What Is the Sequence for Tightening Flange Bolts?


Quick Answer

Tighten flange bolts in an "X" sequence of repeated torques. After lightly setting the first flange bolt, tighten the one directly across, or 180 degrees from it. Set the third flange bolt directly in the middle, or 90 degrees from the first and second, followed by the fourth flange bolt, 180 degrees or straight across from the third.

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Full Answer

Lubricate any bolts, nuts, bolt threads and flange assemblies before changing or tightening. Once lubricated, begin the tightening sequence. Mark each flange bolt with crayon or grease pencil after each round to keep track of the order in which each flange bolt is tightened.

Using a hand wrench, perform the first tightening to lightly set the bolts. Repeat the same sequence to firmly tighten each bolt. Use an electronic wrench for the remaining rounds of tightening, starting with 25 percent of the total required torque. Apply 75 percent of the required torque in the fourth tightening sequence, followed by 100 percent torque strength in the fifth round of tightening.

Flange bolts are completely tightened when they no longer turn under 100 percent torque strength. Re-torque all flange bolts after 24 hours to ensure loss of tightness has not occurred in any bolt or joint.

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