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BS 5422-2009 pdf free download

BS 5422-2009 pdf free download.Method for specifying thermal insulating materials for pipes, tanks, vessels, ductwork and equipment operating within the temperature range —40 °C to +700 °C.
5.6 Vapour barrier — Permeance requirements
NOTE 7 Condensation of water vapour will occur on a surface that is at a temperature below the atmospheric dew point temperature. Moisture can be deposited within the insulating material and on the insulated metal surface. Where the insulated surface is likely to be at or below the dew point temperature during any part of its operating cycle, an effective vapour barrier should be applied on the warmer face of the insulation to avoid deposition of moisture within the insulating system. The presence of water within an insulation system can reduce thermal effectiveness and lead to corrosion of metal components.
For the purpose of this standard an effective vapour barrier shall be deemed to be one that meets the water vapour permeance requirements given in this subclause.
Different levels of water vapour permeance shall be specified according to the type of application. Where the insulating material itself does not conform to the water vapour permeance requirement, a “vapour barrier” on the outside (warm side) of the insulation shall be used.
The vapour barrier shall take the form of a coating or sheet material. Any joints in the coating or sheet material or in the insulating material itself, where it is providing the water vapour permeance requirement, shall be fully sealed.
NOTE 2 This is to ensure that the vapour permeance performance is maintained continuously in the system as installed. Particular care shall be taken at termination points. The external vapour barrier, where required, shall be pre-applied or applied before the fluid in the pipe, duct, or vessel is cooled.
When a vapour barrier is used, the system as installed, shall have a fire performance at least equal to that specified in 6.2.2, 7.2.2, 8.2.2, 9.2.2 and 10.2.2 as appropriate to the type of application.
The water vapour permeance of flexible sheets used as external vapour barriers shall be assessed in accordance with the method given in 853177. The test conditions, e.g. temperate or tropical, arid the thickness of the test specimen shall be stated. Where the apparatus for the method in BS 3177 is unsuitable because of the thickness of the test specimen, BS 4370-2:1993+A2, method 8 shall be used. The water vapour permeance of the insulated system shall be selected according to the relationship between the cold surface temperature of the plant and the temperature difference, in degrees centigrade (°C).BS 5422-2009 pdf free download.

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