Page 168 - Machinery Component Maintenance

150 Machinery Component Maintenance and Repair

Check alignment of mating flanges. Avoid use of force to achieve
alignment. Verify that:

1. The two flange faces are parallel to each other within 1/32 in. at
the extremity of the raised face
2. Flange centerlines coincide within 1/8 in.

Joints not meeting these criteria should be rejected.

Controlled Torque Bolt-Up of Flanged Connections

Experience shows that controlled torque bolt-up is warranted for cer-
tain flanged connections. These would typically include:
All flanges (all ratings and sizes) with a design temperature
> 900°F.
All flanges (all ratings) 12 in. diameter and larger with a design tem-
perature > 650°F.
All 6 in. diameter and larger 1500 pound class flanges with a design
temperature > 650°F.
All 8 in. diameter and larger 900 pound class flanges with a design
temperature > 650°F.
All flanges not accessible from a maintenance platform and > 50 ft
above grade.

In addition, it is generally appropriate to apply the above criteria to
flanged connections on equipment and other components such as:

0 Valve bonnets, where the valve is positioned to include the above ref-
erenced design temperature/size/f lange rating category.
0 Flanged equipment closures where they qualify for inclusion in the
above categories.
All flanged connections which will eventually be covered with low
temperature insulation within the above reference criteria.

Adherence to the following procedure is recommended for controlled
torquing of line flanges, bonnet joints, etc., when specified.

Preparation

Thoroughly clean the flange faces and check for scars. Defects ex-
ceeding the permissible limits given in Table 4-1 should be repaired.