Est 1967
95 Second Street, Booysens Reserve, Johannesburg
South Africa
PO Box 38653, Booysens 2016
Tel 27-11-835 2127
Fax 27-11-496 1263
E-mail vm@netdial.co.za
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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 vapour 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 formulae 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 enquiry.
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 fibre 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 bevelled 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 insulant.
It is incumbent on the manufacturers to provide all the necessary values such as thermal conductivity (K factor) and water vapour permeance 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.
Vapour barriers
All insulation designated as Cold must be provided with a Vapour 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) Galvanised steel
(b) Pre-painted steel
(c) Aluminium
(d) Stainless steel
(e) Other specialised 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 vapour barrier, great care must be taken to avoid puncturing the vapour 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, galvanised wire mesh for the plaster and fibreglass 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.
Support:
vm@netdial.co.za
SYSTEM OF MEASUREMENT
Method of measuring completed Thermal Insulation
Method A
Applicable where contractor has quoted unit rate per linear metre of straight pipe and per each for pipe fitting.
Straight pipe
Shall be measured from origin to terminus point or junction, along the centerline of pipe.
Measurements shall be though pipe flanges and fittings, but only if the flanges and fittings are insulated.
Elbows or bends shall be measured through to the intersection of the centre lines of the pipe.
Reducers shall be counted as one fitting of the larger size involved, and omitted from the count of the smaller size.
Tees shall be counted as one fitting, and if an unequal tee, shall be counted as a fitting of the smaller size.
Quantities shall be to the nearest whole number (0.51 and larger to the whole number above).
Fittings Shall be counted per each.
Method B
Applicable where the contract has quoted unit rate per square metre of completed insulation.
Areas of completed insulation will be measured. Should there be any items not detailed, the client and the contractor are to agree a system of measurement in advance.
Notes:
(i) All external insulation is measured over the outer surface area of the completed insulation.
(ii) All internal insulation is measured over the surface area which has been insulated.
(iii) The method establishes actual areas of insulation, and makes no extra over allowance for difficulty of work as regards form work or height.
Should the contractor wish to charge an increased rate for difficult work he should specify to which items the quoted increased rate will apply.
(iv) Quantities shall be calculated to the nearest whole number (0.51 and larger to the whole number above).
General
(a) Cut-outs under 1.0m2 are not deducted.
(b) End cap areas are measured to establish the actual surface area of insulation.
Cut outs in such areas are treated as follows:
(i) If gross area of end cap is less than 1.0m2 cut-outs are not deducted.
(ii) If gross area of end cap is 1.0m2 or greater, deduct cut-outs, but subject to rule (a) above.
(c) Pockets, niches, flattening shall be measured as if the cladding remains symmetrical.