Page 246 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 3 .27 Compressor Best Practices
important facts concerning condition monitoring. These facts
are presented in Figure 3.27.20. All performance condition monitoring instruments must have
known, accurate calibration values!
If:
T as measured is off 5%, efficiency is affected 20%!
Specific data (to confirm field guarantees) requires pre-planning Inaccurate gas analysis of 5% can affect efficiency 20%
to ensure accuracy Pressure gauge inaccuracy has much less of an effect on
Trends produce relative change in values
efficiency!

Fig 3.27.20 Turbo-compressor performance condition monitoring Fig 3.27.22 Instrument calibration facts
facts

Refer back to the ‘Life cycle of equipment’ in Chapter 1,
Figure 1.3.2. If specific data is required to confirm field guar-
antees, the project team must pre-invest and plan for the proper
instruments, number of and location in the design phase of the Take samples from the top of pipe
Measure gas temperature
project! Be sure to analyze gas at temperatures equal or greater than
One (especially the rotating equipment engineer) must re- field conditions
member the words in Figure 3.27.21. Confirm laboratory experience and methods

Fig 3.27.23 Gas analysis guidelines
‘The field is a place to produce product, not conduct laboratory
experiments’
1981 A.D. a production supervisor relative change, the starting point must be established.
Figure 3.27.25 defines the baseline condition.
I can’t remember how many times in my career I have said, “I
Fig 3.27.21 Remember these words!
sure wish we had established the ‘baseline condition’”.
The baseline turbo-compressor performance condition
Figure 3.27.22 presents important facts concerning in- should be established once the process unit is on spec, imme-
strument calibration. diately, not one day, week, month or year later. The sooner the
Inaccurate gas analysis procedures can produce some pretty baseline is established, the more data there will be in your
wild results! Efficiencies that exceed 100%! Figure 3.27.23 machine historical file. Many problems occur in the initial period
presents guidelines for accurate gas analysis. of operation; be sure you have recorded the data. The baseline
Location and number of field instruments are just as impor- condition then represents the first point on the trend graph of
tant as instrument calibration. I cannot overemphasize the im- any measured parameter. Figure 3.27.26 recommends when
portance of this fact. Convince management (plant management baseline conditions should be taken.
first, then project management) to pre-invest in turbo-com-
pressor performance and instrumentation. If you don’t know Trending
accurately what’s happening inside the patient, you can’t ef-
fectively prevent problems! That old medical analogy to a turbo-
compressor again! Figure 3.27.24 presents some guidelines from Trending requires that a parameter be monitored over a period
the ASME Turbo-compressor Test Code (PTC-10) regarding of time to determine if significant change occurs. These factors
the number and location of instruments. The field is not are defined in Figure 3.27.27.
It should be noted that significant change is not synonymous
a laboratory!
Field turbo-compressor condition monitoring must be with alarm point. If an initial value is small, a small change can be
significant and still be far away from the set alarm point!
planned such that it does not impact production rates.
Details concerning field performance testing will be
discussed in the next chapter. We have presented suggested
Establish a baseline turbo-compressor performance trend parameters in the final
figure of this chapter; Figure 3.27.28.
Before we discuss trending or fully understand turbo-compres- We have included printouts of our excel spreadsheets used
sor performance condition monitoring, the baseline condition for centrifugal compressor CCM. These sheets can be used to
must be defined. Since performance condition monitoring, as completely trend centrifugal compressors using the CCM
well as any type of condition monitoring, is concerned with approach.

220