OVERVIEW OF INSULATION SYSTEMS

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You are reading the entire article to describe your mindset about heat insulation.
Consequently, this handbook has been produced as a reference for common practice in South Africa. If more extensive detail is required, BS 5970 “The code for heat insulation of pipes is code
work and equipment in the temperature range – 100°C to 870°C” be consulted.
If there is a temperature differential between the process and ambient conditions, heat will flow from the higher to the lower temperature.
Throughout the handbook the following shall apply:
• Hot insulation in areas where insulation is used to prevent heat loss
used.
• Where the insulation is used to prevent heat gain to the process the term cold insulation will be
used.
• Where the insulation is used to prevent heat loss and heat gain in buildings the term Ambient
Insulation will be used. The Ambient Insulation section is currently under preparation and will be
published at a later date.
In addition to the basic insulation material, a system may need:
• Supports for the insulation
• Fastenings for the insulation
• A vapour seal in case of cold insulation
• Mechanical or weather protection of the insulation, for example, metal cladding
• Supports for the protection
• Fastenings for the protection
• Finishing, for example, paint coatings, decorative finishes or identification bands
• Heat tracing with or without heat transfer cement


In this handbook unit designations are (according to the SI system):
• Density kg/m3
• Thickness mm
• Temperature °C
• Differential temperature K
• Thermal conductivity W/mK
“PRE-INSULATION APPLICATION”
2.1.1 Before insulation is applied; all surfaces to be insulated shall be thoroughly cleaned
to remove dirt, oil, moisture, loose rust or any other foreign matter.
“PRESSURE AND LEAK TESTING”
It is recommended that pressure and leak testing be carried out and any repairs
effected prior to application of insulation. In many cases this is a statutory
requirement.
“HEAT TRANSFER CEMENT AND HEAT TRACING”
If a temperature is to be maintained by means of external heat sources such as heat tracers, heat transfer cement may have to be applied to improve the heat transfer from the tracer in severe cases. The manufacturer’s recommendations should be consulted.
“CORROSION PROTECTION”
Where the operating temperature is less than 130°C and the equipment or pipe work 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.
Most thermal insulations will not, of themselves, cause stress corrosion cracking as may be shown by tests. When exposed to elevated temperature (boiling point range 80°C and 200°C), environments containing chlorides, moisture and oxygen, however, insulation systems may act as collecting media, transmigrating and concentrating chlorides on heating stainless steel surfaces. If moisture is not present, the chloride salt cannot migrate, and stress corrosion cracking because of chloride contaminated insulation cannot take place – ASTM C692-97.
If insulation is to be applied over certain austenitic alloy steel where the operating temperature is between 80°C and 200°C, it is recommended to apply a stress corrosion barrier before the application of the insulation so as to prevent stress corrosion. At 500°C and above none of the stress corrosion barrier materials can withstand the temperatures and therefore should not be used.
It should be noted that during startup and shutdown, operating temperatures might occur within this temperature band and under such circumstances stress corrosion could occur.
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.
“PRE-INSTALLATION SUPPORTS”
Insulation supports shall be installed prior to the application of the insulation.
“DESIGNING INSULATION SYSTEMS”
Factors, which influence the design of an insulation system, are:
“LOCATION OF PLANT”
• Indoors
• Outdoors protected from the weather
• Outdoors exposed to the weather
• Shape, size and elevations all need to be taken into consideration
“TEMPERATURE CONDITIONS”
• The normal operating temperatures
• The extreme temperature if other than normal operating temperature
• Any fluctuating temperature
• Duration of extreme or fluctuating temperatures
“SURROUNDING ATMOSPHERIC CONDITIONS”
• Ambient temperature
• Relative humidity to establish dew point for cold insulation
• Flammable conditions
• Potentially corrosive atmosphere
• Acidic conditions in atmosphere
• Air flow over insulated surface (wind velocity)
“SPECIAL OR SERVICE CONDITIONS REQUIREMENTS”
• Resistance to compression, for example, foot traffic
• Resistance to fire
• Resistance to vibration
• Resistance to mechanical damage
• Resistance to corrosive fluids or gases
• Anticipated wide fluctuations of temperature, for example, steam out
• Resistance of insulation protection to ingress of oils and flammable liquids
• Application of insulation over special alloys
• Resistance to moisture and other weather conditions
• Resistance to Vermin

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