|
|
| |
Submitted
Articles: ARTC02020101
Article: Coriolis flow meter maintenance
Submitted
by: Mass Flow Technology, INC.
Submit date:01/02/02 |
Coriolis
Flowmeter Maintenance
Have you ever seen fire ants excitedly swarming over a
dropped sandwich? At first glance, you might believe that
you were looking at a bunch of ants running around with
no organization or direction to their movements. Take
another look a few minutes later and you will see that
the sandwich is noticeably smaller. Each of those ants
has a purpose and an objective. They are working as a
team to disassemble and transport the sandwich to a specific
place. A unit shutdown has a similar appearance. First
glance shows group of workers swarming over a piece of
equipment with no organization or direction. But, like
those ants, each worker knows what he is expected to do.
Many hours of planning and preparation preceded the start
of maintenance. By the time the workers swarm the unit,
the job has been planned and organized down to the number
of man-hours it will take to finish the task.
Although Coriolis mass flow meters are not always included
in the planning of a shut down, this may be a good time
to perform some preventative maintenance on the critical
flow meters. You may have heard that Coriolis meters are
so dependable that they should work forever with no attention.
In reality, as long as man makes Coriolis meters using
man-designed machines there will be a few that perform
a little outside factory specifications. Shut downs are
an opportunity to check and calibrate your critical flow
meters. The best way to calibrate a Coriolis meter is
to remove the meter, clean it and send it to a facility
that has a gravimetric calibration flow laboratory. In
place "proving" may be acceptable for applications
that do not require great accuracy, but for a critical
measurement, there is no substitute for direct mass-to-mass
calibration. Master meter comparators and "inferred-mass"
volumetric provers cannot approach the accuracy of a gravimetric
facility. Mass Flow Technology in Baytown, Texas has a
gravimetric flow calibration laboratory with 0.052% system
uncertainty. Some factories have equivalent facilities
for calibrating production meters and may provide certified
calibration services for customer meters.
If your process fluid is likely to coat or plug, check
the meter for internal deposits. Deposits on the inner
flow tube walls will degrade meter accuracy. Decontaminate
the flow element and use a bore scope to check for deposits
inside the flow tubes. If deposits are found, a good hydro-cleaning
company can clean the flow tubes. Mass Flow Technology
has had considerable success is cleaning Coriolis flow
meters that are plugged with set-up concrete.
You don't have to wait for a shut down to keep up with
basic and periodic maintenance. Several valuable checks
can be made on Coriolis meters during normal operating
times. Flow meter zero (the flow meter output during non-flowing
conditions) can be checked any time the process flow can
be blocked for a few minuets. When process flow is blocked,
the flow meter should indicate zero flow. The procedure
is simple. Close the upstream and downstream valves and
read the flow rate. The best time to check the meter zero
is immediately following a batch, not before the batch.
The process should be stabilized to operating conditions
and entrainment should be purged. Also, make sure any
parameters that determine a flow cutoff threshold is set
to "0.0" before checking the meter zero. After
checking the meter zero, return the original cutoff threshold
parameter.
Periodic checks can be a valuable indicator for conditions
that gradually grow from nothing into a big problem. Most
manufacturers have test points that can be measured and
compared to previous checks made under similar conditions.
Make a chart for recording these test points and compare
the most recent checks to past checks. This may show a
trend.
This article has been contributed by Mass Flow Technology,INC.
|
|
|
