Overview of insulation systems

In order to describe all the complexities of thermal insulation a large volume would be required.

If more detail is required, it is suggested that BS 5970 A Code of practice for thermal insulation of pipework and equipment in the temperature range  -100 deg C to +870 deg C be consulted.

Throughout the webpage, where the operating temperature is greater than the ambient temperature, the insulation will be termed Hot otherwise it will be termed Cold.

In addition to the basic insulation material, a system may need:

(a) Heat transfer cement

(b) Supports for the insulation

(c) Fastenings for the insulation

(d) A vapor seal –  if Cold insulation

(e) Protection of the insulation, for example, metal cladding

(f) Supports for the protection

(g) Fastenings for the protection

(h) Finishing, for example, paint coatings or identification bands

In this webpage unit designations are:

  • Density            kg/m3
  • Thickness         mm
  • Temperature     degrees centigrade

Pre-insulation application Before insulation is applied, all surfaces to be insulated should be thoroughly cleaned to remove dirt, oil, moisture, loose rust or any other foreign matter.

Heat transfer cement

If a temperature is to be maintained by means of external heat sources such as steam tracers, heat transfer cement should be applied to spread the heat from the tracer.

The manufacturers recommendations should be followed.

Corrosion protection

Where the operating temperature is 130 deg C or less and the equipment or pipework is other than austenitic alloy the surfaces should be coated with a suitable paint.

It has been found that below this temperature corrosion conditions can occur.

If insulation is to be applied over certain austenitic alloy steel, it is recommended to apply a barrier before the application of the insulation so as to prevent stress corrosion.

At 500 deg C and above none of the barrier materials can withstand the temperatures and therefore should not be used.

It should be noted that under such circumstances stress corrosion can occur when the operating temperature falls below 500 deg C during a shut-down.

The barrier may be aluminium foil not less than 0,06mm thick or a specially formulated paint may be applied.

The recommendations of the manufacturer should be followed particularly in respect of limiting temperature of the dried film.

Designing an insulation system

Factors which influence the design of an insulation system are:

Location of plant

(a) Indoors

(b) Outdoors protected from the weather

(c) Outdoors exposed to the weather

Temperature conditions

(a) The normal operating temperatures

(b) The extreme temperature if other than (a) above

(c) Any fluctuating temperature

(d) Duration of extreme or fluctuating temperatures Surrounding atmospheric conditions (a) Ambient temperature (b) Relative humidity to establish dew point for cold insulation (c) Flammable conditions (d) Potentially corrosive atmosphere

(e) Air flow over insulated surface Special conditions or service requirements (a) Resistance to compression, for example, foot traffic (b) Resistance to fire (c) Resistance to vibration (d) Resistance to mechanical damage (e) Resistance to corrosive fluids or gasses

(f) Anticipated wide fluctuations of temperature, for example, steam out

(g) Resistance of insulation protection to ingress of oils and flammable liquids

(h) Application of insulation over special alloys

Design calculation

The design of an insulation system is governed by the insulated operating values which the plant requires after insulation.

The values may be:

(a) Surface temperature

(b) Heat loss or gain

(c) Temperature drop or rise

(d) Condensation prevention Calculations are by the formulas which are to British Standard BS 5422.

Other international standards may be used.

The calculated values are theoretical and should be adjusted by practical, design and atmospheric consideration.

Support systems Support systems may be required for insulation, cladding or composite for both.

The cost of fabrication and attachment of supports to the equipment forms a significant part of the insulation cost and therefore the method of attachment must be well defined prior to the issue of any insulation inquiry.

It is recommended that where post-manufacture welding is not permitted, the fitting of supports be undertaken by the equipment manufacturer.

Cylindrical vessels Where post-welding is not permitted and supports have not been included by the manufacturer the contractor must fit support rings using a non-welding method.

The criteria for this method are:

(a) Suitable pitch

(b) The total weight of the system to be supported

(c) Thermal expansion or contraction of the equipment

Flat surfaces Support systems on flat surfaces should take into account:

(a) The disposition of the surface ie, underside, vertical, horizontal or inclined

(b) The total system mass to be supported

(c) Thermal expansion or contraction of the equipment

Heat bridges

Where metal cladding comes in contact with support steel, hot spots for hot insulation and condensation for cold insulation will occur.

It is therefore recommended to insulate between the contact points.

Main insulation types

Boards or batts – A rigid binder bound fibrous insulation for use on flat or large cylindrical surfaces. Felt – A semi-flexible binder bound fibrous insulation for use on all surfaces where vibration is of a low order.

Loose – Loose or granulated insulation with a low binder content for filling voids.

Mattress – A flexible low binder fibrous insulation for use on all surfaces. The mattress shape is maintained by a wire mesh fixed to one or both sides by through stitching. Because of the low binder content the material is able to withstand higher temperature without binder breakdown.

Pipe section – Insulation preformed to fit in two halves round cylindrical surfaces of various diameters.

Pipe section covered – As for pipe section except that the outer surface is fitted with a cover by the manufacturer, for example, canvas or foil.

Segments – Cylindrical insulation for fitting round large cylindrical surfaces in more than two parts. (Confined to the closed cell insulants)

Slab – All the closed cell flat insulation and white insulants fall into this category and may be applied to all surfaces provided it is suitably shaped.

Rope – Usually of fibrous material for spirally wrapping around small pipes.

Spray fibre – Used for insulating irregular shapes such as turbines.

Spray foam – Usually polyurethane or polyisocyanurate. The main applications are for large regular surfaces such as roofs or tanks and for cavity filling.

Tape – Usually of fiber and used for spiral wrapping on pipework where conditions so demand.

2.6 General notes of insulation

The use of felt or mattress is not recommended over cylindrical shapes of less than 200mm outside diameter.

Under certain circumstances boards or slab may be used on cylindrical surfaces by cutting the insulation into beveled staves.

Where the total insulation thickness exceeds 50mm, a multi-layer system should be used with staggered joints to reduce heat  loss or gain through direct paths to atmosphere.

When very high or very low temperatures are encountered expansion or contraction joints should be provided.

These are usually 40mm wide and packed with a suitable insulation.

It is incumbent on the manufacturers to provide all the necessary values such as thermal conductivity  (K factor) and water vapor permanence based on the tests conducted by a testing authority.

If required, the test number and date should be given.

Important: Because of the health hazards involved, products containing asbestos should not be used.

Vapor barriers

All insulation designated as Cold must be provided with a Vapor Barrier Protection of insulation

Protection of the insulation may consist of metal cladding or a coating system  Metal cladding The main metals used are:

(a) Galvanized steel

(b) Pre-painted steel

(c) Aluminium

(d) Stainless steel

(e) Other specialized formulations

Depending upon the requirements of the application the metal may be flat sheet or profiled.

The thicknesses are dependent on the degree of mechanical damage which the cladding is expected to withstand and may vary from 0,5mm to 1,2mm.

For areas susceptible to heavy damage a thicker gauge may be required.

In the application of cladding it should be ensured that:

(a) Good water shedding exists all joints or sealing of joints where this is not possible.

(b) At point where dissimilar metals may come in contact with one another precautions must be taken to prevent galvanic action.

(c) All metal joints must be straight and square to prevent a symmetrical appearance.

(d) The cladding system must be constructed so that due allowance is provided for the expansion or contraction of the equipment.

(e) Where the cladding is applied over a vapor barrier, great care must be taken to avoid puncturing the vapor barrier either during or after erection, for example, a spacer or protective liner.

Plaster finishes

The term plaster includes both hard-setting plaster and mastics which may be used separately or together. Plaster may be used on all surfaces but when exposed to the weather it should be over coated with mastic. If plaster is to be used over a fibrous insulation the insulation must be of sufficient density to withstand the trowel application.

Mastic is not suitable for direct application to fibrous insulation. Generally, the purpose of the plaster is to provide a surface resistant to mechanical damage and/or a foundation for the mastic which provides the waterproofing. Both the plaster and the mastic should be applied in two layers with a reinforcing between the layers, ie, galvanized wire mesh for the plaster and fiberglass mesh for the mastic.

The first coat in each case should provide an anchor to ensure a key for the second.

Because of its high mass, the plaster coat is subject to slipping on large vertical surfaces. The wire mesh reinforcing must therefore be tied back, with binding wire, to fixed supports on the equipment.