A hydraulic expander for use in a tube containing a U-bend region is disclosed and claimed. The tool includes a sheath for transmitting hydraulic fluid therethrough to an inflatable bladder. The sheath is flexible, allowing it to be inserted through the U-bend region of the tube. The bladder is fluidly connected to the sheath and is thereby in fluid communication with a supply of hydraulic fluid. The length of the bladder and the metal end caps, along with the centering spacers on the expansion sheath, allows it to pass through the U-bend region of the tube such that it can be positioned inside the tube adjacent to a support outside the tube, such as an AVB. Hydraulic expansion of the bladder causes it to exert an outward force on the tube inner surface, causing it to plastically deform such that its outer surface comes into contact with the tube support, such as an AVB. This expansion will increase the friction between the tube and the AVB to minimize the risk of tube vibration damage.