Surge is characterized by fast flow reversals through a compressor and is caused by a large-scale breakdown of flow patterns within the compressor. Surge happens at low flow rates, often when the downstream demand decreases. When flow decreases below a certain minimum point, flow patterns in the compressor become unstable and fluid can move back through the compressor from the high-pressure side to the low-pressure side.
Because surge is a fast, high energy phenomenon, it can introduce excessive dynamic loads on internal components, such as thrust bearings, seals and blades as well as introduce unwanted pipeline vibrations. The cost of replacing compressor seals alone is on the order of $20K to $50K. Over time, surge can introduce fatigue failures that can damage the entire compressor.