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These bearings, either tapered or thrust, ball, straight or
needle roller, are encased in oil to aid the free movement of the
stem.
The gooseneck, wash pipe and its retaining cover, bonnet
and stem comprise the core. These are constructed to receive,
deflect and smooth out the high pressure, pulsating action and
abrasive content of the drilling mud. The wash pipe is the heart of
this focal point.
All possible wear is directed to this short heat-treated
cylinder. Around it there is a packing cartridge of rubber or fiber
and metal rings to prevent drilling mud from reaching the bearing
and to hold the protective lubricant. Manufacturers often provide
complete packing box cartridges and wash pipes to be set into
place in one operation. The life of these parts is prolonged by the
use of extreme pressure lubricants.
The indication that the swivel is overburdened by extreme
mud pump pressure may causeexcessive replacements. In the
drilling circulation system it is always possible to increase the ID
of pipe, hoses, connections or drill collars, this will decrease the
drilling time and replacement cost on related parts. If erosion at the
wash pipe and similar connections persist it is necessary to check
for faulty shale shaker screens, grit-filled mud pits and lumpy mud
mixtures.
Some manufacturers rate their swivels by the size of the
stem. For example, one manufacturer puts out a selection
numbering 3-S, 4-S, 6-S, the numbers representing the
approximate overall dimension of each, specifically 3 ½ in 4 ½ in.,
and 6 ½ in. OD stems.
Others use maximum rated depth.

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