Page 270 - Root Cause Failure Analysis

258 Root Cause Failure Analysis

Thrust Bearings
While process instability can affect both the fixed and floating bearings, the thrust bear-
ing is more likely to show early degradation as a result of process instability or abnor-
mal compressor dynamics. Therefore, these bearings should be monitored closely, and
any degradation or hint of excessive axial clearance should be corrected immediately.
Gear Mesh

The gear mesh vibration profile also provides an indication of prolonged compressor
instability. Deflection of the rotor shafts changes the wear pattern on the helical gear
sets. This change in pattern increases the backlash in the gear mesh, results in higher
vibration levels, and increases thrusting.

RECIPROCATING, POSITIVE DISPLACEMENT
Reciprocating compressors have a history of chronic failures that include valves,
lubrication system, pulsation, and imbalance. Table 22-3 identifies common failure
modes and causes for this type of compressor.

Like all reciprocating machines, reciprocating compressors normally generate higher lev-
els of vibration than centrifugal machines. In part, the increased level of vibration is due

Table 22-3a Common Failure Modes of Reciprocating, Positive-Displacement Compressors