Bolt Torquing / Tensioning
In most Industries, precommissioning and maintenance schedules are placing an increased emphasis on 'flange management' from the design stage, with the objective of a 'leak free' start up. Alstern Technologies promote the benefits of 'controlled tightening'. . . being the use of specially designed equipment, proven bolt loading calculations and written procedures, to tighten joints to the desired tolerances in a controlled and safe manner.
Hydraulic bolt torquing is the more familiar technique for the prevention of leaks in bolted assemblies such as pipe flanges. Given the wide range of sizes and specifications, it is important to choose the right tool and the right application. The hydraulic torque wrench is simple to use, and sometimes the only practical tool . . . but it does have speed and accuracy limitations. It is the varying friction between the threads of the stud and the nut, and between the nut face and the flange, that causes inconsistencies between the applied force and the residual bolt load. Surface finish, lubrication and material type, all change the effects of friction.
Hydraulic bolt tensioning is a semi-automated process, substantially faster than bolt torquing, and delivering a precise residual bolt load. Bolt tensioning enables a hydraulic load, more commonly known as the applied load, to act upon the stud bolt. The effect is similar to the stretching of a spring, and the stud bolt elongates. This extension is retained by simply tightening the nut. Given the hydraulic load was calculated to cause the stud bolt to retain a specified residual load when the tensioner is released, there is an inherent high degree of accuracy and repeatability not available with bolt torquing. The most accurate residual bolt loading and uniform compression of a joint gasket, is achieved by multi-stud tensioning. In a gasketed flange, no less than 50% of the bolts should be tensioned simultaneously, with 100% tensioning providing the greatest accuracy and shortest assembly times.
The disciplines of 'flange management' can be extended to incorporate project database systems, and the application of electronic tagging to provide detailed historical information and proven quality control of every system component. The integration of flange management with our Nitrogen/Helium leak detection and other services can produce substantial reductions in manpower, interfaces to be managed, and lead to a more efficient and cost effective plant start-up.
