Pig Velocity Control with Mass Flow Controller
Pipeline pigging is a vital and common process used in many industries, but rarely is pig velocity control performed. It is used to clean pipes, ensure proper flow and perform diagnostics on the pipe itself. Too often, this process is controlled with pressure, resulting in damaged pigs and pipes. The damage occurs when the pig gets stuck and pressure is increased until the pig breaks free at a very fast and uncontrollable rate.
By controlling the flow in the pipe, the velocity of the pig can be controlled. When the pig gets stuck, the mass flow controller allows pressure to build up – to break the pig free, but as soon as the pig breaks away, the mass flow controller senses the increase in flow and immediately reduces flow, thus reducing the velocity of the pig and the potential for damage.
This sketch shows pig velocity control by controlling flow in the pipe. An FQB3 and F-Series flow assembly are being used to control the speed of a pig as it is moved through a pipe for cleaning. Since the FQB3 servo control valve closes the loop around the signal output of the F-Series flow transducer, constant velocity can be maintained or pig velocity can be varied.
Update speed from the F-Series is less than 10 milliseconds which ensures there is no lag in pig velocity control as things change in the pipe. Pig speed is adjustable based on a command signal from the controller and a signal output showing flow from the F-Series is available on pin 5 of the FQB3 electrical connector for data acquisition.