Hydrocarbon Processing - February 2022 - 21

Process Controls, Instrumentation & Automation
stability specification, the longer the calibration
interval will be.
Step 5. Step 5 takes all these factors
into account for the final calibration frequency
calculation (Eq. 1).
Calibration frequency =
(Required performace - TPE) /
Stability per month
(1)
Required performance minus the TPE is
divided by stability per month to determine
the proper calibration interval. Be
sure to keep units of measure consistent
across the equation. The two variables
that affect the outcome most are TPE
and the device's stability specification.
These factors make a significant difference
in the expected calibration interval.
A real-world example of significant
maintenance cost reduction. By utilizing
these equations, operators can obtain
and analyze interval data at a more
granular level. These precise calculations
may result in meaningful savings and
maintenance cost reductions for facilities.
This method has already proven beneficial
to producers. One such real-world
example impacted a major U.S. refinery.
This refinery was unsure how to perform
calibration in a way that would satisfy
the U.S. Environmental Protection
Agency's new greenhouse gas requirements
(Title 40 CFR Part 98-Mandatroy
Greenhouse Gas Reporting).
They decided to take the most conservative
approach to their calibration program,
performing expensive annual calibrations
to no benefit. Often, technicians
would apply pressure and find devices
well within their performance limitations.
The refinery had installed cuttingedge
pressure transmitter technology but
was not taking advantage of its benefits.
With a stability specification of 15 yr,
their transmitters could remain accurate
and reliable for much longer periods of
time. Extensive field data was gathered
to test this theory. Every time a technician
calibrated a device, they noted and
tracked the data.
A database was built to analyze the
pressure transmitter calibration data.
They found that out of 89 devices, only
one required recalibration during the
6-yr data collection period. Every other
device was within specifications. The device
that fell outside of accuracy requirements
was a much older, legacy technology.
The refinery decided to replace that
device, along with several other older
transmitters, with the newer model.
Based on this data, the refinery moved
89 differential pressure transmitters from
a 1-yr calibration interval to a 3-yr calibration
interval, while remaining greenhouse
gas compliant. Not only did this change
free up resources and keep personnel from
doing unnecessary testing in the field, but
they also saved approximately $22,000/yr.
Ongoing field data suggests the refinery
may extend the interval to 5 yr. Refinery
personnel are making considerations to
extend this program across their installed
base of more than 4,000 devices.
High-performance pressure transmitters
deliver longer calibration
intervals. Facilities may want to embark
on their own field studies to test these
estimated calibration intervals and further
justify the move towards optimization
of calibration frequency plantwide.
The activity is worthwhile, with potential
cost savings of tens of thousands of
dollars each year.
The extended stability specifications
available in advanced pressure sensing
technology heighten the need to reevaluate
traditional calibration schedules.
There is no need to spend resources on
constant physical checks when instrumentation
can withstand production
environments, while remaining within
specifications for much longer windows
of time. These maintenance cost savings
may even offset the initial purchase price
of newer models.
As measuring equipment becomes
more robust and dependable, operators
must reconsider outdated methodologies
that drive unnecessary expenditures.
Analyzing current calibration procedures
for pressure instruments throughout a facility
is a step in the right direction and
could save thousands of dollars a year in
operating costs.
BRAD BURTON is a Senior Product Manager
with Emerson's Automation Solutions business,
supporting Rosemount core pressure products.
Mr. Burton has been at Emerson for 23 yr, with
experience in manufacturing, customer care and IT,
as well as working with Rosemount flow products.
NEW VERSION
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Please contact J'Nette Davis-Nichols
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Hydrocarbon Processing | FEBRUARY 2022 21
Hydrocarbon Processing - February 2022

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