Baker Hughes Panametrics PanaFlow LC, User Manual

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4.4 Fluid and pipe problems
If preliminary troubleshooting with the Error Code Messages
and the Diagnostic Parameters indicates a possible
problem, proceed with this section. Measurement problems
fall into two categories:
• Fluid problems
• Pipe problems
Read the following sections carefully to determine if the
problem is related to the fluid or the pipe. If the instructions
in this section fail to resolve the problem, contact
Panametrics for assistance.
4.4.1 Fluid problems
Most fluid-related problems result from a failure to observe
the flow meter system installation instructions, as described
in Chapter: Installation.
If the physical installation of the system meets the
recommended specifications, it is possible that the fluid
itself may be preventing accurate flow rate measurements.
The fluid being measured must meet the following
requirements:
• The fluid must be homogeneous, single-phase,
relatively clean and flowing steadily.
Although a low level of entrained particles may have
little effect on the operation of the XMT1000, excessive
amounts of solid particles will absorb or disperse the
ultrasound signals. This interference with the ultrasound
transmissions through the fluid will cause inaccurate
flow rate measurements. In addition, temperature
gradients in the fluid flow may result in erratic or
inaccurate flow rate readings.
• The fluid must not cavitate near the measurement point.
Fluids with a vapor pressure relatively close to process
pressure may cavitate near the measurement point.
Cavitation can usually be controlled through proper
system design.
• The fluid must not excessively attenuate ultrasound
signals.
Some fluids, particularly those that are very viscous,
readily absorb ultrasound energy. In such a case, signal
warning and error message will appear on the display
screen to indicate that the ultrasonic signal strength is
insufficient for reliable measurements.
• The fluid soundspeed must not vary excessively.
The XMT1000 will tolerate relatively large changes in the
fluid sound speed, as may be caused by variations in
fluid composition and/or temperature. However, such
changes must occur slowly. Also, fluctuations in fluid
sound speed due to changes in temperature will likely
recover independently. Rapid fluctuations in the fluid
sound speed, to a value that is beyond ± 20% from that
programmed into the XMT1000, will result in erratic or
inaccurate flow rate readings. This may occur when
changing batch fluids.
Note: Refer to Chapter 3: Programming, to make sure the
appropriate soundspeed is programmed into the meter.
4.4.2 Pipe problems
Pipe-related problems may result from improper choice in
meter location or errors in programming. The following may
result in problematic installations:
• The collection of material at the transducer location(s).
Accumulated debris at the transducer locations will
interfere with the transmission of the ultrasound signals.
As a result, accurate flow rate measurements are not
possible. Realignment of the transducers often corrects
these problems but, in some cases, wetted transducers
must be used. Refer to
Chapter: Installation for more details on proper
installation practices.
• Inaccurate pipe measurements.
The flow rate measurement accuracy relies greatly on
the accuracy of the programmed pipe dimensions.
Measure the pipe wall thickness and diameter with
the same accuracy desired in the flow rate readings.
Also, check the pipe for dents, pitting or rough surfaces,
eccentricity, weld deformity, straightness and other
factors that may cause inaccurate readings. Refer to
the Chapter: Programming, for instructions on entering
the pipe data.
• The inside of the pipe or pipe is not sufficiently clean.
Excessive buildup of scale, rust or debris inside the pipe
will interfere with flow measurements. Generally, a thin
coating or a solid well-adhered build up on the pipe
wall will not cause problems. Loose scale and thick
coatings (such as tar or oil) will interfere with ultrasound
transmission and may result in incorrect or unreliable
flow rate measurements.
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