Flange joints should align without excessive stress. When a joint is out of alignment it means that the bolts cannot be installed.
Alignment tools are designed to move the joint precisely until the bolts are able to be inserted. The tools provide the capability of moving the joint until it complies with the piping code for lateral and rotational misalignment.
The ASME Piping code B31.3 (1999 Edition) 335.1.1 9 (c) specifies the following Flange Joint Misalignment Tolerances:
The maximum for lateral or center-line offset is 1.5 mm or less than 1/16”. For rotational misalignment the Piping code specifies that it be a maximum 3 mm or less than 1/8”.
The above tolerances refers to pipe work being connected to pumps, rotating equipment & pressure vessels.
How to Check Flange Alignment
Before installing bolts, check the joint in three ways:
- Face parallelism. Measure the gap between the flange faces at four points, 90 degrees apart (12, 3, 6, and 9 o’clock), using a feeler gauge or calipers. Unequal readings mean the faces are not parallel.
- Centerline offset. Lay a straightedge across the outside edges of both flanges at several points around the joint. A step between the two flanges indicates lateral offset.
- Bolt hole alignment. Insert a bolt or alignment pin through the bolt holes. Holes that don’t line up indicate rotational misalignment.
Compare your measurements to the tolerances above. If the joint is out of tolerance, use a flange alignment tool to move it into position rather than forcing the bolts. Flange alignment tool rentals →