Feasibility Study of Optical Fiber Surface Condensation Sensors for Sewer Pipelines

High humidity and condensation contribute significantly to the corrosion of concrete wastewater pipelines. Condensation promotes the growth of a biofilm that converts hydrogen sulfide gas emitted from the wastewater into sulfuric acid, which corrodes the concrete. Due to the harsh gaseous environment in sewer systems, conventional electronic sensors are unsuitable for use where they typically fail in a few weeks. Optical fiber temperature and relative humidity (RH) sensors have demonstrated long-term operation in hostile wastewater environments. Though for insights into condensation formation, dew point measurements can provide more valuable information than RH measurements. In this article, we show how optical fiber temperature and RH sensors can provide an additional layer of information pertaining to dew point. It was found that fiber sensors could accurately calculate the dew point and detect the onset of condensation in a static laboratory environment. However, there are nuances around the absorbing nature of concrete surfaces which have been investigated to help unpack how this additional feature can be unlocked for existing deployments in sewer pipelines. The implementation of these sensors into corrosion management can inform preventative strategies such as ventilation and chemical dosing, whilst also providing important data for modeling corrosion across the network.