Flange tensioner is a device that hydraulically loads the flange by pulling against the studs. The tensioner consists of a segmented annular ring with a number of internally connected hydraulic chambers. It simultaneously tightens all bolts in the shortest possible time. Only one connection is necessary for each segment to pressurize the rams simultaneously and sealing is achieved in single operation. This is compared with the conventional method of sealing that requires tightening each bold individually. These are used in pipeline flanges, swivel bearing joints, riser clamps and vessel covers.