A method for detecting leakage at a fluid connection for a gas turbine fuel supply system is disclosed herein. The method includes closing a flow control valve at an upstream end of the fuel supply system and pressurizing the fuel supply system with a compressed medium via a compressed medium supply to a target pressure. The target pressure is less than a pressure threshold of a check valve that is disposed downstream from the compressed medium supply and upstream from a corresponding combustor of the gas turbine. The method further includes pointing a receiver portion of an ultrasonic detection device proximate to at least one tube fitting of the fuel supply system located between the flow control valve and a combustor which is fluidly coupled to the fuel supply system. Detection of an increase in sound level and/or the sound of popping at the tube fitting is indicative of a leak at the tube fitting.