Abstract: A method for hydrodynamic cleaning of a piping system using two-phase flow. A model for predicting peak wall shear stress for two-phase flow is used to determine an optimum flow rate ratio which achieves a maximum wall shear stress in the particular piping system to be cleaned. The optimum flow rate is first established by turning on the liquid and gas flows through the piping system to be cleaned and allowing the flow to reach steady state conditions. The back pressure of the system is measured and the optimization model is used to determine the optimum flow rate ratio. Once the optimum flow rate ratio has been calculated, the liquid flow rate and the gas flow rates can be adjusted such that the optimum ratio is achieved. The two-phase back pressure is then measured to verify that the optimum flow rate ratio has been used. This is done by comparing the measured optimum two-phase flow back pressure with the initial two-phase back pressure used in the equations.