Page 469 - Compression Machinery for Oil and Gas

450 SECTION III Applications

include: pressure pulsation, vibration, strain, and sound. Pressure pulsation is
primarily used to diagnose acoustic resonance or flow-induced vibration prob-
lems. Vibration data such as acceleration, velocity, or displacement is used to
diagnose mechanical resonance or forced response issues. Strain is used to eval-
uate potential for cumulative fatigue or mechanical overload. Sound intensity or
pressure level is used to determine likelihood of mechanical damage or person-
nel annoyance. Instrumentation and data to be used during dynamic testing will
depend on the compressor design characteristics and the specific problem that is
being dealt with.

Test Measurements and Uncertainty

The accuracy with which the performance of compressors can be calculated
depends directly on how accurately the measurements are made. In pursuit
of best obtainable accuracy, the following are employed: calibrated high-
quality transducers, state-of-the art automated data recording system, and data
reduction programs. Industry standard test procedures aid in selecting appropri-
ate equipment and procedures for doing performance and dynamic testing. Field
operations team helps to ensure accuracy by providing stable operating condi-
tions during tests.
For all sensors, it is important that instruments be calibrated regularly and
proper selection, installation, and measurement are made in their use. In partic-
ular, it is important that the range of the sensor and the physical parameter
match, as well as match the output of the sensor to the data acquisition
(DAQ) system.

Test Preparation
1. For field testing, an agenda or plan should be developed as early as possible
before the actual testing. Development and discussion of this test plan
should include all involved parties, such as the test engineers, suppliers,
operators, and end users. This plan should provide details on the following:
the type, quantity, and location of the measurements to be taken.
2. The operating conditions to be used for test points.
3. The method of data reduction, including the equation of state to be used for
performance calculations.
4. The selected approach for determining the test uncertainty.
5. The acceptance criteria (specified in terms of maximal uncertainty
allowable).

Instrumentation
Pressure
Pressure sensors used for performance testing need to be of the type that will
measure the static pressure of the system. It is an accepted practice to calculate