Abstract
Micro-sized voids (1 0−1 0 0μm) and nanostructured tracks with sodium chloride (NaCl) impurities have recently been observed in semi-conductive (SC) screens of high voltage subsea cross-linked polyethylene (XLPE) cables. Large vented water trees were observed growing from the nanostructured tracks at the XLPE-screen interface. In this paper, we show that by embedding NaCl in the semi-conductive compound in model samples prior to wet ageing, voids similar to those observed in the cable screens are formed. We propose that the formation of the spherical-like voids occurs through a mechanism involving the condensation of water vapor on the NaCl crystals, followed by deliquescence of NaCl, which generates osmotic pressure leading to void inflation.