exposure to fire and ultraviolet degradation (in case of foam material). The protective cover could be in the form of

  1. Coating (asphalt, polymer or resin)
  2. Membrane (felt or paper)
  3. Sheet Material (fabric, metal or plastic)

Vapor Barrier:

Cold Insulation Systems operating at subzero (below 2 OC) are normally provided with Vapor Barrier and sealed at the joints to prevent condensation and vapor transmission. Metallic Foils and Mastic embedded Glass Fabric are commonly employed for this purpose.

Insulation Thickness Selection

This Standard provides the recommended thickness for various pipe sizes for the following Insulation Systems-

  1. Cold Insulated Piping System
  2. Hot Insulated Piping System
  3. Personal Protection System

Insulation Material Properties:

Insulation Material in general shall be chemically neutral, rot-proof and free from impurities. In addition following properties are required to be considered in selecting the Insulating Material

Mineral Wool/ Glass Wool

  1. Thermal Conductivity
  2. Density
  3. Fire Resistance (to be rated as incombustible)
  4. Chloride Content
  5. Sulphur Content
  6. Moisture Absorption
  7. Shot Content
  8. Recovery after Compression
  9. Heat Resistance

Foam Insulation/ Thermocole

  1. Thermal conductivity
  2. Density
  3. Compression Strength and Hardness
  4. Water Vapour Permeability
  5. Auto Ignition
  6. Fire Resistance
  7. Heat Resistance


Following steps are followed while applying Thermal Insulation on Piping/ Equipment Items.

  1. Insulation Supports in the form of Ring, Lugs are welded to the Vertical Vessels and Tanks (for Hot insulation and Cold Insulation).
  2. Horizontal Vessels will not require Insulation Supports
  3. In case of Cold Insulated Vessels the Insulation will extend up to 5 times the insulation thickness where there are protrusions (e.g. skirts/ leg supports etc.). Supports and Brackets in case of hot insulated Equipment are normally not insulated.
  4. The materials forming part of Insulation System (e.g. Cement, Coating, Fabric etc.) shall be free from Asbestos except mill board used for avoiding metal to metal contact.
  5. The Carbon Steel and Low Alloy Steel surface to be insulated shall be painted (for corrosion protection) with paint system as per Painting Specification recommended for the service.
  6. The Insulation Work shall commence only after the Hydro Test on Equipment/ Piping is completed and the items handed over for Insulation.
  7. Generally the Insulation shall be applied over the entire metal surface including flanges and stiffening rings etc. except over the parts (e.g. Gland Plate for valve gland packing etc.) which require frequent dismantling for maintenance purpose.
  8. As far as possible and practical the voids due to the profile of the external surface of any item (e.g. Valve body) will be filled with loose insulating material.
  9. In case of Cold Insulation the cladding shall be done without using self-tapping screws to avoid rapture of the Vapour Barrier. This however does not apply to in-situ foaming.
  10. Wherever applicable the joints between the Vapour Barrier and steel surface/ cladding are sealed to avoid ingress of moisture.
  11. In case of Insulation Thickness in excess of 75 mm it is recommended that the Insulation will be applied in multiple plies.
  12. Insulating Material used in the Process Plants in which Nitric Acid or Ammonium Nitrate are produced, shall not contain organic binding materials (e.g. Phenolic Resins).
  13. In the Process Plants with likely hood of formation of volatile flammable vapours, only insulation material with a closed surface (e.g. Foam Glass) shall be used.
  14. In case of application of Insulation in multiple plies, the seams shall be staggered.
  15. Insulation material on vertical or nearly vertical surfaces shall be prevented from sliding by means of suitable supports and tie wires or banding.
  16. Closely spaced lines (small bore) or Tubing may be insulated in a common envelop (up to 6 lines)
  17. In case of insulation of Heat Traced lines it is recommended to place a thermal shield (metallic foil) between insulation material and the tracing/process pipe for better heat transfer and for preventing the insulation from penetrating between the tracer and the process pipe.
  18. Vapour Barrier Foils in case of Cold Insulation shall be overlapped (approximately 50 mm) at the joints.
  19. Installation of Insulation Material is done in following steps:


i. The purpose of providing Spacers is to enable the cladding to retain its shape and concentricity with respect to the surface to be insulated

ii. The spacers are required only for mineral fiber mats or for in-situ foaming

iii. The spacers are fabricated as per the details given in company standard for Insulation

iv. The spacers are positioned (fixed) at the required spacing on metallic/ plastic surface as per the details given in company standard for Insulation

v. In case of Vertical equipment the spacers are attached to the vessels by means of Insulation Clips as per company standard for Insulation

Insulation Material:

i. The Insulation Material in case of Mineral Fiber Mats is fixed to the cylindrical surface by means of metal wire tied in a helical manner around the cylindrical surface.

ii. The Insulation Material in case of Mineral Fiber Preformed Shell or Slabs is glued to the metal surface or held together with closely butted joints.

iii. Insulation Material in case of preformed foam shells and slabs are held in position by gluing the end seams. In case of multiple layers the seams shall be staggered with respect to each other.

iv. In case of in-situ foaming the foam is generated within the cavity formed between the metal surface to be insulated and the external cladding.


Depending upon the contour of the surface to be insulated, it may be necessary to fill the cavities and voids by means of loose mineral fibers or with the same type of foam


i. Standard Sheet Metal (Galvanized) shall be used as Cladding Material. Aluminum Sheet can be used as alternative material (except Caustic Chlorine Plants)

ii. Metal Banding or self-tapping screws may be used for attaching the Cladding. Suitable Turn Buckles or Snap Catches may be used connecting the ends of Banding

iii. Cladding Joints shall be sealed by elastomeric sealing tape.

iv. The Cladding Joints are made by crimping or folding.

3. Applicable IS Standards:

Glass Wool IS 3677 / IS 3690

Rock Wool IS 8183/ IS 9842

Polyurethane Foam IS 12436

Expanded Polystyrene IS 4671

Determination of Thermal Conductivity IS 3346

Cladding Sheet IS 737

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