Health monitoring of corrosion resistant plastics exposed to alkaline solution by using pH indicator

摘要

Polymer and its composites are widely used in chemical engineering plants as corrosion resistant materials. It is required to establish a health monitoring technology for chemically degraded FRP structures. In this study, the authors proposed a new health monitoring technology that could simply detect the penetration of corrosive environment solution into plastics by using pH indicator. At first, FRP laminates for corrosion sensing were fabricated. The laminate consisted skins of glass mat reinforced unsaturated polyester (UP) resin, and inner corrosion sensing layer. In the sensing layer, phenolphthalein was added to UP resin. The laminate was immersed in NaOH solution. The sensor layer was colored in reddish purple and it was easy to distinguish from the color before immersion. Then, detection of NaOH penetration into unsaturated polyester resin was carried out by using an optical fiber and a spectrophotometer. A narrow slit was machined in an optical fiber and the slit was filled by phenolphthalein added resin. This sensing module molded in UP resin was immersed in NaOH solution. The optical fiber connected to a spectrophotometer and transmittance was measured. It was recognized that penetration of NaOH was detected by change of spectrum. This system could be easily applied to on-line health monitoring of chemical equipment structures.