Hydraulic Bolt Tensioning is a controlled technique that applies a calculated tensile force to a bolt using a specialized hydraulic tensioner. The tensioner is positioned over the stud and connected to a hydraulic power source. Hydraulic pressure moves a piston that stretches the bolt by a predetermined amount. While the bolt is stretched, the nut is tightened against the joint surface. When the pressure is released and the tensioner is removed, the bolt returns slightly toward its original length, generating clamping force across the joint.