Abstract
There are many International and National standards for flanges and clamp connections. Different bolt pretension values are required by these standards. In general, two bolt tightening methods are recognized: by torque or tension tools. The tensioning method is more accurate; however, this requires temporary higher pretension. ISO-27509, for example will need temporary bolt pretension equivalent to 90–95% of yield strength, API 6A allows up to 83% of bolt yield strength. Metric and Imperial bolting types can be used. Both types have related thread standards with specific tolerance classes. It is known from field experience that in some cases combination of thread tolerances, bolt size, and tightening with tension tool, the induced interference between the nut and stud threads can prevent the turning of the nut preventing the correct pre-load. This paper investigates the problem and proposes some solutions to avoid jamming. Paper will present general overview and deep problem investigation based on Finite Elements nonlinear analysis results. The requirement for smooth nut turning thread clearance will be calculated. The thread tolerances will be compared and investigated in light of existing standards and beyond. The threads load carrying capacities will be also addressed in light of analytical calculations. The thread stripping phenomena will be also addressed. In addition, the torque tool method will be discussed in term of bolt stress and accuracy. The bolt scatter will be included in the discussion.
