The thermal conductivity of pipe sections and flexible mats can be measured with the hot pipe apparatus according to EN ISO 8497 or ASTM C335.
The core consists of a hot pipe with a length of 3 metres. The thermal conductivity is calculated at the mean temperature between the hot and cold side and expressed at the mean temperature.
The main difference is that the hot pipe apparatus test method includes the seams within the insulation. This explains why the measured values will be higher than the guarded hot plate
apparatus test.
A distinction is drawn between the definition of thermal conductivity.
Laboratory thermal conductivity Thermal conductivity is measured under laboratory conditions with the guarded hot plate apparatus or hot pipe apparatus test method.
Nominal (or declared) thermal conductivity Thermal conductivity specified by the manu-facturer, allowing for production related variations in quality and possible ageing, for example caused by gas exchange in closed cell insulation materials.
Practical thermal conductivity
Declared thermal conductivity including the influence of joints, design uncertainties, temperature differences, convection, changes in density, moisture absorption and ageing.
These effects are taken into consideration using supplementary factors.
Operational thermal conductivity
Practical thermal conductivity, whereby the supplementary values for insulation related bridges, such as bearing and support structures are included in the value.
2.2.3 Maximum service temperature
The temperature at which an insulation material is used should be within the temperature range specified for the material, in order to provide satisfactory long-term service under conditions of use.
This temperature is defined as maximum service temperature. The following factors should be considered when selecting insulation materials to be used at elevated operating temperatures.
Ability to withstand loads and vibrations Loss of compression strength after heating Linear shrinkage are heating
Change in thickness after heating and loading Internal self-heating (exothermic reaction or
punking) phenomena
Type of finishing of the insulation Support structures for the insulation Support structures for the cladding
Important note
The maximum service temperature of insula-tion materials can be tested in accordance with the test methods: EN 14706 and -7 (replaces AGI Q 132), ASTM C411 or BS2972. Each test standard has a different ttest method and its own criteria. ASTM C411 and BS2972 can be used to determine the maximum operating temperature at which an insulation material can be used, without its insulating capacity deteriorating. EN 14706 and -7 are used to classify insulation materials according to their behaviour at high temperatures based upon time-load exposure. Due to the effect of load during testing, the measure maximum service temperature in accordance with EN 14706 and -7 is lower than the other standards and therefore tends to reflect a more practical temperature limit for design performance.
ASTM C411
ASTM C411 is the standard test method for hot-surface performance of high-temperature thermal insulation.
This standard covers the determination of the performance of mats, slabs and pipe sections when exposed to simulated hot-surface applica-tion condiapplica-tions.
Mats and slabs are tested with the heating plate or pipe apparatus. The heating plate or pipe is uniformly heated to the declared maximum service temperature. Products are exposed to one sided heating.
ASTM C411 places no specific demands on the product performance after heating. Only the following results must be reported.
Extent of cracking, other visible changes Any evidence of flaming, glowing, smouldering,
smoking, etc.
Decrease in thickness, warpage, delamination Sagging pipe (pipe insulation)
BS 2972
This standard specifies test methods for the various properties of inorganic thermal insulation materials. Section six “heat stability of this standard” is designed to determine the perfor-mance of insulation materials when exposed to heating for 24 hours in an oven or furnace at the designed temperature.
BS 2972 places no specific demands on the product performance after heating. Only the following results must be reported:
Average percentage change of length, width, thickness and volume of specimens;
Percentage change of mass of the specimens before and after the test
Change in compression strength of the specimens before and after the test.
2.2.3 Maximum service temperature
According to BS 3958 “standard specification for thermal insulation materials”, the insulation material shall maintain its general form and shall not suffer visible deterioration of fibrous structure when heated to the maximum service temperature.
EN14706 (replaces AGI Q132)
The maximum service temperature replaces the term classification temperature, which was still the customary term in the AGI G 132 of 1996. It is recorded in the laboratory under steady condi-tions, and takes into account the delivery form.
The maximum service temperature for flat products is determined according to the EN 14706 standard and is determined according to the EN 14707 for pipe sections. During the test, the sample insulation material is loaded with 500 Pa pressure, which is equal to a load of approximately 0,5 kN/m².
The sample is then heated on one side at a heating rate of 5 K/min, until the target maximum service temperature is reached. The temperature is then maintained for 72 hours, before the insulation is allowed to cool down naturally to the ambient temperature. The deformation of the insulation is measured throughout the entire procedure. The deformation is not permitted to exceed 5 % throughout the entire testing process.