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isolation design

The design of an insulation system is governed by the insulated operating values, which the plant requires after insulation.
The values may be:
• Emissive
• Thermal conditions – Heat loss/Heat gain
• Process temperature drop or rise
• Condensation prevention
• Personnel protection temperature
• Optimal economic conditions (See page 1)
• Thermal conductivity of insulation material
• Ambient temperature
• Wind velocity
Calculations are by the formulae as set in Section 5.2, which are to British Standard BS 5422.
Other international standards may be used. The calculated values are theoretical and should be adjusted for practical, design and atmospheric considerations.
“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 equipment manufacturer undertake the fitting of supports.


“CYLINDRICAL VESSELS”
Where post-welding is not permitted and the manufacturer has not included supports the contractor must fit support rings using a non-welding method.
The criteria for this method are:
• Suitable pitch
• The total weight of the system to be supported
• Thermal expansion or contraction of the equipment
“FLAT SURFACES”
Support systems on flat surfaces should take into account:
• The disposition of the surface, i.e., underside, vertical, horizontal or inclined
• The total system mass to be supported
• 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 – Semi-elastic material, attached fibrous insulation for use on all surfaces.
vibration is a low order for example Boilers
• 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. A wire
mesh fixed to one or both sides by through stitching maintains the mattress shape.
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 expanded/extruded insulants fall into this
category and can be applied to all surfaces provided that it is properly shaped.
• Rope – Usually of fibrous material for spirally wrapping around small pipes.
• Spray fibre – Used for insulating irregular shapes such as turbines and also for
fireproofing.
• 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 pipe work where conditions
so demand.
“GENERAL NOTES ON INSULATION TYPES”
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.
The general practice on certain applications when installing 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.
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 together with the particular test method and conditions.
Important: Because of the health hazards involved, products containing asbestos should
not be used. Where asbestos has to be used, adherence to the OSH act and
regulations should be followed.
Local insulation is normally preferred due to cost, delivery and wastage factors.
“VAPOUR BARRIERS”
All insulation designated as “cold” must be provided with a vapour barrier and this procedure is set out in

Chapter 4 – Cold insulation.
“PROTECTION OF INSULATION”
The insulation required to be protected from mechanical damage and the elements (weather
barrier) Protection of the insulation may consist of metal cladding or a coating system.
“METAL CLADDING”
The main metals used are:
• Galvanised steel
• Pre-painted or pre-coated steel
• Aluminium
• Stainless steel
• Other specialised formulations

Depending upon the requirements of the application the metal may be flat sheet or
profiled.
The thickness depends 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:
• Good water shedding exists at all joints or sealing of joints where this is not possible.
• At point where dissimilar metals may come in contact with one another precautions must be taken to prevent galvanic action.
• All metal joints must be straight and square to preserve a symmetrical appearance.
• The cladding system must be constructed so that due allowance is provided for the expansion or contraction of the equipment.
• 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 a mastic or finishing paint.
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, i.e., 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.

Our previous article Where water insulation is made in our article titled issues of water, Specialists ve water insulation information about the

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