A method and system for detecting corrosion on a pipe or a pipeline. An electrical or electromagnetic pulse is transmitted into a pipe or pipeline to travel as a propagating electromagnetic wave along the pipeline to a receiving location. Both the distance traveled from the transmitting and receiving location, and also the time interval for such travel are measured. Velocity of the wave is detected as a means of ascertaining whether corrosion is present. Various embodiments, using both multi-channel and single cables, are used to transmit the detected waves, and the waves are received at a plurality of spaced locations along the length of the pipe or pipeline. For an insulated pipeline, the signals can be received by a directional antenna, and the pulses can be transmitted into the pipeline by means of either an antenna placed directly adjacent to the pipeline or a magnet electrical contact member in direct contact with the pipeline.