Page 116 - Compression Machinery for Oil and Gas

Centrifugal Compressors Chapter 3 103

FIG. 3.69 Temporary bypass piping with mesh screen used to flush contaminants from the lube oil
system [23].

required on the lube oil pumps for protection. The bearing and seal areas are
bypassed with the use of jumpers until the system is proven to be clean
(Fig. 3.69). Temporary bypass piping to the reservoir is installed along with
a mesh screen at the end of the bypass.
The key to a successful oil flush is a high velocity to ensure turbulent flow.
This may require the use of an external pump and such preparations should be
made in advance. However, simultaneous use of the main pump and auxiliary
pumps may be sufficient to reach the required flow rate. Filter differential pres-
sure can be quite high during flushing. Effective flushing will typically involve
variation of oil temperature, vibrating the piping, and many hours of flushing.
The flushing should continue until the required cleanliness is achieved based on
inspection of the flushing filters or strainers, patch test, particle counters, or ISO
4406 cleanliness level. Once the system is clean, the flush continues through the
bearing housings until they too are clean.
Lube systems must be periodically inspected and maintained to ensure their
proper operation. As a minimum, the following regular checks should be
performed:

l check filter pressure drop and replace elements as recommended,
l check the oil reservoir level and add oil as required, and
l check operation of auxiliary oil pump by operating pump periodically.

Special Considerations
Interaction With Reciprocating Compressors and Aerodynamic
Stability
Strong pressure pulsations into the suction or discharge of a centrifugal com-
pressor can move its operating point into operational instability regions such