Page 131 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

114 Major Process Equipment Maintenance and Repair

bly of bearings, impellers, and collets will include sliding these parts
down over this portion of the shaft. Strap wrenches are suitable for this
purpose and are preferable. The use of pipe wrenches on shafting, al-
though quite appropriate for servicing deepwell pumps, should be dis-
couraged, because this practice easily could carry over to the servicing of
process pumps where it is completely unacceptable. Threaded line shaft
couplings always have left hand threads that tend to be tightened by the
transmitted torque.
Threaded inner column generally has left hand threads because right
hand threads would tend to loosen from the torque applied as the result of
a bearing failure. The threads are internal and straight, not external and
tapered like pipe threads. This is shown in Figure 2-4. The joints are
sealed by the metal-to-metal contact between the smooth ends of the col-
umn. It therefore is necessary to avoid nicks, scratches, or burrs on the
ends of the column. The threads should be coated with a thread lubricant
or a thread sealant. Inner column may be tightened with pipe wrenches,
strap wrenches, or chain tongs.
Threaded outer column and bowl assemblies generally are tightened
with chain tongs. The threads are external, right hand and straight, not
tapered. This is also shown in Figure 2-4. These joints also are sealed by
metal-to-metal contact between the ends of the column. Column and
bowl threads should be coated with a thread lubricant or a thread sealant.
Submersible pump column has tapered external pipe threads that must
be coated with a thread sealant and tightened both to seal the joints and to
keep them from loosening from the starting torque. The threaded bowl
joints and the joint between the cast iron top case and the steel column
should be cleaned with Loctite@ Primer T and coated with Loctite@ 277.
The Loctite@ 277 joints may require heat for disassembly.

Care of Flanged Pressure Joints

Flanged mating surfaces must be thoroughly cleaned prior to reassem-
bly and sealing surfaces inspected to be sure that they are free from
burrs, nicks, or scratches. Static seals such as O-rings, flat gaskets, and
spiral-wound gaskets should not be reused but should be replaced after
each dismantling of the pressure joint. Additional information on static
seals is contained in Chapter 7 of Volume 1. After installation of the static
seal, assemble the joint hand tight and check for uniform gap or metal-to-
metal contact of the flange mating surfaces. Tighten bolts alternately in
pairs 180" apart, then another pair 90" clockwise from the first pair, and
so forth until the entire flange has been tightened. The bolt-tightening
sequence for a 12 bolt flange is shown in Figure 2-33. Bolts should be
tightened in three steps, 113 torque, 213 torque, and full torque.