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Surface analysis of 400 kV silicone rubber composite insulators is presented. These insulators have experienced 15 years of service on a coastal 400 kV transmission line. Inspection of the insulators shows low levels of degradation through cracking and oxidation of title surface. This has been quantified by microscopy, energy dispersive X- ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The analysis shows non-uniform ageing over each shed and ageing on the south side more advanced than on the north side. It is believed that non-uniform ageing was due to environmental factors including natural UV radiation and prevailing wind direction, and the resultant pattern of growth of organic species. EDX and FTIR were found to be the most useful and effective tools for analysis of these polymeric insulators.