The pipeline is fed at one end with a supply of heated air from an air compressor. Heat energy is absorbed by the water in the pipeline which speeds evaporation. The water vapor is transported by the flowing air out of an exit port located at the opposite end of the pipe to the hot air entry. A capacitive instrument located at the air outlet will indicate the completion of the drying process when the outlet air dewpoint reduces significantly from its starting value. During the process, the air will be close to saturation at the prevalent ambient temperature. When the pipeline is dry, the dewpoint will reduce towards that of the feed air from the compressor.