Q. Flange Assembly with Bolt Elongation Measurement?

Bolt elongation measurement may be used, with COLT engineering approval, at flanges where Hydraulic Bolt Tensioners are impractical.

Ideally, the elongation of each bolt on each joint should be measured to assure uniform bolt tension. For the finished joint, bolt elongation should correspond to recommended stress in the bolt +/- 10%. The effective length, L0 is determined by measuring the distance from the centers of the nuts. This is the same as the distance from inside nut faces plus one nut height.

Center punch end faces of bolts on which elongation will be measured. It is suggested that every fourth bolt be used as a reference bolt.

Install bolts and gasket and make initial reference measurements.

Determine the proper elongation values from the Flange Closure Sheet, Form ES-PPG-9011. Tighten bolts using a torque wrench, making elongation measurements after each "criss-cross" round has been completed. (Each round consists of 30% elongation, 70% elongation and full elongation).