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R-values of Pipe Insulation

This note is intended to clarify how the r-values for pipe insulation materials are determined.

The R-value of preformed pipe insulation can be calculated using the methods detailed in ASTM C335. There are overseas laboratories that can test to this standard, but I believe that this method is not available at any registered testing laboratory in Australia.

Here, all insulation materials are tested on a planar section of insulation of the same specification as that of the preformed pipe section. In other words, if your pipe sections are to be 125kg/M3 rockwool then the flat sheet must also be 125kg/M3 rockwool.

Once the k-factor of the material has been determined in the “planar mode”, the k-factor, or factors if the material has been tested at multiple thicknesses, are used to determine the R-value of the pipe insulation.

The R-value of the pipe insulation is determined by using the formula detailed in AS/NZS 4859.1:2002 clause (new) “Alternative method for calculation of R-value for pipe insulation”It should be noted that the formula detailed in this clause (unless since corrected) is incorrect. The reference to log e should in fact be log n.

The R-value of pipe insulation utilising this formula, or if testing to ASTM C335, will always be higher than that of a flat sheet of identical construction.

This technical note is intended as a guide only and any information of a technical nature should be checked with a qualified engineer.